The fix on the Pro
- Thread starter beamslayer
- Start date
Please do. We need a benchmark cost for replacing Cat clutches and belts to compare against a set of pistons, a base gasket and some o-rings.
Diamond drive anyone?
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Questions, Answers and the "FIX KIT" Theory
Wow this is a thread! Kudos to you guys in trying as best you can to state the facts about our engine kit. I appreciate the comments that are not too uncommon anymore about the “FIX KIT” doing wonderful things for owners of Polaris snowmobiles. I want to make sure everybody understands what it is that the “FIX KIT” is doing in your engine and how it helps out so much. First I want to talk about what we believe is going on in the engines as provided by Polaris.
Starting with the CFI4 Polaris built a great engine but as many have experienced there were some short comings. The engine as delivered had some very large piston to cylinder clearances, this we found through hundreds of engine teardowns and rebuilds. We work closely with Performance Motor Sports (which is a Polaris dealership) and witnessed this first hand on a grand scale. A few of the factors that affected this engine during the conception/production were as follows. First, we have reason to believe that there were some piston seizure problems during prototyping and some quality issues in production that led to the excessive clearances. Regardless of the cause, the effect led to the piston having a little more freedom to move around in the bore. Second, modern high output two strokes have large exhaust ports which have done much in the way of making power, but large ports allow pistons to diverge from the perfect path of concentricity in the cylinder bore and slightly slip out into the port if even for just a fraction of a second. Third, unfortunately for the engine, sled riders are a very picky bunch and have driven manufacturers to make drastic changes (for the better I might add overall) to make them lighter and smaller and the engine is no exception. The Polaris CFI engine was designed to be a very compact engine and as light as possible. Here is the real clincher, theoretically those changes should not make any compromises in durability or power (well they tried didn’t they!). Human judgment, quality control, modern two stroke design theory, and design compromises are the reason that this engine became the perfect storm of engine devastation. There are three major groups of failures that we saw and most can be categorized into; 1) mechanical failure or incorrect calibration of a part such as an oil pump, 2) piston knife-edging, 3) piston skirt/cylinder skirt failure. The first of these is subject to the human error factor and not much can be done about it, except a watchful eye and careful checks during quality control and the production process but it is the least of the three. Failure number two is due to the design. When the pistons rock in the bore they use the upper and lower edges of the piston to bear the load instead of the skirt/face of the piston. This causes the piston to knife-edge. When a piston becomes knife-edged it scrapes the bore usually displacing the oil that normally would allow the piston to glide near frictionless. This creates an enormous amount of heat and leads to the scuffing and damage that so many have experienced. The third failure is also related to the design and subsequently the piston to cylinder clearance as the knife-edging that has been stated but a different problem arises. If you can imagine as the piston travels through its stroke it is subject to many forces. In a perfect world or rather a perfect reciprocating engine the piston would stay seated completely to the cylinder wall all the way around the cylinder having only a line of lubricant molecules (all the same size like little roller bearings, hey I can dream can’t I it is a perfect engine!) between it and the cylinder wall. In the real world though the different expansion rates between cylinder and piston, lubricant qualities, manufacturing tolerances, cost of materials and other such things play a role on the end result. This ends up requiring that the piston be smaller than it should so that when the heat loading from combustion is added it will grow no larger than the cylinder bore. Since the piston is now smaller than the bore the piston has room to move and the connecting rod influence pushes the piston from side to side as the crankshaft turns. Dynamically (when the engine is turning) the piston rocks much more than just once at TDC and once at BDC. The piston rocks back and forth dependent on rpm and load. This is one of the reasons some engines fail repeatedly every few hundred miles and others fail many miles down the trail. On a side note it has seemed that those who rode the most gently failed the most frequently. This repeated rocking in the bore becomes more and more severe as the piston to cylinder clearance becomes greater. Aluminum has several desirable qualities but has one that is not as helpful. In metallurgy most metals like steel have a defined point which as long as you do not exceed this point when stressing it, whether it is bending, tension, or compression it will return to its original size and have no mechanical change. This is called modulus of elasticity. Aluminum has no modulus of elasticity. It has a yield point, but it is a contrived number called the two tenths offset. It is number generated from the actual yield point of aluminum but then is reduced by two tenths of a percent and that is the assigned yield point. What this really means is that aluminum having no modulus of elasticity can never be stressed without some mechanical change happening. It can be stressed greatly a few times, or it can be stressed only slightly for a long time but in either case it will fail. This is why the rocking is so damaging in the Polaris CFI engines. The hammering causes cracks to form and eventually breaks off either the piston skirt or the cylinder skirt.
Do these engines have a rod ratio problem that causes the piston to rock in the bore more than normal? Perhaps it does. By the numbers the rod is not overly short, but in this engine it may be a contributing factor to the problem. A longer rod would alleviate some forces transmitted through the piston to the cylinder wall, but in my opinion it will not totally eliminate the problem. A much shorter rod could be used in another two stroke design but have no problems because the other factors that lead to the failure are not present. If you were going to make a big bore engine or rev it higher then I definitely think a longer rod would help make power, it just costs more. We use a piston that we had specifically built to change the most significant factor in these engines that causes them to fail. The piston we use is taller significantly and it is from the wrist pin to the top of the crown that we made the change. The OEM piston dimensions have quite a short distance from the pin to the crown as far as two strokes are concerned. If you can imagine the rod angled over midway through the stroke making a right angle from the crank center to lower rod pin and out to the wrist pin and then connected to the piston. Now draw a line up the center of the rod through the piston to the cylinder wall. This is the thrust line that force is transmitted through and the point when the rod is the most angled. The shorter the piston is from the pin to the crown the more this line will start to leave the point where the cylinder and piston meet, instead pushing through the crown of the piston. The CFI engines are very close to pushing through the crown of the piston. Normally this would not be a problem and in fact is a very small thing to even consider in most engines. When you have a piston that rocks in the bore excessively and is quite short, and then throw the exhaust port into the mix it sets up conditions that lead to premature failure. The height added to the piston adds a significant amount of stabilization and dramatically decreases piston rock. Not to mention we reduced the amount of taper from top to bottom on the piston, and decreased the piston to cylinder clearance in a three-fold assault on the problem.
There has been some discussion about whether our piston is supported at BDC as much as the stock configuration. We added the exact same amount in a cylinder shim as we did to the piston. This means there is the exact (yes exactly) the same amount of piston inside the cylinder as there was before. Yes the wrist pin is lower than before, but the thrust load from the rod is at its smallest magnitude at this point and is an insignificant factor. Also there has been discussion about the cylinder skirts not being supported by the crankcase. In this family of engines (and most engines I might add) the cylinder skirts are not supported by the crankcase. I know this may come as a shock to you but it is not. The locating dowels located around the cylinder hold down bolts are the datum points that align the cylinder to the crankcase. The cylinder skirts cannot fit tightly into the crankcase or there would be a tolerance issue. It would not be cost effective to manufacture a cylinder and crankcase that would mate so completely that they support one another. The more points that locate any mating component add restriction and complexity to manufacturing. It is true I have pulled apart engines that seem like the skirts touch and fit snuggly. They may have very well had collapsed skirts. I have also pulled apart many with large tolerances between the skirt and crankcase. It would be and is (we have done it before) possible to machine on a case by case (no pun intended) basis a cylinder and crankcase that mate perfectly, just not in a large scale production.
Now on to the crankcase volume and what it is really doing. I do not ascribe to the theories presented earlier in this thread that there is some sort of need to have reduced crankcase volume at different altitudes or that a smaller crankcase is better. It has been found by many different researchers, tuners and engineers and cited in SAE papers (sometimes it gets a little dry, but I like to switch off between those and patent documents) that as long as you are using a modern (post 1975) tuned multi segmented expansion chamber that two strokes make more power the larger the crankcase volume becomes. Of course this has a limit, you could not have an infinite crankcase volume or you would have no primary compression, but in generalities larger crankcases make more peak power. The bigger the bore/swept volume the larger reserve you need in the crankcase to fill it effectively. I believe the CFI family of engines have a slightly small crankcase, which boost low end throttle response but sacrifices peak power. The evidence of this comes from our dyno (we have a real dyno, because our butt dyno kept coming up with larger and larger numbers to keep up even though nothing was changing) and with nothing else changed but the fix kit installed it produced 5 horsepower more than a stock engine. The filling the pond theory as presented earlier is correct except the assumption is made that the head gate letting the water into the pond is too small to keep up in the time allowed. This is not the case in this engine. In most engines there is a period of dead time that the intake port (read transfer ports) is plugged and no more charge air is allowed into the combustion chamber. This gives even the largest crankcases plenty of time to fill with fresh air. There must not be too many restrictions because the time is still short, but overall the crankcase has plenty of opportunity to fill especially since the use of reed valves in two stroke engines.
Now on to the question of warranty. We do not offer an expressed warranty, that unconditionally is granted no matter how incorrectly it was installed or improperly used or treated. We have literally thousands (yes plural) of kits out there and less than 1% failure rate. There have been a few that have been installed incorrectly or have other circumstances like oil pumps that are incorrectly calibrated which have contributed to the failures. The amount of engines that are working better is definitely the acid test and the undeniable truth that it just flat works. Those that have had an issue will all testify that if they have reached out to us in an attempt to understand why their engine still had a problem then we go out of our way to help them. Only if you are rude, derogatory, or we feel intentionally trying to defraud us then we cannot help you because of YOUR attitude. We do offer an implied warranty on all the done. Other companies offering their products usually deal directly with the customer and have implied warranties just the same. We have an extensive dealer network throughout the world and so we rely on those dealers to stand behind their work as we stand behind the product. We cannot offer a warranty to engine components that are installed on another system that has other critical failure points. Along those lines there have been zero failures in our product as far as mechanical components go. It has only been incorrect assembly and overlooking previous problems, parts failing other than our supplied, and incorrect calibrations that have failed.
To sum up the discussion and get back on topic, we designed and tested a product that has proven to be sound and of an incredible value to our customers. If you still think you are taking a chance with our products then go try someone else for a while. The CFI 2 is very similar to the CFI 4, and unfortunately (we love Polaris products and wish we could just make them faster instead of holding them together) this engine is not free from the problems associated with the CFI 4. It is without a doubt longer lasting and better than previously, but it still benefits from having our piston kit in it. I might add it will be less expensive to fix it sooner than later if your warranty is expiring. The two biggest issues with the CFI 2 are worn out ring lands causing lost compression thus lost power and cylinder/piston skirt cracking and breaking caused by piston rocking (slap). Feel free to call us and further the discussion. Please excuse the long post, sometimes it is just easier to lay all the information out and continue a flow of ideas than to peck and scratch all around the subject talking in circles. Shawn
Wow this is a thread! Kudos to you guys in trying as best you can to state the facts about our engine kit. I appreciate the comments that are not too uncommon anymore about the “FIX KIT” doing wonderful things for owners of Polaris snowmobiles. I want to make sure everybody understands what it is that the “FIX KIT” is doing in your engine and how it helps out so much. First I want to talk about what we believe is going on in the engines as provided by Polaris.
Starting with the CFI4 Polaris built a great engine but as many have experienced there were some short comings. The engine as delivered had some very large piston to cylinder clearances, this we found through hundreds of engine teardowns and rebuilds. We work closely with Performance Motor Sports (which is a Polaris dealership) and witnessed this first hand on a grand scale. A few of the factors that affected this engine during the conception/production were as follows. First, we have reason to believe that there were some piston seizure problems during prototyping and some quality issues in production that led to the excessive clearances. Regardless of the cause, the effect led to the piston having a little more freedom to move around in the bore. Second, modern high output two strokes have large exhaust ports which have done much in the way of making power, but large ports allow pistons to diverge from the perfect path of concentricity in the cylinder bore and slightly slip out into the port if even for just a fraction of a second. Third, unfortunately for the engine, sled riders are a very picky bunch and have driven manufacturers to make drastic changes (for the better I might add overall) to make them lighter and smaller and the engine is no exception. The Polaris CFI engine was designed to be a very compact engine and as light as possible. Here is the real clincher, theoretically those changes should not make any compromises in durability or power (well they tried didn’t they!). Human judgment, quality control, modern two stroke design theory, and design compromises are the reason that this engine became the perfect storm of engine devastation. There are three major groups of failures that we saw and most can be categorized into; 1) mechanical failure or incorrect calibration of a part such as an oil pump, 2) piston knife-edging, 3) piston skirt/cylinder skirt failure. The first of these is subject to the human error factor and not much can be done about it, except a watchful eye and careful checks during quality control and the production process but it is the least of the three. Failure number two is due to the design. When the pistons rock in the bore they use the upper and lower edges of the piston to bear the load instead of the skirt/face of the piston. This causes the piston to knife-edge. When a piston becomes knife-edged it scrapes the bore usually displacing the oil that normally would allow the piston to glide near frictionless. This creates an enormous amount of heat and leads to the scuffing and damage that so many have experienced. The third failure is also related to the design and subsequently the piston to cylinder clearance as the knife-edging that has been stated but a different problem arises. If you can imagine as the piston travels through its stroke it is subject to many forces. In a perfect world or rather a perfect reciprocating engine the piston would stay seated completely to the cylinder wall all the way around the cylinder having only a line of lubricant molecules (all the same size like little roller bearings, hey I can dream can’t I it is a perfect engine!) between it and the cylinder wall. In the real world though the different expansion rates between cylinder and piston, lubricant qualities, manufacturing tolerances, cost of materials and other such things play a role on the end result. This ends up requiring that the piston be smaller than it should so that when the heat loading from combustion is added it will grow no larger than the cylinder bore. Since the piston is now smaller than the bore the piston has room to move and the connecting rod influence pushes the piston from side to side as the crankshaft turns. Dynamically (when the engine is turning) the piston rocks much more than just once at TDC and once at BDC. The piston rocks back and forth dependent on rpm and load. This is one of the reasons some engines fail repeatedly every few hundred miles and others fail many miles down the trail. On a side note it has seemed that those who rode the most gently failed the most frequently. This repeated rocking in the bore becomes more and more severe as the piston to cylinder clearance becomes greater. Aluminum has several desirable qualities but has one that is not as helpful. In metallurgy most metals like steel have a defined point which as long as you do not exceed this point when stressing it, whether it is bending, tension, or compression it will return to its original size and have no mechanical change. This is called modulus of elasticity. Aluminum has no modulus of elasticity. It has a yield point, but it is a contrived number called the two tenths offset. It is number generated from the actual yield point of aluminum but then is reduced by two tenths of a percent and that is the assigned yield point. What this really means is that aluminum having no modulus of elasticity can never be stressed without some mechanical change happening. It can be stressed greatly a few times, or it can be stressed only slightly for a long time but in either case it will fail. This is why the rocking is so damaging in the Polaris CFI engines. The hammering causes cracks to form and eventually breaks off either the piston skirt or the cylinder skirt.
Do these engines have a rod ratio problem that causes the piston to rock in the bore more than normal? Perhaps it does. By the numbers the rod is not overly short, but in this engine it may be a contributing factor to the problem. A longer rod would alleviate some forces transmitted through the piston to the cylinder wall, but in my opinion it will not totally eliminate the problem. A much shorter rod could be used in another two stroke design but have no problems because the other factors that lead to the failure are not present. If you were going to make a big bore engine or rev it higher then I definitely think a longer rod would help make power, it just costs more. We use a piston that we had specifically built to change the most significant factor in these engines that causes them to fail. The piston we use is taller significantly and it is from the wrist pin to the top of the crown that we made the change. The OEM piston dimensions have quite a short distance from the pin to the crown as far as two strokes are concerned. If you can imagine the rod angled over midway through the stroke making a right angle from the crank center to lower rod pin and out to the wrist pin and then connected to the piston. Now draw a line up the center of the rod through the piston to the cylinder wall. This is the thrust line that force is transmitted through and the point when the rod is the most angled. The shorter the piston is from the pin to the crown the more this line will start to leave the point where the cylinder and piston meet, instead pushing through the crown of the piston. The CFI engines are very close to pushing through the crown of the piston. Normally this would not be a problem and in fact is a very small thing to even consider in most engines. When you have a piston that rocks in the bore excessively and is quite short, and then throw the exhaust port into the mix it sets up conditions that lead to premature failure. The height added to the piston adds a significant amount of stabilization and dramatically decreases piston rock. Not to mention we reduced the amount of taper from top to bottom on the piston, and decreased the piston to cylinder clearance in a three-fold assault on the problem.
There has been some discussion about whether our piston is supported at BDC as much as the stock configuration. We added the exact same amount in a cylinder shim as we did to the piston. This means there is the exact (yes exactly) the same amount of piston inside the cylinder as there was before. Yes the wrist pin is lower than before, but the thrust load from the rod is at its smallest magnitude at this point and is an insignificant factor. Also there has been discussion about the cylinder skirts not being supported by the crankcase. In this family of engines (and most engines I might add) the cylinder skirts are not supported by the crankcase. I know this may come as a shock to you but it is not. The locating dowels located around the cylinder hold down bolts are the datum points that align the cylinder to the crankcase. The cylinder skirts cannot fit tightly into the crankcase or there would be a tolerance issue. It would not be cost effective to manufacture a cylinder and crankcase that would mate so completely that they support one another. The more points that locate any mating component add restriction and complexity to manufacturing. It is true I have pulled apart engines that seem like the skirts touch and fit snuggly. They may have very well had collapsed skirts. I have also pulled apart many with large tolerances between the skirt and crankcase. It would be and is (we have done it before) possible to machine on a case by case (no pun intended) basis a cylinder and crankcase that mate perfectly, just not in a large scale production.
Now on to the crankcase volume and what it is really doing. I do not ascribe to the theories presented earlier in this thread that there is some sort of need to have reduced crankcase volume at different altitudes or that a smaller crankcase is better. It has been found by many different researchers, tuners and engineers and cited in SAE papers (sometimes it gets a little dry, but I like to switch off between those and patent documents) that as long as you are using a modern (post 1975) tuned multi segmented expansion chamber that two strokes make more power the larger the crankcase volume becomes. Of course this has a limit, you could not have an infinite crankcase volume or you would have no primary compression, but in generalities larger crankcases make more peak power. The bigger the bore/swept volume the larger reserve you need in the crankcase to fill it effectively. I believe the CFI family of engines have a slightly small crankcase, which boost low end throttle response but sacrifices peak power. The evidence of this comes from our dyno (we have a real dyno, because our butt dyno kept coming up with larger and larger numbers to keep up even though nothing was changing) and with nothing else changed but the fix kit installed it produced 5 horsepower more than a stock engine. The filling the pond theory as presented earlier is correct except the assumption is made that the head gate letting the water into the pond is too small to keep up in the time allowed. This is not the case in this engine. In most engines there is a period of dead time that the intake port (read transfer ports) is plugged and no more charge air is allowed into the combustion chamber. This gives even the largest crankcases plenty of time to fill with fresh air. There must not be too many restrictions because the time is still short, but overall the crankcase has plenty of opportunity to fill especially since the use of reed valves in two stroke engines.
Now on to the question of warranty. We do not offer an expressed warranty, that unconditionally is granted no matter how incorrectly it was installed or improperly used or treated. We have literally thousands (yes plural) of kits out there and less than 1% failure rate. There have been a few that have been installed incorrectly or have other circumstances like oil pumps that are incorrectly calibrated which have contributed to the failures. The amount of engines that are working better is definitely the acid test and the undeniable truth that it just flat works. Those that have had an issue will all testify that if they have reached out to us in an attempt to understand why their engine still had a problem then we go out of our way to help them. Only if you are rude, derogatory, or we feel intentionally trying to defraud us then we cannot help you because of YOUR attitude. We do offer an implied warranty on all the done. Other companies offering their products usually deal directly with the customer and have implied warranties just the same. We have an extensive dealer network throughout the world and so we rely on those dealers to stand behind their work as we stand behind the product. We cannot offer a warranty to engine components that are installed on another system that has other critical failure points. Along those lines there have been zero failures in our product as far as mechanical components go. It has only been incorrect assembly and overlooking previous problems, parts failing other than our supplied, and incorrect calibrations that have failed.
To sum up the discussion and get back on topic, we designed and tested a product that has proven to be sound and of an incredible value to our customers. If you still think you are taking a chance with our products then go try someone else for a while. The CFI 2 is very similar to the CFI 4, and unfortunately (we love Polaris products and wish we could just make them faster instead of holding them together) this engine is not free from the problems associated with the CFI 4. It is without a doubt longer lasting and better than previously, but it still benefits from having our piston kit in it. I might add it will be less expensive to fix it sooner than later if your warranty is expiring. The two biggest issues with the CFI 2 are worn out ring lands causing lost compression thus lost power and cylinder/piston skirt cracking and breaking caused by piston rocking (slap). Feel free to call us and further the discussion. Please excuse the long post, sometimes it is just easier to lay all the information out and continue a flow of ideas than to peck and scratch all around the subject talking in circles. Shawn
Shawn, thanks for posting this info...
That was awesome thanks.
Excellent post Shawn.
I posted my decission on the wrong thread I put it on the 858 thread instead.
Too much coffee this morning or not enough Jack Danials last night.
Too much coffee this morning or not enough Jack Danials last night.
Thank you Shawn, awesome post!
But to you and anybody, since some last a long time with zero problems and some break down before 600miles; where is the variable in the engine?
Do polaris produce pistons of variable tolerance?
Do polaris produce cylinders of variable tolerance?
Or do you mean this is caused by other production tolerances/production tolerances or use/abuse?
But to you and anybody, since some last a long time with zero problems and some break down before 600miles; where is the variable in the engine?
Do polaris produce pistons of variable tolerance?
Do polaris produce cylinders of variable tolerance?
Or do you mean this is caused by other production tolerances/production tolerances or use/abuse?
The "FIX KIT" was designed to add durability to modified engines just as it adds durability to the stock engine. With our turbo kits about half the customers add the fix kit right away with a new purchase, and the other half have been adding after running the stock stuff for awhile, usually to freshen up the engine for the next season. So it is all ready to add to a turbocharged or otherwise modified engine.
I am just telling you what we have found. You don't have to accept it. I can't give you a so called explanation for why Polaris hasn't fixed it. Keep reading.
As we see it there are 4 variables that directly contribute to the life of these engines. 1) Assembly Clearance. The engines do have varying piston to cylinder clearance, mostly the cylinder. They do have a problem with distortion in the cylinder when torqued down which could be why the piston to cylinder clearance was so excessive in 08 and has progressivily gotten better (not right just moving in the right direction). This does not change the fact that Polaris sent them out with excessive clearance. We have a very reputable source that stated at the last minute before production in 08 Polaris started seeing problems with engines on the dyno's. They opted to grade cylinders and pistons into A, B, and C's. Then assembled the engines so the pistons and cylinders matched. You may have noticed on the cylinders of 08's and 09's a yellow paint marker A, B or C on the front of the cylinder. I think this could be what that is from. Complete hearsay though. 2) Oil Qualitiy and Quantity. Oil pumps fail or are incorrectly calibrated. This is why I believe Polaris went to a link rod on the oil pump instead of a cable. 3) RPM and Load. Customer riding styles and abuse do contribute to how an engine lasts. I can not count how many times I sit at the bottom of a hill and then one guy fires up his sled and goes to the bar all the way up the hill. I hold my breath the whole way up. 4) Mileage. Some simply have not reached the magical point in time that the assembled clearance in the cylinder + normal wear + customer induced wear = walk home.
J
Jimb
Well-known member
Well I kind of agree with you, knowing how big companies work they might well have their heads in the sand wouldn't surprise me in this industry. Thanks for taking the time to try to figure out better reliability, without innovators we'd still be in the dark.
I also agree riding style plays a big part, from having cold seized a motor before I know the pull and rip riding can lead to failure.
I also agree riding style plays a big part, from having cold seized a motor before I know the pull and rip riding can lead to failure.
Injectors on throttle body???
I know it does nothing to address mechanical issues, but cooling and lubrication was easier to "tune" when your gas went through the case.
Has anybody looked at modifying the fuel system so the injectors sit on the throttle body like the old ones?
When you port/big-bore/pipe/turbo etc. your sled you add a fuel controller and jump outside EPA regs anyway, so why not extend the life of your reeds and take full control of your cooling and lubrication??
Thoughts?
RS
I know it does nothing to address mechanical issues, but cooling and lubrication was easier to "tune" when your gas went through the case.
Has anybody looked at modifying the fuel system so the injectors sit on the throttle body like the old ones?
When you port/big-bore/pipe/turbo etc. your sled you add a fuel controller and jump outside EPA regs anyway, so why not extend the life of your reeds and take full control of your cooling and lubrication??
Thoughts?
RS
that was my thoughts as well, figured if I did a BB or a turbo, use Neils boost-it with the extra pair of injectors sitting right between the throttle bodies and reeds..should save the reeds..
T
TurboMatt
Well-known member
There are getting to be some many different options to "fix" the CFI2 motor its starting to get mind boggling. Who do you believe?
I plan on doing something over summer. I'm starting to lean back towards the "fix kit" again. It just is that much more proven, many more liels on these kits. All theories aside. Hell if its proven to "fix" the CFI4's and the concept is the same it has to be benificial for the Pro too.
I plan on doing something over summer. I'm starting to lean back towards the "fix kit" again. It just is that much more proven, many more liels on these kits. All theories aside. Hell if its proven to "fix" the CFI4's and the concept is the same it has to be benificial for the Pro too.
proper clearance
I feel one of the problems with the stock cfi is too much piston clearance. The only person out there that replates the cylinder and hones it to an exact clearance to match the piston is Indy Dan which I feel is why we are doing this anyway.
I know this is more expensive, but I feel it to be important to get good power and runability. I think these engines are a victim of being mass produced and allowing to wide a range of specs for the piston and cylinder,which explains why some motors are in perfect specs and last longer, while others do not make it.
The other issue is rod-ratio, angermangement 890 said that the engine that he did had more power with the longer rod. More case volume certianly would be a plus with this motor. This guy never posts anything that he himself has not tried. The longer rod would definitely side load the piston less. Indy Dan does this also and the fix-it kit somewhat addresses this also.
Just my thoughts, what a great thread.
I feel one of the problems with the stock cfi is too much piston clearance. The only person out there that replates the cylinder and hones it to an exact clearance to match the piston is Indy Dan which I feel is why we are doing this anyway.
I know this is more expensive, but I feel it to be important to get good power and runability. I think these engines are a victim of being mass produced and allowing to wide a range of specs for the piston and cylinder,which explains why some motors are in perfect specs and last longer, while others do not make it.
The other issue is rod-ratio, angermangement 890 said that the engine that he did had more power with the longer rod. More case volume certianly would be a plus with this motor. This guy never posts anything that he himself has not tried. The longer rod would definitely side load the piston less. Indy Dan does this also and the fix-it kit somewhat addresses this also.
Just my thoughts, what a great thread.
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This is what Curt @ Fastrax has been doing since the D8. Says pistons are fairly constant in size, cylinder bore not so much...
Still talking less miles before rebuild, but he feels this is why some run trouble free to even 3000+ miles while others die within 600.
Have about 685miles on mine now and will tear down to inspect and measure things. If things are bad, plating and new pistons (of some kind) will be minimum steps.
