Compression

[Turbo11T]

So I did a compression test a while back on my sled because I was having issues. It came up 130 psi on every cylinder. I thought this was ok because they were all equal even though I thought it seems a bit low.

The motor is a vector motor with a PL head shim and cam timing set to 114 degrees.

I found a calculator on a bike website that you can enter in all the info on the motor including cam info and it says it should be about 160 psi cranking compression. I also contacted hurricane racing and told him my dilema and he said it sounds like the motor had 9:1 pistons in it too. Well this motor is suppose to be bone stock before I changed anything and the pistons look bone stock. The same calculator says that if it did have 9:1 pistons in it that it would have 126psi of compression. Makes me sure think that this may be the issue. But here is a pic of the pistons, looks stock to me.

<a href="http://s115.photobucket.com/albums/n281/mnflats/?action=view&current=DSCN5440.jpg" target="_blank"><img src="http://i115.photobucket.com/albums/n281/mnflats/DSCN5440.jpg" border="0" alt="Photobucket"></a>

 

[Ak nitro]

Does the calculator take in to fact the headshim? I have the thicker Impulse headshim in my nytro engine, and I have 120 psi on all three cylinders, Paul said that is good, so just to check things further I did a leak down test on all three cylinders and they were all almost perfect, Like 2% leakdown on all three cylinders, Compression may also be different at the elevation you test the compression. Everything I have read has stated leak down test is the best way to properly diagnose any engine issues, because you can track down the exact valve or rings that may be leaking. I have 3000 miles on my engine and thought I would check everything out last summer and everything is still great, so every summer I am going to just continue to do leak down test to try and find any issue before it gets bad.

 

[Turbo11T]

I am sure that compression is different at higher elevation. I think it is almost 30 psi difference at 8500 to 1000 ft. I could go to the calculator and see again.

Either way I just got off the phone with Dave at hurricane and he suggested a leak down test as he said it sounds like something is seriously wrong. So I will be doing that first. I need to figure this thing out it is driving me insane.

 

[Ak nitro]

What is the problem you are having that you are looking into the engine?

 

[Turbo11T]

The darn thing just is not making power. It honestly feel like about 150 at best. I have troubleshooted everyother part of the turbo system. I think this is why I can't get my clutching nailed down because it has no power. I am leaning towards bent valves. I think the leak down test is going to give me what I need to know. And then I will pull the motor and figure it out. I overreved it hard out west with no load when I blew a chain and I am thinking that the valves maybe floated and got bent. And it is just pure luck that all cylinders test the same. I have checked and rechecked the cam timing and it is right on.

I think that if the motor comes out and the head has to come off I may take the shim back out and run low boost or better fuel when I am out west. I want to boondock through the trees at slow speed and the throttle reponse is important to me.

 

[Turbo11T]

Just made a leak down tester. Should give me the answers I am looking for.

 

[Ak nitro]

After you do a leak down test you will have answers to your questions, I built a homemade one also, but for my orfice I used epoxy and a very small drill bit, I can't remember what size now, it was whatever the website specified. Found it easiest to pull the valve cover and drop a long screwdriver in the cylinder so I new exactly when the valves where closed and the piston was TDC. I was having a hard time doing it until I pulled the valve cover. Let us know what you find.

 

[Turbo11T]

Well I tell you what I found was very healthy valves and motor. I had a hard time finding the right spot where the valves were closed. But once I did I had from 2-4% leak down. I redid my leakdown tester with a .040 orifice as this seems to be the norm if not the standard. I am unsure where to go from here. . . . . . . I still think my compression is to low. Is it possible I was checking it wrong and should have put some oil in the cylinders? Is it possible that I am not checking cam timing the right way? I think I may have to take it to a professional.

 

[Ak nitro]

130 psi seems a little low for your elevation, but If you did your leakdown test right, and only have 2 to 4 % leakdown your motor should be fine, that would prove your cylinders and valves are not leaking so the compression test means nothing. For compression test they say you can add some oil to a cylinder that may be reading low to see if the rings are leaking, but there is no need to do it on a leakdown test. An automotive motor can have way more leakdown and be perfectly fine, these motors are a lot tighter than autos. If your valves were bent you would never get them to seat that tight, and air would be blowing through the exhaust or intake valves, maybe some other people could chime in and state what compression they have at elevation. Unless you are using a bunch of oil, have a lot of blow by, or blowing out antifreeze I would look back at the turbo kit fueling system, good luck.

 

[Turbo11T]

Hurricane Racing told me today that if the leak down tests ok I should think about rechecking my cam timing once again. Of course I am questioning myself on everything now. I will be checking it in the morning. It doesn't do me any good to pull the motor out of the chassis and find nothing wrong and put it back in to find it still doesn't work. I need to know what the problem is first.

 

[zebiraross]

On my old Apex I had 140 psi at 4700 ft elevation. 130 is totally fine, the leakdown tells you more then the compression test and that 2-3% is great. What are you comparing your power to? The vector doesn't make the power like a Apex or Rx if that's what your measuring it against.

 

[weezer79]

when i got my sled put back together this year i could not get it to rev up right all the time, wasnt making any power, went through fuel system and turbo everything was fine, leak down tested fine, i eventually pulled the valve cover and checked the clearances on my valves, found 2 intake valves that were a little out, (not opening in time) put the right valve pad in and this fixed my problem, might be another place start looking. good luck!

 

[Turbo11T]

On my old Apex I had 140 psi at 4700 ft elevation. 130 is totally fine, the leakdown tells you more then the compression test and that 2-3% is great. What are you comparing your power to? The vector doesn't make the power like a Apex or Rx if that's what your measuring it against.

I am comparing the power to a 09 800 ski doo stock. I should pull away from him like nobodys business and I can't. My sled feels like 150 hp and from what my cousin told me it looks like 150 hp as well. Something has got to be wrong. I think I am going to try to take it to proline racing and have them figure it out for me. I think if the motor was making power the clutching would not be hard to make work, which is what leads me to beleive it is not clutching related. I have the same setup that many guys run for clutching now.

 

[Turbo11T]

So. . . . . I am sitting here, I have checked the following.

Cylinder Leak Down. . . . OK
Compression Test . . . . . Seems low but equal
Cam Timing. . . . OK
TPS Sensor Resistance. . . . OK
Trigger Coil Resistance. . . . OK

In review the sled feels like it is only making about 150 hp at 10lbs of boost. I know it should be making right around 185 at 8lbs. so almost 200 at 10lbs.

As I am sitting here looking through the shop manual on what diagnostic checks I can make. And I am reading and thinking about the speed sensor. I don't have the little gear on my driveshaft. At some point in time I zip tied a steel nut to the sensor. I thought this maybe would make the "Code 42" go away. Either way it didn't, and I never took it off either. Now I have myself wondering if this could be somehow giving the system a false reading and maybe pulling the ignition timing way back. Like I said I can't remember when I did this.

Does anyone think this could be a problem?

 

[zebiraross]

Your problem is you need to turn up your boost. Turn it up to 15 and you'll wake it up.

 

[Turbo11T]

Your problem is you need to turn up your boost. Turn it up to 15 and you'll wake it up.

I have still not impressed. Am getting beat by a 300 lb man on a 09 summit 163. I am geared to run faster and I should be making 70 more hp than him. It is flat out embarrassing. I ran 14 lbs out west the first day. The clutching was off. . . The jetting was wicked fat but it would pull like a frieght train at full throttle. I cannot get it to do that anymore. So It has some problem . . .

 

[t_thall]

If you do end up needing pistons i have a set of forged wiseco lower compression pistons w/ swain tech skirt and dome coatings and brand new rings. A guy on here sold them to me claiming they were for a nytro and they have been sitting on my shelf ever since....

 

[t_thall]

I am just doing some motor work on my nytro, my rb3 crapped out and it went way lean. It would still run decent but it lost 2 lbs boost and was pressuring the crankcase causing the turbo to burn oil, engine wasn't burning any oil though. My compression was 175/130/170, figured i popped the middle, tore it down and the ring grooves were disstorted on all three and pinching the bottom two rings..

 

[Turbo11T]

So I think I may have not got the carbs seated in the carb boots on the head ever since I was out west. I am really angry at myself about this. The only excuss I can make is that it was wicked cold out. and it sucks to change pull the carbs off on the vector. This is where i am reight now I am not sure if this is the problem for sure but I think it may be.