800 Engine Rebuild -long post-

[Goinboardin]

That's interesting, I had no idea it was supposed to go under. The case didn't have much oil in it though, just a coating on everything. But, on the next rebuild I'll route it under for sure.

The motor is out, completely tore down, and cleaned up now. I think my plan of action is rebuilt crank, new pistons, clean up my one good cylinder and either port match it to the ported cylinder I have on the shelf or pick up another renick'd stock cylinder, run an SLP head, run a little less ignition timing, and switch to either ceramic twins (non-race twins) or an SLP single pipe.

Thanks for reading guys. I hope this is a useful thread.

 

[Goinboardin]

If a bearing spun in the cases you would see it. I suspect you are right in thinking detonation, alltho maybe the piston failed? bits of the piston took out the mag side? Eitherway it sucks.

Yeah after looking more closely it appears that some of the bearing debris dragged along the case, right next to the bearing and left a light scratch. The area in the case under the bearing is fine. So no spun bearing, which is sick, saves me a couple bucks.

My mag cylinder skirt has two half dime sized pieces cracked off, but not on the intake or exhaust sides, just the sides that line up with the wrist pin. I figured it wouldn't be repairable, so its not even a useable core for an exchange program. Is that right?

Do most small airports sell AV gas to anyone?

 

[Goinboardin]

Some Pics (finally)

First Pic is PTO side piston last summer. 900 miles on it, 98% of the time I was running 330 mains and non ethanol 91 octane fuel.

Second pic is MAG side piston at the same time, same jetting.

Third pic is PTO piston after the engine went down. About 1500 miles on it at this time, no longer running non ethanol fuel but still had 330's for most of those miles (maybe 100 miles on 320 mains).

Fourth pic is MAG piston after engine went down. Yuck.

Fifth pic is PTO rod bearing. Junk.

Sixth pic is MAG crank bearing. Junk.

Seventh pic is MAG cylinder. Notice the chips missing from the skirt.

So I thought it was running cool enough. Probably not. Should have backed the timing off, ran a larger radiator, and ran better fuel. Lesson learned, maybe someone else can learn the easy way from this post.

 

[Jay]

For what it's worth I snapped the crank in 2 on my old '97 700 last saturday. My kids boyfriend borrowed it and at least he had the good sense to shut it down when it started rattling. 4400 miles and few of them easy, psi twins but other than that bone stock and never been touched. It always thought it was an 800, it certainly embarassed more than a few of them, but I didn't think it would decide to snap a crank like one. Anyway when I topped it up I had run out of premium so it had a half tank of regular in it, first time I've ever run regular in it, and it snaps the crank, coincidence??? who knows

 

[Hardass]

Pretty sure the edge or escape the oil line went over the top of the carb boots. And if any ones oil was leaking down into the case when not in use there was some other issue.

 

[XCRacer440]

^ Can we get 100% verification on this. One guy says above, the other says under. Which is it because I just bought an 01 XC 800 with a 136x2" that just had the motor out to do the bigger pto bearing, machine cases, balanced crank, 1 new cyl, and 2 new pistons. I want to make sure 100% of where the lines should be routed.
Thanks, and great read!

 

[Hardass]

Regardless over or under will not matter in any way

 

[Goinboardin]

I had some light scoring on the cylinder that didn't get the skirt broken when the engine went down last spring, but it wasn't very deep (could feel it with a finger nail), so I was curious if I could make it work. Reading on here, seems like everyone has enough money to not make that kind of gamble without batting an eye. With some of the guys driving across country to ride, I don't blame them, but when I drive 40 miles to ride and don't make much $, I'm ok with a little experimentation.

The first pic shows the cylinder with light scoring that I bolted back up this fall. I rode with that about 5 miles in November on the MAG side, with a lightly honed cylinder off Ebay on the PTO side. New pistons and rings, rebuilt crank, SLP head, SLP twins. After a couple miles I checked compression. 110psi on PTO side, 92 on MAG side (pretty high up, thus the low numbers). It ran well, but I didn't like the numbers. SO I figured I ought to tear it down and have a peak. I figured either the light scoring was causing compression loss on the MAG side, the cylinder was not true/straight, or the rings were not seating because I didn't run a hone thought that cylinder.

I ordered a Flex Hone, 240 grit meant for Nikasil. Ran the hone through both cylinders, washed them, put the motor back together, cylinders on the same sides as previous assembly, checked compression (oiled cylinders but cold) here in Laramie. PTO 120psi, MAG 102 with WOT and 5 pulls. So still uneven. Pulled cylinders, honed the MAG cylinder again (pic of that cylinder is shown below). This time when I reassembled I wanted to see if the poor compression followed the cylinder of if it was because the rings hadn't seated on the MAG side. The Ebay cylinder went on MAG side, my old cylinder that I have now honed went on PTO side. PTO compression 120, MAG 102. So the poor compression stayed with the rings that didn't break in. Good news for me. I suspect the compression will become even once the MAG rings seat now that they have a honed cylinder to break in on. I'll report back after a break-in ride, but I'm waiting on SS exhaust valves on a clutch cover bushing.

Anyway, just thought I'd share, because it seems like few on here ever try to save $ on stuff like this for fear of a wrecked trip, which is understandable, but makes it hard to get any idea of what corners can be cut to save cash.

Oh and I didn't have the pipes on doing the compression checks in Laramie, I imagine that drops the numbers down some too.

For the record, oil lines go over the carb boots, and that's how I have them routed. http://www.polarispartshouse.com/oe...-s04nk8cs-a-b-c-s04nl8cs-a-b-c-s04nm8cs-a-b-c
This link shows the OEM orientation of the oil line hoops, over the boots, just zoom way in at the carb boots. But as Hardass pointed out, and Jay explained in a PM, it wouldn't matter either way. If the case fills with oil, the check valves are bad.

 

[Jay]

Great info, thank you, More than once I have hemmed and hawwed about using that "used but looks ok" cylinder on the bench for fear of having to tear it down again. I've talked to some very knowledgable people that don't have a second thought about using a good used cylinder, they probably have more experience building engines than I do. Who am I kidding, they have WAY more experience than I do. I'll have to pick up a hone like your describing and give it a try, any recommendations for brand or where to buy? Good on you for trying this out and helping others get over their fears. A good friend of mine likes to say "God hates a coward" and then he'll jump off a cliff or do something stupid. I'll stop being a coward about used cylinders.

 

[Goinboardin]

I bought this one, from this company: http://www.enginehones.com/312240ao.html Showed up in a few days.
They have some good info here:
http://www.enginehones.com/technical.html


I think 320 grit would be more ideal especially just to get the cross hatch back for break-in of new rings, but with the light scoring I had I went with the more coarse grit that was still recommended for Nikasil. I coated everything with a bunch of 10-30W oil during honing, and did 15second intervals to check the condition before any further honing, running the hone up and down the bore about as fast as I could. The Nikasil is not thick, so I didn't want to hone right through it. I would like to pick up a cylinder bore gauge so I can check cylinders in the future for out of round, as a ball hone can't help there. If I wear out my rings in a 100 miles I will have learned my lesson that 240 grit is too coarse.

The first time I built this motor I had a good used cylinder, but didn't want to chance anything, so I sold it ebay for like $75 and picked up a set of rebuilds from Hardass (which were great). I was doing the same himming and hawing before doing this, but for the cost of some base gaskets and a new tool, along with very little snow, I figured what the hell. And imagine that, with the motor apart, it snowed! I always get a good laugh from your stories Jay, thanks.

 

[Jay]

Thanks for the link, I'll be phoning them monday morning. They have some nice tools as well.

 

[Goinboardin]

Now the question is do I want to run the 13.5:1 heads (SLP 12-533 domes) or the 14:1 heads (also SLP but not listed)? I have both. Probably need a little av gas either way...

 

[Jay]

We have lots of snow here but I recently had knee surgery and can't do much of anything, the shop is getting backed up and it's not real big to start with. The '02 700 is a friend of my daughters, it needs a top end and straighten out a few things, the '98 700 is mine, I'm waiting on the local shop to rebuild the skid shocks and the gen 2 chassie is a stalled project I don't know what to do with. I'm working on a couple of 800's and slowly collecting parts for a 1200 triple. When I get all this crap out of the way I want to go through the 1200 IQR I bought for my wife last spring and I haven't even pulled the cover off my gen 2 1200 triple in the shed yet. Anyway snow I got but no riding for me till ?????

 

[m8magicandmystery]

We have lots of snow here but I recently had knee surgery and can't do much of anything, the shop is getting backed up and it's not real big to start with. The '02 700 is a friend of my daughters, it needs a top end and straighten out a few things, the '98 700 is mine, I'm waiting on the local shop to rebuild the skid shocks and the gen 2 chassie is a stalled project I don't know what to do with. I'm working on a couple of 800's and slowly collecting parts for a 1200 triple. When I get all this crap out of the way I want to go through the 1200 IQR I bought for my wife last spring and I haven't even pulled the cover off my gen 2 1200 triple in the shed yet. Anyway snow I got but no riding for me till ?????

willikers...you shop is jammed packed with stuff more then a dollar store at xmas..

 

[Goinboardin]

Mistakes Continued

Don't let your belt to sheave clearance grow large...

This fall I dropped in a rebuilt crank. Ran the sled for a while. Early January I thought it was shaking pretty good. So I checked runout, 0.0095" and thought ah ****. Then I noticed my belt to sheave clearance was very large. Ran the sled one more day, knowing full well the crank could snap at any time, it was a crap snow day and I was just puttsing around. Checked runout, 0.0105" Ok she's done done.

Pulled the motor down last night. PTO rod pin was shifted off center: Exactly like IndyDan said will happen when the belt to sheave clearance is excessive. The clutch acts like a slide hammer, pulling the PTO end of the crank right off the PTO rod pin, or in my case pulling the PTO rod pin outward with the PTO part of the crank.

I'm still a cheap bastard though, can't convince myself to spend 1800 on a well made bottom end. SO instead I'm buying a rebuilt crank (with new PTO end) and a brand new clutch gone through by Dan. This sled will hopefully become my mod/backup sled next season. My cases still put a nice slight crush on the bearings.

That first season after I rebuilt my motor I had 0.0015" runout, healthy looking motor. That was with a clutch fresh from Dan, running good gas with lots of cooling. Running another fresh clutch from Dan, better head, and good cooling again I think she'll live. I just can't be lazy about clutch shimming, good fuel, or good cooling.

Anyone running premix on these motors? I was thinking hell may as well drop some parts/clutter and drill the case while its apart. I've read they run more crisp too?

 

[Goinboardin]

Well the good news is I'm pretty fast at pulling the engine out and apart these days. Snapped the crank in April and didn't touch it until last night. The last crank I put in looked good: 0.000-" runout on MAG side (I didn't measure any runout, needle didn't move at all!) and 0.0008" runout on PTO side (needle didn't quite move a thousandth). Brand new clutch from Indy Dan (shimmed, balanced, perfect) with weights all equal weight.

Non-ethanol fuel, wash & plugs looked about right.

I was running premix, drilled the case to get oil to outer bearing. It had the wide bearing in it (I've now run both). I ran between 30:1 and 35:1, all the bearings looked good when I pulled it apart. Clutches would get warm but not hot. Actually it was running awesome this year after the rebuild in February.

Crank snapped in deep snow at wide open throttle. Maybe 700 miles on it? No speedo so I'm not really sure. It wasn't vibrating like when the crank is way out of true leading up to this.

The day it broke, I was adding a bit of oil to the fuel at the trailhead and added more than I meant to, so that day it was more like 25:1. So a little lean on fuel? Didn't melt the pistons though?

I originally thought I took out the rod bearings from deto (again), but the rod bearings look good and the piston damage is from shards of rod pin not moon craters you see from deto.

I have no idea why this one broke. Pretty over it. I think I'll just part it out and buy an M8. It's been fun, and I have learned a lot, but obviously I'm not an engine builder, so I should ride something that was put together right from the factory.

 

[Jay]

Sorry to hear of your troubles. I don't think it's anything you've done, it's just the nature of the beast with these cranks. I'd let you build me an engine anyday.

 

[retiredpop]

In reading this thread I must give kudos to you for attempting to make this engine as reliable as possible. It sure sounds like you know your stuff. In retrospect do you think the indydan crank would have made any difference or do you think it is just a combination of poor design, poor fuel and bad luck? I'm glad I have never felt the urge to buy a Polaris 800.

 

[Goinboardin]

I'm sure the 174x2.5 track with race twins, deep snow and plenty of throttle had a lot to do with it. It was still a fun season.
I suspect Dan's motor would have lived these last two scenarios as they seem to be more from clutch issues (not that I would have been okay to neglect proper clutch shimming) and lack of brute strength, but deto still would have taken the rod bearing in the first time it broke. Nothing can replace good fuel. As for the mag main bearing spring of 2012 I think that was part bad luck and me not realizing the cause of the return of the hanging idle.

Either way, I don’t regret having this sled. I learned a ton and likely won't have to rely on shop mechanics because of it.

 

[Goinboardin]

http://www.hardcoresledder.com/foru...860-very-good-info-800-crank-failures-11.html

Page 11 has an old Snowest discussion posted in it; by IndyDan. Its probably about the most valuable read for anyone looking into making one of these motors live.

What my most recent engine failure comes down to is case fit. That was the only thing I never actually measured. I just used an old bearing to see what kind of crush there was in a qualitative way (feel) not quantitative way (measurements). Maybe it was only 0.0005" crush, maybe it was 0.0015" crush, I have no idea just that there was some crush.
Reading that thread again (3rd separate time at least) makes me want to try again...must.fight.the.urge. Sell now.... haha