I'm working on a 04 450 foreman and having a problem. It's been bored and honed .030 over with a new piston and rings. I'm used to the beveled ring going on the top grove but this is a aftermarket piston and the instructions said to put the beveled ring in the second grove and it didn't matter how the top ring went on. Well, after putting it together it only has 50 lbs of compression and won't fire. The beveled ring won't go on the top grove because it's too thick to fit. I'm sure I got the rings right but I think the torque on the head bolts are wrong. What are they supposed to be torqued to and how much compression should I have?

 

The head bolts should be torqued to 29 ft.lbs, The compression would be around 78-121 psi if the decompresser is working and will be 178-206 if it is not affected. You could back off the exhaust valve about 1-1.5 turns and see if that brought the compression up. That way you could figure out if it could still be in your rings causing the lower compression. I would tend to think you will find your problem in your rings unless you have something within the head that causes the loss of compression.

 

The head nuts are only torqued to 20 lbs right now. Do you think this has something to do with it? I've reringed several stock foremans before and the beveled ring always went on the top groove. This has a Wisco piston though and the beveled ring won't fit the top grove so the instuctions said to put it in the second grove. Do you know anything about this? Thanks for the help.

 

It could have something to do with it as I should have said flange nuts instead of bolts. They still torque to 29 foot lbs. Before installing the rings did you check the ring end gap? If so proceed:
Second ring: Using a piston ring expander, install the second ring with the marked side up. An unmarked 2nd ring with an inner bevel should be installed bevel side down. If the ring is not marked on one side near the end gap, either side can be up.
Top ring: Using a piston ring expander, install the top ring with the marked side up. An unmarked top ring with an inner bevel should be installed bevel side up. If the ring is not marked on one side near the end gap, either side can be up.

 

Yes, that is what the instructions said. They didn't tell me which ring should have gone in the second or first groove though but the beveled ring was thicker than the other so they would only go one way. I put the beveled ring bevel side down on the second groove and the other ring, which didn't have a bevel or mark, on the top groove. The four wheeler started and run like crap for a while then shut off and won't start back up. The compression checks in at 50 lbs. The valves are set right, it has new gas and spark plug and the carb has been rebuilt. The head has been reworked with new guides and the valves have been done as well.

 

Ok, I didn't know that you actually had got it to run. With the rings being new they are not going to have real high compression until they seat after breaking in some. However you should have more than 50 psi. If you know for sure that all other areas are covered and you have the right torque as well , I would look at the timing next. I know you might think its fine but just check to make sure. I once rode my foreman for over 30 miles one day and rode back to camp only to have the chain slip while starting it to load up. Like yours it had compression but no start. The chains in these will stretch easily over time and some with not to many miles. The tensioner's tend to go bad sometimes but not as often as the chain. Might be worth a look if you think your rings and top end are not the problem.
Alsop you mind try to add a little oil to the cylinder to see if that would bring the compression up any , just to rule out it being an issue with the rings.

 

I will try the oil trick. I knew I'd heard of it but wasn't sure. I will check the timing as well just to be sure. I'm about to go work on it now. I'll write back this afternoon on what I find. Thanks again.

 

Ok, I put a little oil in there and the compression jumped to 120 lbs for just a a couple of cycles. Then it went back down to 50 lbs so I know it's a ring problem. Like I said earlier, I'm used to the beveled ring going in the top groove on the piston with the bevel up but it wouldn't fit in this case so I put it in the second groove with the bevel down. I'm going to look on the Wisco website to see if they have any info for me on this piston. I guess I'll start tearing it back down now. With no compression I guess that's the next step. I told the machine shop I wanted a stock piston for it, I don't know why they give me this pop top racing crap!

 

I got it torn down. Everything looked ok so I took the rings and piston off and checked the ring gaps. The compression ring with the bevel that I had in the second groove has a .013 gap and the top compression ring only had a .001 gap. The gap on that top one is almost non-existant. What is it supposed to be?

 

Ok, I used the piston to push the rings in the cylinder so I knew they were in there straight I checked the ring gaps again. The top ring is supposed to have a .014 gap and doesn't have a gap at all. The ring is butted up in there. The second ring is supposed to have a .017 gap and has a .013.