Finally got her apart

[MikexG]

Hi

 

I have been struggling with low compression (80 v. 120 on other side) in my left cylinder since I bought this 2001 V11 Sport a few weeks ago. I figured it was rings because compression jumped when I squirted a bit of oil in the cylinder. After trying marvel mystery oil and other things to free what I thought was a stuck ring, I finally pulled her apart. I am trying to figure out what I have. Btw - pulling other side off this weekend.

 

The piston skirts seem abnormally scuffed. Any thoughts would be appreciated.

 

Mike

[Kiwi_Roy]

Are we to assume you do the compression test with wide open throttle?

 

A slight unbalance of the throttle bodies will make a huge difference if the throttle is in idle position, a common mistake.

 

I've seen a lot worse looking pistons.

[MikexG]

Kiwi Roy - the throttle was wide open. Also did lots of other stuff like adjust valves, check injectors, plugs, etc. the one thing I didn't mention is that the exhaust temperature was half the temperature of the other side using an infrared thermometer.

 

By the way - I am bringing that thermometer with me any time any time I buy a bike or car.

[MikexG]

Ok. Here is a picture of the other side that has decent compression.

[GuzziMoto]

Sorry to give you this info after the cows are already out of the barn, but here goes.

If you do a compression test and one side is lower than the other to the point you think something is wrong, the next step is a leakdown test. During the leakdown test you are pressurizing the combustion chamber, so based on where the air is escaping to it typically gives you an idea of why the compression is low. Air escaping out the crank case breather is rings. Air escaping out the exhaust pipe is a leaking exhaust valve, and out the airbox is a leaking intake valve. Without all that we are guessing.

If you are losing compression most likely it is either getting past the rings, or one of the valve/valve seats is leaking. There are other possible issues, like valve train issues (bent pushrod, etc), but it is more guessing.

Since you have it apart you may want  to throw a few new parts at it. If Mike Rich still offers his pistons I would go with those, new rings, have the valve checked and maybe do a valve job/porting job on it. That is, other then Mike's pistons, what I did to the wife's V11 a few years ago.

[docc]

I can't tell that the pistons look much different. Is the scoring on the cylinder walls much different on the affected side?

[MikexG]

I know I could have down a leak down test - but I figured if I am taking off heads - I will look a rings anyway. Remember the compression jumped way up with a bit of oil in there.

 

I am including another picture. It looks like the oil ring was broken. I tried taking it off and it broke as I pulled it off.

 

Let's see.

[docc]

mike, how many miles on this Sport?

[MikexG]

17,000.

[jwh20]

Those piston skirts just don't look too bad to me.  The cylinder walls look OK as well.  Did you check your valves?  From the photos the rings look good.  I'd expect to see a broken ring and scoring on the cylinder walls if this were a ring problem.

 

BTW, I'd expect the compression to go up after adding oil.  You have the oil in there taking up space and being a liquid it's not compressible.

 

Since you have it open check for:

 

1) Bent rod on the low compression side.  (Rare but easy to miss.  Perhaps there was a hydro-lock issue and it got bent before you got it.)

2) Burned or poorly seating valves.  This is, IMHO, the #1 issue with low compression.  I'm assuming, of course, that before you went through the trouble of tearing down your engine you checked the valve clearance??  If it's too tight you get poor seating and a leak.  On the V11 it's easy to fix this!!

3) The piston looks good but a cracked piston will obviously end up with low compression.  

[dangerous]

hey ok so... IMO and what I have found with my engine rebuilds and remember 90% were two strokes... If I saw scratchs like that on a piston and bore Id say tempory seizing

[MikexG]

GuzzMoto - t I spoke to Mike Rich. I am leaning towards using his pistons - but I am concerned about higher compression. Have you heard good things about these pistons? Btw - I am sending the heads out - might have Mike do them.

 

Jwh20 - the bent rod check is a good idea. I looked and it's fine - I think. But I did see that's the connecting rod pin bushing shows wear - is this normal? Both sides look the same..

 

Thanks for all the avoid advice, you guys are great.

 

MG

[gstallons]

If it were me , I would pull the rods and have them checked. The procedure is not that difficult to do . While you are in there , new rod cap fasteners , ( price the bearings to see how expensive ) , keep the rod bearings indexed where they were when you tear it down. Spend the $$$ and get the Roper plate .

[MikexG]

Gstallons - it's a slippery slope....

[GuzziMoto]

Everything I have heard about Mike Rich pistons has been great. They are higher compression but that is offset by the improved squish band which reduces the motors tendency to ping by improving turbulence in the combustion chamber. I did not use them because they were out of stock at the time I was doing the work. So I had the cylinders cut down to try to accomplish the same thing, higher compression but better squish. It seemed to work, more power and less ping.