Replacing piston rings. Should I do anything else?

[Jenya]

Hi all,

I took off the top end to replace the piston rings. Was getting a fairly low compression: 115 and 124 before and a lot of oil burning.

Since I have the head off, I wonder if I should service that as well. What is the common practice - have a shop to take care of it or invest into a valve compressor tool and hassle with valve lapping yourself?

I was going to call a shop tomorrow and ask them how much it would cost for them to take care of the valves if I bring them the head.  What price quote can I expect?

By the way, is it just the way these bikes are  - some 30-40K miles and the new rings are in order? I will also have the shop to hone the cylinders. Don't want to invest into a honning tool that I may be using twice in my lifetime.

Cheers,
Jenya

[fred]

You pulled the head on a bike that had above service limit compression? That's bold. The GS does burn oil, it is an air cooled bike, there's no getting around that. You should have been able to get at least double the mileage out of that bike before oil consumption and compression became an issue unless it was abused way more than your average GS, which already seems to be saying a lot. Are you sure you weren't loosing oil from somewhere else? Perhaps somewhere high up on the engine where most of the leak burned off before it hit the ground? I have a pretty massive leak from the cam chain tensioner right now and even consuming a half quart of oil in 200 miles, the bike hardly leaves any puddle, it just kind of smells like burning oil all the time...

[Jenya]

You saying that I was dumb to pull the top end becasue the compression in one of the cylinder was a whooping 1 PSI above the service limit?
Holly cow - I could have ran the bike for another 50K miles on that one last PSI!

I have to admit that I don't regret deciding to service the cylinders when the compression read 115PSI and the service limit says 114PSI.

But of course none of that was my origional question.

[08GSSteve]

Ok Here goes,

The biggest mistake I made with my KLR650 when I did the top end was not doing the rest of it.......The owner before me cooked the engine (broken thermo wire) so I did the pistons and rings etc.  I only got 45k km out of that minor rebuild as then the bottom end went and was not worth fixing.

In relation to your question........While the hood is up check out the rest of the engine and replace anything that looks worn or is CLOSE to service limits.  May as well while you have gone to the hassle and done the top end.

Good luck 

[bobthebiker]

You're going to need to check that the head and cylinder block are square and not warped while you've got em out.  a new base gasket between the cases and cylinders, headgasket,  may as well just order a complete gasket kit.   

If you're doing a top end, you should be pulling the cases apart and fitting new bearings for the mains, and rods, along with checking your crank journals with a micrometer to confirm no excessive wear.     

This is just standard stuff if you're tearing a top end down and want to do it RIGHT so you can feel confident your engine will last and not just blow up 5 miles later.

[Jenya]

for some reason I was under an impression that the last thing one wants to do is to split crank case. I don't know why exactly I've gotten that impression. Probably from some other posts on this site.

Is there any potential problem or complication I may get myself into, if splitting the case? Do I need to pull the case out of the frame?

Jenya

[bobthebiker]

If you're doing ANY sort of motor work pulling the motor is best.  it takes a lot of headaches out of it.   get a manual for proper torque specs and you'll be ok.   I've only torn down a bunch of motors and reassembled em myself.

[bill14224]

I agree with Bob and Steve.  You're halfway there already so you may as well go all the way.  That way you won't have to do it again.  This especially makes sense if the rest of the bike is nice and is how you like it.

My guess is a top end job and replacing any worn engine bearings will get you to 100,000 miles.  If I were that deep into it I would go with an overbore and bigger pistons just for the fun of it!

Just curious.. how many miles did it take for your engine to reach the service limit on compression?

[bobthebiker]

Bill, you're pretty much right on the money. 

In my book, if you're doing a top end, you're going to tear it all down and do a proper rebuild to assure maximum reliability.  there is NO excuse for doing things halfway and blaming the motor for failing later.   

Besides, I find it much easier to pull the cases apart, and reinstall pistons with fresh rings through the top of the cylinder block. much less headache that way.

[intergalactic]

Personally, I would pull the valves (often you can rent a compressor) and lap the valves and de-carbonize the ports, if needed. And check the valve guide condition. Be careful you don't get/leave lapping compound in the guides. I wouldn't crack into it more than that unless it needs it.