I am nearing the heart of my rebuild and am in need of advice. Here is the story as briefly as possible. Itís an 85 k100rs with 96,000 miles.
After driving it for years and performing just the minimum regular maintenance I decided that it was time to give it an overhaul and clean it up. I didnít realize that I was going to completely rebuild it so I didnít do some things initially that might have helped me with the question I have now.
I needed to replace the sprag clutch, fix oil leaks on the cylinder head and timing chain cover and also remove the frame to paint it. Because of these, I decided to strip the bike down completely. So far, all has gone smoothly and the cylinder head is off and the engine is out of the frame.
Here is the issue: This bike always smoked when left on the side stand. I was told this was normal when I bought it at 26,000 miles so I almost always kept it on the center stand. One time at about 80,000 miles I left it on the side stand for some reason and when I returned and started the bike it literally filled the street with thick whitish smoke. I was worried but it lessened a little and in driving home it completely cleared. When I restarted from the center stand all was fine, still smoking a little bit as usual but not ridiculously. I never put it on the side stand again. Since about that time the smoke has been increasing when I start it from the center stand. I donít know how to quantify it but it is enough where you wouldnít want to be standing behind me for a good minute. Once warm there is not much smoke, if any at all. It does not burn through the oil. I change the oil every 5000 miles and never have to add between changes.
So I assumed it was either a piston ring or valve problem. I should have given it a compression test or done some other diagnostics before dismantling the bike but I didnít. Now that I have the head and block sitting in two pieces in my garage I need to decide what to do.
I spoke with a person at a locally recommended cylinder head service shop ( http://www.perf-concepts.com/
) and he said that if I am not loosing much oil then it is more likely a valve problem than a piston ring problem. The cost to teardown the head and inspect is $40 to $80. (if service is needed then this is credited.) the cost to replace the seats and seals is roughly $240. If guides need to be replaced then the guides are an additional $40/guide.
I am now debating whether it is best to:
- pay for the inspection ($40 to $80) with the anticipation of needing $240-$300 valve job
- or to buy a used engine with lower miles at roughly the same cost?
As for the piston rings, I can either:
- assume they are ok
- try to replace the rings myself. It does not look too difficult but requires a double headed ratchet tool to tighten the bearing caps. Does replacing the rings myself and then bringing the block in to a professional for the cap tightening sound like a reasonable option to consider?
- buy a used engine with lower miles and replace the cylinder block and head.
If buying a low mileage used engine is the best way to go, what recommendations do you have for evaluating the engine before purchase? They usually seem to be already removed from the bike so seeing them run might not be possible.