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Discussion Starter #1
I am nearing the heart of my rebuild and am in need of advice. Here is the story as briefly as possible. It’s 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 didn’t realize that I was going to completely rebuild it so I didn’t 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 don’t know how to quantify it but it is enough where you wouldn’t 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 didn’t. 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:
  1. pay for the inspection ($40 to $80) with the anticipation of needing $240-$300 valve job
  2. 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.
 

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Guess it's too late for a leak down test :D Valve seals are a possibility, but new rings would never seat on that nikosel (?) cylinder lining. And I've never heard of anyone trying to recoat one with used engines being so cheap. Actually, if it wasn't burning any significant amount there probably wasn't a problem. Some hints....keep the oil level no higher that the dot in the sight glass. When you shut down, tilt the bike to the right for 10 - 15 sec to let oil run out of the cylinder bores. Did you change oil type or weight when you noticed more smoking? I've heard synthetics smoke less, (don't know for sure). As far as determining the condition of an out of bike engine, hmmmm, well,,,,, good luck!
 

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Discussion Starter #3
The oil level has never been too high and I've always used the same oil. I'd never heard of the tilt right trick. I'll remember that one and give it a try in any case.
 

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You really should have done that compression test prior to disassembly and omitting that step might give you cause to reconsider going full rebuild. Even if you are doing the rest of the engine yourself, I would still take the heads including valves to a specialist for inspection and service, it will be well worth the expense. I'm thinking the heads won't need much attention and your 'smoke' is indeed piston ring related. It's a judgement call better based on what you've seen inside there so far, do ya go all the way or service just the heads and re-assemble to compression test what's left ...how much do you like takin her apart so far ?

There were a number of 'claimed' improvements between the 85 and 86 or later K100' and oil scraper rings were on the hit list. I very rarely use the K side stand for the same reason you describe and even then, only for very short periods with the engine running.

Best of luck and hope all goes well, I have great respect for anyone that does their own service.
 

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Discussion Starter #5
I decided on a used engine. I found a 1990 with 56K on it for $200. It comes with a working starter clutch and a fuel rail. Both of which I needed and which would have cost me $100 anyway. Having already removed my own engine, trading it for a younger model at this point was not too hard of a choice.
 

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leak down how

Any tips how he could have done a leak down test on a sideways engine? I have hit this prob on boxers and never solved it. Usually, for a leak down test, you spritz a little oil inside the cylinder to oil the rings. With the engine sideways, you can't do that, can you?
 

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Ocelot said:
Any tips how he could have done a leak down test on a sideways engine? I have hit this prob on boxers and never solved it. Usually, for a leak down test, you spritz a little oil inside the cylinder to oil the rings. With the engine sideways, you can't do that, can you?
I just did a compression check on my '03 K1200GT ... measured compression once with dry cylinders, then again with a squirt of oil in each cylinder. The wet test jumped the compression by 15 or so psi so it definitely worked. Not hard to do, just squirt oil into the cylinder, the oil will work its way around the rings as you cycle the engine.

Leakdown test is more difficult ... trying to find TDC with the valves closed and the engine hot is difficult ... I kept the valve cover on, and made an attempt, but struggled with it. Gonna try it with the valve cover removed (gonna make an oily mess, I'm sure).
 
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