When I got the bike in the fall, it came with no history. Thanks to the help here, I've made good progress on this project bike. So far I have replaced the wiring harness, fixed the electric starter, added battery tray, added a missing starter relay, and upgraded to a Dyna S ignition. I also cleaned, rebuilt, and re-jetted the carb.

The bike is running pretty good right now. It starts right up and idles nicely. After the bike warms up, I start to see some blueish colored smoke coming from both pipes. Granted its not a smoke screen, but increases when I rev it up. The front cylinder plug has oil on it as does the rear plug (though much less).

On a warm engine, I did a compression test according to the manual. The front was 150 and the rear was 130. I added some oil to rear cylinder and did another test which didn't change the reading. According to the manual, the difference is greater than 10 psi so I should be concerned.

I pulled the plugs and used an inspection camera to take a look around. The piston crown has 010 on the top which I'm assuming means 10 over. There was some standing oil on the top of the front piston as it was almost to the top of its stroke.

My question is this. My plan is to ride this summer if I can. Should I start tearing it down and consider a top-end rebuild?

Thanks

 

Nick,

I'm not an expert in these things, but it sounds like the exhaust valves are leaking and you will need a valve job.

My 80 shovel showed exactly the same symptoms. When I took the heads off it was apparent that the front exhaust valve was leaking badly. The rear showed some oil but not as much.

If you take the heads off to have the valves done, it's not much more work to pull the cylinders and pistons and have them honed or rebored and fit new rings and/or pistons as appropriate.

Personally, I'd tear it down and do the top end - otherwise I'd be worried about it all summer when I was riding it.

 

I've been thinking a lot about it and might as well do it now. I will make sure it gets done right and I've wanted to learn more about wrenching on this motor anyways. With a service manual and the expertise on this site, I should do fine.

 

Smart move there.... Time for top end job.... Valve job with guides and yea at this point, bore, pistons and rings.

 

Be careful.....:-) That was my thinking and attitude when i started wrenching on my top end, I said "what the hell" and now I'm in the middle of a frame up rebuild!

I'm also (probably vainly) hoping to have the bike on the road for the summer. I'm not specifying which summer yet though.

 

Ha ha! Nick - I have enjoyed following your posts. Do the top end now, then ride all summer in confidence. You seem to have a good perspective on things, and deferring something like this can often lead to other, less desirable, consequences.

My '79 FXS Lowrider will be ready to go about the same time you start riding... here is to a great summer for both of us! Keep up the good posts... I have fallen behind on my blog, but picking up steam again!