TOPIC:

Hey guys I must ask for your expertise once again. I rolled out my 76 900 with 30k on the motor. I heard some valve noise, and saw some smoke on startup. I assume the valve stem seals are dry/worn out, and the valves need adjusted. To my knowledge the bike has never been torn down and had the clearances checked. How big of a job is replacing/re-shimming the valves, and replacing the seals? Also what all should be replaced on the top end? Such as the cam chain and all hardware associated with the cam chain?

Adjusting the valve clearances is no big deal. It's really helpful to have the valve adjusting tools, especially the metal widget to hold down the valve bucket while you're changing the shim out. You'll probably need a valve cover gasket as well as appropriate sized shims if any need to be changed.

As far as the seals and cam chain and such, you need to decide how much you want to get into it. You're going to need to pull your head to change out the valve seals, unless maybe someone here knows how to remove and install the valve springs without pulling the head. You'll at least need a valve spring compressor and of course head gaskets, seals and such. While you have it off, it mightn't hurt to get the valves and seats ground.

Replacing the cam chain and associated idlers, dampers and so on is really getting to a point of maybe doing a proper top end job. Replacing some of that stuff gets pretty pricey though, like the idler wheels. The dampers and tensioner aren't bad. Changing out the cam chain, well I suppose the most reliable way is to split the cases and put in a new one but I have seen cam chain master links. I don't know how reliable that is though, anybody else?

Just an opinion, if the smoke is not too bad maybe I'd check and adjust the valve clearances, maybe just ride the bike for a bit and make the motor a next winter fixup job. Maybe do a proper job with rings and such.

Even if you could get the valve springs out with the head on the motor, it would be dificult to change the seals with the valves in them.

best to remove the head. At which time, you can pull the exhaust valves half way out and see if you can rock them in the guides. If you can, then a complete head rebuild is in order.

Jay

What Jay said...
So many times,the heads get neglected,and cause other problems that can be a real P.I.T.A. to diagnose.
What the heck...good time to learn,if You haven't already been in there...do those valves need resurfacing/lapping?...is that gasket leaking?...why DO I get a puff of smoke out the pipe,when I first fire the bike up?...has My timing chain stretched,and if so...how much HAS is stretched?(beyond service)...are all the rubber idlers and other rubber parts hardened up?...NAWWWW...can't be...they're only 25-30 years old.
Part prices are reasonable(depending on what You want to replace)...piece of mind...
Seriously...it's fun(if You aren't FORCED into tearing it off),and You WILL learn a lot about Your engine...

I could make a valve spring compressor that would work with the head on the bike, and I could use compressed air to hold the valves in place while I removed the keepers, retainers, springs, and replaced the valve seals, but it's easier to just pull the head so I won't
Plus while the head is off I can check (and lap if needed) the valves, and check the valve guides.

Thanks for the info, at least now I know what Im looking at if I tear it all the way down. Ill prob just work over the shims until next winter, then take it down to the machine shop and see about some quality engine displacement upgrades!

Prune1 wrote:

...then take it down to the machine shop and see about some quality engine displacement upgrades!

theres no replacement for displacement, unless its NOS or boostB)