Tight valves on 120

murphus

murphus

Senior member
Location
Lost in the Midwest
Looking for some insight/ideas/thoughts on why the exhaust valves on my 83 RGS like to tighten up. Engine's just shy of 62,000 miles. This has been a problem since I bought it with about 42,000 miles on it. My experience has been that the intake valve clearance stays fairly consistent, while the exhaust tightens up regularly. At about 58,000 miles I pulled the head, as I was at the end of the line on shims. My local machinist, whom I trust completely and who has years of experience with the odd, the powerful and just about every sort of engine one might imagine, said it was valve seat recession. The original owner had installed hardened valve seats years back. Doc, my machinist, took it apart, measured all the valves, determined there was nothing odd there such as stem stretch, and replaced the seats. He did an excellent job and set it up such that when I put it together it shimmed up consistently. He's pretty meticulous and takes pride in his work. My notes are not as coherent as I'd hoped, but I see that I adjusted them once about 1,500 miles after putting it all back together. The exhaust valves were tight, the intakes within range. Now, after another 1,500 miles or so, the #3 exhaust valve has almost zero lash, coming in at about 0.001in. What would you look for in a case like this? It's pissing me off, mostly because it's a pain in the ass to pull the cams every 1,500 miles, especially when I read other people's experiences of running up to 10,000 miles without needing to adjust the valves. My riding style is only mildly aggressive. I like to give the engine plenty of head, but I don't run it like a race bike because obviously it's not. I'd call myself a sympathetic owner with plenty of mechanical empathy. Any thoughts appreciated. I don't really want to pull the head again, but ...
Richard in Kansas
 
Richard,
If the job was done well, and you've only covered 1500 miles since doing it, there's a good chance that what you are seeing is just initial settling in which is perfectly normal, it usually stabilises after a few thousand km.  If it continues then you might have some other problem.  Were the valves replaced?
Cheers
Steve B
 
No, valves weren't replaced. Still had plenty of meat on the, and no indication of stretch or any other possible ills, which i wouldn't have expected given the relatively mild treatment the engine gets. They were reground. I still have plenty of room for adjustment, I guess I'll reshim it and check again in another 1,500 miles. It frustrates me as I have plans to pile on some miles this season; I want to ride, not worry!
Richard
 
Richard,

I'd check jetting and/or float levels.  It is not uncommon for float valves on 120 engines to wear, elongate and lower float height, leaning out the mixture considerably.  This will cause the valves to stretch, fast!  Float height is 18mm from float bowl gasket surface to lower float edge with the valves just closing.

Can't quite understand why hardened valve seats should wear so quickly.  First, the original seats would wear out, consider about 100000km/60000miles for that.  If new seats were then fitted and were worn out, mileage is bound to be considerably higher.

I fitted hardened seats to my 3C in 1991, 70000km later, shims are all in the 2.50-2.70mm range with minimal adjusting required.

A sure sign of low float levels is a tendency for the engine to hesitate slightly at around 5500rpm while accelerating and once over 6000, pulling cleanly again..... but that's where the danger factor sets in. :D

piet
 
rico, i think it was a moto journalist that coined the phrase ride it like you stole it  :D

did doc compare the valve lengths to the dimensions of NOS exhaust valves?
did you recheck your last valve adjustment with cam chain attached?

"A sure sign of low float levels is a tendency for the engine to hesitate slightly
at around 5500rpm while accelerating and once over 6000, pulling cleanly again.....
but that's where the danger factor sets in."

thanks piet, that's a new one to me

cheers,
scott
 
Thanks for the tip, Piet. I'll check the floats. I don't believe I have any sort of stumble off idle. Fact is, it's always pulled like the proverbial train, strong and fast as soon as the revs lift. Scott, are you suggesting checking the lash with and without cam chain attached? And no, didn't check the stems against OEM, but against each other. Granted, if they're all stretching that's a fairly worthless reference, but it seems unlikely? I think I'll just go with my first inclination, which is to reshim (and check floats, per Piet), then ride it and check again. If they're still closing up, guess it's time to pull the head again.
Richard
 
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