tight valves

[schrader7032]

If your bike had been an '81-'84 model, the likely cause would have been clear to me. These years had bad seat material which didn't transfer heat from the valve into the head. Consequently, the valves retained more head and deformed, reducing the valve clearance. Oak Okleshen has called this valve face plastic deformation.

Prior to 1981, any of the bikes could have could have the other situation which is valve seat recession, the slow wearing away of the seat, and reducing the valve lash. The theory was that the lack of lead in the gas is not giving the lubrication needed between seat and valve, and bits of the seat are disappearing.

How many miles on the bike? Do you run the bike hard, well above 5K RPMs a lot? Running hard will result in more heat which will hasten the valve recession.

What about head bolt torque? One possibility is that the head bolts are pulling out of the case from being overtightened. Or it could be that the bolts have never been torqued in a long time, and they're just loose.

I would check the head bolt torque. They should be first loosened say a quarter turn and then tightened in stages, say 10, 18, 25 ft-lbs. Use a criss-cross pattern.

After that, I'm not sure what else to do, but probably pull the heads and have them examined. The last thing you want is to drop a valve...the cost goes way up at that point. If the valve clearance is gone in just a short ride, that is serious indeed.

Kurt in S.A.

[Darryl.Richman]

Just to clarify, do you mean that your valves tighten up when measuring them after you ride the bike, when they are still warm? That would be natural, and in fact that is the whole reason for setting the valves with a gap in the first place, when cold.

But if you mean that the valves, when measured cold, tighten up over a few hundred miles, then it probably does mean one of the things that Kurt has suggested.

If you are still losing clearance after checking the head torque, then you are probably looking at a top end job, new seats, valves and guides. The faster the valve lash changes, the more desperate your need to have this repaired. If you burn a valve, it may stick and hit the piston.

[mcclelland7640]

thanks for the response. first i don't know the exact mileage as the speedo is broken it says 60,000 but i don't trust the number. my educated tack says i've been over 5 grand i took it on the highway maybe a bad idea. i checked the valves cold(next day) and torqued the heads so i guess it's time to pull the heads. thanks for the advice i'll let you know what i find.

[VBMWMO]

i have a 72 r75/5 and have done 3 valve adjustments and have had them checked so i know the adjustment is correct. after a i ride it a little bit they tighten up what might be causing this