Hello again,
I am working on a CB77 and am tackling the head. I see in Silver's book that the valve guide clearance is about .0005" to .0015" when new but am looking for the service limits. The valves feel loose in the guides to me and measure roughly .002" to .003" clearance. I say roughly because measuring the bore using a small bore gauge set and a micrometer is a little tricky. Is there another way to decipher if I need new guides beyond measuring using the gauge set and a mic?
Thanks,
Rich
Valve guide clearanceValve guide clearanceCL77
CT90 RE5 49 Harley RT3 Yamaha
When challenged to measure something that small I use this method............a valve-guide should not allow you to feel the valve 'wiggle' with your hand when the valve is inserted to its operating position. After cleaning the stem and assuming no stem-wear, if the valve literally 'drops' under its own weight you need a new valve guide. A new guide needs to be reamed to make sure there are no burrs. A good valve with minimal lube (wipe with a slightly oiled clean rag) should slowly descend in the guide under its own weight.
If you have the dial-indicator...........try to measure the stem for any wear...........or simply gauge the stem at various places. All of this attention will lead to checking the valve seats in the head..........especially if the guides and / or the valves were replaced. I have rebuilt 5 305 motors.............all with less than 17,000 miles..........and no valves or guides were out of spec..........just needed cleaning and a light lapping. I am now rebuilding a 250-twin motor but everything going in is NEW because of heavy rust. When I buy a bike or just a motor............I pay a lot less if the exhaust valves are rusty.
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