Valve guides finishing

[raspii]

Hi Guys,

Just a quick question regarding my upshur twin, when making the valve guides i'm making them out of bearing bronze.

I just wanted to check what sort of tolerance is required between the valve and the valve guide. Do you normally make some type of small reamer to make the fit very tight, or in this instance is the use of a drill sufficient, and then making the valve so it's a nice fit through the drilled hole.

Any assistance would be greatly appreciated,

From Pat

 

[Herbiev]

For a snug sliding fit I would use a reamer. Drills often drill a hole larger than their specified size.

 

[rklopp]

I reamed the ones on my Upshur Twins to a sliding fit with the valve stems. You want them to move easily, but not leak. I'd guess a 0.0005 - 0.002 clearance on the diameter would work. Mine are probably around 0.0005-0.001. Oil forms some of the seal, and a 0.001-in radial clearance is not likely to leak much on either the intake or exhaust strokes. Exhaust leakage past the valve stems hardly matters.

 

[Charles Lamont]

You should be able to buy a reamer the right nominal size. It will probably cut oversize though. So I would ream the holes and then make the valve stems to fit, ideally with no friction but no play either. It may help to make a dummy spindle to check what size to aim for.

 

[Tom Jamboretz]

Make the guides first the make valve/stems to fit. Keep in pairs.

 

[Brian Rupnow]

If your machinery is any good, an "on size" reamer will cut "on size". I always ream for valve stems using an "on size" reamer. All of my engines have 1/8" valve stems and I use a .125" "on size" reamer for my valve guides. I make the valve cages, Loctite them into the cylinder head, then turn my valves and keep trying the cages onto the valve stems for "sliding fit" without taking the valves out of the lathe. It is so easy to inadvertently turn a valve stem "undersize" that I turn to within about .002" to .003" oversize, then polish them with 220 grit paper while they are still in the lathe until I get a perfect sliding fit. It can't be a sloppy fit, but it can't bind either.

 

[Tom Jamboretz]

I agree with Brian's method. Same thing I do. Always have success.

 

[raspii]

Thanks guys, sorry if it's a very basic question, but i really appreciate your assistance.

I can't wait for the day when i can post the running video of the engine as a thank you to all of you who have helped to make it happen

From Pat