Valve Lapping and Grinding

This seems like a good time of year to ask these questions. What is the proper way to lap valves? When do you need to grind vs. lap them? I've not done a valve job since High School 20+ years ago.

Sorry for the cross posts, but I didn't get any response on the 250F side of the house yet.


Don't waste your time trying to hand lap the valves. If your gonna do it, take the cylinder head to an automotive machine shop with the valves in the head. Give them photo copies of your service manual with the info on the valve and seat angles, pay your forty bucks, and live happily ever after! I don't know the specs but I'm sure there is multiple angles the seat has to be cut at. And the valve has to be cut at an interferance angle so it is resting in the seat on a razor sharp edge (best seal).

If your replacing an intake valve in your 79 chevy truck, lap it by hand. In your crotch rocket, leave it to the pro's. money well spent.

Do a cylinder leak down first, with a go fast motorcycle, 2% leakdown is real good. anything more than that, you have leak. listen to the exhaust, and airbox for any air leaking out. That is how you check the integrity of the valve seal!

Good luck!

I am rebuilding my 2001 426 right now and I had 2 valves on the intake side thad had sunk into the seat, thus giving me a negative cam to bucket clearance.

I talked with the owner of my dealer about regrinding the valves and shiming to make up the difference, keep in mind that this guy is an older Veteran and a good friend with vast knowledge in this area.

He said that even on the Suzuki race bikes running Ti valves, it is not recommended to regrind because the hardening is not thru hardened.

I am inclined to believe him, since I am a Machinist and have alot of experience with Machining exotic metals including Titanium, and the heat treating process also.

Titanium, 17-4 ph, and 15-5 ph are heat treated in a very similar process that involves what is called Conditioning, which you bring the metal to a certain temperature depending on the Mass of the metal and cross-section of it.

When this is done it creates a Thru hardened part with very little distortion, there is more to it than that , but I dont have time to go in to that right now, however when parts are made in a much larger quantity as in production like these valves, they are usally Carburized, which is like a case hardening but harder, but the hardening is only about .020 thick.

Keep in mind if you grind them and they loose there hardness the valve clearance will close up rapidly........and you know the rest.

I just purchased 2 valves today, all the seats looked good and the other 3 valves were all in spec.

Also if you regrind them be sure the Mechanic after he does the grind on the Umbrella he also grinds the end of the stem to make up for the metal removed on the seating area.

There is only .010 thousands of usable land area on the O.D. of the umbrella before its out of spec., so be carefull if you regrind.

Later, Jason

Replace Titanium valves!dont grind them. Grind the seat at specified angles. Then lap in with lapping compound ,lightly. Easy test when done, pour some gas in each port and see if it leaks through, It shouldn't. 2001YZ426F - 1996XR650L

YZ Abuser, You should only need to lap the valves after cutting the seats or when installing new valves. I don't know of any modern (70's up) motorcycle valve that it is safe to "grind". Light weight high performance design leaves no room for reconditioning like on the old buick.

If you can find someone skilled enough to use a valve seat "grinder" that hasn't already purchased a multi angle seat "CUTTER" I would be suprised. A Serdi valve seat cutter can cut a beautiful hi perf 5 angle seat in short order.

The valve seat and angles in and out are the single most important part of a high performance four stroke engine. I would not trust an automobile "machine shop" at all. The width of the valve seat is criticle, as are all valve seat angles. All the auto work I've seen uses a huge wide seat. And thats it!

So measure the width of valve seat and refer to the shop manual for allowable tolerances. If out of spec cut them suckers.

If the valve face shows any wear, replace them.PT

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