Valve lapping

always a good idea to get a finish lap.. if nothing else, to CONFIRM it is correct..

Like them all, but love the "B"s.

HELL NO !! Ask yourself this: do you think GM or FORD for example take the time to "lap" valves and seats after their modern and expensive valve grinding equipment has just mass produced hundreds of cylinder heads a day ?????? NOPE.

When Grandson and I used my 100 year old Van Norman valve grinder and my Chinese-made seat cutters from Amazon to do a valve job on Mr Cato's Model C Allis-Chalmers head with the sloppy valve guides and cast seats, why yes, we most certainly felt it appropriate to hand lap the valves. Tongue

Edited by Les Kerf - 21 Nov 2025 at 7:22am

lapping it for 30 seconds would give you an idea of the seat and verify that all is well.. Just a quick test.

Like them all, but love the "B"s.

I have always lapped valves. Why not? You can see the width and placement on the valve face and it shows on the seat as well. Just me I guess. Never had any problem. Now i wonder how many hundreds of valves and seats I have ground.

I've always used Prussian bluing to double check on seats & valves, it just takes a few seconds per valve.

AC 200, CAH, AC185D bareback, AC 180D bareback, D17 III, WF. D17 Blackbar grill, NF. D15 SFW. Case 1175 CAH, Bobcat 543B,

I was taught not to lap valves with compound because compound introduces abrasives residue. I have been surprised at the number of folks that lap valves. We were also taught to put an interference angle of one degree. Not sure how prevalent that procedure is in the working world. I do remember checking with the prussian blue for the fine clean contact circle that provides the tight seal.

DrAllis wrote:

I was taught the same thing. Lapping compound wasn't getting cleaned off good enough. I always ground my seats 1 degree more than the valve (46 versus 45 for example) and once you were done, you could slap the valve on the seat 3 or 4 times and see whether you had a good seat or not. Bluing confirmed the width of the seat.

Agreed

That truly is 'best practice' so long as you have good tooling and the skills to use it properly.

I set my 100 year old valve grinder to 45 degrees (as best as I can eyeball it), and heaven only knows how close my chinese seat cutters are to 45 degrees.

On my last job we measured stuff in microns, and I had access to optical measuring systems that I could have used to measure those angles in arc-seconds, but since retiring I no longer get to play with that equipment.

These tractors were designed to be maintained by the average farmer with the help of the village blacksmith. If you feel the need to lap the valves, go for it!

I challenge anyone to prove the difference after 1000 hours of run time Tongue

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