OT? Lapping of automotive engine valves

I am assuming this is old iron. IIRC, now a days the seat and valve are ground at a slightly different angles to get better sealing. Lapping isn't the best way to refinish your valves.

Wes

A good valve job includes a 3 angle grind/cut on the seat , with the center bevel at 45 deg and quite narrow . The sealing surface on the valve is usually also at 45 deg , and the last part of the process is to lap the valve to the seat . This takes out minor imperfections and gives a visual confirmation of fit . Feel free to disagree , this is the way I was taught way back when . Folks I know still do it this way .

I too have a triumph, but with a 4 cylinder engine. I have done my valves in the past with first corse and then fine grinding paste. I sent out my last head rebuild to APT (aptfast.com) and got back a ported beautifully machined piece.

cheers T.Alan

Doesn't leave much contact area for heat transfer ... are the newer materials *that* much better ? --

Snag aka OSG #1 '76 FLH "Bag Lady" BS132 SENS NEWT "A hand shift is a manly shift ."

none to one to reply

Snag wrote in article ...

It's actually a case of the materials being that much *different*.

No matter what you lap in for a seat at room temperature, it moves around when the valve and valve seat - being different materials and under different constraints - expand to different degrees as the cylinder temperatures rise.

IOW - The seat you so carefully lapped in doesn't come close to matching under actual operating conditions and temperatures.....especially considering the higher combustion chamber operating temperatures - thus greater material expansion - of today's engines.

A one-degree interference fit between the valve and seat will pretty much guarantee you a knife-edge seat that seals well.

If any additional angles are cut on the valve and/or seat - as in the case of the standard "three angle" valve job - they are related to flow only.

I guess I wasn't very clear . My understanding is/was that the valve was cooled partly by contact with the seat - particularly exhaust valves , intakes being cooled by the incoming fuel/air charge. Less contact , less heat transfer . I also have a basic understanding of the differences in coefficient of expansion of different materials . There's a lot of gaps in my education , though , and I appreciate the knowledge y'all are willing to share with me !

The valve guides carry away a lot of the heat. The guides are always in contact with the valve.

Wes

Skip the coarse lapping compound, start with the fine compound. If the fine compound isn't enough to clean up the seat then you could try coarse. You should really consider having the valves and seats recut if the fine compound doesn't work.

Cheers,

Kelley

The seat and the valve face are generally ground 1 degree off to make a "line contact seal", which then wears in. Using lapping compound to verify the seating CAN be done, but a bit of prussian blue, or a bunch of radial pencil lines, does the job just as well and preserves theangle differential.