18 replies to this topic

[Project_1275_GT]

How much contact surface area should there be after a new valve has been installed and lapped?

Excuse the black maker pen but I have no engineers blue. The picture shows only a very small contact area. Should this cover the whole angled area?

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[Steve220]

How much contact surface area should there be after a new valve has been installed and lapped?

Excuse the black maker pen but I have no engineers blue. The picture shows only a very small contact area. Should this cover the whole angled area?

93119114-FE74-4307-B24B-5ECFDEDA365B.jpeg

Keep going until you get the majority of the seat.

[whistler]

I was always led to believe that the exhaust valve needed full lap whilst the inlet only need a fine line lap. Is that still true?

[Spider]

For road use, you really want no less than 0.060" seat face contact for the exhausts.

 

Looking at that, I think you'll want to have the seats re-cut, then lap them.

[Project_1275_GT]

Thanks for the replies. Should it be the same contact area for the inlets valve and exhaust valves?

 

Looks like i will get busy with it today and see if i can improve the contact area, if not i will as advised get them re cut. They were supposed to already be done. 

[Spider]

Again, for road use, yes, but you can happily go down to 0.040" on the Inlets.

The Exhausts need more to help disperse the heat out of the Valve Head.

[Project_1275_GT]

It’s a turbo engine so do the same rules apply? Not for race use. Only pretty standard engine.

Thanks

Rob

[Turbo Phil]

Valve OD and seat OD should match.
For performance heads the ex seat width can be 0.065”, for standard stuff leave it wider this will increase its lifespan.
Regardless of actual seat width, the seat contact area in the head should match that of the valve.
If the seat in the head is wider it doesn’t necessarily matter as long as the valve gets full contact. The seat in the head can be narrowed by adding a 60deg bottom cut and 30deg top cut (if required) this will improve flow. Similarly the valve can have a 30deg back cut applied to leave the seat at the desired width. Incidentally the 30deg back cut on the valve is one of the single best mod modifications you can do to increase flow.

Phil.

[Project_1275_GT]

I’m now onto valve No 2. I believe head work should have had 3 angle seats. But I am no expert with this stuff. I think this is correct. After lapping the contact area is looking like 0.050 to 0.060. With a even surface all the way round and equal on valve and seat. I think this is now ok from descriptions. I’ve added a picture where the slightly shaded area is now improved.

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[Project_1275_GT]

This is with black marker not engineers blue but shows pretty good contact now.

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[Turbo Phil]

Looks like a multi angle seat from the pictures. Now if you back cut the valve as I described above you’ll see a really decent gain in flow for the small amount of work required.
If you skip to 3.30 in this video I did it describes multi angle seats.

https://youtu.be/mA3iIG1ddSY

Phil.

Edited by Turbo Phil, 31 May 2020 - 10:26 AM.

[Project_1275_GT]

Thanks for the info. At least I’m going in the right direction.

[Project_1275_GT]

How do I know if the exhaust valve guides are sodium type? Don’t want to sound an idiot but I am!!!

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[Turbo Phil]

It’s not the guides that are sodium filled, it’s the valve stems. They’re larger at 8mm diameter.

Phil.

[Project_1275_GT]

Thanks again for the info. Im learning a lot today. All valves now lapped and happy with contact area. The valves fitted look like they have been supplied from mini spares. The guides look standard cast iron type but maybe the exhaust enlarged to 8mm. As i have no idea what im doing here but would like to get it correct, what is the correct material used for the guides? I have done some reading and see other materials available. Is the standard cast guide ok for standard boost turbo engine? With the current valves that are fitted. Material not stated on mini spares.

 

Thanks

 

Rob