LC Geezer

Is it fair to test cylinder head valve seats by turning the head upside down, filling the dished area with fluid (so that the valve heads are covered by the fluid), and watching for fluid making it's way into the inlet and exhaust ports? In other words, should valve seats be water-tight (not that I'd advocate using water for this test)?

Ta.

Slowboy Racing

Yes they should, turn the heads upside down and spray WD40 leave to rest for a while you should see NO leakage past the valves.

JohnD

iTrader: (5)

An old accepted method, but not water - paraffin was the usual liquid.
JohnD

LC Geezer

Thought as much. Many thanks.

p1mark

Yep Parrafin is the stuff to use.

If you have a small leak, a relap may well bring it back in. If not you will have to have them re-cut.

Another good way is to use a thin smear of engineers blue (some call it micrometer blue) on the valve head. Pop the valve in, give it a turn and you will see very clearly if you have full contact. (should be about 1-1.5mm on the 45 degree seating angle)

Obviously you need the collett and spring un-installed for this.

ZEN Performance

Sorry the method isn't sufficient. You need to check all the valves are perfectly straight, otherwise you can have seats that have shifted in the head, and valves that have bent to fit the seat.

I would use the method described by P1 Mark, and also give them a very light lap with fine past, the seat should clean up all the way round with no "shadows".

paul

p1mark

Yes good point Paul.

The valves can be seating / sealing even when bent. When the engine is running though and they rotate (which the design of the valve train will cause it to do) they suddenly do not seat very well.

So you need to ensure a) they are straight, B) they are lapped in.

Slowboy Racing

What part ?

This assumes heads “have” been work and tolerances correct with valves lapped in etc etc and finally check for leakage as above.

p1mark

Sorry *un-ink*, i don't understand if this is directed at Zen, the original poster, or myself. Nor do i understand what you are asking?

LC Geezer

Agreed - no leak doesn't defiantely mean they are OK but a leak definately means something is wrong. Why paraffin though? Would an engine degreaser such as Gunk, Jizer, or simillar be OK? Or even good old petrol.