Petrol engines aircooled Valves
Valve lapping; valve seat angles, valve seats re-cutting
leroy99: I'm rebuilding my cylinder heads and am regrinding the valve faces. does anyone know the angle at which they should be ground. cheers
Fritz: You have won yourself a coconut for this evenings 'most likely question that no-one can answer' :-)
Give some of us some time to swat up on the answer,,,,,,
camper: Tell us first what VW transporter engine its ie aircooled 1.6 or 2ltr or water cooled petrol or diesel and engine code. Obtain a manual for the engine. Example looking at a Haynes manual i have for 1979 to 1982 all models 1584cc to 1970cc. Page 28 gives valve seat angle inlet 29 30 degrees. Exhaust 45 degrees.Are you wanting to recut your valve seats with a cutter or grinding in .If so consider limits max permissable depths and the valve it self.I am sure there is some one on here who would no about this subject.
leroy99: It's a cu 2ltr aircooled engine, from the advise of the lectures at college (motor mechanics course)they said grind the valve faces on this machine we have where you put your valve stem in a drill like holder and it is rotated one way then a grinding wheel rotates the other way, (to get rid of the crap and pitting on the faces),just got to find out what angle to grind them,any help much appreciated (ive got a haynes manual but for water cooled)
camper:I did a valve job on a 2ltr cu some time ago.Best bet is to obtain new valves if you look at g.s.f website you can order them.Price wise thay are cheap and are made with correct valve seat angle for the inlet and exhuast.There are limits for grinding valves in on the heads remember the heads are alumunium with steel inserts pressed in for valve seats.Provided the inserts are not badly burnt or damaged or they will need replacing only lightly lap the new valves in.
Ivorblueun: If you are using the original valves and just want to get rid of pits in the lips and valve seats providing they are not major you should only have to lap them with a bit coarse paste followed by fine on the exhaust and probably find you will only need fine on the inlets, the angles should not have changed. you can use one of those reciprocating thingies s in a drill or use the old fashioned rubber sucker on a dowel job and make like a boy scout trying to make fire. _________________ Stu
Quote:old fashioned rubber sucker on a dowel job and make like a boy scout trying to make fire.
Don't machine lap them with a drill.. above method is best, spinning with a drill tends to make them whirl about a centre rather than just rotate.
Do a few fire-lighting spins back and forth, lift up, wipe grinding paste back onto seats in head and valve with finger, rotate valve 1/3 turn from where it was, plop back downand repeat, repeat, cleaning every now and again to see the state of the faces, looking for a smooth unpitted matt finish, not a shine. After cleaning off re-apply grinding paste and continue, till happy, happy happy, happy.. Add 3-in-1 oil if paste is too dry/sticky..
NB. Lift & turn frequently, stop lapping when seats are clean and matt finish all over
Don't get it down the valve stems!
If they really are badly pitted replace with new as suggested above.., grind new ones in to existing seats, though if seats look pocketed or also badly pitted, then you may have to re-cut them.
Seats have 3 angles: 15 deg. entry, valve seat angle, 75 deg. chamfer (inside edge)
valve seat angle (Exhaust) ~ 45 deg. valve seat angle (Intake) ~ 30 deg.
(from Bentley manual for US AFC spec Air-cooled anyway)
There are other criteria when re-cutting seats i.e. if you're going to start actually cutting the valves or seats, best take a looksee at Section15.1 and 15.2 in the bentley manual first!
PS. Generally when cleaning up a valve ona lathe, you are only chipping off the carbon, which can be done manually with a scraper, without setting the cross-slide, just rest on it, as a wood turner would