3 angle valve job

[whipsey]

Do i need to find out what angles the valves need cutting at or would most engineering shops already know?

[maggspower]

Hi there again

Your machine shop will know, but so you do, 30o top cut, then the 45o valve seat, then a 60o bottom cut is what they will do.

To be honest the port throat is blended very well, for a factory finish. Good ol' BMW. Are you going to have the valves reused, and laped in, or get new ones?

[whipsey]

gonna get the old ones cut and lapped in i'm glad you appeared on here lol i've been offered a 2.0 2002 head would this be a better bet for more power?

[BadDave]

From what i've heard, the standard 2 angle valve job is good enough as it is.

[whipsey]

im just tryin to get as much out of the engine as possible there is still a bit of room for porting the head so will do that as well

[maggspower]

I'm not an expert on the 2002, but I reckon only having 4 cyilnders is going to hold you back a bit

Your best bet is to sell yourself the 731 head you have for sale in the for sale section, and put a wanted in the wanted section telling people that you want an ETA bottom end

[whipsey]

I'm not an expert on the 2002, but I reckon only having 4 cyilnders is going to hold you back a bit

Your best bet is to sell yourself the 731 head you have for sale in the for sale section, and put a wanted in the wanted section telling people that you want an ETA bottom end

i may do both though

[maggspower]

Whet do you mean?

[GrindCulture]

I think the tii spec head is the head of choice for hot M10s, not sure on the specs though (chocolate teapot moment)

[whipsey]

the m10 and m20 engines i have most of the parts for them so may build both engines

[maggspower]

sorry for a second there I thought you meant use the 2002 2000cc head for the 2.7

[whipsey]

nope lol i just thought that the 2.0l head would be a better head than the 1.8 on the m10

[reggid]

also don't waste time lapping the valves..........

[Jhonno]

also don't waste time lapping the valves..........

??

[reggid]

cut seats actually flow better, and what good is lapping them unless the head is bolted to the block, then there is thermal expansion meaing all the work you do with a cold valve and seat is thrown down the toilet once the thing heats up.

[maggspower]

What!? You mean the way it has been done for the last fook knows how long is no good?

All seats are cut or ground both in the head and on the valve itself but new metal is exposed in this process, they will be cut to the same angle but looking at these areas through a microscope would reveal a ragged and rough surface. In alot of cases these mating faces would "run in" as with piston rings and bores, but some times they would burn too, so take the opertunity to do something about it while its there in front of you.

I know they can be checked with a vacuum gauge to check if they are sealing, but the seat has another function too, heat disipation, particulary the exhaust valve, you cant check that with a vacuum gauge. You need the maximum area to transfer the heat, not by making the seat wider but by making them contact each other like two pieces of glass rather than two pieces of sand paper.

Thermal expansion, I reckon the valve and the seat are going to get quite warm I know they may be dissimular metals (en52 steel or 21/4n stainless for valves, cast iron, cobalt alloys, nickel alloys ect for the seat) but leaving them in a freshly machined state is not going to be better than lapping them in.

If the machining is done correctly the valve will only require a few spins to reveal a nice seat, not hours of blister ridden palms twiddleing a stick. I have never heard of missing out a process to make somthing better, do things like that and you end up with a Ford

Rant over maggs

[Gunni]

lapping valves is the ONLY way to secure a seal between valves and seat

[reggid]

What!? You mean the way it has been done for the last fook knows how long is no good?

All seats are cut or ground both in the head and on the valve itself but new metal is exposed in this process, they will be cut to the same angle but looking at these areas through a microscope would reveal a ragged and rough surface. In alot of cases these mating faces would "run in" as with piston rings and bores, but some times they would burn too, so take the opertunity to do something about it while its there in front of you.

I know they can be checked with a vacuum gauge to check if they are sealing, but the seat has another function too, heat disipation, particulary the exhaust valve, you cant check that with a vacuum gauge. You need the maximum area to transfer the heat, not by making the seat wider but by making them contact each other like two pieces of glass rather than two pieces of sand paper.

Thermal expansion, I reckon the valve and the seat are going to get quite warm I know they may be dissimular metals (en52 steel or 21/4n stainless for valves, cast iron, cobalt alloys, nickel alloys ect for the seat) but leaving them in a freshly machined state is not going to be better than lapping them in.

If the machining is done correctly the valve will only require a few spins to reveal a nice seat, not hours of blister ridden palms twiddleing a stick. I have never heard of missing out a process to make somthing better, do things like that and you end up with a Ford

Rant over maggs

no its not that its no good just not really any better.........lapping gives a nice warm snuggly feeling but often a false sense of security as even lapping does not guarantee a seal.

The idea is to seal the chamber when the engine is running not when its on a bench in the workshop with differing thermal expnasions and torquing the head down it can't be assured.

Several world class engine builders who have tried hundreds if not thousands of engine combos, porting technigues, seat angles, finishes valve shapes, etc and they don't lap and they chase ever single hp, that says more than a whole lot of theory.

The ones that do lap, do so because thats how "they've always done it" not that they have neccesarily have done tests to show its advantageous to the actual operation of the engine.

Proper machine work does not require lapping and if things are checked and rectified if needed then its a redundant step.