m20 head work

Post Tue Apr 07, 2015 7:56 pm

Engines out heads coming off soon,

Basically planning on doing a 2.8 build so planning on refreshing the head and doing a bit of head work...

Are there any recommendations on what to do with the head and what to avoid?

Still deciding on a camshaft but any advice appreciated on this as well to go with a 2.8 crank..

planning to refresh the head new rocker arms and shafts, valves, springs, however is there anything I can possibly reuse?

as in if I was to do a DIY water test on the valves and they were all seating properly I could simply change the springs polish them up possibly give them a light reseat if seats are pitted,

The engines got 170k on it atm...

But in terms of head work was planning on porting the head and polishing up both inlet and outlet chambers smooth, read up a bit on fuel atomisation and apparently this mainly applys to non fuel injected engines?

also planning on polishing up the combustion chamber around the valves,

lower block work I havnt decided if I will tackle as yet, as there are measurements and bearings which I am not clued up on!

Post Tue Apr 07, 2015 10:47 pm

don't polish anything, a 270-280 cam is as much as you'll need with a lowish CR.

a nice multiangle valve job blended into the port, back cut valves, fix the short side radius to stop flow separating, stream line the casting around the guide area. you don't need much metal removal to improve things noticeably its already a little too big you just want to shape things to be more efficient.

the exhaust port seems to be important on the old m20, getting the shape right is important. without someway to measure if you are making an improvement then its easy to make things worse.

Post Tue Apr 07, 2015 11:41 pm

reggid wrote:
a nice multiangle valve job blended into the port.

Which will be wasted if you start with worn valve guides, and at 170k, the exhaust guides are likely to be past their best.

Post Wed Apr 08, 2015 3:47 am

that kinda goes without saying. no head specialist (and this a specialist job) worth seeing will try and cut a new seat with worn guides

Post Thu Apr 09, 2015 8:34 pm

cool planning to take it to a specialist who used to build these back in the day,

in terms of porting and polishing would this not help?

Post Thu Apr 09, 2015 10:45 pm

bmw9818 wrote:cool planning to take it to a specialist who used to build these back in the day,

in terms of porting and polishing would this not help?

proper porting is good when done correctly, leave the polishing out. the idea is not to make things look pretty which is mostly what polishing does its about function.

Post Thu Apr 09, 2015 11:11 pm

Id rather have the extra material in the head, especially around the valve seats

Post Fri Apr 10, 2015 2:18 am

to port or not that would depend on what the goals are, if you are happy with about 190-200bhp then you can just refresh but if you want more...where to stop

there isnt going to be a problem with removing too much material because you dont need to remove very much to improve things, its already pretty big. i guess the porter needs to have a clue about things though