Valve clearances???

[B7]

on a M20B25. Finally got round to getting the new head ready to fit (see http://www.e30zone.net/modules.php?name ... t=ran+rank). Nearly there now.

However I know these engines like a loose valve clearance but how loose? Bentley manual states 10 thou across the board. Experts, the question is "should there be any drag on the feeler gauge or should I be able to squeeze an 11 though in there (very loose 10 though)?

Easier to do this while on the bench so any info would be handy.

Cheers

[HairyScreech]

it should be just tight enough to give a little drag on the blade but not enough that its pinching it.

[HairyScreech]

it should be just tight enough to give a little drag on the blade but not enough that its pinching it.

[maxfield]

0.25mm cold.
0.35mm hot.

All this 'thou' stuff means fuck all to me

[daimlerman]

Stop talking in French,Jamie!! I set mine so that the feeler blade is nipped. Too wide and they rattle.But I do try to observe a modest 6000rpm limit...

[B7]

daimler and hairy. Thanks for that. So a very slight resistance is okay, 11 though should not fit. Cheers, I'll reset before fitting it. I've set them at a very loose 10 thou at the moment, I reckon too lose.

Max, keep the "L" plates on mate

[pacerpete]

Tappets set on the bench will be wrong once the head is fitted and torqued down .

[B7]

Tappets set on the bench will be wrong once the head is fitted and torqued down .

Possibly a good point. But how comes? The cam is set fast in the head as are the valves and rocker shafts. Please let me know Pete as this is the first m20 head I've done (built loads of CVH fords, Pintos, A sries etc.). One of the articles I'm following is the Zone M20 head build:

http://www.e30zone.net/modules.php?name ... lhead2.htm

States last of all, "now is a good time to set the clearances. Makes life a lot easier off the car".

[daimlerman]

Not too sure where Pacerpete is coming from either,but you will want to check your clearances anyway when you change the oil after your first 500 miles or so.(I assume you have built a new motor)One problem I had with mine was that one of the rocker retaining clips came out of it's groove,let the rocker slide to one side resulting in a loud tapping...I was lucky,'er indoors was backing the car out and I heard it and investigated at once.

[pacerpete]

The reason not to adjust clearances on the bench is that the headbolts when torqued pull down on the rocker shafts and tighten up the previously set clearances. By all means set them on the bench, then check them again when the head is torqued down, you will then need to readjust them !
Best results are obtained by setting them with the engine hot at a snug .35mm not the .30 (hot) as recommended .

[B7]

Thanks guys. I'll leave as is and then reset them on the car to be sure.

Daimler. It's just the head thats been rebuilt. Bottom end is good but the old head was shot in many ways. I'll update my post once it's back together with how it's running (thats if it does!!!)

[daimlerman]

Of course it will run!!You are using new head bolts,so cut the heads off two old one's and use them as dowels to position the head.I did'nt,and scratched a head,causing the gasket to blow...I tend to learn from my mistakes.. I hope!!

[B7]

Of course it will run!!You are using new head bolts,so cut the heads off two old one's and use them as dowels to position the head.I did'nt,and scratched a head,causing the gasket to blow...I tend to learn from my mistakes.. I hope!!

Now thats a cool tip. I'll sort that tonight. Thanks

[dannyboy759]

0.25 cold, it runs a lot better and gives a bit more poke!

[Simon13]

0.25 cold, it runs a lot better and gives a bit more poke!

too tight tappets lead to snapped rockers potentially.

Trebor as Pacepete says is the best way imo

[dannyboy759]

too tight tappets lead to snapped rockers potentially.

Opps thats the bmw spec! shouldve said 0.30 cold

[Theo]

Well a bigger clearance isn't going to gain you any performance, quite the opposite infact - the valves are opening .05mm less. It will probably also make your car tap more.

[Simon13]

it's 0.25mm cold and 0.35mm hot is BMW spec for an M20

There's trails of thought for setting them hot and cold but those are the factory specs

[Heyho]

Well a bigger clearance isn't going to gain you any performance, quite the opposite infact - the valves are opening .05mm less. It will probably also make your car tap more.

That's not the case in my experience. M20s much prefer loose valve clearances. It may "tap" a little, but an M20 with "audible" clearances will always run smoother, return better MPG and put out less HCs than one with tighter (quiet) clearances.

[Simon13]

Theo is right, but as they say a noisey tappet is a happy one. All M20's tick if one is totally silent then thats just as bad as a really noisey one! They have to tick right!

[B7]

Theo is right, but as they say a noisey tappet is a happy one. All M20's tick if one is totally silent then thats just as bad as a really noisey one! They have to tick right!

Pacer P was right. Tourqued it down and the clearances closed up.

BUT bottom line is..............................SHE BREATHS LIFE AGAIN. and she ain't run as well all the time I've 'ad 'er. I'll update the other post with the photos of the engine bay now it's back together. You're gonna mess up your pants Si!

[Simon13]

good man

[B7]

I do appear to have one issue but thats another matter I need to post under Tech help. Maybe one for Brian Moore

[ricey46]

Tappets set on the bench will be wrong once the head is fitted and torqued down .

I found this too, I'd set the valve clearances on the bench, but once bolted down they were too tight, and had to reset them. so check once the heads on and torqued down!!