Bimmerheads reground cams?

[digger]

if they give a duration at a specified lift e.g. 1mm then its at 1mm when the specified lash has been set. if you change the lash setting then the duration changes

schrick duration are minus the ramps but they dont tell you how long the ramps. if the ramps are the same as the lash then thats one thing but it isnt always. its also very close to meaningless giving 1 duration

catcams give proper defined specs and are more comprehensive but still short of what you would want

[zaq123]

what about typical cam specs? In your experience, do they write specs for cams with zero or when set to recommended lash?

mine are all a zero lash you can tell because the ramps are shown

here is same cam with and without lash of 0.25mm

the opening of the lash curve is -22* closing 248* (where it crosses the y=0) so duration seat to seat of 270*

if you look at curve without lash, then look at the 0.25 mm opening -22* and 0.25 mm closing 248* (where it crosses y=0.25) so its still the same 270*. so its its just offset up. one has net lift of 9.75 mm lift and the other is gross of 10 mm

so to get duration at 1 mm with lash set then pick off the opening 1 mm and closing 1 mm. if you don't set lash then you read the 1.25 mm and 1.25 mm closing assuming its 0.25 mm lash spec

[digger]

month later.....lol can you please explain the above a little more detailed? I don't think it sinks in 100%

Are all those graphs were mapped at 0 lash?

is advertised cam duration specified at zero lash? I mean based on your graph, if advertised duration is provided at 0 lash and one is measuring it at spec lash, there will be about 20 degree difference (based on that b25 graph)

mine are all a zero lash you can tell because the ramps are shown

here is same cam with and without lash of 0.25mm

the opening of the lash curve is -22* closing 248* (where it crosses the y=0) so duration seat to seat of 270*

if you look at curve without lash, then look at the 0.25 mm opening -22* and 0.25 mm closing 248* (where it crosses y=0.25) so its still the same 270*. so its its just offset up. one has net lift of 9.75 mm lift and the other is gross of 10 mm

so to get duration at 1 mm with lash set then pick off the opening 1 mm and closing 1 mm. if you don't set lash then you read the 1.25 mm and 1.25 mm closing assuming its 0.25 mm lash spec

[zaq123]

If you put 0.25 lash in before measuring the 0 to 0 will be same duration as 0.25 to 0.25 on graph that had zero lash

.

month later.....lol can you please explain the above a little more detailed? I don't think it sinks in 100%

Are all those graphs were mapped at 0 lash?

is advertised cam duration specified at zero lash? I mean based on your graph, if advertised duration is provided at 0 lash and one is measuring it at spec lash, there will be about 20 degree difference (based on that b25 graph)

[digger]

Usually decked mean a lot of material was removed to maximise compression or similar , you just had it cleaned up.

[So Live]

Fair enough. Guess I’m just not confident enough in my measuring abilities to take the chance with a 20+ year old motor and not have it surfaced. Don’t like doing head gaskets twice.

So needing to surface a head makes it not worthy of a cam? Guess I should source a new head?

[TobyB]

Anyone here build a motor and not have the head resurfaced?

yeah... several times.
If you measure carefully, and have good surface finish, there is no reason to cut it.


t

[So Live]

Why are you putting in $325 camshaft in a thrashed cylinder head that had to be 'decked'? There is thicker head gasket that compensates for decking, unless it is decked too much and ruined.

Please enlighten me, where are you finding pristine m20 cylinder heads these days?

Anyone here build a motor and not have the head resurfaced?

I’ve never reinstalled a head that wasn’t resurfaced while it was off.

Little background on my head... I put this b25 in my 325e and after some time its coolant consumption kept getting worse. Not to the point where I’d say the gasket was blown but definitely getting some leakage into a combustion chamber. So I pulled the head and didn’t see much wrong with anything, head was flat enough overall and the gasket didn’t look terrible. No binding in the cam or rocker shafts so confirmed it wasn’t warped. Brought the head to the machine shop and had him check for cracks, surface it, and do a 3 angle valve job if everything checked out. Everything checked out, no cracks, valve guides in good shape, flat enough to surface and still within the deck height requirements. When he skimmed the sealing surface there were low spots. Upon closer inspection the head looked like it was gone over with a scotchbrite wheel earlier in its life. Indicated by some soft lines around the domes and a few low spots where there was less material, like between the coolant jackets and the domes and also between the domes. Still, my machinist had to take .004” off to make it flat. That’s not a ton of material... At the end of the day, besides being gone over by a scotchbrite wheel which led to coolant leakage, the head is in otherwise perfectly useable condition. So why wouldn’t I put a cam in it?

[DesertBMW]

Problem is that my head has been decked and my p2v clearances are way too tight on the intake side with everything at “zero”.

Why are you putting in $325 camshaft in a thrashed cylinder head that had to be 'decked'? There is thicker head gasket that compensates for decking, unless it is decked too much and ruined.

[digger]

Catcams recommend 1mm. The important thing is good valve springs and cam grind if you dare go that close

[ForcedFirebird]

Those are just the clearances I had on a build with no issues. Just confirming you have plenty. :)

[So Live]

Nice diagram Doug, thanks for posting! I was looking for that a while ago. Makes sense with the valve position relative to the centerline. My exhaust side tool was closer to the stud. Had to use set screws instead of cap screws on the stop to clear.

John, what do you mean by accurate? Accurate measurement from an engine that works? Mine won’t be “high effort” but it is a bottom end with unknown miles so I’m more comfortable with it a little looser. There are a lot of mixed opinions on p2v but most people say .060” is the minimum. The only concensus I’ve found is that bigger clearances are safer haha. Either way, interesting to see some numbers that actually work on these motors. Funny that sometimes info like that is tough to find...

[digger]

for reference here is some data to help

head bolts are pitched at 91mm in crank axis and 88mm transverse

[ForcedFirebird]

FWIW .057" and .073" are accurate numbers for a high effort 2.8l m20.

[So Live]

haha thanks guys. Just doin what I can to get it done as well as I can.

Got the reliefs cut and p2v clearances checked. Smallest clearance is about .085” at +/-6 degrees of cam adjustment.

I’m happy haha.