M20 maching specs

[digger]

1 degree is not enough to worry about on an average engine.

[Ether-D]

Lj, please explain.

[LJ851]

^ According to your math the cam timing would move 1.5 degrees.

[Ether-D]

Ok, I was just playing with my spare block and heads.
With a head with the divots intact installed with the old head gasket, or with the .030" decked head and old gasket, there was no noticeable difference in the timing marks' relation to one another. I mean, we're talking three hairs' width. I do see now how the timing becomes retarded, because the slack is so minute, it's created on the tension side of the belt.

I did a few calculations:
1 cam gear tooth is VERY close to 5/16" which is equal to .3125".
My decked head has about .030" removed which is very close to 1/10th of a tooth.
The timing gear has 48 teeth. 360 degrees divided by 48 teeth equals 7.5 degrees per tooth.
7.5 degrees per tooth divided by 10 equals .75 of a degree retard on cam timing.
How much can this affect performance?

Thanks folks. Sometimes, when people like you guys are being helpful, R3V can be very informative.

[Ether-D]

Then for a stock cam gear, with a .030"+ deck on the head, which way should the cam be rotated off it's TDC mark, with the crank timing marks lined up, to get belt and cam gear to align and to get the torqier result?

Sorry for the run-on...

[whodwho]

The cam would rotate in same direction as engine rotation so that would retard it.

[Ether-D]

It must depend on where you put the belt. In my head, if you keep the timing marks lined up it wont be enough for a whole tooth to be skipped leaving a tiny bit of slack on the left side. That would allow the right side of the belt to be pulled tight by the crank, pulling the cam clockwise, advancing the timing. Right?

Edit: I'm not saying you are wrong, I just want to understand. I'm having trouble wrapping my brain around it.

[LJ851]

^^ Use a thicker MLS head gasket to make up the difference and avoid the cam timing issues. And digger is right, the timing gets retarded.

[digger]

i always thought that reducing thickness introduces retarded timing which can hurt power everywhere but mostly at low to mid rpm

[Ether-D]

Well, to revive a dead thread. I have a new(used) head that's been decked past the divots. How far past I don't know. I'm going to clay the clearance with the normal (not thicker) gasket and report back here. What will the resulting advance on the cam timing cause? Less than ideal running? or lumpy idle or poor running etc.? I'll be getting my gasket, bolts and seals and whatnot by mail later this week...

[digger]

as little as 4* makes a difference and dont assume stock is ideal even if the change from some machining is small, there is performance to be had by playing around some....you need a dyno though

[AlphaE]

nice bit off info thanks.

i talked to Jim at Metric yesterday about cam timing. from the sounds of it, youd have to deck the block and take the head to the limit in order to make any real impact. something about the # of teeth on cam sprocket, spacing on teeth minus the amount removed= crazy small impact on cam timing.

any other input?

[jlevie]

For grins, and to see if it would help while still using a stock engine management system as mandated by Spec E30 , a friend used a head decked to the max and took 0.020" off the block. The valve clearance was checked with clay and found to be okay. The experiment didn't yield more power, primarily because there is no Spec E30 legal way to advance timing.

[digger]

clay or plasticine works. use an old gasket. no need to torque it too full specs just amke sure its snug tight with old cycled gasket ( if the amount a head gasket squashes is critical you're too close).

measure the difference between the rocker cover gasket face and the divots see if aligns with min thickness spec in bently?

i've never used elring only goetze and dealer (wont touch others)you can tell the quality difference between the ones in a VRS and the goetze and dealer

[AlphaE]

Thanks Digger. im using a stock i cam. the block is untouched as far as i know. i got a elring 1.75 full upper gasket kit .

how would i actually check the clearance. does it have to be special clay? or can i use silly putty or something like that? So i use the old (already compressed) HG, torque head w old bolts to like ???? 20Lbs???? set up TB and turn by hand. pull head. cut clay/silly putty, measure. Right??

i gotta mic them divots. they are crankin DEEP!!! way deeper than the +.3 (.012) fatter gasket. there is now way the slightly fatter than stock gasket makes up for shavin down to the divots..

Jlevei, does that min thickness you buzz it down to to bump comp get you to the bottom of the divots?? according to all data the min thickness is only .012 off. you know how much you cut off?

thanks for the input guys..