Clearances and Cam timing advice
 

Hi
I’m in the middle of a test build of my 1987 3.2 engine and I have a couple things working against my intended plan and hoping some folks here have some thoughts on solutions. I just timed my cams and found I have .44mm exhaust valve to piston clearance somewhere around 15 degrees before TDC overlap. My minimum intake Valve Clearance is 2.73mm. I’m wondering if this amount of out of spec can/should be fixed by changing the cam timing setting, changing cams, or if I’m fighting a losing battle because I also have a low deck height of .80mm.

I have my cylinder head #2 setup with testing springs and I’m measuring the valve lift at the retainer with digital indicator.

Here are the parts! Mahle 3.4 10.1:1 P&C kit, new Pauter rods standard length, webcam 20/21 cams. The mahle cylinders are 85.07mm tall which is shorter than the old cylinders by about .35mm And I’m currently setup with .50mm base gaskets.

Thanks for any advice.

I currently have the cams set at 2.05 and the card indicates a range of 1.8 to 2.2.

Where did you set the cam? Try advancing the cam and rechecking. Recheck at 2.2mm and see what you have.

Okay, I just went back out and retired the cams and got the clearances back to about where they should be. In the process I realized I disturbed the timing in between measuring the intake clearances and exhaust clearances so that cam wasn’t even set correctly when I measured the exhaust clearances.

Now what I really need is a reliable setup to identify TDC without relying on my eyesight are the tools that thread into the cylinders good for this or is there a good pointer system that people have success with?

You will need the Stomsky cam tools, they are very precise., to reach your exact #’s.
Jay.

Why .8 mm deck height? That's cutting it awful close.

From what I read on here, it seems smaller is better than larger for reducing detonation potential while providing some enhanced performance via increased compression ratio. I think my choice is stay at .8 or add a shim and go to 1.05.

I’ve realized Today that I don’t have a valve clearance problem.

If My interpretation is wrong, please let me know.

Have you calculated your actual compression ratio? You may be above 10 to 1 with your setup as is. That may or may not be a concern, but may make a difference in the choice you make concerning base gaskets and your deck height.

Also a degree wheel on the crank pulley will help. A dial indicator on the piston will help establish TDC.

https://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/1040125-fs-digital-degree-wheel.html

Works perfect.

My calculated comp ratio is 10.16:1 at .8 deck height, or if I add a .25mm shim, comp ratio is 9.89:1. I did CC my heads and they all came out at 91. The heads have been chamfered slightly for the 98mm cylinders.

Does anyone think going with the .8 deck height and 10.16 compression on single plug, mostly driven at altitiude of Colorado is a bad idea?

Because of our thin air in Colorado the effective compression (pressure) will only be about 80% of calculated in actual use. That's also the reason we can get away with regular gas being 85 octane in normally aspirated cars. If you ever go to a lower altitude you may need higher octane gasoline.

john