Cylinder base shim, how thick is too thick

[jgparker]

According to CE's web page, the offer shim sizes from 0.5 to 1.0mm. I think I'm back to stacking. I'm sure larger custom shims are do-able but expensive.

[ChrisBennet]

I know you said your motor has 1.0mm shims now, but does it really? That's 4 times as thick as stock.
-Chris

[jgparker]

Yup, I'm sure. I have a 1.0mm set that my machine shop provided and the 0.25mm set that came with my rebuild kit. I measured them all. I also measured the deck height on all 6 pistons at 4 separate spots, and it keeps comming to ~0.75mm with the 1mm shims. I'm plan to stack a 1mm and 0.5mm shim on each. Boy, the flat lip on the J&Es make it easy to measure the deck height.

Has anyone ever gotten dome volume numbers from either EBS or J&E? Both referred me to the other.

[ChrisBennet]

Originally posted by jgparker
Yup, I'm sure. I have a 1.0mm set that my machine shop provided and the 0.25mm set that came with my rebuild kit. I measured them all. I also measured the deck height on all 6 pistons at 4 separate spots, and it keeps comming to ~0.75mm with the 1mm shims. I'm plan to stack a 1mm and 0.5mm shim on each. Boy, the flat lip on the J&Es make it easy to measure the deck height.

Has anyone ever gotten dome volume numbers from either EBS or J&E? Both referred me to the other.

Well, had to ask. I measured the dome volume myself.
-Chris

[kstylianos]

JP,

Call EBS and talk to Don. He'll need the order number off the JE box/invoice. Or you can probably just call JE and skip the EBS middle man. Since I ordered the JE's from EBS, they did not give me a problem.

[jgparker]

Ok, I went with one 1.0mm and one 0.5mm shims, and my deck height is now 1.30mm on all cylinders. Here is a pic:





Thanks everyone.

[ChrisBennet]

Them's purty.
-Chris

[afterburn 549]

im only as inteligent as i am read.about some time ago there was a eng. report that stated 2 strokes will try to move thir rings around thats why they are [pinned]. (a little pin where the gap is stops them from moving on account harmonics.
all the 4 strokes i have taken apart always had thir ring gap right where i left them.
further most eng. manuals will tell never to put the gap over the loaded part of the piston (wrist pins) t.m.o.

[911pcars]

After adjusting the deck height, verify the bank of cylinders have the same installed height, otherwise the cylinder heads/cam housings will not be parallel to the crank centerline. The result is uneven clamping force on the entire top end.

That is also why the cylinder heads (on a bank) should be flycut (if at all) an equal amount. If not, then the aforementioned clamping force will not be the same from cylinder to cylinder, and subsequent efforts to rectify this will result in uneven cylinder heights and/or deck heights.

Once the above is in order, then, as Wayne and others suggest, make sure the chain box mounting surfaces are machined to accommodate the new position of the cams.

This tolerance stack is why it's a little trickier to correctly assemble a modular engine like a 911 compared to "one-piece" engine blocks found in the majority of cars.

Sherwood Lee
http://members.rennlist.org/911cars

[Wayne 962]

Originally posted by 911pcars
This tolerance stack is why it's a little trickier to correctly assemble a modular engine like a 911 compared to "one-piece" engine blocks found in the majority of cars.

This is also completely undocumented in the Bentley and Porsche factory manuals, as they assume you are assembling a brand new engine. My book takes into account that you are rebuilding it from one that is worn out...

-Wayne

[jgparker]

Yup, I did have my case surface fly-cut, and the cylinder tops are all on the same plane. I measured it, since I was also concerned about the tolerance stack-up.

If the extra cylinder base shims were required to make-up for material machined off the case, then it seems to me that I would need to shim the chain housings, not machine them, to keep them in the stock location. Is my thinking backwards? I'm assuming my cams will be close to the stock locations with all the shims.

[911pcars]

If you machine X mm off of the crankcase cylinder spigots, but then add an equivalent gasket thickness under the cylinders (over and above a factory ring), then you should be back to "zero" and the chain housings should be fine. However, I suggest machining the chain housing mount surfaces as there are usually other machining operations that need compensation as well.

As in all things related to assembling mechanical components, proceed as far as your correct assumptions take you. In other words, don't assume too much.... it's your engine.

Sherwood