TheSamba.com :: View topic - OK Now I have a real question / Problem

Sun Feb 21, 2021 7:02 pm

I have been building this kit motor for awhile now. Took me a long time to get a set of main bearings to fit. Anyway I got the case together a few days ago and yesterday I set up cylinders 1 & 2 to check deck height. They were both right on .040". Today I was measuring and cutting head studs and I found that I could push the cylinders around a lot. I had checked piston and bore clearances, and ring gaps, but had not measured the cylinder to case fits. So tonight I miked the upper and lower cylinder and case fits, and damn, they are between .052" and .066" loose. I should have measured the cylinder to head fits also, but will have to do that tomorrow. What do I do now? The cylinders are 90.5 mm. Could this case have been bored for 94's?

CYLINDER TO CASE FITS CYL CASE CLR

1 OUTER FIT 3.779 3.831 0.052
1 INNER FIT 3.763 3.829 0.066

2 OUTER FIT 3.776 3.832 0.056
2 INNER FIT 3.765 3.825 0.060

3 OUTER FIT 3.778 3.833 0.055
3 INNER FIT 3.766 3.825 0.059

4 OUTER FIT 3.778 3.832 0.054
4 INNER FIT 3.764 3.825 0.061

Sun Feb 21, 2021 7:29 pm

Case is big enough for 94 cylinders (3.831)

Sun Feb 21, 2021 7:47 pm

Got to make a call tomorrow. The top of the cylinders measure 3.851". Head bores are 3.872", for .021" clearance. What should be the head bores for 94 mm cylinders?

Sun Feb 21, 2021 8:19 pm

94 cylinder would be 3.976 at the head end

Sun Feb 21, 2021 8:35 pm

Well, I don't see an easy way to fix this mess. I really need to start all over with a new case bored for 90.5 cylinders. If I ran 94 cylinders with this case, the heads won't fit. Even if the heads fit, I would have to run a barrel shim and raise the deck height to .070 to .080 to get the compression back down. Just Ducky

Mon Feb 22, 2021 7:22 am

Aren't there 92 mm thick-wall cylinders? Would those fit????

I just don't know; I use 92mm thin wall cylinders in my 1835cc engine, been like that for decades.

Mon Feb 22, 2021 12:34 pm

What do you think of the AA 92 cylinders and pistons? Isn't the pin height a little different between the AA and Mahle pistons?

Mon Feb 22, 2021 12:39 pm

Just run some thick wall 92's or just regular old 94s and call it a day.
Have the heads bored out a little bit to fit the 94's.... that would be cheap and easy

AA are good but pin height does vary I think maybe 1mm from Mahle. But it's nothing some shims or spacers can't take care of. No big deal IMO.

Mon Feb 22, 2021 12:45 pm

I believe the pin height on the AA thick wall 92’s is 35mm. 1 mm more then standard 90.5’s.

The thick wall cylinders are 114mm in length versus ~112.5mm for standard 90.5’s

Mon Feb 22, 2021 1:37 pm

The thickwall 92 is a good solution
may need to switch to 5.5 rods and adjust deck height with shims.
The compression ratio should not be a big deal, it's only 1.5mm more bore
If it's ALL the cb kit, they want 8.7? I think you could run 9.3 with that, the 8.7 is very conservative.

In order to use 90.5 mahle B pistons with a 78 stroke and stock rods, the case SHOULD have been decked 1mm and bored to 96mm

-instead you have it bored for 97.3 and decked....??? an unknown amount.
Check deck height real quick, with no rings
No need to bolt it down just put it sideways and let gravity do it.

Mon Feb 22, 2021 2:45 pm

Well, I have been talking to CB today. They are going to make me another case, if I send this one back. The kit stated that the compression would be 8.7. But based on my measurements of the deck height and head cc, it was going to end up around 9.2. Would someone want to check me on that? 90.5 bore, 78.4 stroke, 0.040" deck height. The chambers were, 56 cc, 56 cc, 55 cc, 54.5 cc. I was going to try and clean up the small ones to get closer to the larger ones, if the decks all came out the same. Only checked 1 & 2, before finding the case problem. Hope the new case is the same height. This is turning into a delayed gratification thing.

Mon Feb 22, 2021 3:17 pm

So you bought this messed up case directly from CB?

Yes, 9.2 CR at 55cc chambers

Mon Feb 22, 2021 5:30 pm

There is nothing wrong w/ the case...looks like even on each bank. One side just happens to be shallower. This might be a builder issue. :D

I tell people all the time to do a trial-assembly on every build. But some insist on just buttoning up the shortblock before they even look at the cylinders and pistons.

The case is machined loose. Too tight for a proper 94mm.

To address the case, either trim the high cylinders to match the shallower ones. Or shim the shallow ones = this will give you lower compression. Anyway, this is gonna be an asymetric build if you don't remachine or re-deck the case. It will also work w/o machining the case.

Just a thought.

Mon Feb 22, 2021 5:39 pm

ZEKE65 wrote: Well, I have been talking to CB today. They are going to make me another case, if I send this one back.

Nice. :D
Yes you could carve a little out of the small combustion chambers to get it closer, just make sure #3 isn't the small chamber everything should work fine.