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Join Date: Dec 2001
Location: Off grid in Eastern ONtario
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Does this 3.2 case need machining? with data

The case has been cleaned, and bolted together with the bolts torqued.
#8 bearing is in place for alignment.
I measured bearings 1 through 5 ( all I can reach with #8 in place), measuring in 5 places:


From these measurements, in addition to determining the bore, I used measurements 1-2-3 to calculate ovality, and used 4 and 5 to calculate the size of the step between the case halves.
The results were as follows:


Since all of the dimensions are above the maximum spec of 65.019, with some ovality, and a step at the joint, I thought that this means the case needs to be reworked.
BTW, the IMS bores are within diameter specs from the manual.
Just for fun, I installed the original main bearings, after cleaning them carefully.
When installed one end of the shell stood proud of the case by 0.003” to 0.005”, so they crushed a bit when the bolts were tightened.
The results :

The range of measurements and the ovality tightened up.

Based on the measured crank journals ( 58.980mm) the clearances are:

All of the clearances are above spec, but the variance in each bore is small.
Another thing I noticed is that two of the bearings had wear spots – all of the other bearings are very uniform. When the case is assembled, the wear marks are on the same side.

The dimension at the wear spot is about 0.01mm larger than the adjacent area, although I think my measuring there is +/- 0.005mm at best.
I am not sure what this indicates – possibly those journals are slightly out of line?

All of this data leaves me completely uncertain about whether or not there is something to be fixed.

It seems to me that a new set of bearings, with clearances in the 0.05mm range, will be fine, since the clearance is bigger than the various deviations.
I am leery about sending the case for machining to make corrections of 0.001” and smaller.

Has anyone gathered data from a case that has gone through the bore correction process?

Assuming that the bore measurements without the bearings in place are accurate, they are oversize about 0.015mm. I am thinking of using GT3 bearings, which are available in three thicknesses. Does anyone have data on the thickness – as I understand it the yellow is nominal, the red is 0.0005” under, and the blue is 0.005” over. If that’s the case, it would seem the blue would be the correct choice.

Or is all this unnecessary and should I just get some Glyco’s and call it a day?
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'84 Carrera - MAF, Wong chip, RSR flywheel, ER bushings and other bits, CTR fiberglass F/R bumpers, 7/9 Fuchs, 22/27 TB, 22/21 SB, bunch of other little stuff
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Old 07-08-2018, 03:45 PM
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I'll jump in here.

If it were me, I would buy the Glycos AND use plasti-gauge to check your clearances.

If good button it up. If not, perhaps the GT3 bearings are needed?

I don't think your case warrants an alignbore. JMO.

Now let the real experts chime in.
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Old 07-10-2018, 03:17 PM
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.001 inch is correctable and guaranteed at a measurable level?
Bruce
Old 07-11-2018, 05:00 PM
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Did you mean to end with a question mark?
I assume you mean that 0.001 is indeed correctable.
If so, I guess the question then is whether it is needed for what is essentially a street engine.
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'84 Carrera - MAF, Wong chip, RSR flywheel, ER bushings and other bits, CTR fiberglass F/R bumpers, 7/9 Fuchs, 22/27 TB, 22/21 SB, bunch of other little stuff
'69 Lotus 7 Series 3; '74 Fiat X1/9
'14 X5 diesel
Old 07-11-2018, 05:45 PM
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No the whole line was a question for thought. I don’t see it possible or making a quality difference.
Bruce
Old 07-12-2018, 11:36 AM
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I think we are on the same page - that the deviations are too small to be able to be corrected with reliability.
If I changed the resolution on the measuring tools from 1 micron to 10 microns these deviations might not even appear.
I have discussed this with an experienced engine shop and have decided to proceed as-is. Once new bearings are installed I will recheck and decide then if anything needs more attention.
Thanks for your input.
Old 07-12-2018, 11:57 AM
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