I am putting together a motor (olds 324) and had new ARP studs installed on the rods and the big ends resized. The rod caps are pretty snug on the studs, and require a bit of tapping to remove the rod cap. Nothing violent, but they are more snug than the original rod bolts. I checked #1 rod clearance tonight (between .0015 and .002) but I am a little suspicious that tapping on the studs to remove the bearing cap could be throwing off this measurement, since it would definitely apply a load to the bearing surface. I have inside and outside mics and can check it that way I suppose, but I would still want to use the plastigauges to double check. Am I worrying about nothing or is there a better way to check this?
You're worrying about nothing IF the big ends were sized with the ARP bolts at their recommended torque . It's usually significantly higher than stock bolt specs . For a mild /stock type engine , ARP's aren't really needed & the elevated torque settings they call for can be a problem if no accomodations were made during the machining process . lmo Milodon & moroso both market quality engine bolt kits .
They were done with the rod bolts torqued. Surprisingly the ARP spec (50 foot lbs) is within the factory range (40-50 foot lbs) so the main difference is probably in the secret sauce they require. I upgraded mostly because the threads on the stock studs showed signs of stretching and new bolts were cheap (ish) insurance. I was worried that I was essentially smashing the plasigauge with the mallet when tapping the studs, and therefore getting a bad reading. Does this make sense?
Yeah, it makes since. Use the plastigage on the con rod body side. And not under the cap. That way when you're tapping the con rod apart. You won't deform the plastigage. I would be using your mic's to double check the plastigage. Not vice-versa. Since they will give you a definitive accurate measurement.
I don't feel that what you're doing will damage the plastigage , put the plastic gage more toward the split if it's a concern.
Rod bearings are built with a certain amount of eccentricity to them. You can't get an accurate vertical bearing clearance measurement. Measuring close to the parting line. It may miss led you, into believing you have adequate bearing clearance.
Yes put plastigage 90 degrees out from parting line. Using mics is a more accurate method. I doubt you changed the plastigage reading by tapping on the cap. A lot of engines have been assembled using plastigage with good results. A couple of times I have checked clearances at different points on the bearing that is I used plastigage at 90 degrees from parting line and then close to parting line maybe 15 to 20 degrees out I saw no real difference. Dan
If you have good inside and outside mics,,,,,then you don’t need the plasti gauge . Mics are much more accurate than the plastic strip . Tommy
If you're truly concerned with it, throw the Plasti-gage in the garbage and get the right tools to measure the clearance. The mics you mentioned having should get you close, I always check with a dial bore gauge.
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