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As I was checking all tolerances in mains and rod bearing clearances with newly installed pistons on original rods, I came across a rod that had one bolt slide partially out of its hole but was seated back in with gentle tapping. These are the original connecting rod bolts. These were all sent out to the machinist I used who installed the new pistons on the original rods.
This is not a high horsepower rebuild, just an L-36 rebuild with .040 over pistons and a new cam (close to stock). It never occurred to me to check the bolts to see how tightly they were in place by tapping on them to see if they would unseat or not.
Is this a concern or not? I read that new bolts are basically tapped in with a punch, or pressed in, but it wasn't clear if these were meant to be so tight so they could never be unseated without a lot of pressure. Once torqued down, will it be fine? The head of the bolt is a rectangular shape, I presume, to keep it from rotating more than a certain amount, but I'm not sure.
Any input is appreciated.
Kirk
Just for clarification-
Once this rod bolt is seated flush with the con rod surface, I can turn it about 15º in either direction, before the head of the bolt hits the connecting rod. I'm not sure what you mean by a "seat" so it can't turn. Did you mean it can't turn much? Sorry for my confusion, but I've never seen a rod bolt move as I was tapping apart the cap when plastigaging.
I would be concerned that the bolt or the rod may be stretched a bit. Did you have any work done to the rods? Reconditioned? It's about the same money anymore to replace rods as it is to have them reconditioned with new bolts.
From: Las Vegas - Just stop perpetuating myths please.
Yes you need new rod bolts that fit securely. This will require reconditioning the rods for the new bolts also since the pressing in will distort the rod journal. Always recondition the rods (big end) when replacing the rod bolts. As for new rods Tim is right - they are all most the same money to buy new as to recondition and replace the bolts. For some reason rod bolts are expensive.
so, a machinist handled all 8 rods. one had a rod bolt not seated all the way down.
Took a big screwdriver. Smacked the head about 6 times with the plastic handle. Then i put this 3 inch ratchet on it and pulled it back in place.
There is no way i put enough stress on that rod with a 3 inch ratchet and 1 hand to distort that big end. When you knock pistons out of a block you pop rod bolts loose all the time. You never hurt a big end in the process. If that rod needed work, that machinist would have told you all 8 needed resizing. They only need resized if the bearing was spun or trashed.
Yes it is a 427 corvette engine. Any expense added to a bottom end rebuild can be justified. But necessary and justified aren't the same thing.
Last edited by derekderek; Jul 12, 2020 at 06:10 PM.
From: Las Vegas - Just stop perpetuating myths please.
Originally Posted by Kirk H
Just for clarification-
Once this rod bolt is seated flush with the con rod surface, I can turn it about 15º in either direction, before the head of the bolt hits the connecting rod. I'm not sure what you mean by a "seat" so it can't turn. Did you mean it can't turn much? Sorry for my confusion, but I've never seen a rod bolt move as I was tapping apart the cap when plastigaging.
You need rods with bolts that aren't loose enough to turn by hand or whatever. A floppy rod bolt is gonna slip around at even low RPM.
I have replaced GM rod bolts with new Pioneers, measured them after torquing them down and they were still round. ARP will distort some as they install a lot tighter than the Pioneer.
Anymore I won't mess with GM rods when a set of Eagle SIR rods are $190 a set and are about 10 x stronger than stock.
Anyway.....a seriously sloppy bolt will be an issue, but one that has some interference fit but somewhat loose (Tap out with screwdriver handle for instance) is fine but I urge a person to put new bolts in at $40 a set.
When I re-built my 427 from my 1968 C3 I replaced all the hardware inside and out with ARP hardware. I would never re-use anything like rod bolts myself. The higher quality ARP hardware is insurance that it will stay together (I hope).
68 BB rebuild question
