Having fitted new arp conrod bolts to my 1098 rebuild. It turns out one of my rods has an issue, have now decided to change to another matching set of 4x rods. My question is do the bolts have to be taken up to the 55 ft lb specified by the arp fitting instruction, or as they have now been torqued once (prestretched) they should be taken to the bmc spec of 35-38 ft lb. I understand not many people will be able to answer this and is aimed at the serious piston heads. I did have a good look online but was unsuccessful. P.s engine has never been run.
Arp Con Rod Bolts
Started by
limby2000
, Oct 17 2015 09:48 AM
5 replies to this topic
#2
Spider
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Posted 17 October 2015 - 10:06 AM
By rights, the bolts should be replaced, but having said that, I'd reuse them without issue, but did you take a length measurement of them before fitting the first time? They should be exactly the same length as 'new', any residual stretch and they should be replaced. As a substitute, you can measure the diameter in 3 places on the plain shank, and that will also show residual stretch.
Being what they are, I doubt there'll be any, but without checking, it's only a guess.
If found OK, re-torque as per ARPs instructions, if they say 55 ft / lbs, then that's what they should be torqued to, though I seem to recall these were only done to 45 ft / lbs. If they have been over-torqued, bin them.
Edited by Moke Spider, 17 October 2015 - 10:09 AM.
#3
Swift_General
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Posted 17 October 2015 - 10:47 AM
As above use the same figure if you're re using them. From memory when I installed mine I think ARP do spacify maximum allowable stretch though - can't recall the figure but it was pretty minimal.
Edited by Swift_General, 17 October 2015 - 10:48 AM.
#4
limby2000
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Posted 17 October 2015 - 11:05 AM
The arp pack instuction does specidy 55 lb, if not using a stretch gauge (whatever that is). Do they mean radial dial?.
#5
limby2000
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Posted 17 October 2015 - 11:07 AM
Has anyone noticed they also come up shorter than standard length.
#6
Swift_General
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Posted 17 October 2015 - 11:18 AM
The arp pack instuction does specidy 55 lb, if not using a stretch gauge (whatever that is). Do they mean radial dial?.
No. This means you measure the length of a bolt before tightening then as you tighten until the bolt is stretched by a specified amount. This is technically a better way of tightening a bolt as there are a number of variables (friction) that come into play when tightening by torque which bring in inaccuracies.
Edited by Swift_General, 17 October 2015 - 12:03 PM.
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