500 Rod Bolts

[victormeldrew]

I am getting ready to rebuild my engine, and just assembling parts.

Common wisdom is not to reuse con rod bolts, which seems reasonable. However, the rod bolts for the 500 are specially made for TVR, and cost £12 + VAT each. That's a fair amount of wedge. According to the factory I'm told, they are NOT a "stretch" type bolt. This seems odd. I thought all bolts stretch when you torque them.

Now I am a bit confused. I don't want to take any risks with my engine rebuild, and I am buying a bolt stretch gauge to make sure the rod bolts are torqued down properly. I'm going to need to know what stretch to aim for, but if the bolts aren't "stretch" bolts ...

I have measured the original bolts with vernier calipers, and they range between 1.630 and 1.637 inch - this is from under the flange to the bolt end. These are all untorqued, bolt on the bench meaurements.

Measurements are:
1 1.630 1.630
2 1.634 1.633
3 1.630 1.632
4 1.630 1.632
5 1.634 1.637
6 1.635 1.634
7 1.635 1.632
8 1.632 1.631

Clearly some HAVE stretched. Piston no 5 had hit a dropped liner and broke the piston skirt, so maybe the 1.637 on that piston is to be expected.

While I don't want to take any unnecessary risks, I don't want unnecessary expense either. I'm tempted to reuse the bolts which are 1.630 or 1.632, and replace the others. There is of course also the argument that untested rod bolt may be risker than a used one that is within tolerance which has already proved its mettle.

So, my questions are:
Do I just replace the longer bolts, or all of them?
When I do torque them, what stretch am I looking for?
Or should I put down the spanners and step away from the engine again?

[pete500]

Hi Victor. Doing some mods on my 1996 Griff500 right now I had the same questions. A well known RV8 tuner told me this: We do re-use them and have never had a problem. 45ft/lb is the torque setting. I'm going to follow that. Also tried a mail to PRD Fasteners Ltd who actually made the bolts, but they never gave me an answer. pt

[victormeldrew]

Thanks for that Per.

>> Edited by victormeldrew on Tuesday 24th January 23:56

[David H]

I got mine from TVR power, the set came to around £80 delivered.

[edtvr]

I think it would be worth while spending the money on new bolts.
I know from experiance that most critical bolts on engines are tightened to either Torque and angle or Torque to yield.
In both cases the bolts would have passed their elastic limit and liable to fail.

Edtvr