Lotus Elan

ARP Bolts v Socket Cap Screws to Con Rods

PostPost by: terryp » Thu Jul 05, 2018 9:55 am

Hello
I have a spare 2731 short engine that I am going to try to rebuild on the cheap. The thing is whether to change the con rod bolts?
When I built a full race Imp engine 20 years ago , we just used Cap Screws but now everybody seems to use ARP bolts but they are so expensive. Do you really need them up to 6000 rpm?

Cheers
Terry
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PostPost by: CBUEB1771 » Thu Jul 05, 2018 12:59 pm

ARP, SPS or other aftermarket connecting rod bolts are certainly not necessary for normal road use. You mention socket head cap screws in your topic header. I would be cautious in making that change without knowing the alloy and heat treatment used in their manufacture. Connecting bolts need to be ductile, not just have high tensile strength. I would be more inclined to reuse the existing bolts after a good inspection.
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PostPost by: rgh0 » Thu Jul 05, 2018 1:58 pm

I have never tried it but theoretically they should be fine for a 6000 rpm engine. Make sure they are stretched correctly to get the right preload. No matter how good the rod bolt if the preload is wrong it will fail. Just make sure also you get them genuine from a high quality manufacturer and not some cheap knock off. Also make sure the radius under the head is right to fit the rods correctly and the shank length is right so the threads are fully engaged and you dont have the threaded section in tension ( a reduced shank bolt makes this much easier to achieve)

Probably easier to get some original Ford rod bolts if they are cheaper than the ARP bolts

cheers
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PostPost by: terryp » Thu Jul 05, 2018 2:44 pm

Thanks for the advice chaps, so basically keep with the original or get new original.

Cheers
Terry
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PostPost by: Lotus14S2 » Sat Jul 07, 2018 1:55 am

If you are not over revving the engine, I'd keep the standard rod bolts.
Rod bolts are not only made to a particular strength, but they are designed to fit the rod and rod cap.
When I was racing cars, specifically sports racers, and small formula cars, although it has been over 40 years ago, we used the bolts recommended by the engine builder. At the time this was from suppliers like Cosworth, Vegantune, et al., and we used their hardware.
ARP has sort of replaced these companies' fasteners, as these companies either no longer exist, or longer make parts for such old engines as the Twin Cam. ARP has been around for quite awhile, and many years ago they were reasonably inexpensive, but now that they have a captive market, I think they are a little over rated, unless you are making an all steel racing engine, and also like the decal.
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PostPost by: StressCraxx » Mon Jul 09, 2018 12:56 am

terryp wrote:Thanks for the advice chaps, so basically keep with the original or get new original.

Cheers
Terry


I would be reluctant to re-use the original bolts. You don't know what abuse they have been subjected to.

I think if you buy new original type bolts, you may find the OEM Ford bolts are as expensive as the ARP bolts, at least here in the U.S.

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Dan
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