Conrod Question

[literarymadness]

Are the OEM 125e conrods forged steel or cast, and how high of a rpm limit can they handle with a lighter forged steel crankshaft and forged high compression pistons (10.5)? 

[EuropaTC]

I've read in one Lotus book that the original 116E Cortina rods were replaced with a stronger part (125E 6200C) for the end of the run on Mk1 TC engines and subsequently fitted to all Mk2 engines, which is what we should have in our cars.  Both are apparently forged steel H section, just that the later ones were stronger.

I checked with Dave Vizard's book "Tuning Twin Cam Fords"  and that also mentions the 125E rods. He also describes the weak points and how to improve them and recommends fitting stronger big end bolts.  Apparently the OEM bolts are grade 8.8 HT;  one option is Cosworth items or a slightly cheaper gr 12.9, 1 3/4" by 3/8" UNF HT socket cap screw mentioned in the Robinshaw & Ross book on the Elan engine.

None of my sources mention a rev limit for the standard rods.

It's worth trying to pick up a copy of Vizards book if you can, lots of details from when tuning these engines was a big deal.

Brian

[literarymadness]

Thanks Europa TC! It's funny you mention the Vizard book.  I just lost the bid on a copy on eBay.  Ken at Dave Bean told me that a guy there swapped out his crank to a lightened forged steel one and JE pistons (kept the 125e rods) and runs it at 8500-9000 rpms at the track.  I am thinking about doing a similar set up (already running a hot street cam) and would like to comfortably run at 7000-7500 (the top end of the powerband for my cam).