Suitability of 4-bolt crank and caps for greater power

[RotoFlexible]

As I noted in a previous post, I am in the process of upgrading a '66 Twin Cam to Sprint camshafts and compression. Everyone agrees that the old-style con rods are not up to the task and I have accordingly bought a set of 125E rods on eBay. The man who will be doing my head work (a local race engine builder) is not keen on the crankshaft and he can't stand the sight of the main caps. I haven't heard that the 4-bolt crank and caps are not adequate for a road engine - only the rods. We are crack-testing the crank. If the caps are OK for the intended use, I would like to avoid the expense of new caps and machining. Any opinions?
(If the crank is no good, he's going to try to talk me into a 1700cc stroker, but that's a subject for another post!)
Thanks in advance for your advice.

[garyeanderson]

Hi Andrew

The round caps are weak, but people have used them for years and most have not had problems. If you are at this point after 30 or so years of ownership it wouldn't hurt to put the Square cap on your block, nice insurance. Bills got one of my Dave Bean 1600 cranks in his shop, I need to get $550 for it to break even. The extra torque from the displacement increase is a nice thing. I might have a 1500 6 bolt crank around but in any event you will need a new pan and rear main seal holder to go with either 6 bolt crank. I'll be in Ayer tomorrow stop by Carl's if you can.

Gary

[rgh0]

Andrew

I know of know problems with the earlier round crank caps or 4 bolt crank when used in reasonably developed engines. Certainly OK for a 126hp sprint spec road engine.

The round caps are really only a concern if replacing the cast iron crank with a steel one and seeking more than 7000 rpm.

regards
Rohan

[Dag-Henning]

- fully agree ! The 125E crank and std. caps are more than adequate in a road engine ! Re the crank ;
Literature says that 040 undergrind is the safe limit, but for street use I would even consider 060, - if you can get hold of the bearings.....

DH