Looking at a car that owner just rebuilt the engine with a rajo head. Issue is that he has a stock T crank in it still. Is this a time bomb, or a non issue? If i was doing it I would have put a scat in it and called it a day... but he swears the stock T crank is just fine.
Rajo Head and a stock crank on this speedster, before the Rajo there was a roof that was a bit too hot. Years ago there was a T crank that had been welded (counterweights) and drilled. When it broke it was replaced with the stock T crank that's in it now.
That is a slick car you got there! like the look of it
more than likely over half of overhead valve heads made for model T's spent most if not all of there time on stock bottom ends the reason being there is not a compression difference on the majority of ROOF, RAJO, FRONTENAC etc with stock type pistons
It's all in the use of the new power..
If using it without spending much time in the high rpm register above 2000 - and if you avoid the rpm bands where the internal twisting tends to get multiplied by resonance (the worst is at about 1350 rpm in my 1926 crank) then your std crank should last much like in a std car, but it's always impossible to say how much fatigue life a used crank has left in it, as long as there isn't any cracks.
I meant no comp. difference between stock model T and low comp. (most sold) overheads
My 1919 speedster has a Rajo Model 30 head (8 valve) that has been on it since 1927. Block, crank, cam are all original, with aluminum pistons (0.040" oversized). Cam and crank were re-ground in 1980, and the engine has a few thousand miles since (sat for 33 years after the rebuild before being installed in the car). No problems with it since 1927. Just my experience, YMMV.
Just depends how hard you beat on it. You can break any crank if you really try, no matter what head you're using.
Most importantly, you can over rev. No problem. Don't lug it down.
Ed aka #4