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TR2/3/3A Back on the Road

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Hi Randall,

The broken crank was stock size, the lower end of this engine was original, never rebuilt with undersize journals according to the machinist who did the rebuilding for me. It also had the original stock size piston liners. I acquired the car about 10 years ago; the history prior to me is fuzzy. The fan looks to be original or at least it shows its age.

I think I just got unlucky....of course it IS a 50+ year old car.
 
Thanks, Red.
 
All it takes is a nick in the wrong place, and a few million cycles. Glad to hear you're "back on the road" again!
 
The Dude from Canada here. Been away for a few days so sorry for the slow response. I have not had the broken crank spec'd so not sure of it was turned in the past. The pistons were 86 mm so the engine has been done before. I will raise all the issues mentioned here with the engine builder next week and look at the broken pieces. Mine broke in the same spot as the image above. I did have someone tell me about harmonics being a possible cause. I rarely if ever lugged the engine, however. The block was sent to the machine shop for honing and the centre main was a "little" twisted but fixable. No idea is that was the cause of the result. The donor crank was virgin and a new cam is going in with 89 mm pistons and sleeves. ARP bolts, new oil pump, timing chain and cam vernier, head re-done. It should be good come end of April. I will report on the outcomes.

Frank D…….. IMG_0872.jpg
 
Related..and not related...
I broke a Merc crank in my Flathead Ford several years ago. I've been running flatties since...1965, I think, rebuilt them professionally....speed work and all.....I had never had it happen before, nor heard of it.
Had to ask far and wide.....apparently it does happen on occasion with Forged Mercs (not cast Fords) IF the main line is out.
And it was.
Fixed, 'nother crank...so if your main was out just a wee bit...that flexes the crank continually...and you'd probably see it manifest in odd main bearing wear indications.
Dave
 
I always thought that a broken crank would be a disaster, but I broke mine near the number 1 journal. It did not brake completely, but a good crack. I thought that it was rare and mine broke because of the supercharger. From what I am hearing it is more common than I thought.
 
In mechanical engineering school we learned to model a whole lot of structures to analyze the loads. I remember studying that crankshaft design is still in the dark ages, in that there are so many forces and resonant forces that it is not possible to model them. Crankshaft design is still a matter of trying something that looks about right, see if it works, and beef up the area that breaks.
 
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