broken crank!

[gtx1967jewison]

Can anyone shed some light.......
Lotsa A's &G's with 9" plus stroke & huge 6" plus bore, 100-120 hp, even 10" strokes, a tiny WELDED B crank at 8", 6"plus plus bore,
Yet everyone says an R with 70-80 hp will break the much larger diameter, factory stock, 8"stroke crank?
Seems to be highly unlikely.

Im guessing ONE factory-flawed crank in a very built/ over revved R broke & the chunks landed in the rumor mill....
All comments welcomed.....
I do understand torque but come on...

 

[jd b puller]

You don't see a lot of R's built up much to compare to. One thing that's different from the other JD Diesels is that they all have center main bearings where the R does not.

Keep in mind a diesel is a lot more violent than a gasser (Much higher compression)

 

[gtx1967jewison]

Right but a 70hp R v.s. a 70 hp B with a half-diameter welded crank, the B has a larger bore & thus more firing psi (more sq inches) on the crank journal which is at or near the same stroke......I do surmise the combustion forces far exceed the compression forces or it would turn backward, a G has to be as wide a crank as an R....how bout a 500 c.I. D, burning #2 Fuel oil, detonating & water injection etc putting out 40+hp for 1000's of hrs. Remember the fear by JD of their first diesel failing....thus grossly overbuilt....after 13 YRS (1,1/3 DECADE) of testing (abusing)

 

[gtx1967jewison]

If this has ever really happened how come nobody has personally ever seen it? I wanna see pictures!

Its always "they say" or 'ive heard". Well tell me then, what's it sound like?! LoL...

 

[gtx1967jewison]

There was recently a billet crank mentioned for a 70steel that broke a crank, but they're hollow @ the journal. Im NO expert......Lookin for thoughts......
Thanks!
.......it can be fun to learn even at our age.....

 

[BenAlbert]

Can't speak about the crank, but there is a fellow here that has a v12 Allison mated the back end of an R. The transmission and finals must be half decent.


I think maybe the bigger reason not too many are built into pullers is that they are kinda heavy for the power you start with.

 

[gtx1967jewison]

Yes I've seen Dons allison R in person. 1200 hp through a bone stock R transmission & rear end, even several 1st reductions in series, & no trouble.

 

[MNJDG]

Ray is right, without the Center main the crank has too much flex and can break.

 

[gpuller]

A crank can break in anything. There are plenty of R's that are running 720/30 pistons and make more power than stock. I think if they were breaking cranks somebody would hear about it.
Personally I think its a myth.