Rash of Broken Stroker Cranks

[AlteWagen]

I just saw pyromans 82mm welded stroker crank (in pieces) and read he broke the crank in his bug too. A buddy of mine also cracked his forged CW crank in the same spot (unknown crank builder).

I recently went to look at some VW parts for sale and the owner had a 74mm welded stroker for sale as well. As I looked over it I noticed some cracks on the main journals. Looks like they were cracking where the bead was laid.

Is anyone else having these problems?

Since I have only heard of one CB one piece crank breaking in the same spot, are welded cranks more susceptible to breakage?

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[miniman82]

Probably not made by any of the reputable folks, but reasons like this are why I felt it was better to risk it on a one piece forged crank from China rather than a welded one. I've seen a few CB 69mm welded cranks break in this way; I don't know who does their welding, but there's obviously some QC issue there with regard to the welding process. I've also had engine built on their cheaper 4140 strokers with no issues, so my suggestion will be to see if you can verify who it was made by. If it's not DMS or the other well known places I'd pass.
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[modok]

Yeah, it happens
But it's rare enough that you don't have to worry.

[gerg]

My CB forged crank has 4 years of pretty good running on it, no breakage so far.
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Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab

[AlteWagen]

Do the 40hp cranks break in the same spot?
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[modok]

Pretty much all cranks can break like that, it's the thinnest spot you know.

[VWporscheGT3]

yeah the 40hp cranks break in the same spot... my buddy had a 67 bug witha 1300 in it and becuase of wheel hop going onto his street there was enough shock through the drive train to crack the crank. we didnt know it was broken until it was pulled apart for a bottom end rebuild, he had put 80K on it in 2 years and it was still running strong when it was dropped from out the car. im sure just a freak occurance on it being runnable and drivable till we discovered it. and the crack was clean and looked like one peice until you tried to remove the assembly....again prolly a freak occurance

-Trevor
69 Fasty
71 Beetle
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[SGKent]

are you running lightened flywheels about the same weight? You may have moved the center of rotational mass into that weak spot.
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[AlteWagen]

Are the one piece CB cranks cross drilled?


Are there different part numbers for 1500 bus cranks?
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[mark tucker]

hmm did it have a heavy pully???? how much stroke? hevy pullys can and do do that. hmm yup that is doodoo dont step in it.

[modok]

Cb's cranks are uhh, like "T" drilled.

[mark tucker]

I think it was crower that had cranks that were pumper cranks.the oil holes were drilled in the corect locations so they would act like a cintrifical pump or something like that.so it dosent have to overcome toe forces of nature but works with it.. and the holes were in the high load area.not in the lowest load area like some(vw)
looks like that crank needed some gussets added to it. or possiably an extra main bolt in the center to hold the crank still and that would not of happened.

[DarthWeber]

[gerg]

What is T drilled? I thought both of mine were cross drilled. One is a CB, the other is a no name Chinese crank.

The Chinese crank looks just like the CB without the name, probably the same foundry.

They are drilled from one flange, through the center to the opposing flange, meeting at a main I think?
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Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab

[modok]

i donno i guess I'd have to make a diagram.
It would look like a T in cross-section
They drill from where that allen head setscrew 8mm oil plug is to the main journal, then drill a hole through the rod journal, connecting to the first passage. Maybe it's more like a cross with a plug in the top.

Point is there is only one passage drilled through the web, whereas the X drilled ones have two passages that cross in the web.
I think the single drilled is fine, don't know why CB goes to the trouble.
Believe scat crans are single drilled, at least some of them are.

[BugMan114]

i always thought a heavy (equalizer) pulley was a good thing, to distribute weight? tho that pulley side bearing on the crank is pretty small . maybe a lightened flywheel, and equalizer pulley? they would be a lot closer to weighing the same. Do you even want to achive even weight on both sides of the crank, or is that just a myth?
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1960 Baja Bug
1969 Baja Bug
Sand Rail- Homemade
Sand Rail- FUBAR

Aircooled Airheads

Why the hell do they call it a gland nut. its obviously a big fat bolt!!!

[pyrOman]

Some possible important factors to know regarding my broken crank since it is the one referrenced to begin this thread. Don't know what it was originally since no markings show though they may have been covered over the flange weldings. So it could have been originally a vw crank, welded and reground. I bought it used at the swaps on Drag Days so who knows what kind of history/milage it actually had before I used it for 2-3 years. When first put togethger I "broke it in" going to Havafew, 300 some miles one way. It took me all the way across the country and back for an 8000 miles in 20 days trip. About a year and a half ago I went with the IRS and just a few months ago I stupidly installed some tall assed tires on top of that. Where I didn't had to before, now I've had to drop to third a number of times seemingly because of lugging down the engine. Any or ALL these factors could have very well contribute to the stress failure of the crank.


All that said, just prior to the Havafew trip, going to get some parts for the NEW transaxle, drove the Bug a few miles and it also broke the crank!!! This one is a stock vw 69mm on a very stock 1600, though it was built with a bunche used parts from my stash.

Shit breaks sometimes. In some cases a lot of shit breaks on you "in a row" as much as you may not like it. I surely don't! But it happens. I am going to use a forged 78 vw crank that though I also got from the swaps at OCTO/Classic, it was from one of the machine shops from the OC area, either KYMCO or RIMCO or whatever. It came with stock rods but I will used the CB rods I already had. They are both the same length.
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[pyrOman]

On a side note, I'd also like more input from the "experts" on the use of the 5lb pulley!?!?!


Been using one for over 10 years now without issues unless it could be attributed without question that it broke my crank!
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[79SuperVert]

FYI, here's how mine broke.

Maybe 10,000 miles on a rebuilt engine, .010/.010 crankshaft, apparently VW, oversize pistons. Ran great until I started to hear what I thought was pinging over the summer. Checked timing, put in premium, still would "ping" on hills. Then on a really steep hill, I heard "bang bang bang bang", I could feel it through the pedal, and the engine lost power. I pulled over, and looked at the engine as it was running: the crankshaft pulley was bouncing up and down.
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[mark tucker]

when that 5 lb pully is spun up is is storing energy.where does that energy go when you drop the clutch or shift hard?? what about luging the motordown befor you shift to 3rd? it IS twisting the crank back & forth.no the flywheel dosent do that it is at the out put side and the power go's to the trans.not through the crank to power something on the other end.. there is no need for a heavy pully on a performance engine.on a bus or other stock motor it may be helpfull to some point.and what good or deferance would it make to "hang" extra weight on the other end of the crank any way?? to balance it out?? no thats not how they are balanced.
like I said before in the early days of hot roding & porting&"cam timing"(no cam but changing the port timing is the same effect)jetski's the power & rpm was bumped up a lot from like your lawn mower to a dirtbike.and when reentering the watter they would twist the crank in two. very heavy pully was the cause so we started removing weight, they got faster and nolonger were breaking cranks. the dirtbikes also went to a very small rotor instead of a flywheel to keep from killing cranks.and it dosent matter what is stamped on the valvecovers or hood when you try to stop stored energy it has to trans mit through something. I have a new heavy equlizer pully hanging on my wall for many years now. I also have the lighter steel burg pully & had on my 1874 & 2332.it may or may not go back on.I havent had any problems at all with the aluminum pullys. do either dampen harmonics??I doubt it.do they need to yes. but I cant afford a fisher damper.& dont realy want to rework my aluminum ati to fit a vw.& it has no belt gruve. it would be nice it there was a thick heavy aluminum pully that could be turned into a damper.
so the answer is yes that heavy pully probly had a hand in the crank breakage.and if it had a week cylinder and the pully was "smoothing "it out a bit.that just speed up the breaking prosess.