Likelyhood of breaking a 64 mm crank

[bcrazy]

Did a search and found som examples of broken 64 mm cranks.


Question is how common is this?
If i were to upgrade my 63 1200 with 83 mm cylinders, 1300 heads, dual 32 PDSIT carbs and a better flowing exhaust

Should i worry about the crank breaking?

[[email protected]]

You should be fine no problem ..the only 64mm crank i would be worry about was the early 36hp/40hp 1959-60 "bastard" crankshaft those cranks were cast and would break ... but i doubt you have a cast crank since yours is a 63 ..if your worried about breakage you should take it in to a shop and have them check it by magnaflux the crank .... I would even have it counter weight but some will say no need to counterweight it ..

[Chickensoup]

the issue lies when people over rev a non balanced engine. keep it under 5k, or have it balanced. or better yet just buy a 64mm c/w crank from dpr and have the rotating assembly dynamically balanced.
_________________
-'85 c10 5.3 LS, 222 cam, long tubes, x pipe, 3 inch spin tech's
-'05 B5.5 TDI Wagon 17in sport rims ;EGR + BSM + ASV Delete, Stage-2 Tune, straight pipe
'65 Tourist Delivery Build
'66 RIP
'69 RIP
Hosea 4:6 "My people are destroyed for lack of knowledge"

[esde]

Somewhere here I read about having a 69mm crank "destroked" to 64, and using 1600 rods.
This way they got the thicker rod throws like the 1600, but kept it 64mm. WHY, I cannot tell you, but I read it here so it must be true.
Counterweights help minimize crankshaft flex, which helps the crank (and case) live longer.
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modok wrote:
Bent cranks are silent but gather no moss. I mean, ah, something like that.

[Chickensoup]

1600 rods are longer than 40hp. wont be a direct swap. plus, you would need adifferent flywheel
_________________
-'85 c10 5.3 LS, 222 cam, long tubes, x pipe, 3 inch spin tech's
-'05 B5.5 TDI Wagon 17in sport rims ;EGR + BSM + ASV Delete, Stage-2 Tune, straight pipe
'65 Tourist Delivery Build
'66 RIP
'69 RIP
Hosea 4:6 "My people are destroyed for lack of knowledge"

[bcrazy]

If i go down this route I will not split the case.
So another crank is out of the question

(my other option it so build on a 1600 with AB case, but do not want to discuss this here.. )

I just want to know the probability of the stock 64 mm crank breaking under ~55 hp/5000 rpm

[Jacks]

I have a ‘64 40hp under my workbench wit a broken crank
_________________
Jack Staggs
Actual name

[esde]

[earthquake]

If you were to offset grind a 69mm crank pin to Chevy std size what would the stroke be?

eQ
_________________
74 CLASS 11 LOOK-A-LIKE
69 DUNE BUGGY
79 INTERNATIONAL SCOUT II
05 SCION XB SERIES RELEASE 2[#437]
95 Chevy C3500 dually
98 Ford E150
Link to Kelly J. Nolte 3/20/53 - 11/6/08
https://time-zonelabs.blogspot.com/p/about-kelly.html
DEATH TO CHINGERS!
[From a military recruitment poster in the novel "The Stainless Steel Rat" By Harry Harrison]

[[email protected]]

[TinCanFab]

I broke one driving normal. Here are the common reasons I've read on the samba:

-lugging/over revving
-improper machining of the bearing journal during a rebuild, causing a stress point
-someone mentioned Okrasa did tests and determined the 40hp cranks were forged at too low of a temperature?

Mine broke after using in a Bus, but it came from a Beetle. Obviously more load, did that cause the break? Take it as you will
_________________
Check out my truck brought back from the dead... http://www.thesamba.com/vw/forum/viewtopic.php?t=420762&highlight=sprayed+blood

They're never really ever finished 58 rag build...
http://www.thesamba.com/vw/forum/viewtopic.php?t=658092

[fl59bug]

In either the Bill Fisher or Tom Wilson book it relates the use of the 83mm big bore P&C kit to crank breakage.

To paraphrase the book, the 83 big bore kit makes the little 40hp engine feel smooth and powerful, and leads the driver to keep their foot in it more, which overrevs the engine, which over time pounds out the center main allowing the crank to flex and finally break.

I can personally attest to the 83s making me want to rev out my '59 bug. I have a '61 tranny, and although I have absolutely no proof it helps, I try not to go above 15 in first, 30 in second, 45 in third and 71 or 72 in fourth.

As stated under-revving (lugging) is also detrimental.

[Teeroy]

40hp cranks used to break all the time. Get a counter weighted one from DPR and have it all balanced.

If you destroke a 1600 have have to figure out the rods (length and pin size will be wrong for a 40hp).

earthquake I think you end up with a 71mm crank when offset ground.
_________________
Pres. Rivercity VW Club www.rcvwclub.org
Founder Derr Wheat Panzers (DWP)
ARR #3
www.autosportsnorthwest.org

[esde]

[Teeroy]

True, that would be the easiest/cheapest option.
_________________
Pres. Rivercity VW Club www.rcvwclub.org
Founder Derr Wheat Panzers (DWP)
ARR #3
www.autosportsnorthwest.org

[Chickensoup]

[Teeroy]

VW rod journal is the largest/strongest anyway, only reason to go smaller Porsche or Chevy is to help for clearance on larger strokes.
_________________
Pres. Rivercity VW Club www.rcvwclub.org
Founder Derr Wheat Panzers (DWP)
ARR #3
www.autosportsnorthwest.org