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  View original topic: Crankshaft Questions VW 36hp with a Porsche vs 356 crank
Rwoodshvac Fri Jul 30, 2010 1:09 pm

I read where a lot of vintage guys use a Porsche 356 Crank in the 36 hp vw case.

Specifically what 356 Cranks are being used? Does it have to be a crankshaft from a Pre-A 356 with a two piece engine case. Or can a crank from a 356 A/B 3 Piece case work . What are the differences?

Thanks
Rick

gimmesomeshelter Fri Jul 30, 2010 2:33 pm

Hello-

I don't believe you can use a Super 90 crank.

The 'A' and 'B' cranks have 50mm mains, so they'll fit as long as you have the correct bearings.

The 'C' and 'SC' cranks use a 50mm main at the flywheel, but the two center mains are 55mm. You'll either have to grind it down to 50mm, or add oil grooves and bearing tab slots to the center mains. As for this later option, I've read about it being done (by Pre-A Porsche owners who are getting rid of their roller cranks), but I have no idea how difficult/expensive it is.

Paul

PS. For more crank info, check out Duane Spencer's book http://www.amazon.com/Porsche-Performance-Guide-Du...amp;sr=1-3

Tom Simon Wed Sep 01, 2010 2:29 pm

Rwoodshvac wrote: I read where a lot of vintage guys use a Porsche 356 Crank in the 36 hp vw case.

Specifically what 356 Cranks are being used? Does it have to be a crankshaft from a Pre-A 356 with a two piece engine case. Or can a crank from a 356 A/B 3 Piece case work . What are the differences?

Thanks
Rick

I'm no Porsche expert, but with the help of several guys here, Jose at DPR, I am fitting an early 912 crank (74 stroke and counter weighted), and an Super 90 crank (also 74 stroke and counter weighted), to my 36hp VW race-cases.

The thing that makes a 36hp and Porsche crank unique from type 1 VW is the cylinder bore and rod-to-rod spacing, the rear main bearing, and flywheel hub/dowel pin spacing. They do share cam drive gear diameter, (and crank to cam bore centerlines) so with some cam mods, you can use VW cam gear sets.

Porsche made several varieties of cranks, again, I'm no expert, but I've researched this a fair amount before purchasing my used cranks, and have seen 64mm stroke non-counter weighted, 74mm non-counter weighted, and 74mm stroke counter weighted IMO, 74 stroke counter weighted is the one to use if you are going to the trouble of fitting a Porsche crank to a 36hp VW. Oh, and some Porsche guru is going to chime in and add to the list of cranks Porsche offered for the 356/912 cylinder bore spacing, but in a nutshell, this is what I found. Most, if not all, came with 53mm Porsche rod journals, that accept oem 356a,b,c and 912 rods.

Both my cranks have counterweights and 74mm strokes with 53mm rod journals, commonly known as 'Porsche journal". But the super 90 crank has all three larger 55mm main bearings. The early 912 crank has the forward 2 mains 55mm, the rear main is just like a 36hp VW crank with 50mm. As such, it will accept a VW 36hp rear main bearing.

We ground the diameter of the Super 90's rear main journal, to be the same as 356 Porsche/36hp VW. We didn't have enough room to bore the 36hp VW case's rear main saddle to accept a Super 90 bearing, the studs are in the way.

I had both 36hp engine cases align bored .25mm over stock vw 36hp specs, to now accept standard OD Porsche 356 main bearings. Their are less expensive ways to go, like having Jose grind the front and center bearing journals to 50mm (it's done all the time) so you can use an inexpensive 36hp VW main bearing set. he can also grind the rod journals to accept 50.8mm Chevy rods (but the rods and rod bearings will need narrowing) I wanted the extra strength of both larger main and rod journals, since I will be racing and likely beating the pi$$ out of them :)

Another interesting tid bit; Apparently, when Porsche started with the early 2-piece case, Porsche took new 36hp cases and blueprinted them. Like any good engine program, they started with a high quality main bearing tunnel align bore (maybe the Porsche engine guys were not satisfied with the VW machining quality for their premium car?). Thus, standard 356 main bearing tunnel bore ( bearing OD) = first oversize (+.25mm) 36hp VW bearing OD.

As time marched on, Porsche went to their own cases (3-piece), then increased 2 of the 3 main journal sizes to 55mm, but they retained the same bearing OD as their standard case bearing bore size. :idea:

I spent a lot of time figuring all this out for my engines, I hope it helps you.

gimmesomeshelter Wed Sep 01, 2010 2:41 pm

Tom-

It sounds like you're installing a crank with 55mm center mains, yes? If so, who is going to machine your case for the oil gooves and bearing tabs?



Thanks,

Paul

oval56 Sat Sep 04, 2010 12:59 pm

you have ti use a pre a crank wit 50mm mainjournal... or regrind the 55 mainlournal to 50mm

or buy one from demello or dpr...




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