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Broken Cranks from Vintage Speed enhancements?
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79SuperVert
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PostPosted: Wed Nov 05, 2008 6:56 am    Post subject: Broken Cranks from Vintage Speed enhancements? Reply with quote

I understand there was a tendency for 40hp crankshafts to break when performance enhancements were added to stock engines. I experienced this myself when my otherwise stock 40hp with oversize pistons broke a crankshaft last year. Were crankshaft upgrades ever recommended by vintage speed suppliers?
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John Moxon Premium Member
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PostPosted: Wed Nov 05, 2008 7:08 am    Post subject: Re: Broken Cranks from Vintage Speed enhancements? Reply with quote

79SuperVert wrote:
I understand there was a tendency for 40hp crankshafts to break when performance enhancements were added to stock engines. I experienced this myself when my otherwise stock 40hp with oversize pistons broke a crankshaft last year. Were crankshaft upgrades ever recommended by vintage speed suppliers?


I think the broken crankshaft thing was more of a problem with the 36hp engines.

The main problem with the performance upgrade came with applications that relied on extending the rev range to get the extra performance.

The relatively flexible 36hp crank could pound the hell out of the mains if you constantly overreved it and the whippy crank would not stand up to this.

Having said that 36 and 40hp cranks would fail on stock cars too so it's difficult to know if it would have happened anyway.
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Last edited by John Moxon on Fri Nov 07, 2008 7:13 am; edited 1 time in total
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Rome
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PostPosted: Thu Nov 06, 2008 4:59 pm    Post subject: Reply with quote

79Super, I suggest buying the old VW book "How to Hotrod VW Engines" and read about stock cranks. That book explained alot about the relative weaknesses of VW cranks when you start modifying the engine, and recommending counterweighting, balancing, adding 4 more dowels for the flywheel, etc. Another excellent info source is GeneBerg's Tech article on crankshafts.
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79SuperVert
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PostPosted: Fri Nov 07, 2008 6:22 am    Post subject: Reply with quote

Thanks! Very Happy
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Erik G
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PostPosted: Fri Nov 07, 2008 8:45 am    Post subject: Reply with quote

40hp cranks were known to fail in stock aplications
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Spezialist
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PostPosted: Fri Nov 07, 2008 10:35 am    Post subject: Reply with quote

Stock cranks failed from over revving, and roller cranks fail from under revving.
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myb356
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PostPosted: Fri Nov 07, 2008 12:53 pm    Post subject: Reply with quote

My father managed to break 2 different 40 horse cranks. The first was around 1978 on his factory built engine...The second was around 1988 with the same engine and a 1385cc big bore kit. He was still able to drive it 15 miles home. I think they might just be weak.
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EverettB Premium Member
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PostPosted: Fri Nov 07, 2008 6:07 pm    Post subject: Reply with quote

I broke the crank on a stock 40hp engine in my Bus. It was pretty loud on the freeway but still ran, just with a little less power. I drove home on the freeway at 55 mph for about 25-30 miles. I stopped at one point when I was almost home because it was going really slow up a hill but it was REALLY loud at idle so I jumped back in and drove a few more miles home.

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Spezialist
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PostPosted: Fri Nov 07, 2008 7:15 pm    Post subject: Reply with quote

EverettB wrote:
I broke the crank on a stock 40hp engine in my Bus. It was pretty loud on the freeway but still ran, just with a little less power. I drove home on the freeway at 55 mph for about 25-30 miles. I stopped at one point when I was almost home because it was going really slow up a hill but it was REALLY loud at idle so I jumped back in and drove a few more miles home.

Smile



Well, I drove a 62 panel van between boulder creek California and Santa Cruz for close to a month, with a broken 40hp crank.
I never took one apart but I think it breaks between the rod section, and the cam gear, its a "harmonic crack" as far as I know.
My boss, Lou of Lou's Volkswagen Repair of Santa Cruz either felt sorry, or was tired of hearing that thing drive up to the shop,, come to think of it, prolly not good for business either Laughing
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gimmesomeshelter
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PostPosted: Fri Nov 07, 2008 8:49 pm    Post subject: Reply with quote

Hello-

If your crank suffered an harmonic crack, maybe you needed a damper pulley? http://www.aircooled.net/new-bin/viewproductdetail.php?keyword2=ESM0037&cartid=

BTW, has anyone purchased one? If so, what are your thoughts?

Thanks,

Paul
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