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79SuperVert Samba Member
Joined: May 31, 2002 Posts: 9758 Location: Elizabeth, NJ & La Isla Del Encanto
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Posted: Wed Nov 05, 2008 6:56 am Post subject: Broken Cranks from Vintage Speed enhancements? |
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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? _________________ Central Jersey VW Society
Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt. |
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John Moxon Samba Moderator
Joined: March 07, 2004 Posts: 13943 Location: Southampton U.K.
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Posted: Wed Nov 05, 2008 7:08 am Post subject: Re: Broken Cranks from Vintage Speed enhancements? |
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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. _________________ John.
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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 Samba Member
Joined: June 02, 2004 Posts: 9602 Location: Pearl River, NY
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Posted: Thu Nov 06, 2008 4:59 pm Post subject: |
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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 Samba Member
Joined: May 31, 2002 Posts: 9758 Location: Elizabeth, NJ & La Isla Del Encanto
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Posted: Fri Nov 07, 2008 6:22 am Post subject: |
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Thanks! _________________ Central Jersey VW Society
Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt. |
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Erik G Samba Member
Joined: October 16, 2002 Posts: 13247 Location: Tejas!
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Spezialist Banned
Joined: July 01, 2005 Posts: 1941
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Posted: Fri Nov 07, 2008 10:35 am Post subject: |
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Stock cranks failed from over revving, and roller cranks fail from under revving. _________________
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myb356 Samba Member
Joined: October 14, 2004 Posts: 408 Location: bay area california
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Posted: Fri Nov 07, 2008 12:53 pm Post subject: |
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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 Administrator
Joined: April 11, 2000 Posts: 69734 Location: Phoenix Metro
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Posted: Fri Nov 07, 2008 6:07 pm Post subject: |
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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 Banned
Joined: July 01, 2005 Posts: 1941
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Posted: Fri Nov 07, 2008 7:15 pm Post subject: |
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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.
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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 _________________
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gimmesomeshelter Samba Member
Joined: May 08, 2004 Posts: 1468 Location: San Carlos, CA
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Posted: Fri Nov 07, 2008 8:49 pm Post subject: |
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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 _________________ "I would rather have questions that can't be answered than answers that can't be questioned."
Richard Feynman |
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