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jimwar Samba Member
Joined: April 03, 2007 Posts: 147
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Posted: Sat Jun 06, 2020 2:11 pm Post subject: Crank broke |
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Driving my 65 beetle with stock 1200 motor and the engine seized due to crank breaking. Machine shop asked if I’d been running big bore pistons and I had. He said he had seen it before. Anybody heard that big bore pistons can break the crank? |
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Glenn Mr. 010
Joined: December 25, 2001 Posts: 76941 Location: Sneaking up behind you
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Posted: Sat Jun 06, 2020 2:12 pm Post subject: Re: Crank broke |
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Stock crank?
If not was it cast or forged? _________________ Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare |
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mukluk Samba Member
Joined: October 18, 2012 Posts: 7028 Location: Clyde, TX
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Posted: Sat Jun 06, 2020 2:54 pm Post subject: Re: Crank broke |
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Big bore alone isn't necessarily the cause; 40hp cranks are known to not hold up to high revs well, a problem more likely to occur when the engine power has been increased. Another common cause is if the crank was reground incorrectly where the radius between the journal and cheek was not maintained.
https://www.thesamba.com/vw/forum/viewtopic.php?t=261915 _________________ 1960 Ragtop w/Semaphores "Inga" |
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glutamodo The Android
Joined: July 13, 2004 Posts: 26325 Location: Douglas, WY
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Posted: Sat Jun 06, 2020 3:34 pm Post subject: Re: Crank broke |
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It's kind of unusual to see it happen now, it was certainly an issue in years past, but my opinion is that most of the ones that were going to fail, did so a long time ago and the ones around today are the survivors.
I'm surprised that it seized as a result though. The original engine from my 62 Beetle... got transplanted into a 61 that I sold and later the crank broke. I helped her rebuild the engine after this happened, but the engine was still drivable, it just made a hell of a racket.
Many years later, I had a crank break on me, this one a 1600, while I was driving... again, the engine still ran but did not sound at all well! _________________ Andy T.
IMAGE NOTE: It has been noted that Chrome based browsers may have issues in displaying my vast image library, which use non-secure links and are on an FTP server. Images should still be viewable if the link is clicked though.
I do not know how to fix this. All I can say is it all works fine for me with what I use, Firefox. |
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Chickensoup Samba Member
Joined: January 06, 2018 Posts: 5368 Location: Good Hope, GA
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Posted: Sat Jun 06, 2020 4:22 pm Post subject: Re: Crank broke |
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any pictures of the teardown? _________________ -'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" |
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Zundfolge1432 Samba Member
Joined: June 13, 2004 Posts: 12468
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Posted: Sat Jun 06, 2020 4:49 pm Post subject: Re: Crank broke |
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Here’s my broken crank. |
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fl59bug Samba Member
Joined: November 23, 2005 Posts: 1976 Location: North Carolina
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Posted: Sat Jun 06, 2020 6:09 pm Post subject: Re: Crank broke |
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Yes I've heard about broken cranks when running the big bore pistons. What is hypothesized is that the big bore kit makes the engine feel more powerful and the driver tends to rev it out farther, like past the stock shift points. This pounds out the #2 center main eventually causing the crank to whip around and break at the #2 journal. |
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gt1953 Samba Member
Joined: May 08, 2002 Posts: 13848 Location: White Mountains Arizona
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Posted: Sun Jun 07, 2020 7:48 am Post subject: Re: Crank broke |
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Been there before in July 1975. Driving from Mesa Verde to Kansas City.
It let go near Salina Kansas middle of now where on I-70. Engine still ran but um not to well. _________________ Volkswagen: We tune what we drive.
Numbers Matching VW's are getting harder to find. Source out the most Stock vehicle and keep that way. You will be glad you did.
72 type 1
72 Squareback
({59 Euro bug, 62, 63, 67, 68, 69, 73 type ones 68 & 69 type two, 68 Ghia all sold}) |
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Eric&Barb Samba Member
Joined: September 19, 2004 Posts: 24764 Location: Olympia Wash Rinse & Repeat
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Posted: Sun Jun 07, 2020 12:49 pm Post subject: Re: Crank broke |
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Check that the crankshaft has proper radius where the bearing journals meet the webs. Had two cranks break due to no radiuses there, just a sharp 90 degree angle that put all the flex of the crank in those narrow areas, causing cracks.....
The below from the "Without Guesswork" technical booklets you can access thru the "Technical" button above at right.
Left click on image below to bring it up in its own window. Click on image again then to blow it up to easily read it.
_________________ In Stereo, Where Available! |
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Helfen Samba Member
Joined: January 19, 2009 Posts: 3450 Location: Vulcania
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Posted: Sun Jun 07, 2020 2:51 pm Post subject: Re: Crank broke |
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glutamodo wrote: |
It's kind of unusual to see it happen now, it was certainly an issue in years past, but my opinion is that most of the ones that were going to fail, did so a long time ago and the ones around today are the survivors.
I'm surprised that it seized as a result though. The original engine from my 62 Beetle... got transplanted into a 61 that I sold and later the crank broke. I helped her rebuild the engine after this happened, but the engine was still drivable, it just made a hell of a racket.
Many years later, I had a crank break on me, this one a 1600, while I was driving... again, the engine still ran but did not sound at all well! |
Andy, I'm not surprised. You should have seen the difference in weight on my pistons in my big bore kit. And I'll bet most people think they can install this stuff without equaling the weight and then not taking the rotating assy. parts to the machinist to balance the whole rotating assy. |
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glutamodo The Android
Joined: July 13, 2004 Posts: 26325 Location: Douglas, WY
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Posted: Sun Jun 07, 2020 8:36 pm Post subject: Re: Crank broke |
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You know, I've never come across new sets of pistons that were really that far off in weight. Usually pretty easy to correct. But oh boy, have I seen some "sets" of connecting rods that were not even close! _________________ Andy T.
IMAGE NOTE: It has been noted that Chrome based browsers may have issues in displaying my vast image library, which use non-secure links and are on an FTP server. Images should still be viewable if the link is clicked though.
I do not know how to fix this. All I can say is it all works fine for me with what I use, Firefox. |
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Danwvw Samba Member
Joined: July 31, 2012 Posts: 8892 Location: Oregon Coast
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Posted: Sun Jun 07, 2020 8:51 pm Post subject: Re: Crank broke |
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Nice car! Are you wanting to keep it Original 40 horse engine? It may have messed up the case. Note The 65 40 horse engines had better square boss heads! Something to hang on to if you want to keep it a 40 horse. _________________ 1960 Beetle And 1679cc DP W-100 & Dual Zeniths! |
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glutamodo The Android
Joined: July 13, 2004 Posts: 26325 Location: Douglas, WY
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Posted: Sun Jun 07, 2020 8:55 pm Post subject: Re: Crank broke |
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The change to square boss heads was MIDYEAR in 1965, so they were not all created equal. The change happened near the end of November 64, so nearly a quarter of the production year. _________________ Andy T.
IMAGE NOTE: It has been noted that Chrome based browsers may have issues in displaying my vast image library, which use non-secure links and are on an FTP server. Images should still be viewable if the link is clicked though.
I do not know how to fix this. All I can say is it all works fine for me with what I use, Firefox. |
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