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71ghiavert Samba Member
Joined: February 21, 2017 Posts: 98 Location: Mill Valley, Ca.
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Posted: Wed Sep 15, 2021 10:56 pm Post subject: Crank snapped in two. Oil starvation or crank flaw? |
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So here's wassup:
Last year I built my first engine, a 1968cc, 74x92, 9:1 compression, Web 218 cam, L3s, dual Weber IDF 40s. Ran well and made 90 hp on the dyno.
Two weeks ago I upgraded a bit, adding Panchitos, 1.25 rockers, a 1 1/2 exhaust, and 32mm venturis. Re-jetted and tuned. Much fun. Lotsa pop. It was the engine I wanted. Maybe boosted to 110-120hp? Cool!
Two days ago I was driving it up a local mountain road--not lead-footed by any means, but having fun around the curves--when I heard a sudden clunk-clunk-clunk. I pulled over immediately and had it towed. My mechanic checked the dipstick and, yikes, the oil was dead low--just at the bottom of the dipstick, well below the "low" line. Looking under the valve covers, he found that one of the silicone seals had split, as tho someone had cut it with scissors along the bottom edge. I had driven maybe 60 miles since last checking the oil; the assumption is that in that time the engine pumped out a lot of oil. The flywheel now had a LOT of endplay, and his guess was that oil starvation had destroyed rod bearings, main bearings or both.
Today I took the engine apart, expecting to find a gruesome mess. Instead, all the bearings looked perfect. Not a sign of internal distress. But when I lifted the crankshaft, it came away in two pieces. It had snapped right next to the center bearing.
So now I'm wondering what happened. Was it the oil loss? Or was there a defect in the crank, revealed when it had to deal with the engine's increased torque? On the one hand, the oil was very low, and it's easy to imagine a quick, severe heat problem. On the other hand, the bearings are still perfect, and I would have thought they would have been destroyed before the crank itself gave way. Also, tho the oil was really low on the dipstick, there was still some oil in the case, plus the 1 1/2 quart deep sump, and the spin on oil-filter. Because the engine is "new", I watch the gauges pretty closely; before the clunk, the oil pressure remained high and the temp never went past 200. If the pressure remained high, that makes me think that there was still oil flowing to the bearing where the crank broke. But maybe I'm wrong about that.
Anyway, trying to figure out what happened. Killed by oil starvation? Or a defect in the crank? Or something else? FYI, it was a high quality crank, built on a German core, by a good supplier.
Thoughts? Thanks. I don't know enough draw a strong conclusion. |
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glutamodo The Android
Joined: July 13, 2004 Posts: 26325 Location: Douglas, WY
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Posted: Wed Sep 15, 2021 11:14 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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I don't think oil starvation would cause this, especially since you say you don't see signs of it on the bearings.
So, it was a German Forged crank that got built up then. Not one I would expect to suffer this. I had a replacement cast stock crank break on me once before, but it was not a quality crank like this one seems to be.
If you checked end-play at the pulley end, it means nothing when the crank is broken. The thrust bearing is where end-play is determined and is out of the picture once the crankshaft snaps. Since your thrust bearing was intact to the flywheel, I wouldn't expect much endplay there. Not like when this happened to me:
_________________ 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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anthax Samba Member
Joined: October 21, 2016 Posts: 283 Location: Hälsingland, Sweden
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Posted: Thu Sep 16, 2021 1:03 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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Oh thats a sad sight. :/
Is it me or does the rotating assembly looks like it overheated? Both crank and rods looks blueish/black from heat. It could be my monitor not being 100% in reproducing colour.
71ghiavert wrote: |
So here's wassup:
Last year I built my first engine, a 1968cc, 74x92, 9:1 compression, Web 218 cam, L3s, dual Weber IDF 40s. Ran well and made 90 hp on the dyno.
Two weeks ago I upgraded a bit, adding Panchitos, 1.25 rockers, a 1 1/2 exhaust, and 32mm venturis. Re-jetted and tuned. Much fun. Lotsa pop. It was the engine I wanted. Maybe boosted to 110-120hp? Cool!
Two days ago I was driving it up a local mountain road--not lead-footed by any means, but having fun around the curves--when I heard a sudden clunk-clunk-clunk. I pulled over immediately and had it towed. My mechanic checked the dipstick and, yikes, the oil was dead low--just at the bottom of the dipstick, well below the "low" line. Looking under the valve covers, he found that one of the silicone seals had split, as tho someone had cut it with scissors along the bottom edge. I had driven maybe 60 miles since last checking the oil; the assumption is that in that time the engine pumped out a lot of oil. The flywheel now had a LOT of endplay, and his guess was that oil starvation had destroyed rod bearings, main bearings or both.
Today I took the engine apart, expecting to find a gruesome mess. Instead, all the bearings looked perfect. Not a sign of internal distress. But when I lifted the crankshaft, it came away in two pieces. It had snapped right next to the center bearing.
So now I'm wondering what happened. Was it the oil loss? Or was there a defect in the crank, revealed when it had to deal with the engine's increased torque? On the one hand, the oil was very low, and it's easy to imagine a quick, severe heat problem. On the other hand, the bearings are still perfect, and I would have thought they would have been destroyed before the crank itself gave way. Also, tho the oil was really low on the dipstick, there was still some oil in the case, plus the 1 1/2 quart deep sump, and the spin on oil-filter. Because the engine is "new", I watch the gauges pretty closely; before the clunk, the oil pressure remained high and the temp never went past 200. If the pressure remained high, that makes me think that there was still oil flowing to the bearing where the crank broke. But maybe I'm wrong about that.
Anyway, trying to figure out what happened. Killed by oil starvation? Or a defect in the crank? Or something else? FYI, it was a high quality crank, built on a German core, by a good supplier.
Thoughts? Thanks. I don't know enough draw a strong conclusion. |
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Igpoe Samba Member
Joined: February 24, 2019 Posts: 853 Location: South Boston, VA
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Posted: Thu Sep 16, 2021 3:17 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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I'm thinking the crank let go and a sliver of metal from it traveled to the seal and split it. You pumped the oil out AFTER the crank broke. That crank could have had a crack in it for years or even always. Of course you'll never be sure and I'm just guessing. _________________ '73 super. |
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oprn Samba Member
Joined: November 13, 2016 Posts: 12740 Location: Western Canada
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Posted: Thu Sep 16, 2021 5:23 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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I once bought a '73 Beetle that was still running with a stock crankshaft broken just like this. The case bearing saddles were pounded out beyond repair too. Not knowing the history on the car and being a stock non counter weighted crank I just assumed it was from high rpm abuse. _________________ We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age) |
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gt1953 Samba Member
Joined: May 08, 2002 Posts: 13848 Location: White Mountains Arizona
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Posted: Thu Sep 16, 2021 6:01 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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Had a stock crank break in the middle of Kansas. Oh boy no fun no cell phones back then but hitch hiking was safe then.
Not sure why it snapped. Well maybe driving it for like ten hours straight. _________________ 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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oprn Samba Member
Joined: November 13, 2016 Posts: 12740 Location: Western Canada
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Posted: Thu Sep 16, 2021 6:11 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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gt1953 wrote: |
Not sure why it snapped. Well maybe driving it for like ten hours straight. |
How long you drive it has absolutely NOTHING to do with engine failure of any kind! We regularly take trips of 8 to 12 hours straight through with any and all of our vehicles from our air cooled ones right through to our Dodge 1 ton. _________________ We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age) |
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Dale M. Samba Member
Joined: April 12, 2006 Posts: 20380 Location: Just a tiny bit west of Yosemite Valley
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Posted: Thu Sep 16, 2021 6:45 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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Fault is with crank shaft, could have had stress riser in it for years and the day it broke was the day it decided to break.... If bearings look good it was probably not oil starvation problem, because there would have been galling on bearings if they ran dry....Some have had engines that actually ran decent with broken crank other that it hammers case to a point it is not useable....
Had a engine in an crap BAJA for a while that had about 1/4 inch of endplay at pulley end, always suspect it had broken crank but never tore it down to see (whole project was a disaster) Sold it to a fellow with understanding engine was bad, but never heard from him what he found out about engine... _________________ “Fear The Government That Wants To Take Your Guns" - Thomas Jefferson.
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ... |
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1105 Location: North East Pennsylvania
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Posted: Thu Sep 16, 2021 9:08 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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So, crank is toast. How much else is still usable? Case? Rods? Definitely following your thread.
Mike T _________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue. |
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Clatter Samba Member
Joined: September 24, 2003 Posts: 7549 Location: Santa Cruz
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Posted: Thu Sep 16, 2021 11:15 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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This happens a lot, actually.
Just like yours, right next to the center main.
Aftermarket, factory, counterwieght, stock, stroker, doesn't matter.
When your number comes up, it comes up.
It's not something you did wrong or anything else.
It just happens.
Hopefully your line-bore is still good.. _________________ Bus Motor Build
What’s That Noise?!? |
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Zundfolge1432 Samba Member
Joined: June 13, 2004 Posts: 12468
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74 Thing Samba Member
Joined: September 02, 2004 Posts: 7394
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Posted: Thu Sep 16, 2021 1:25 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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Was it a 4140 or 4340 crank?
At least you got to drive it a bit and find out it was the engine set up you wanted. Now you will have to go through the case etc and get a new crank.
It happens-machines break. Don't be hard on yourself and get to building a new engine.
Who do you use for machine shop work in your area, Jansen? |
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Pruneman99 Samba Member
Joined: February 22, 2012 Posts: 5013 Location: Oceanside
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Posted: Thu Sep 16, 2021 3:33 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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It's an OG crank with welded counter weights. If it's 74mm, it was offset ground. Maybe to a smaller rod diameter (Buick)?
Who knows how much abuse it had on it before it got worked over. I would assume that the shop that did the work magnafluxed it before welding. But maybe not. Maybe it just broke..
Doesn't really matter. The results are the same. Hopefully since you shut it down fast, the case and everything is still ok. |
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74 Thing Samba Member
Joined: September 02, 2004 Posts: 7394
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Posted: Thu Sep 16, 2021 3:42 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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My bad, I did not look close enough to see the welds on the crankshaft! |
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liquidrush Samba Member
Joined: July 18, 2018 Posts: 588 Location: MO
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Posted: Fri Sep 17, 2021 11:10 am Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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Can you provide close ups of the break on both sides? Thanks. |
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bugguy1967 Samba Member
Joined: January 16, 2008 Posts: 4343 Location: Los Angeles, CA 90016
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Posted: Fri Sep 17, 2021 12:10 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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Yep. It just broke because it was its' time. The area where it broke doesn't get touched by the crank grinder, except to turn-down the journal during a regrind, so it woulda happened regardless if it was modified or not. _________________ "A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine" |
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71ghiavert Samba Member
Joined: February 21, 2017 Posts: 98 Location: Mill Valley, Ca.
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Posted: Fri Sep 17, 2021 2:07 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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Thanks for the input, everyone. In the end, yeah, I think it broke because its number was up. There was no damage to the bearings or the case, so I came away lucky. The engine felt a lot snappier with the new heads and 1.25 rockers, so there's even a chance that it was just the little increase in torque that proved too much for a weak spot on the crank.
Also, I liked the engine a lot with its new modifications, so will rebuild it exactly the same way. New bearings everywhere, have everything balanced again and re-check deck height, and a general cleanup. If it performs the same, I'll be happy.
Not sure what steel, just that it was built on a German core by a reputable supplier. Supposed to have been magnafluxed. I guess this now falls into the immortal category of: "Stuff happens."
Liquidrush: I'll post some close-ups when I have a moment. |
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rosevillain Samba Member
Joined: December 28, 2005 Posts: 1290 Location: roseville, ca
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Posted: Fri Sep 17, 2021 3:13 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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Contact the supplier and let them know that you had a problem. Have pictures ready and be cool. Maybe they provide a better product in the future, maybe they help you out with the next one. |
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modok Samba Member
Joined: October 30, 2009 Posts: 26790 Location: Colorado Springs
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Posted: Sat Sep 18, 2021 6:55 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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It's a bit out of warranty, being some 30-40 years old
Offset grinding it "could" have brought a flaw to the surface that wasn't a problem before, something like that, but, I'd just say it's bad luck.
On a long enough time line.... every crank will ultimately break,
just in MOST cases we never run them long enough to find out. |
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71ghiavert Samba Member
Joined: February 21, 2017 Posts: 98 Location: Mill Valley, Ca.
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Posted: Sun Sep 19, 2021 3:35 pm Post subject: Re: Crank snapped in two. Oil starvation or crank flaw? |
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By popular demand, broken-crank close-ups!!!
I think I'm going AA next time . . .
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