I know 2 local guys that have had problems with the Compstar cranks, both motors were built in the last year.
LML Callies Durastar Crankshaft Issues??
- Thread starter Duramax_9505
- Start date
They are regrinding the thrust face to "true" up the surface. At least that's what we were told from the 2 we had to send back. One is in a running truck now and the other will be up and running within 2 months. We are keeping an eye on the current runner as we are skeptical of the issue being truly fixed.
I did two engines with the durastar last year, one is a race only truck that only made a few passes. The other is a 950 rwhp street truck. They are both good so far....
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I had PPE build me an engine with a durastar crank in it summer of 2019. Crank was purchased from SoCal and they supposedly checked it prior to install. I have been cutting open every oil filter and they look okay, but I’ve had a small rear main seal leak since day one. My question is do you think it’s worth dropping the transmission and checking the crank with a dial indicator? This thread makes me uneasy. Engine was 16k with no warranty, 2500 miles on the build. Any input is appreciated.
If it ain't broke, I wouldn't mess with it. If any major issues, you won't need a dial indicator, just grab the damper and push/pull to see the problem.. Good point, doesn't seem to damage anything else of value before the oil leaking becomes an issue.
Hopefully this issue has been fixed and or the 360° thrust bearing of the SoCal Deisel billet caps helps.
Have around 150 6 second passes on mine. Recently pulled botton end apart. Mahle thrust bearings look new.
Sure looking like was just a single/early batch issue on those. Been thrashing the crap outa the ultra billets, no complaints yet. 
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Thank you, was looking at the durastar one, not looking to make a lot of power with this one. I found a core engine that has a broke crank so was looking to build off that if the prices are right.Sure looking like was just a single/early batch issue on those. Been thrashing the crap outa the ultra billets, no complaints yet.
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FYI, The block has about a 50% chance of being junk. I’ve pulled apart about a dozen motors with broken cranks, and about half of them wrecked the block.
I figured it may be damaged, it’s a friends I’m waiting for him to get it apart to see if it’s good first. I plan on doing a 3388 cam, some SoCal rods, stage 2 heads, billet main caps and a few other things with it. Keeping it mild, I need to be able to tow with this one
Your luck must be better than mine. I see maybe 25% that are usable.
What parts of the block usually get trashed?I've only seen a few broke cranks myself and none of them ruined the block.
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Don't have any pics handy, but main journals get chewed up. Typically when they break in the front.
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I ran across this blog and it brought back some memories (screen clip below of 20+ YO email, I have other info that I probably should not send). I was involved in BBC / Allison transmission adaptation 20+ years ago. I have little knowledge of the Duramax, so this info may not be of much use.
Thrust surface alignment (thrust washers halves) during assembly is very important. Otherwise thrust loads will only be taken up initially by one of the thrust washers. This will lead to distress of the crank thrust wall which will then take out the other thrust washer half once enough wear happens to the initial contact thrust washer half.
Not sure about Duramax, but BBC should have forward thrust load applied to the crank flange (say 100 lbs) with 1/2 thrust load (say 50 lbs) applied rearward to the main thrust cap prior to and during initial tightening of the main thrust cap fasteners. The thrust loads used during assembly are arbitrary and do not need to simulate running loads. Not sure if this actually applies to Duramax though, especially if caps are doweled.
Seems like actual torque converter thrust loading should be considered. There is more to this than just T/C charge pressure.
Flexplate stiffness (axial spring rate lb/0.001") should be kept to a minimum to keep axial thrust loads to a minimum. Some thick billet flexplates have very high axial spring rates which lead to very high thrust loads. Crank thrust surface and bearing on stock BBC can tolerate 2500+ axial force when properly aligned, but will certainly show some wear at high hours. Super stiff flexplates can certainly lead to overload failure.
Are there any thrust failures associated with builds using non-stock flexplates, much thicker material, no or limited spring rate holes or billet flexplates?
Thrust surface alignment (thrust washers halves) during assembly is very important. Otherwise thrust loads will only be taken up initially by one of the thrust washers. This will lead to distress of the crank thrust wall which will then take out the other thrust washer half once enough wear happens to the initial contact thrust washer half.
Not sure about Duramax, but BBC should have forward thrust load applied to the crank flange (say 100 lbs) with 1/2 thrust load (say 50 lbs) applied rearward to the main thrust cap prior to and during initial tightening of the main thrust cap fasteners. The thrust loads used during assembly are arbitrary and do not need to simulate running loads. Not sure if this actually applies to Duramax though, especially if caps are doweled.
Seems like actual torque converter thrust loading should be considered. There is more to this than just T/C charge pressure.
Flexplate stiffness (axial spring rate lb/0.001") should be kept to a minimum to keep axial thrust loads to a minimum. Some thick billet flexplates have very high axial spring rates which lead to very high thrust loads. Crank thrust surface and bearing on stock BBC can tolerate 2500+ axial force when properly aligned, but will certainly show some wear at high hours. Super stiff flexplates can certainly lead to overload failure.
Are there any thrust failures associated with builds using non-stock flexplates, much thicker material, no or limited spring rate holes or billet flexplates?
