locked up 340 update

I scrolled back 100 pages & could not find my orig thread. The guy called me 2 days ago & the machine shop said that the #4 main had spun. Some info to refresh: locked up in 4 minutes during the breakin. polished std crank/new bearings/oil psi was 80/water was 160 or 180 (I forgot which but no big deal either way)/platigauged at 2& 1/2 thousands. He said the rest of the bearings were "smooth". he is saving em so I can take pics of em when we get together/stat was out. Another shop is line boring it & I found him some 340 caps (just needed the one). No debris in the filter.

Original thread: https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2180815/1.html

Spun bearing was my guess. What do I win?

Bro you get public recognition that you are the "man" with the top notch diagnostic skills due to your intelligence/vast (Mopar) experience/common sense. If you were closer I'd buy you a steak.

Thanks,
Got to give Sport440 credit more so, he called it dead on with no hesitation in the first few pages of replies. This is his quote down below.

Alright I will hang onto the steak (for now). Yes he said that everything pretty much looked pristine ex for the carnage on that main. I asked him if he could have them mock it back up & mike everything but he said it was already at the other shop being line bored & not sure if that main etc was in a condition to be measured or not but he is saveing the bearings. Not sure if I will get in on the rebuild or not, I might be invited for the breakin tho he was not happy that I did not adv the dist enough tho I'm sure he finally came to the conclusion that that was not it, tho he might suspect my conscientiousness cuz of that gaff. I felt the love on this one, all the views & replies. thanks guys!

IMO. I would only watch and not participate as you may get blamed again if something else arises.

Agreed, & resolve to stay more focused on the next one. One missed detail can wreak havoc.

Glad you found closure Robert...I'm not sure I would go back out on that limb again...
Trying to be nice and helping some people doesn't always work out well...

actually he was not out of line at all & he early on just reasonably asked about the timing not being bumped up that that might be it & I'm sure he asked about that possibility (as did I) to several people/shops & after they said no way hose A & then the machine shop finally finding the turned main that I was off the hook as far as the cause but my inattention to a critical detail could DEFINITELY keep him from requesting my help again in the future & I wouldn't blame him cuz if the roles were reversed I would be the same way.

Thanks for the wrap up. I didn't respond to the first thread because it seemed endless, same stuff I was thinking was already said a bunch of times, etc.

this was a polished, undercut radius standard 340 crankshaft with new standard MS 540 Clevite bearings right ? plastiguaged at .0025 clearance ? was this Assembly balanced ? Make sure the bearings weren't MS 540H champhered bearings, those are for the race cranks with full radiused fillets on the crank journals, and the rod journals. Bad news on a production crank. Just saying... also, if it was only hand polished with 600 grit paper, the crank may have even been eccentric or even bent at the #4 main.

Please explain how a chamfered bearing would cause any problems.

A non-chamfered bearing will grab the radiused area of a radiused crank, unless the bearing is narrow enough that they don't run into each other.

The decreased amount of bearing surface area will decrease the load carrying ability of the bearing, but you also lose a significant amount of area with a full groove and there aren't problems with them. This leads me to believe that the bearing was sized with a significant factor of safety.

So, practically, losing that small amount of area on the bearing shell should have negligible effects on the engine.

And IMHO the crank being a rolled fillet crank, didn't need chamfered bearings.

R.

I'm not saying it DID need champhered bearings. But, if they were to be used on a production crank with undercut fillets, and at. 0025" clearance, could bleed out oil at an alarming rate. The radii keep the oil on the fillet and under the bearing cap. without it, and with a champhered bearing, nothing to keep the oil from bleeding straight out the side clearance

No that was somebody elses deal. Not sure about the balance but I will find out & yes he said he plastigauged em at .0025".

The whole concept of the side clearance allowing more oil to escape the bearing is nonsense. This has been discussed 'til we're all blue in the face like smurfs. The difference in diameter between bearing and journal is so much smaller than anything else downstream of it, that the diametral clearance acts like an orifice.

The concept of piston-guided rods sprang from this concept, and racers found horsepower by eliminating rubbing friction between rod cheek and the crankshaft.

R.

Without pics and alot more info I think this is a "S--t Happens" file situation, the motor ran for four minutes, knowing the mis matched bearing related combos ive done for claimer/beater/pull tractor motors something had to be jacked pretty good to lock up a motor in four minutes.

More on the side clearance deal, my last project with scat I beams on a oem crank had ALOT of side clearance but even with narrow full groove bearings and a hydro cam, straight 30 weight and a hv pump keeps things in check and im sure its spraying oil like a shot up pirate ship leaks air.

Narrow bearings, weather mains or rods has never killed a motor that ive done or seen and going back to the four minute deal again says something was wrong from the gate.

I really wish there would of been more pics and info, before and after.

Agreed, I did not even know the guy & he had called on the phone several times over the prior year with questions then many months later out of the clear blue he called the night before fireup & I offered to be there to help with the breakin. After the mishap & it was taken back to the shop, then later he called & said they said they "had never seen nothing like that in their life" which I find a bit suspect!. He said what they originally did was polished it & not sure what else (I didn't get build details as it was all finished) & he assembled it so I ain't sure if he did something wrong or if they did & afterwards I asked him to have them mike/measure everything & he said that it was now at another shop getting line bored (evidently the first shop does not have that capability) so finding the exact cause is gonna be a lost cause now but he said he is going to save the bearings for me to look at which I don't think will enlighten me much. My only gaff was not bumping the dist up but I did not know the guy & it was a strange place & he was as nervous as a expectant papa & that made me somewhat distracted & that was not the cause of the problem. I did find him some 340 main caps. That is all I know.

so with assembly lube on the bearings, how long would that motor have run with zero oil to that main?

likely the 4 minutes it did last (if that). Yes that is a very good possibility. it did have good psi (60 or 80 I forgot which) but for sure there coulda been a blockage down there. I wished I coulda been more involved in it but as said it was pretty much a third party deal from the getgo.

If I was a betting man, I'd bet the bad main bearing was probably installed upside down with the oil hole facing the cap instead of the block.

Narrow bearings would definitely not have caused the failure.