+1

If it was only one mess up I would maybe say "**** happens", but after 4 times and still can't get it right. I would be looking for a new builder.

If anyone has a list of clearance specs it would be appreceated starting to believe the bypass valves have created most of the problems. Crank is not an Eagle. Will get the brand from the builder. Mains were shot and line bored.

I dont think the clearances are your issues .However, I'd think a engine builder would be able to look at the failed parts and see a lack of oiling issue. Im going with bypass valves causing your grief.

Was this a automotive block? Who made the call to retain or install the automotive 11psi bypasses as would say a 1993 454 Truck have.

blow up
 

ive always replaced the cooler lines because the metal fragments will embed into the rubber an as soon as it gets hot they will run thru your motor again

this was a REBUILD ... correct ? what was wrong with it that caused you to rebuild ? what bypasses were in it before and how long had the thing run before rebuild ?

if this was just a hi hour motor that timed out , then there is no reason why that spec and configuration should not continue to work, if it was an unknown or a repair on one that blew up, then maybe there is a root cause as yet undiscovered. i think you start from scratch... not in the sense that you throw everything away, but that you subject every component to a fine inspection and testing regime for quality, serviceability and dimension and go with a known good configuration for by pass and clearences. in other words, " the basics" . repair time is over. its time to reboot.

as an aside... what were the oil temps and pressures as the " blowing up" process occurs each time ? is all the rods, or all the mains or the same one every time ?

and honestly, the guys suggesting a change of shop might have a point. if you built this in your garage, maybe having a discussion about clearences etc might make sense but you are saying this guy knows what he is doing and is a professional... what advice is there to give that he shouldn't already know ? if he needs the advice then you need a new shop.

If your "engine builder" is an automotive shop ,a lot of them aren't familiar with the abuse a boat motor goes through. Even if you ran the crap out of your car,it's impossible to hold it wide open for long .In a boat some hold them wide open for hours.
Clearances are a little tight for a hi-perf marine engine .You do know the oil running by bearings helps cool them,right?.......btw ,what is capacity of oil pan .Don't run a hi-volume pump with a stock pan,all the oil could end up "up top"...my 2 cents.
chit does happen ,but an experienced builder should be able to figure this out. All the clues are in front of him

Guys, you do realize this is a 6+ month-old thread that was resurrected, right? Hopefulle the OP is still around to benefit from our analysis.

I think others are on the right track in regards to tight clearances and bypass valves. If hot, dirty oil was sent back through the bearings with clearances this tight I can certainly see where bearing damage could result. From there it can snowball - a little scuffing, dirt and oil starvation startes the bearings on a downhill roll and pretty soon you spin one or more of them. Are you spinning only mains, only rods, or both? If just the mains are having a problem, take a close look at how that line hone job was done on the mains. I found out from painful personal experience that not every shop has the capability to do this the right way. Find an experienced independent third party to look at the parts that failed, and if possible take some measurements. Since the bearings were trashed, not much point in checking them, but you could measure the main bearing bores and the big ends of the rods, along with the crank journals to make sure all of that is in spec. If your current builder set the clearances so tight, that tells me that he may have limited experience building performance marine engines.

Not the first time I was late to the party

HaHa - I know what you mean. I only noticed because I happened to go to the first post to see what all problems he was having and the thread seemed familiar. ;)

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Bump..........