Just detected a knock in my new BBC truck engine. Haven't torn it down yet. Went to the local Napa Auto Supply and was told the last guy the bought a rebuilt engine for his big truck "spun a bearing" and had to get get it replaced. Is this a problem with these engines, what causes it, and how do you prevent it. Thanks guys not looking forward to replacing this thing again and again and again.
Tow Vehicle 427 after about 500 mile break in. Towing about 5,000 lbs with duelie. Started hearing knock. Come on guys lets hear some stories. I'm not an experienced rebuilder. Got the engine form one though. I know go back to him but it has gone through another guy before I got it. Just looking for a little feedback here. Thanks
I havent found BBC's to be particularly prone to spinning bearings either. But I dont have any heavy towing experience. Rod? Did it see some detonation?
No detonation. Was able to pull over and get towed before anything broke. Not sure what the trouble is as of yet but just trying to get some info so it doesn't happen again. break in procedures? type of oil? anybody else that has had this trouble with new engine. Come on experts. Does a spun bearing always mean a scored crank?
Could be bearing clearance issues or the rod bolts were not torqued to specs... What was your oil psi readings during "break in"???
Were the rods reconditioned or was the crank turned? A lot of pretenders out there as far as machine shops go. These are two areas that I have seen problems. I have seen crank kits with journal sizes all over the place. A set of mic's goes a long way when you bring stuff home from the machine shop. You said you bought it from someone else that had it done so no telling what you got until you tear it apart and check things. A well machined BBC should be trouble free for a long time. Anymore, I just buy new stuff as it's cheaper than having things machined.
when you disassemble the engine, make mental note of how tight the other bearings are in the rods. Also look for a band of blue heat discoloration on the exhaust valve in the affected cylinder where the head of the valve flares into the stem.
Some VERY good advice here, ESPECIALLY of you are buying a crank kit with those aftermarket rods that the magazine guys like so much. In my experience, usually the "new" rods you buy need to be re-sized anyway, so I dont know about them being "cheaper", but never put anything together without checking EVERY measurement first. "Trust in God, but tie your camel to a tree."
Apparently somebody did something wrong on the rebuild. Did you buy a rebuilt from NAPA? You hear horror stories on engines these days as companies buy from vendors that are often some guy throwing together parts in his garage.
The biggest issues I've had with BBC's is clearances. A lot of engine builders increase the clearances because the BBC holds heat more [ a big bullshit myth ] Then they try and "float the bearings" with a heavier oil which doesn't pull too well through the pickup when the oil is cold. You end up aggravating 2 problems. If you use tight stock clearances and the block and crank is straight the BBC will last a long time. I've also had good success using Diesel Grade Oils in a BBC race car If I had a BBC that was parked for long intervals I would consider an oil accumulator for start up oil pressure [ we use these on road race cars with success ]
Before the big trucks took over we used 454 chevy dualies to tow all over the US ,with big trailers to go racing and put 100,000 miles on them
A lot of BBC connecting rods WERE NOT resized in a rebuild. I always resize the ones I do. Cheap insurance. I have found that most of them have become out of round and out of tolerance. I have found this to be true on BBC more than a SBC ... because the rods and pistons weigh more ... than the SBC stuff. .
Thanks guys that's what I'm looking for. I'll study it all. I know the BBC is a great engine when done right. Shit it gave the hemi. a run for the money in the 60s.
from past experience working in a mass production rebuilding machine shop. rods are not always resized they are inspected to be with in a tollerence range.
Knocking won't alsays mean scored or damaged crank. Worn or bad wrist pins "knock". More so do broken or collapsed pistons. If the rod bearings have excessive clearance they will knock. A "spun" bearing had so much clearance that the bearing halves have rotated in the rod bore. More often than not a "spun" knock will have a squeak to it as well. Only way to tell for sure is to tear down. killing the offending cylinder will usually reduce or eliminate the knock. I've seen more spun bearings in sbc's than in any other engines. ( of course I've rebuilt way more sbc's)
Hi, when i lost a lobe on the cam on my bbc it made a loud hollow knocking noise. Maybe pull the rocker covers and check push rods and valve train.
Back in the day, we had a 429 Cobra Jet in a C-600 hauler. We were going down the highway about 70 when it started rattling and dropped oil pressure. First thought was a rod knocking. Turned out to be a lifter. A rocker locker came loose, rocker arm came loose and the lifter came out of the hole.
I always check the torque on the rod bolt over and over to make sure because they stretch. A lot of people used a rod bolt stretch guage as well as torquing them to spec to eliminate any possibility of the setting not being right.
I had a 396 bbc spin all its bearings at a prolonged speed of over 140 mph. It was 1:30 a.m in the morning when my neighbor pulled up along side me at 80 mph in his sbc/450 hp Vega. The road was four lanes each direction. We got up to 140+ mph, drifting in the empty lanes as far as we could see. Then, kablunk, kablunk, bap-bap-bap, dalalalalalal, teng, teng,teng ,big loud rattle, engine died, was soon sitting still. Had a high volume oil pump, 8 qt pan, and the damn pump pumped all the oil upstairs drying out the bearings. The bores were discolored at the bottom, when I tore the engine apart.
Update Pulled the magnetic oil plug. Full of metal shavings. Must have spun a rod or main bearing. Might have been 1/2 quart low in oil in the 5 qt. pan. Wondering if the builder might have put a high volume oil pump in and it drained the oil while going up a long hill in second gear. The engine had about 500 miles on it. Not sure where to go from here. Just wanting more input. Will take out engine today and pull pan. Thanks Gary
Starving for oil will cause problems, and in my experience big block chevys use more oil than other engines, so it's common to run low. The truck pans hold a lot of oil, which helps. I worked on one about 10 years ago that lost a rod bearing because when they honed the bores, they didn't get the very bottom of the bore with the hone (the bottom of the bore was undersize a couple thousandths of an inch), so it was grabbing the pistons at the bottom of the stroke. If the oil pickup falls off or breaks it'll suck air instead of oil, which is not good. That's how I spun a bearing in my 396 years ago. They also eat cams....
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