small block HELP...keep spinning the same bearing

[Keithc8]

Jac Mac you are correct about the oiling and the rods. My mistake on that and I must have had a brain fart. The number 7 is the most common to have the problem and then the heat transfers to the number 3 but he had not heat.
Does sound like a dry oil start up problem or something possibly blocking one of the oil galleys. I have gotten a bad bearing and caused this before and could find no reason why it did it.
With the middle three mains feeding two rods each that is normally where you will see a rod bearing problem. Good luck, Keith

[JohnM]

Thanks Keith and Jac Mac,

I was told that the oil pump was spun up prior to me installing the motor. The engine builder came for the start up and break in. The engine builder was there the next day to pull the pan and poped the cap of the crank...was the first to see the bearing.

Probably just human error somewher along the line...or something we will never know.... bad baering etc..just one of thos things

Like I said in a earlier post it was probably be the most looked over rebuild...so lets see what happens

I should have it back one day next week and will keep you all informed

thanks for all your inputs

John

[sdfletch]

John,

I wonder if that block was magnafluxed. Pressure tested? Hot tanked? Never did see that in the posts. Oil galley problem?

f

[Jac Mac]

John, As Keith has mentioned sometimes things happen, for the most minor of reasons, that this has on the same bearing/rod on more than one occasion is a concern & I am sure neither you or the builder want a repeat performance.

Rather than rushing to get it back together, allow him some time to 'look' for what might be the cause.

A couple of ideas you might like to incorporate prior to & during assy.

1. Fit the crank/cam/lifters/oilpump/ and fit the pan without gasket. Now fill the pan with 20 or 30 weight oil, fit filter & prime oil pressure while turning crank slowly-observe thru the cyls that oil is flowing from All eight rod journal feeds and in similar amounts.
This serves three purposes-that you have no blockages & as a final flush of the oil galleries in the motor, & that you have not left any internal gallery plugs out.

2.Once the pistons/rods are fitted & torqued, ensure that each rod has side clearance on each journal and that both rods can be moved freely by hand to check this on any journal, while doing this check that the small end of the rod has side clearance between itself & pin boss of piston. By doing these checks you eliminate any bind or preload that could cause scuffing & failure of the bearings.

3.Like Keith I always start & test run on a test stand with radiator or cooling tower. It eliminates that 'quick run around the block' factor and makes retorque & valve spring replacement after cam break-in a lot easier.

cheers & good luck.

[Don]

Engine Crankshaft Bearings:

http://www.aa1car.com/library/ar797.htm

Club Hot Road posting:

http://www.clubhotrod.com/forums/showthread.php?t=38738

[JohnM]

Thanks everyone for the help and info and links.

During the first "build" 7 years ago everything was done. I had 3800 miles of easy driving...but never liked my oil pressure...then the accident, 5 months out of sight in a body shop....who knows

Then the spun connecting rod. During this second rebuild a few weeks back a new crank & bearings....conecting rods checked, sized, shaved etc etc. maybe a few corners cut? thinking it was basicly a fresh motor, throw in a new crank out of the box and new bearings and away we go

Now rebuild #3 after the same connecting rod spun...The builder is doing it all on his dime....I did buy new connecting rods...and I should of done that for the second rebuild.

I think this rebuild will be possibly the best ever!!

If all works out after this...and I think it will....I will still HIGHLY reccomend this engine builder.

If anyone is in the Cleveland area or wants to bring a motor this an this way...pm me direct and I will fill you in.

John

[c6ae]

I have seen rod bearings pounded out from a mix-up of spark plug wires. It is possible to have one cyl running advanced and another running retarded. It may not be noticed by an amateur as the engine could still run fairly well… meaning it won’t backfire etc.
The advanced cyl will hammer out the bearing; the retarded cyl may seize the piston…
On the 351 this seems unlikely but it could be a 1-3 mix-up.