small block HELP...keep spinning the same bearing
 

Hello All

Here is the background...351W 69 block, so the short deck height. I purchased it as junk yard moter 7 years ago. The engine was already 40 over and took it 60 over. Had it rebuilt nothing to radical all good quality stuff...but never was happy with my oil pressure and figured it was rebuilt loose...maybe not the best engine builder but no problems...ran strong etc

Finished the car and have been driving if for 5 years...only 3800 miles on the car.

Got into an accident late last year 2007 not my fault...mostly fiberglass damage etc...car was repaired and finished this spring. Drove it this summer...came up with an engine knock, pulled the pan and I had spun a connecting rod bearing.

This time took it to a race engine builder....new crank reconditioned the rods...line honed the block, kept the cam, redid the heads...he says he went all through it.

Started it up and broke it in...no problems lots of oil pressure. Changed the oil fired it up the next day to finish setting the rings...came up with a knock...pulled the pan and had spun the same connecting rod bearing...?? The new crank is fine, engine ran for maybe 60 minutes total

Never lost oil pressure

The question is...what do I look for?? Obviously new connecting rods will be installed...but what else should be looked at?

what our we missing?

any help and advice would be greatly appreciated

thanks

John

John,

Maybe look to be sure that you are getting oil to that journal. Spinning a bearing that fast would sound as if it wasn't getting any oil or very little. Do the bearings look as if they have been very hot or do they have worn places in them? Good luck and just hope that maybe you got a bad bearing, but I would have that bore and the alignment of the piston and rod checked also to be sure there is no binding.

Ron

Hello Ron

all of the oil passages lined up when the bearings were installed. The spun bearing had not turned blue from heat.

Of course something could of been missed...I just don't beleive in coincidences...same connecting rod.

Pulled just that one cap off...so had not looked at any of the others . Pulled the engine last night in record time 45 minutes!!

tonight the engine will get torn down...hopefully it will be something obvious

Thanks

John

clearances?

Are the little notches that the bearing tabs fit into clean and open and not distorted in any way?

.

Same rod AND location?

fletch

It was the same rod...the cap bearing, which is why new connecting rods for sure

My knowledge of engines is limited...I am along for the ride with all the technical stuff. My engine builder is taking care of this as he felt really bad...I am just trying to find out as much as I can so that I am not at a total loss when its discussed

My engine builder is a real pro...a full time race shop etc...so its not knowldege...just one of those things

John

Was it line bored?.

I am pretty sure it wasn't line bored for the first rebuild 7 years ago.

It was line honed this rebuild 2 weeks ago

any thoughts

John

Since the 351w is externally balanced I wonder if it would be advantageous to number the piston/rods as they come out. Does anyone do this? I mean is it SOP? If the same piston/rod did not go back in the same location then you might look at the bore. Do you know what reconditioned means to the engine builder? Are these stock rods?

f

Yes the rods are stamped with a number and used in the same cylinder. I do think that is sop in regrds to the pistons etc. I do think the same rod and piston went into the same bore....thats why now new rods for sure

I am not sure what rod reconditioning mens....making sure it is "round" and uniform where it connects the crank etc??

John

I'm leaning toward Vector1's suggestion. That bore could be off center a little. Maybe.

possibly your engine builder missed something. i would just pull the one rod and have it checked along with the rod throw diameter. be my guess since it is the same rod your clearance would be a little tight. make sure when you take it apart that the bearing chamfer is toward the outside, although i don't think it could be otherwise. rod bearing crush could be minimal also, too large on the big end to hold the bearing in place.

Unless the "race engine builder" has/is been taken out of the mix I'll bet he wants to disassemble the engine. What number cylinder did you loose and has oil system been modified for increase and decreased oil flow in different areas.

Rod bearings tend to go south in pairs or common crank throws because they have the same oil supply and other than rod bearings have the same clearances. The radius of that crank throw should be inspected closely as well as rod pair side clearance. The rods should have been checked for twist and being bent when recon'd but double check for sure.

Loosing a rod on start up or break in just about has to be a clearance issue as mentioned already. Crank pin diameter is probably correct if the bearing on the same throw is OK. The rod bearing insert will often turn in rod if not torqued or left loose and rod will often knock before spinning insert. The crank pin and bearing will show you what was wrong. Photos of each will help us back seat drivers form a few opinions. Let us know what you and your builder find went wrong.

You did say you changed the oil and fired it up the next day, never lost oil pressure. After oil change was start up pressure verified for sure? How long after oil change did it run before knocking? Was the common rod bearing good, you mention crank pin was good? Were the rod bolts tight? What hole went bad? Is your last name Murphy?

My swag is the rod bolts for that hole was not torqued if the rod on the same throw is good. Keep chin up, it will only get better.

Not sure I can answer all of that but here goes...The engine builder is warrantying this...very, very upset andd fells bad. I don't want to drop names as things like this can go wrong and possibly not a reflection on him or his work, so far he is taking care of it...I am only out an hour and half of my time pulling the engine out...no problem...and I learn alot

Yes he is tearing down the engine today, so I will fimd out about the adjacent rod and the others

It was cap #3 oil hoiles have been chamfered etc, eased etc. not sure which oil pump was used...but had 60 pounds at start up.

Oil pressure never bottomed...but I never again had 60...now 50 at startup and 40 when warm. The bearing never turned or spun around...but came out of the cap and was all worn...copper in oil and filter after I cut it open

The knocking became more pernounced when the engine was warm...I think maybe the piston hitting the head....was the light knock...will see today when torn down.

Rod bolts were torqued to 50 pounds...sure seems like that when taking off the cap...but .....I'm no expert, I can't answer about the crank pin

What was the stamped size on the back of the bearing? Did it match the others?

Here's my .02

I would replace the rod bolts and recondition the rods. Also, would clean out the motor and and all oil passages in the motor and head and any nocks and crannies.

If your running a oil cooler clean that out as well.

Things happen!!!!!

It could have been contamination, clearances, or torque pressure.

I am sure this time around you will have better success. Retorque your bolts 3 times and dont take anything for granted.

Even the best of us make mistakes. At least your engine builder owned the problem.

all tolerances were at .002 or 2 thousandths both the mains and the rods


John

So the rod journal on the crank was unharmed, as was the other rod on the same journal?

If you did not see any bluing, I would say your clearances are fine.

I would check the crank clean inside crank if it serviceable.