small block HELP...keep spinning the same bearing

vettestr · #1 (**permalink**) 11-04-2008, 07:25 AM

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.

JohnM · #2 (**permalink**) 11-04-2008, 07:59 AM

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

blykins · #3 (**permalink**) 11-04-2008, 08:34 AM

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

priobe · #4 (**permalink**) 11-04-2008, 08:35 AM

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.

JohnM · #5 (**permalink**) 11-04-2008, 08:54 AM

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

John

priobe · #6 (**permalink**) 11-04-2008, 08:58 AM

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.

JohnM · #7 (**permalink**) 11-04-2008, 09:31 AM

The crank was brand new..a scat cast crank. that journal will be polished.,..but no marks or scratches...or by feel. Obviously a better inspection once its tore down

The engine ran for all of 45 minutes to maybe 60 minutes top

We did not open the second cap on the same journal...thats happening today

Rick Parker · #8 (**permalink**) 11-04-2008, 09:38 AM

Just an outside chance but with the 69 block which has a marginally shorter deck height I think there is a specific piston pin height for that engine which is different from the later 351's, check into it. Outside of a twisted rod, be sure the rod cap is installed in the correct orientation and the rod fasteners are retaining their clamping force and have not been overstressed and most importantly that the finished bore of the rod is correct, it must create "Crush" on the bearing shell to keep it captive.

JohnM · #9 (**permalink**) 11-04-2008, 09:50 AM

A question now about the rod bolts...we have already ordered new eagle connecting rods, why take chances as the last set of stock rods were reconditioned.

We did use the old ARP rod bolts as the engine has only 3800 miles. Whats everyones thought that when the first bearing spun...it maybe streached or tweaked those 2 bolts??

is it common to reuse the old bolts when so few miles are on the engine?

John

JohnM · #10 (**permalink**) 11-04-2008, 09:54 AM

DA...I was just thinking....the rod bolts are studs, and the new rods will come with them

John

CobraEd · #11 (**permalink**) 11-04-2008, 10:01 AM

If it is a new aftermarket crank, maybe it is not drilled thru from the main to the rod journal. or maybe there is crud in there.

.

JohnM · #12 (**permalink**) 11-04-2008, 10:12 AM

Yes it was a new SCAT crank.....I hoped he would of checked that

thanks

John