The Stovebolt Site Forums The Shop Area Engine Shop 1957 235 Connecting Rod Woes

Hey all!

Wanted to see if anyone here had some input on an oddity I'm facing.

Before starting my engine I noticed the engine was extremely tight and couldn't be turned over by hand.

Long story short I narrowed down the problem to connecting rod and bearing #3. Plastigauge was showing at .0008 which is out of tolerance by a little bit (.001 - .003). The crank had been turned down so I thought to myself that maybe they forgot to hit that one. Checking it with a micrometer vs the others and it's identical.

Here's where it gets screwy... I checked the cap and the rod sides with a micrometer and bore as best as I could and it doesn't seem out of round at all from any way I've checked it. But as soon as I tighten that rod down to 30-35ftlbs with the oversize bearing in, the engine gets incredibly tight.

Is the difference negligible enough that the engine will still fire and run like this? I don't want to chance throwing a rod.

I've heard of guys taking emory cloth to the back sides of the bearing but I'm not sure how I feel about that.

What's more, all my Googlefoo has failed me and I can't find a place to buy a brand new connecting rod for this engine.


Any input is welcome, thank you!

If it were mine, I would put the insert in another rod and take the reading. It would be rare I think to have a bad insert but who knows. If you determine that the rod is the problem, a good machine shop can fix it up for you.

I see those rods all the time on Ebay. "Brand new" is unobtanium- - - -reconditioned is perfectly OK. The only way to check it correctly is with a dial bore indicator set to the correct housing bore size, or with an inside micrometer, with the rod bolts torqued and the bearing not installed. What's the chance you might have the cap installed backwards? The cutouts for the bearing anti-rotate tabs in the rod and the cap should be on the same side, and it's very unlikely the hole will be perfectly round with the rod assembled incorrectly.

The correct housing bore dimension is 2.4030"-2.4040", according to the Federal-Mogul shop specifications manual.

Jerry

Haha unobtanium is right! I've never bought stuff like that from Ebay, have they been reliable for you?

No dice on the bearing cap, they're all machine marked to idiot proof myself

Am I correct in thinking that if it's that tight, and the plastiguage is showing it out of clearance... the rod HAS to be out of round / off?

If so, my measurements on the dial bore must be off. I'll check it again next time I'm at the garage. Just wanted to see if there was something else it could have been that I didn't think of.

Wishful thinking

I buy bunches of rods on Ebay, and so far I haven't been disappointed. I'm stockpiling Babbit rods, about 60 so far, to start converting them to insert bearings when I get the rest of my rod-boring fixtures set up.

I ran the rod reconditioning department of a big machine shop in Nashville for several years, and it was unusual to find a used rod that was not at least a little out of round. We tried to hold our reconditioning tolerances to +/- .0001".

Swapping the problem bearing to another rod is a good idea- - - -if the tight spot moves, you've got an out-of-spec bearing, not a rod problem. I've been known to mix and match individual bearing shells when I was looking for a specific oil clearance number on some of the race engines I've built.
Jerry

It may be bent.

Good point- - - -I recall a MOPAR hemi engine that would lock up when the main bearing with the thrust face was torqued. We even line-bored that engine without correcting the problem. We finally discovered the main cap was deflected backwards in the middle by almost 20 thousandths, and then the engine owner remembered it had come out of a car that had had a massive front-end wreck. A new cap and a second line bore fixed it.

A rod bent sideways by a hydraulic lock and/or trying to pull-start a rust-seized engine could be causing your problem. I've got a set of 54-62 rods- - - -PM me.
Jerry

Good info guys, thanks much!

I'll see what I can come up with next time I'm at the garage.

The piston on a bent rod will have wear marks significantly higher up on one side (above the pin) than the other.

Figured out the problem. I am a dumb man. Three years of this engine being a PITA and it was the dumbest thing.

I don't even want to say what it was. Huge thanks to Lincoln for making me realize how dumb I am.

As my wife's granny used to say to me frequently, "Wellll stoooopid." (Read with a slowly delivered southern drawl.)
Now you absolutely need to share. How else will we be able to judge our current level of stupidity without knowing what standard was recently set by you.
I can, without hesitation, guarantee that I have done something stupider already earlier today.
bartamos

The easy jobs that work right the first time don't teach us much- - - - - -it's those head-scratchers and hair-pullers that imprint the important, long-lasting lessons. Be sure to pass that wisdom on sometime!

Jerry

Yes, inquiring minds want to know.
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