New connecting rod question - possible problem

I just got a new set of SBC PM connecting rods. It seems like the caps are misaligned at the bevel side (has a ridge) The bearing area & sides are ok though.

Anybody seen this before?

Chevy p/n 12495071

 

While your drawing is very nice, I think a photo would help us better see what you have.

 

gotta find the camera.

The "edge" is on the chamfer side, where the cap contacts the rod.

Will get a pic

 

"The bearing area & sides are ok though."

I'm thinking you >>may<< be describing "cap shift" which is one of the typical bad things that happens when rod or main bearing caps are switched, or rod bolts are replaced.

The horizontal moveable points of the Sunnen bore gage are measuring a diameter just above this rod's parting face.
http://image.hotrod.com/f/techartic..._9903_06_+chevy_connecting_rods+new_bolts.jpg

 

If you're talking about powdered metal rods that are broken instead of machined on the mating faces, I seem to remember that condition being pretty typical and NOT a problem. I've been out of the machine shop biz for a couple of years now, so it's been awhile since I've seen those rods. A picture would refresh my memory, I'm sure.

Ron.

 

Here's a few pics. I tried to illuminate it with a lazer to help show the shadow. My retna's are hurting now...Best I could do

 

step prob measures around .005

 

That does seem a little more "off" than I remember seeing, but could still be OK. Have you taken a cap off yet, and are they all this way?
Are they new from GM?
Do you know what I mean when I say the rods are "broken"?
If you seperate the rod and cap, it should be pretty easy to tell if the cap matches the rod as the irregular surfaces kind of interlock.
The reason I ask if they are new VS. reconditioned is because the reconditioned rods of that type are usually opened up .002" because the mating faces can't be ground on (or at least, they SHOULDN'T be!),
thus requiring special bearings with a larger OD.
Anyway, if the thrust faces line up and there is no step in the bore at the parting lines, the mismatched chamfer really doesn't matter since it doesn't make contact with anything.

Ron.

 

Yeah, they all have the same issue. I do know what you mean. I worked in a shop that pressed PM parts. Brittle as hell until they go thru the oven. Clever idea on breaking the big end - these are new BTW

I'm going to talk to a local machinist & get his opinion

Thanks!

 

I don't use Powdered Krap Con Rods, period... and speaking of
period" what are we speaking of this new type of rod here on the H.A.M.B. for??? I think this belongs on an engine site somewhere... No?? Just my tired ass old as dirt opinion.

 

did you have previous problems with PM rods?

Going in a vintage engine, I hope that's period enuff for you

 

I rebolt/resize a lot of these rods. The left turn racers love them.
It is common for the chamfers to be mismatched. As long as the big sides are parallel and the hole is round and in spec. They will work fine. A tougher rod than the old "Pink" rod.

 

I'd rather have a set of the old school "pink" rods...

 

Rods are typical of GM quality. Lotsa late model corvettes and trucks with blown bottom ends due to GM wanting you to buy more engines/parts more often.

nothing new here...


.

 

Ok, that's good. The mis-match is on the non-machined area of the chamfer. Everything else looks A-ok

 

You mean besides the built in obsolescence? As in they are not re-buildable? Or the New parts and equipment needs created by them? (if you hope to re-build / reuse them someday) or how about the whole "powdered, molten poured in a mold" concept.... No give me an OEM or aftermarket forging any day.... Again just my tired ass, old as dirt opinion, after 38 years doin this for a living
and no, its really not about "the engine" it is not even about your choice of rod, it's your $, but it is about this forum being about traditional Hot Rods and supposedly about building them in a traditional way with traditional "stuff" Your issues deserve attention, on an engine builders site...
again, just my tired ass, old as dirt opinion, after 38 years doin this for a living .

 

I was looking for original z28 or pink rods, $$
These were Plan B.

Thanks for all the info

 

You would have been better off with a Eagle rod. But, you own these already. Have you fitted a bearing in the rods yet, or are you just inspcting them before they go in your closet until your ready to use them.

 

yep - going in the closet for a few months at least

Wanted to stick with GM.

 

Those are chinese rods....No thanks!

 

And you wonder why people either don't ask questions on here, or why you don 't see much fresh blood at shows etc with attitudes like this wanker.

 

Sorry Tjet, you sent me this last night, I didnt get off my lazy ass and look at it till today. Does the crank you are going to use these a substantial fillet radius? That would be the only area that i can see that might create a problem. The photos are hellacious hard to see, but that is a pretty big step. Kinda ugly looking, it would bug the hell outta me too.
And yea, I see what you meant in your pm.

 

I sent those rods back. I ended up getting a set of Crower Sportsmans with 7/16" capscrews & pressed pins. The crank I'm using is a forged "1182". 4 bolt, forged flat-tops, zero decked. Setting rev limiter at 7000 RPM

This is the tunnel ram motor that's still at the dyno. Gonna get it next month

 

No first-hand experience with pm rods, but I've heard good and bad about those rods. They are supposed to be stronger than "pinks", but kinda like hyperutectic pistons, when they DO fail, they FAIL, like disintegrate. Not pretty. I could see that rod causing fit issues on a crank like a scat 9000 series or similar.

 

Good move. Rods are one of those things that you can't cut corners on. Or have odd mis-matched chamfers on. For years I've bought my rods OTC at my local Chevy dealer. Never an issue and the price was always acceptable.

Bob

 

under 400hp pm rods are reliable built a dozen or so motors in the last couple years and the rods didn't fail i wouldn't say the same for hyperutectic pistons. which prefer not to use

 

thanks for asking...I learned something here.
"Hard to tell, not-knowin'!"