[Tom Vaught]

And Pontiac Stock Rods typically have some pretty FAT rod small ends as far as left to right thicknesses compared to most aftermarket rods.

Looks like you have a connecting rod issue for sure.

Tom V.

[grivera]

Are you able to move that rod/piston to another bore to see if it clears somewhere else - for test purposes at least? Also, are all the 5140 rods in your set visually the same on the small end?

[rwfisher]

Originally Posted by grivera

Are you able to move that rod/piston to another bore to see if it clears somewhere else - for test purposes at least? Also, are all the 5140 rods in your set visually the same on the small end?

This is what I would check first. Any chance the rod is bent and the small end was bored that way... If so, it will be bad no matter where is is placed.....

["QUICK-SILVER"]

Does that rod slide back and forth on the crank?

If the wristpin didn't get centered in the rod....one end may be touching the cylinder wall and have the rod shoved to one side. It happens and can be easily overlooked.

Clay

[Schurkey]

Originally Posted by "QUICK-SILVER"

Does that rod slide back and forth on the crank?

If the wristpin didn't get centered in the rod....one end may be touching the cylinder wall and have the rod shoved to one side. It happens and can be easily overlooked.

Clay

Trying to think this through.

If the pin were offset in the rod, so that it pushed the rod into the counterweight...


...wouldn't the bottom-end of the rod be in the counterweight also? "Riding the fillet", so to speak? Of course the bearing could be clearanced for that.

I don't understand how the top of the rod can have less clearance to the counterweight than the bottom, unless the rod is made incorrectly.

How wide is the small-end of a stock rod, and how wide is the small-end of the problem child?

I think the real problem here is the huge mass of metal on the small-end, under the pin drilling. But I've been wrong before.

Is this same rod forging being used to make a shorter rod--for example, for a Ford FE? Drill the pin-hole lower, cut away the top part. One forging, different machining = greater profit.






P.S. Thanks for the picture of the cast-iron stock rod. I got into an argument last week on a Buick web-site about cast-iron vs. forged steel rods; and had to use a photo of a casting line on a crankshaft 'cause I didn't have a photo of a cast-iron rod.

[steve25]

Have the deck heights been checked, is this indeed a 6.625" long ctc rod mated to the right comp height piston?

["QUICK-SILVER"]

Originally Posted by KEN CROCIE

Possibly the rod has been built with no offset.

Assuming the rod got installed correct (tangs/notches up), 'what if' the tangs/notches got machined on the wrong side of the rod? That'ld put the wide beveled side of the big end to the middle instead of against the radius.

Something has the little end off to one side for sure. Looking at the cast rod pic that got posted....appears it would hit if it was pushed over far enough.

Just not that many possibilities here: Bogus rod, backward rod or wrist pin shoving it over.

Shouldn't be too hard to figure out
Clay

[OldGoatGuy]

Hi Guys - "newbie" old guy here- I'm the guy with the engine in question. SD421 started the thread after seeing my situation.
I've been learning a lot reading your posts and have rechecked everything. Pulled rods & Pistons out to ready them to get machined so they would work - not happy about it for sure, but want to understand what is happening.
Rods and Pistons assembled by machinist correctly and I assembled correctly - all chamfers facing correctly, and bearing tabs all up toward cam bearing journals.
I believe there is a problem with how the rods were made/machined and my machinist thinks the rods are the problem too.
I wanted to better understand what some referred to as "rod offset", which many do not think exists, myself somewhat included, but I wanted proof before deciding.
I tried some measurements and it wasn't conclusive, so I clamped some straight-edge DIN rail pieces of metal to the rod crank ends and measured from the outer edge of each side of the rods with some calipers, and I did in fact have different measurements- there does appear to be an offset. Did one RPM Rod and one Stock Rod.
It seems that if the chamfer was done on the other side of the RPM rod, I'd have clearance and the counter weight would be clear the rod piston journal, where it now touches.
It's not very scientific, but what do you guys think about the testing session in the pictures?
Appreciate any feedback. Thanks, Eric

[dataway]

Excellent way to measure. But bear in mind you are measuring to a fairly rough casting with the OEM rod. Looks like about .025 on the stock rod, and about .035 on the RPM rod. To be honest, I don't think either the stock rod, or the RPM rod are made with that kind of precision. I'd bet there is easily .010-.030 variability from rod to rod when it comes to the actual centerline of the beam compared to the big end.


The problem is ... true beam offset would be pretty difficult to measure that way, the beams themselves are just not that precise. Probably the only positive way would be finding the center line of the big end, and compare it to the center line of the small end ... and that would only be valid if the small end was perfectly centered on the beam, and often they are not.

Looks like the rods are your problem ... but I don't think it's a manufacturing error, I think it's a case of the RPM rods not taking into account every situation, every variability in typical engine tolerances.

Those rods you have, have a ton of metal under the pin .... looks like a lot more than a stock rod. If that was gone ... would you have the clearance you need?

See drawing to see what I mean. Or you could gain clearance if the pin boss was not so wide.

[Tom Vaught]

Originally Posted by dataway

Excellent way to measure. But bear in mind you are measuring to a fairly rough casting with the OEM rod. Looks like about .025 on the stock rod, and about .035 on the RPM rod. To be honest, I don't think either the stock rod, or the RPM rod are made with that kind of precision. I'd bet there is easily .010-.030 variability from rod to rod when it comes to the actual centerline of the beam compared to the big end.


The problem is ... true beam offset would be pretty difficult to measure that way, the beams themselves are just not that precise. Probably the only positive way would be finding the center line of the big end, and compare it to the center line of the small end ... and that would only be valid if the small end was perfectly centered on the beam, and often they are not.

Looks like the rods are your problem ... but I don't think it's a manufacturing error, I think it's a case of the RPM rods not taking into account every situation, every variability in typical engine tolerances.

Those rods you have, have a ton of metal under the pin .... looks like a lot more than a stock rod. If that was gone ... would you have the clearance you need?

See drawing to see what I mean. Or you could gain clearance if the pin boss was not so wide.

Good Point Dataway.

I checked all of my Piston/ connecting rod to 455 crankshaft counter-weights and have about .060" clearance before parts would touch. Not much room but even with a bit of 'Crank Flex" per main cap position, more than enough clearance for the pistons/rods to get by each other. If I were doing one of my typical longer rod, reduced pin compression height builds I would have a ton of room.

Tom V.

[Tim Corcoran]

I would take the rods & pistons out pull the crank, clearance the crank clean and reassemble. You wouldn't need to remove enough material off the crank to require a re-balance.

[OldGoatGuy]

Well guys, after much reading, triple checking assembled parts, I decided, with some consternation, that I really didn't want to spend another $200 or $300 dollars (in case I broke a ring removing and reinstalling) on a set of $300 rods ($200 to have them sized properly to start with), so I used a carbide bit and put the rods & piston assemblies in a large vise and ground my own chamfer in the rod small end toward the counterweight to give me the clearance that I need for clear rotation. Didn't remove that much, and rod has a lot more meat than stock rids, so I figured it was the least intrusive method. I did the chamfer on the bearing chamfered side on all rods to try and keep the weight as close as possible.
I know guys have successfully used these for years. I don't know why mine are the way they are, but they have been a disappointment.
Would I ever use the 5140's again? Not a chance.
Here's some pictures of the end results.

[dataway]

I've heard of people doing some pretty unusual things to clearance parts inside an engine, your solution seems logical to me. Although I might have been tempted to just take a sanding disk on an angle grinder and gone after the crank weight. But that would probably have had more effect on balance.

Still looks like it's a case of just too much meat on the bottom side of the small end, combined with an engine that puts it's rods a bit off center (like mine).

Jeez, are all 455's that tight inside? A 400 seems to have a lot more room in there.

[steve25]

Yup!
Don't forget as compared to a 400 you have near a 1/2" longer stroke and the the added counter weight mass to deal with that!

[Tom Vaught]

Originally Posted by dataway

Jeez, are all 455's that tight inside? A 400 seems to have a lot more room in there.

Not much room for the counter weights to go by the pistons on my stock stroke 455 engine with TRW pistons (Street Engine).

Tom V.

[Schurkey]

Where did all the metal shavings go?

[dataway]

Originally Posted by Schurkey

Where did all the metal shavings go?

I was afraid to ask .... a carbide makes a ton of nasty little metal devils.

[STEELCITYFIREBIRD]

On the workbench? Assembly in a vise in pic#4.

[Schurkey]

Originally Posted by STEELCITYFIREBIRD

On the workbench? Assembly in a vise in pic#4.

Thought I was seeing metal shavings on the skirt coating in pic 2 especially, and a bit in pic 3.

[steve25]

I see some on the skirt of the piston in shot 2.