Stock connecting rods out of round

[PaulRV6]

What causes these rods to go out of round so quickly?
I just put the motor together, had the big end resized to factory spec and after 50 miles of easy driving had to tear the motor apart because o brg failure.
Upon inspection of the big end bore they are all out of round by about .001-.003.
What is going on with this? Anyone else seen this before?

paul

 

[Intercooler]

Usually detonation.

 

[PaulRV6]

Well I think in my case it was not detonation since those few miles were mostly street cruisin at an occansional 10-13 psi boost.
But thanks for the suggestion.

paul

 

[S2V6RACER]

Being the bearing failed immediatley and you indicate the rod ends out of round, I'd say they were not done right to begin with. Did you verify they were round before assembley??

 

[Chuck Leeper]

OUT OF RD??

I posted about this just a week or so ago. The problem is the rod is round til you release the bolt torque.. then it goes whacked.. The shop that did the rods HAS to hone, release, measure, re-torque, hone, release and so on and so on.. till they stay where they should be.. BTDT.
On top of that, let me guess, the clearances were on the "tight side"?? SOOO the brg is tite, the rod closes up at the parting line, the edge of the brg scrapes the oil off the crank, and WALA!! the brg and crank are toast.
What's wrong w/ being on the "loose side"?? [My G/F is !!]
Read the brg mfgr's specs in their catalogs for specifics.

 

[PaulRV6]

Close Chuck. The guy that did my rods did not do what you said, but before assembly I rechecked the bore after torqueing bolts and they were right where he said they were, round to within .0003-.0004.
The brgs were on the tight side but no wiping and the crank was fine and so were the brgs (even though I am replacing). The cam brgs were toast.
So I think I still have to ask what causes this. Thanks folks

paul

 

[Nick Micale]

I go with what Chuck says. He and I have had this dicussion and also with other engine builders. Sometimes takes half-dozen torque cycles to get these rod in spec.

Now if you a talking about the FACTORY specs on clearances, my opinion has been that it is too tight. First of all, they use new stuff, not 15 year-old abused parts. The guys that wrote this 20 years ago said the turbo and non-turbo motors should have the same specs? Were they lazy, or have a real-world basis for this?
If we believed and did everything to Buick factory specs, we would not be going as fast as we do, or as reliable.

At least EVERY good engine builder I have discussed this rod clearance issue with says Buick's factory minimum is too tight.

Since we have NOT blown out a rod bearing in a few dozen turbo motors, I go with looser than Buick factory. If you want to go with Buick specs, get a Power Source book!

 

[PaulRV6]

And your looser than factory spec is????????????? Thanks

paul

 

[Tim Cucci]

Just rebuilt mine and also had the rods reconditioned by K+P Machine in Augusta, Ga. I explained the tight clearance situation to the experienced machinist (Rookie to Master). He said the same thing that Nick just posted. Too tight and your toast. He has seen this many times before on these engines.He requested 002" clearance. I took his advice. Everything is good so far, I have about 300 miles on the eng. Oil pressure is 19 hot idle with immediate response to throttle at > 45 PSI.

Tim

 

[Chuck Leeper]

BRGS... Again!!

I posted alot of specs from the Fm spec book about a week or so ago.. Also had some of their info about different composition of the brgs.
For those interested, I'd suggest a search of the prior posts and take a look...

 

[cruzn57]

out of round

Just another opinion,
have your torque wrench checked, makes no difference how new it is, I have half a dozen torque wrenches, (digital, clicker, scale, etc) when I torque rod bolts, I torque and release, at least 2 to 3 times, also watch which lube you use, oil will give a standard reading, moly lube will allow you to over tighten, (less resistance)
every one has an opinion, you need to decide whose 2 cents you want to subscribe to!
Never over tighten any rod bolts, once you have stretched them, they are junk!
Who am I??
just another TR owner!
I have owned a machine shop for close to 20 yrs, have done numerous Buick V-6, never had a engine failure, or rod problem,
( sold last year, retired to a county job)
whose guide lines do I follow? Buick!, (they have a few more dollars for research and development than most other folks!
Not saying anyone is wrong, just what works for me!
research your problem in depth.
Good luck!
cruzn57

 

[BobbyBuick]

also something i do when using stock bolts is to tap the cap back and forth a couple of times to center it.making sure it is alligned properly.i like the arp bolts cause they heve a sholder

 

[Steve Wood]

I don't agree with the "tight" being a problem as they were tight when they came from the factory.

On the other hand, I agree with them probably not being done correctly. I am not sure if I agree that there is more likely to be a problem if they are on the tight side and were not done correctly or not. I think it is more of a question of "when" than "if".

I agree completely on the technique required to do them right, tho. As far as being out now, it could simply be the assembly technique used to check them after the fact (torque, different wrench, differt mic, etc,) or it could be detonation, low oil pressure, heating, etc).

Probably take a ouija board to know for sure. I understand the pain.

 

[bruce]

Originally posted by PaulRV6
What causes these rods to go out of round so quickly?
I just put the motor together, had the big end resized to factory spec and after 50 miles of easy driving had to tear the motor apart because o brg failure.
Upon inspection of the big end bore they are all out of round by about .001-.003.
What is going on with this? Anyone else seen this before?
paul

I can't see that happening.

What most often pulls a rod out of round it the tension loads as the piston passes TDC at OVERLAP.

IF you'd been in massive preignition then you can do some rod bending during compression, and twist and bend the rods.

If the plugs don't show ANY signs of detonation or preignition, and what you say is true, they were fubar'd to begin with.

The loose limit is what I use. The stock specs are for a stock motor. A Hipo motor really increases the thermal stresses on a motor, and they need to be loser to begin with, wrist pin bushing included. Not to mention the bending forces put into the BLOCK.

I dunno about the torque hone retorque hone operation. I've done a fair number of rods in my time and never had rod problems, I did work in an engine machine shop for a number of years. I'd wonder how large of steps they were using in torquing the rods down. If the just were going in one step well you can do em all day like that and they'll never be right. Any serious engine part I go in at LEAST three steps to final torque.

If the arbor they were using to chop the cap ends for resizing weren't exactly 90d, they were generating junk to begin with.

I'm to the stage of I hate having a shop do any machine work, and try to get by with old stock stuff. Resizing for the sake of resizing seems to generate more problems then it's worth, IMO.

 

[The Radius Kid]

Just to add,there's one problem I've seen after the fact,and that is the finish of the splits.I've seen 'em looking like cordouroy,all blued and streaky,rough.Seems some of the donkeys in the local machine shops[well one and they're gone]don't like to dress the grinding wheel.Sorry about that rebuild you're doing!