Uneven bearing wear

[WSLN 6]

When I spun #3 rod bearing, I looked at the wear marks on the other rod bearings. Most seemed to follow the same pattern, with a wear mark starting on one side, down to copper already, like the rod was leaning to one side.
What is the most likely cause of this?
The thrust main bearing had copper showing, but equally on both sides,no big marks.

 

[Nick Micale]

Sounds like a typical problem due to cast crank flex. We are seeing more of this lately as the 20 year old cranks are showing their age and fatigue.

No matter if a girdle and steel caps are used, the cast crank has lots of movement under the higher HP and RPM in a modified engine.

Thanks to cast cranks, our shop always has Buick V-6's engines in process!

 

[Blown&Injected]

Thanks to cast cranks, our shop always has Buick V-6's engines in process!

LOL - my friend's machinist told him "you turbo guy's keep me in business!"

 

[Turbo1dr]

Most seemed to follow the same pattern, with a wear mark starting on one side, down to copper already, like the rod was leaning to one side.
What is the most likely cause of this?
The thrust main bearing had copper showing, but equally on both sides,no big marks.

I figured it's because it's an "off center" engine. The rods are offset from the center of the bearings and puts more pressure on one side of them.

Does the "on center" engine do the same thing??? Maybe not.

 

[tttype]

With the crank reground 40 miles before this failure, I dont think high horsepower induced crank flex was the cause.

You need to supply a bit more info to get a good diagnosis .

 

[WSLN 6]

Maybe I can get some pictures together.....

 

[PEACHS]

That abnormal wear is coming from the piston pin being located to far over to one side on the piston. If the rod is centered on the piston, when rebuilt, once installed in the engine the piston pin will offset even more to one side like .0050-.100. You will have more load on one side of the pin boss and will aggrevate the already off center rod. This will cause addition side load wear on the rod bearing.

You would still see this type of rod side load wear if you use a cast flex crank or a steel flex crank..

 

[WSLN 6]

 

[WSLN 6]

 

[WSLN 6]

MG],

 

[WSLN 6]

 

[Dominic]

I would check the clearances on the rods again if i were you. That rod bearings wiped because it didint have enough oil cushion. That's more than likely the same reason for the spun bearing. The only thing that stops metal to metal contact between the bearing and the crank is oil, and you definately had metal to metal contact there. You either had a oil volume problem (not enough getting to the rod journals) or a clearance issue (too tight).

Rod bearings only spin in two circumstances(most of the time).

1) Not enough oil cushion or clearance and the bearing will contact the journal, if this happens then the bearing will "grab" the journal and try to stick to it if this happens you will spin a bearing. This can be caused by detonation too, when detonation pounds the piston, it trys to squeeze the oil off the bearing and journal.

2) Rod bolts or big end stretch, sometimes called "egg shaping".This can be cause by many things, such as bad fasteners, poor machine work, detonation, or using the wrong rod for the application (example, 900 hp engine with stock rods)

I would contact the engine builder in your case, or if you built it yourself, possibly have a pro do it for you next time around.

Just my .02

 

[tttype]

having seen all the bearings in person;

-The mains dont show anything unusual

-1 rod bearing was ok
-1 rod spun
- 4 rods had very unusual wear
-they were worn to copper in a half moon shape ( see 1st pic )
on the top & bottom , on one side of shell, diagonal from each other.
( front of top, rear on bottom cap , for example ) as if the rod was run tilted towards the front or back ?

Crank was reground .010-.010 only 40 miles before teardown, so crank should not have been bent. Unless bent between grinding & install.

Rods were resized, possibly off axis ?

Builder is new to rebuilding , Anyone think of something that could have been done incorrectly to cause the diagonally worn rod bearings ?

Thought maybe a ballooning convertor pushed crank forward & caused rods to tilt & dig in, But main thrust surface seams ok.

Anyone experienced this before ?

 

[Dominic]

It's very common to have the the bearings wear on one side like that. Most off center engines do that, especially narrow journal/bearing engines like Buicks. But you need to check everything to verify it's not something else.

Everything needs to be taken into consideration. Make sure the rods were machined square to the side, check the rod journals for runout, make sure thrust bearing is set properly and clearance is ok, also make sure pistons are ridingin the bores properly. I feel that you need a little more clearance on the rod bearings too this should help your problem. But like i said most buicks wear like that anyhow. only time i have not seen that is with more clearance.:wink:

Hope this helps.

 

[turbolou]

reply

It's very common to have the the bearings wear on one side like that. Most off center engines do that, especially narrow journal/bearing engines like Buicks. But you need to check everything to verify it's not something else.

Everything needs to be taken into consideration. Make sure the rods were machined square to the side, check the rod journals for runout, make sure thrust bearing is set properly and clearance is ok, also make sure pistons are ridingin the bores properly. I feel that you need a little more clearance on the rod bearings too this should help your problem. But like i said most buicks wear like that anyhow. only time i have not seen that is with more clearance.:wink:

Hope this helps.

I ran into this the other day. In the process of assembling an engine recently the pistons I was using had a notch pointing towards the front. When you have a piston like this the manufacturer has intended it to be installed that way. Since the rods were hung by the machinist he must of got distracted & hung one rod flipped the wrong way. It went in initially unnoticed till I happen to double check myself just by luck. So If my machinist who's been at it forever & myself who knows better almost made a mistake .Is it also possible someone not familiar with these engine to do the same. Also did the installer insure that the oil pump was primed before start up. Was the crank nitrated & hardened after machining. Was the oil cooler verified to be free of debris or better yet completely eliminated. What about clearances, were they correct , were the rods re sized correctly, There are many things that can go wrong even for the best of us.

 

[Chuck Leeper]

My thots..

Crank endplay exceeded the rod side clearance?
Rod was put in backwards, as Lou mentioned. A rod in backwards will push the crank to it's max endplay clearance.
Brgs look to me like they ate a bunch of dirt. I agree on the too tite/insufficient oil volume idea.
What were the assy specs? The builder did give you a build sheet, RIGHT???
If the rods were "rebuilt", they should have been checked for TIR, after they were resized. I've seen some that needed to be sized, loosened, retorqued, rehoned several times B4 they are really round.
Another thing that will eat the brgs is the micro polish after grinding is backwards, and the "fuzz" scores the brgs.

 

[Dominic]

I didin't think about having a rod on backwards, that's a good point.

Like Lou said, i would definately check that.