Spun Rod Bearing

Spun Rod Bearing - 01/11/14 06:29 PM

What would be the cause of a spun rod bearing?

The motor is a 418 small block that has been together since the beginning of 2008. Probably has well over 1500 passes and 1000 miles on the street. The bearing were inspected and look good around January 2012 and they looked good. I run a 7 quart Milodon pan with full groove main bearing and a high volume oil pump.

Last Saturday on my second pass the car felt slow and was slow to pull to 6500 rpm. I went through the traps and lifted and heard a bottom end noise. I pulled the motor apart Sunday and I had spun the #4 rod bearing and pushed it out towards the crank. When it lost the bearing it hammered the rod and bent the rod cap. All the main bearings looked fine.

Why after all of this time did it spin a bearing?

Posted By: Cab_Burge

Re: Spun Rod Bearing - 01/11/14 08:03 PM

Pull the rest f the rod bearings and look hard at them for debris and to see if they have lost the bearing crush, if they are still snug and don't fall out of the rod caps and rods

If they fall out they have lost the bearing crush, probally from detonation or pinging

Detonation, debris and inadequate(SP?, to little) clearances are the biggest reason for rod bearings spinning, your motor live quite awhile so I would rule out the clearances being the issue

IHTHs Let us know what you find

Posted By: fbs63

Re: Spun Rod Bearing - 01/11/14 08:57 PM

What rods? Lower quality rods will go out of round when torque cycled a few times.

Posted By: Brian Hafliger

Re: Spun Rod Bearing - 01/11/14 09:53 PM

Quote:

What would be the cause of a spun rod bearing?

The motor is a 418 small block that has been together since the beginning of 2008. Probably has well over 1500 passes and 1000 miles on the street. The bearing were inspected and look good around January 2012 and they looked good. I run a 7 quart Milodon pan with full groove main bearing and a high volume oil pump.

Last Saturday on my second pass the car felt slow and was slow to pull to 6500 rpm. I went through the traps and lifted and heard a bottom end noise. I pulled the motor apart Sunday and I had spun the #4 rod bearing and pushed it out towards the crank. When it lost the bearing it hammered the rod and bent the rod cap. All the main bearings looked fine.

Why after all of this time did it spin a bearing?

Did you change anything, like tuning, fuel type, old fuel? Over reved?
Same oil always used?

Posted By: MR_P_BODY

Re: Spun Rod Bearing - 01/11/14 10:18 PM

For ONLY one rod... I would guess it was the weakest
point and stretched that cap

Posted By: 70satelliteguy

Re: Spun Rod Bearing - 01/11/14 10:23 PM

"Probably has well over 1500 passes and 1000 miles on the street"

Man that is a lot of PASSES

I would be thrilled if I could get that many passes out of any racing motor!
Mike

Posted By: 416challenger

Re: Spun Rod Bearing - 01/12/14 12:14 AM

One additional rod bearing(#3) was about to spin. The bearing was loose in the rod when taken apart. All other rod bearings looked fine. The rods are K1. The tuning, fuel and timing all the same.

It should not have been overreved, but I changed rear gear from 4.10 to 4.30 back in October. With the 4.10s I was shifting at 6500 and crossing the stripe around 6300. With the 4.30s I am crossing the stripe at about 6600. I have one rev limiter for the burn out box set at 6000 and the second set for 7000. I never hit the 7000 rev limiter.

What oiling modification are typically done on the 340?

Posted By: qwkmopardan

Re: Spun Rod Bearing - 01/12/14 12:56 AM

What is the endplay on the crank? And how does the #3 main bearing look? The #3 main feeds rods 4 and 5. If the endplay is getting wide, you could be starving bearings 4 and 5 because of bleeding oil from excessive endplay.

Additionally, what main bearings were in your engine. The reason I ask is the clevite bearing part #ms963P for the 340, is full groove bearings except for #3 which only has the groove in the block side. If this is the case you were only oiling the #4 and #5 rods 1/2 of the time. I do not know why the ms963 bearings are that way unless Chrysler did it that way for some odd reason. If you use part #ms1344, which is for a 318, all positions 1-5 get the full grooved bearing, and as a bonus they are $25.00 cheaper.

I have over 1800 passes on my 418/360 and shift at 7200 with a 8000 chip in the rev limiter, and hit it ocaisonally during the burnout. Nothing like the sound of an engine near 8000RPM in the burn-out box!

Posted By: mark_gates

Re: Spun Rod Bearing - 01/12/14 08:10 PM

I think if I'd had it apart enough to inspect the bearings, I would've thrown in a new set, just for insurance. Even if it's just pulling the pan, it's still doable and cheap. 1500 runs is plenty; sounds like they pretty much are timed out. I'm glad you didn't throw the rod.

Posted By: Hot 340

Re: Spun Rod Bearing - 01/13/14 01:18 AM

Quote:

I think if I'd had it apart enough to inspect the bearings, I would've thrown in a new set, just for insurance. Even if it's just pulling the pan, it's still doable and cheap. 1500 runs is plenty; sounds like they pretty much are timed out. I'm glad you didn't throw the rod.

with Mark.