Causes of rod bearing failure?

[svtman]

There seems to be a fair amount of talk lately about rod bearings lately - some failing, and others in need of replacement. From what I've read, a lot of people here seems to believe that lugging the engine is one of the major factors in this (under 2000rpms). While this may contribute to wear, I simply think that it stems to two things - either poor service history, or poor engine design. I would consider lugging the SHO engine at maybe 1500RPM up a fair grade - going an a level at that RPM should be safe.

When I disassembled a 5.0L Mustang engine with 230,000kms on it, its rod bearings were like new. The previous history was unknown to me, but I can tell you - at highway speeds the car CRUISES at 1500rpm and I often drove it at 1200rpm around town while puttering around. I'm sure many would consider this lugging, so where was my rod bearing wear? Main bearings were fine as well and I only ended up doing the rings and a hone.

I'll probably think of checking my rod bearings out at 200,000kms with my ATX - which also seems to suffer the same fate as the MTX which can be "lugged".

Kinda hard to "lug" an ATX as it will shift when it darn well wants to!

 

[shojuan]

An ATX has a torque converter which will keep the loads on the engine low at low speed.

Plus the loads are spread out over a lot of area on that big V8.

 

[Doug Waschenko]

Oil breakdown is more closely associated with rod or main failure.
Every engine design is different.
The 289-302 ford engine rarely kills a bearing. The Ford 427's have always had a problem with rod bearing #8 because it is the last to get oil.
The SHO engine is actually on the rugged side as far as bearing design goes.
A better question to ask would be of the people who have rod bearing failure in the SHO, was it all or just one?
Now if everyone says it is #6 that goes and it is the end of the line, the furthest from the oil pump, then perhaps the 8,000 rpm running might have something to do with it?
And maybe running the car flat out at 140 mph until the low fuel light comes on might have something to do with the roll pin coming out of the differential?
Do you think?

 

[Bizzy]

yeah a mustang is putting like ~25hp per cylinder where as a healthy SHO is doing like ~36hp per cylinder

Much more force is comming per cylinder from the SHO motor. Its just a fact of life.

 

[svtman]

netviper:
yeah a mustang is putting like ~25hp per cylinder where as a healthy SHO is doing like ~36hp per cylinder

Much more force is comming per cylinder from the SHO motor. Its just a fact of life.

Typically, engineers take this into account when designing an engine - they are not all designed along the same parameters. Obviously a supercharged engine receives extra fortification unless the normal design is sufficient. AND, there are Supercharged mustangs running around with *slightly* more than 36hp - even normally aspirated 5.0L's can make over 300hp with stock bearings and live to tell the tale.

 

[79pace]

Mine spun the middle one on the rear. I cant remember what number that one is but my Red 93 ATX spun that one pretty bad and the inside of the engine looked fairly clean with 117K Miles on it. My wifes green 93 ATX we just bought looks like its never been apart even for the 60K at 105K miles and seems to be quiet as can be.

 

[sdpatt]

Lugging would be low rpm operation combined with high loads. Maintaining speed on level ground or even a slight grade is hardly a high load. Granted the SHO engine cannot make a great deal of power at low rpms, it can also not make a great deal of oil pressure at those rotational speeds either. The automatic transaxle cars are protected from these conditions by the involuntary downshift when the manifold vacuum is reduced by the larger throttle plate opening. The manual transaxle cars are protected only by a knowing operator.

It's probably a combination of the engine useage (lugging, constant high rpms, etc.), maintainance history (oil change intervals, oil quality, oil filtration efficiency), engine design (bearing loads, bearing surface area, oil volume and pressure) and other intangibles that write the script for the lifetime that can be expected from the bearings. And just a reminder that none of these SHO engines is in the early stages of that lifetime. We are seeing more bearing wear because we are running theses engines well past the normal retirement age of most passenger car engines. We are the sample set for the durability testing of the SHO engine.

<small>[ August 21, 2003, 01:10 PM: Message edited by: sdpatt ]</small>

 

[Bizzy]

well scott has hit one major nail on the head. Many ppl are running these engines well past what the "lifetime" that ford intended. I have a freind that has 318k on his 94 and guess what it's never had a full 60k. Just waterpumps, belts, plugs, and wires I think he's still on the original CPS.

and his car runs great though he wants me to get in there and do a valve lash for him cause his 94 dosen't feel as smooth to him as his 150k mile 95.

I wonder how the bearings on his car look

 

[billyshoe]

rod bearing failure #1 cause is detonation/ping. rod bearing wear #1 cause is dirty/bad oil.