Be Warned - 3100 Failure

[lkurek]

Guys:

OK, as you may or may not know, my 95 3100 died a few months back. I'm dropping in a 3.4 DOHC to replace it, but that's a story for another day.

ANYHOW.....I knew what happened to the engine, it broke a cam (seriously....right in half), but I just finished my autopsy.

Yes, the cam was broke in half, but WHY it broke was a mystery. Not anymore. The actual cause of failure was worn/seized cam bearings. This is NOT the first engine I have seen with trashed cam bearings, so this may be something you will want to watch in your engine too. The cam journals were actualy scored, and the second bearing back from the front was worn to the shell. The third bearing back was not so good either, so my guess is this lack of support let the cam flex, and this is why it broke.

Soooo......not really sure if this is a defect in the engine or not, but the rest of the bearings (crank/rod) were like brand new.

FWIW, the engine had 285K on it, and I used Mobil 1 5w30 exclusively. It was still knocking down 23 avg economy too

Email me if you have a need for any parts....there are TONS of new/good ones on it.....just not the cam

Larry

[1988GTU]

I am thinking it had a limg failure sometime in it's life and prematurely wore the cam bearing causing the end result.
Pics? We all want to see pics!

[Superdave]

Yep, that's pretty common...


once the LIM gasket goes and you get a milkshake it'll pretty much spin all the bearings in the engine. I've seen several like that.

[geoffinbc]

Agreed also. Water in the coolant and one point or another would have been the cause.

[IanSzgatti]

I also know that the pressed on cam lobes like to move around..

[IsaacHayes]

Every time the LIM leaked on me, I caught it very early. The first time where it leaked inside I caught it before the oil was milky. I just had some mayo on the oil fill cap was all. Not enough to make the oil look any different than normal. Over 200k miles and it see's 5500+ RPM every day.

[merlot566jka]

actually its a big problem with almost all of the 60degree v6s. ive had 6 engines in my fireo and 3 of them ate the cam bearings. also had 2 engines eat rod bearings. and i had one that was overheated and the oil had coked up so bad it at the lifters.

neways, yup watch out for the cam bearings.

[IsaacHayes]

Well I'm over 200,000 miles, I'm not taking this thing out to check the bearings! LOL This thing has seen many times sustained 4k rpm or higher. No worries. If it blows hell 200k+ is great. Then I can put a 3500 with a big cam in

[turboD]

Age old update on the cam bearings is to use a set of early V-8 Chev small block bearings, typical # SH-290. The're wider than the OE 60* bearing and support the cam better.

[talon2swords]

Could you please tell us what are some of the "symptoms" of an engine with worn cam bearings. I'm not talking about an engine that is about to bite the dust or already has broken or warped/worn cam, I'm talking about one that just started the condition and is still repairable.

Any noises or anything else associated with it? Or are there any signs I can look for (beside taking engine out). Thanks.

[lkurek]

Hmmmm.......couple of comments here:

I did NOT have the oil milkshake thing at all. Oil has ALWAYS looked brand new (changed every 7500miles), and I always used Mobil1 5w30. Maybe the synthetic doesn't foam up? I do know that when I pulled the LIM, the gasket was definately deteriorated in the lower rear drivers side corner by the crossover. Still, no other signs of coolant in the engine at all..... Oh, and for those of you who may question the 7500miles between changes....I did an oil analysis a while ago to see how long you could run the synthetic brew. It was STILL next to perfect at 10K miles.....but I had enough

That being said.... The engine DID have 285K miles on it, so I shouldn't complain. But....a failure like this is weird and unacceptable. I did hear and see (Rob?) other V6 60 engines that have been pulled that have severly worn cam bearings. The cylinders in my engine still had the crosshatch, no ridge, and the lower bearings (and crank) look brand new. I could easily drop it into a new engine and it is 100% in spec. That is why I am warning you guys......just something to be aware of. Seriously, of the literally dozens of engines I have rebuilt, the cam bearings are normally perfect. If anything, the top flash layer of lead or whatever is worn, but that is it. Especially with stock pressure springs and the like....this is a first.

The broken cam happened right next to a lobe, pretty much right in the middle of the stick. The lobes didn't move, but the base tube did shear....probably from flexing for who knows how long.

Symptoms? I had none until the failure was imminent. There was a slight (and I mean slight) ticking I heard from the top of the engine with the hood open. Sitting next to a car in traffic, I could hear it as well. This "tick" started (and ended) about 10-15miles of normal driving later when the cam broke.

Soooo......what can I say about this. I did all the right things, used synthetic oil, changed it regularly, kept up the maintenance, and it ran like a champ....until 285K miles. I would hazard a guess that this is the longest possible lifespan of this engine.....maybe 250-300K miles. If you are in that area of mileage, I would STRONGLY suggest thinking about dropping a rebuild in.

YMMV.....

Larry

[1988GTU]

Then the next suspicion is this... Due to the oil pump riding off the cam at one end and the chain turning at the other. Then from our weak ass chains developing slop over time and the oil pump gear having enough wear to have slop also... it took the right amount of overall slop and thrust to twist the cam on both ends at unequal times. There go your cam snapping theory.

[lkurek]

I hear you.....but.....

The timing chain, with agin 285K miles, had next top zero stretch. Seriously. The guides were perfect, the gears looked perfect, and the chain had as much "slop" as a new one. Yes, a bit more....but not much.

The oil pump has a constant load on the cam too.....granted, there are "pulses" when the gear teeth actually move the oil, but it isn't significant either. Use a drill to prime a motor sometime and you can feel it.....it's there, but not much.

The cam snapped due to the flexing of it between the front and rear bearings (which, ironically, looked new as well) because of the worn middle bearings.

Take a metal rod and flex it over and over and it will eventually fatigue and snap. Pretty much what happened here.....

[sprucegagt]

Age old update on the cam bearings is to use a set of early V-8 Chev small block bearings, typical # SH-290. The're wider than the OE 60* bearing and support the cam better.

I don't see how wider cam bearings will fix this problem.

[lkurek]

Less load per mm^2 would equal less wear.....

A) I tend to think there is some supplier issue with bad cam bearings in these motors, similiar to the LIM gasket problem.

B) If you have the engine out to rebuild it, then this is a good idea. Only problem is, to change the bearings....you need to pull the motor. As long as you do that....might as well replace/rebuild it anyhow.

I wouldn't be too upset with the 285 I got out of the motor, except that this is such an uncommon (in my engine building years) problem, but seems to be an issue with these engines....