Bent con rod- any ideas?

74inchShovel · Jul 17, 2018

Machine has 3 cylinder Perkins, under 500 hours, out of a ASV PT 30, went out on rent and came back with a miss that mostly went away when warm. Some blue smoke when cold, the renters say no one used ether, it wasn't rolled, no gas in diesel, didn't get water into motor- I'm at a loss. Tear down revealed one bent rod with rest of engine like new. I have same engine in another machine with 3k trouble free hours. Would welcome any comments on how this could have happened, thanks in advance!

thepumpguysc · Jul 18, 2018

If you order the parts from an authorized dealer, ask them if there has been "a rash" of them or if they have been selling afew more of them..{hint, hint}
Quality control issues DO pop up from time to time.. but then again, sometimes sh*t just happens.
I'd get the injectors checked FO SHO.. & it would be even better if you has isolated THAT injector so you knew it had come from THAT cyl..
How did the valve & piston LOOK..??

Tinkerer · Jul 18, 2018

Not unusual to bend a rod like that one is, when someone went crazy with ether.

kshansen · Jul 18, 2018

Tinkerer said:
Not unusual to bend a rod like that one is, when someone went crazy with ether.

That was my first thought.

Does this engine have glow plugs? If so, wonder if the renter was not up to speed on how to use them. Or maybe if it doe have glow plugs are they working properly?

ih100 · Jul 18, 2018

Got any pictures of the piston? Might be a clue or two there. Also the inside of the cylinder and head face.

thepumpguysc · Jul 18, 2018

Wouldn't they all be bent, if ether was the culprit?
& the mechanic would have smelled it.?? I've gone out to machines that have been "squirted" & smelled it DAYS AFTER someone "worked" on it.. Lol
I absolutely love it when I go out to a machine & the customer couldnt get it started AFTER I've done the pump.. They swear to GOD they haven't sprayed it.. & I find an empty can laying under the tractor.. & "nobody else" has worked on it.. The smell is unmistakable..
Only to find the system has air in it or they forgot to hook-up the electric shut-off..
& when it starts, it shakes & skips & they wanna get the injectors done.. lol

hosspuller · Jul 18, 2018

Just an idea … Leaking injector. One cylinder. Forms a hydro lock or increases the compression beyond the con rod yield at start up.

Did the rental happen during the winter ? Don't see anybody, especially a renter, going to the trouble of ether. More likely to crank until the starter or battery dies.

thepumpguysc · Jul 18, 2018

THATS what I was think too Hoss.. FOR SURE get the inj. checked..

74inchShovel · Jul 18, 2018

Lots of great suggestions here, thanks.
I've rented to this guy for 3 years, I kinda believe him when he says no ether.
Rest of motor is like new, no other damage
Great idea on checking the injectors, I did, the shop that bench tested said the injector from the bad hole was the worst of the bunch. He rebuilt all 3. Could there be enough leak by when sitting to cause this damage?
I was thinking along the lines of Pumpguy, maybe not heat treated properly and bent slowly over time time till a miss developed.

thepumpguysc · Jul 18, 2018

I don't think so on the leak down.. UNLESS it was stuck completely/partially open.. then you would get a hydo lock & bend it..
A bad spray pattern or pissing nozzle wouldn't bend that rod. IMO.. Smoke, yes..
I think I would "call around" & talk to a few parts or service mngrs {if you can get'm on the phone} & find out of theres been "a run" on con rods for THAT engine mdl..
Who knows, there might be a service b on it & its covered..?? THAT would be sweet.!!

ih100 · Jul 18, 2018

I've seen a few bent rods over the years, mostly from water ingress, but a couple where the injector had been hosing. On one, the edge of the piston crown had actually broken and the shrapnel was buried in the piston, the other, the diesel had washed the piston almost as clean as when the engine was built. The piston crown was still damp in both cases.

lumberjack · Jul 18, 2018

74inchShovel said:
Machine has 3 cylinder Perkins, under 500 hours, out of a ASV PT 30, went out on rent and came back with a miss that mostly went away when warm. Some blue smoke when cold, the renters say no one used ether, it wasn't rolled, no gas in diesel, didn't get water into motor- I'm at a loss. Tear down revealed one bent rod with rest of engine like new. I have same engine in another machine with 3k trouble free hours. Would welcome any comments on how this could have happened, thanks in advance!
View attachment 183893

A PT30 I had in inventory for a demo machine would go to burning oil heavily if it nosed down with a heavy load. Never caused a problem for me, but I could see it causing a bent rod.

kshansen · Jul 18, 2018

Any chance you had a bad rain storm where some water could have got down the exhaust? It might not take much to bend that rod and once it started it would have worked the water out just fine. I'd look very close at the cylinder walls to see if there was any slight discoloration from water getting in there.

Just some ideas, you may never figure it out but at least you are not just letting it slide and having inside parts become outside parts while it is working!

DIYDAVE · Jul 18, 2018

kshansen said:
Any chance you had a bad rain storm where some water could have got down the exhaust? It might not take much to bend that rod and once it started it would have worked the water out just fine. I'd look very close at the cylinder walls to see if there was any slight discoloration from water getting in there.

Just some ideas, you may never figure it out but at least you are not just letting it slide and having inside parts become outside parts while it is working!

Kshansen, not too likely, on this machine, exhaust goes down, not up...

John C. · Jul 18, 2018

It's a cast rod so I don't think there would be any type of heat treat. Just the precision machining.

My thought is overheat and the head gasket or rubber sealing rings leaking into a cylinder. Enough diesel to bent the rod that much would likely have exploded in the exhaust manifold. Was the head pressure tested for cracks? What does the head gasket look like?

An overheat on Friday might make for an eventful Monday morning startup.

74inchShovel · Jul 19, 2018

John C., are you sure it’s cast as opposed to forged? I’m kinda wondering if the rods aren’t made out of Chineseium. Or like someone mentioned a bad batch. Head was not pressure tested, but no signs of wash out or blown head gasket. Not too late to test it, good thought!

ih100 · Jul 19, 2018

These are forged rods, and heat treated, so there is a chance of a bad batch.

John C. · Jul 19, 2018

If you say so. That doesn't say much for Perkins manufacturing.

ih100 · Jul 20, 2018

If that is the case, no. However, that isn't very likely. Rods don't just bend for no reason, even Chinese forgings. The machine went out okay and came home sick. Something happened in between.

Delmer · Jul 20, 2018

Have you seen the jobsite? How about taking apart the air intake and looking that over closely?

Bent con rod- any ideas?

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