Bearing Failure

[Underdog]

I tore down the thermodyne today after last week's breakdown. Prior to the failure, I noticed excessive blow-by from the crankcase vent tube. The blow-by got much worse accompanied by a severe rod knock. With these symptoms in mind, I expected to find an issue with a piston or liner. The only failure I found was a spun bearing on #2 connecting rod. I pulled that piston and all looks normal. All 6 pistons appear to have 1 or 2 hairline cracks in a starburst pattern on the crown. How would a spun bearing relate to the original symptom of excessive blow-by?

I am also accepting any and all advice on a cost effective repair for the crankshaft journal. I assume to do this right the engine and crankshaft need to be removed.

Gregg

[rhasler]

I would speculate that the original failure was in fact the pistons. From what you have described it sounds like maybe the pump to engine timing may have been off. Since you found the cracks on all 6 cylinders I would lean towards a problem with the pump and not the individual injectors. Advanced timing results in increased cylinder pressure which will cause cracks as you have found as well as the blowby you noted. I've personally seen a brand new Remack engine ruined by timing that was set at 45 degrees btdc in a little less than 2 hours of run time. I would definitely look at the rod that had the bearing failure to make sure it isn't bent and at the remaining bearings as they may give you some clues as to what happened to the failed bearing.

BMT member JOxborrow posted a helpful failure analysis guide in the wiki that may be of help: http://www.bigmacktrucks.com/index.php?app=tutorials&article=58

[theakerstwo]

When a brg goes bad it will develope blue smoke from burning oil and some may think its blow/by.Those old engine was none to have some cracks in the tops when the fuel is set up just a bit.The non turbo engine was a higher compression piston and you could set the fuel up 2 turns and crack piston before their time was up.The non turbo engine was timed around 28 degrees and then the sancrovace would add another 8 to 13 degrees to that.Also to look for coolant in the oil. That will cause a brg failure as well as steam out the vent tube cause a blow/by efect.

[Rob]

It can get real expensive quickly if you purchase a set of pistons and liners, machine the heads for the fire rings that never existed as the replacement overhaul kits are for "Maxidyne" conversion liners, plus weld up and machine the crank, replace and/or resize the existing rods, etc. Although not original, you would more cost effective to replace the engine complete with a known good one.

Should you be interested in a known good replacement, I know of a serviceable replacement not far from you. I believe this engine to be good but is surplus to the owner's needs.

Shoot me a pm if interested and I'll forward the contact information.

Rob

[Underdog]

Thank you all for input so far. I have owned this truck almost 3 years but as a hobby truck have not put many miles on. Upon teardown, evidence suggests that engine work was done not long ago (most gaskets appear new, the engine is very clean inside, and head gaskets are aftermarket). This all relates to the comments so far. I had the injection pump redone, but did not check or change the timing.

I also had concerns about the oil in the last few weeks, it seemed to be gaining oil on the stick, but I did not detect coolant or fuel. Oil appeared normal upon drain, only a lot of bearing metal in the pan.

Originality is not my pimary concern, as I do plan to work this truck a bit. Heck, I was starting to line up work for it this summer!

The best option in my mind at this point is to repower as Rob suggests. I already have 2 donor trucks out back, now to choose which one to part out.

Gregg

[Rob]

Thank you all for input so far. I have owned this truck almost 3 years but as a hobby truck have not put many miles on. Upon teardown, evidence suggests that engine work was done not long ago (most gaskets appear new, the engine is very clean inside, and head gaskets are aftermarket). This all relates to the comments so far. I had the injection pump redone, but did not check or change the timing.

I also had concerns about the oil in the last few weeks, it seemed to be gaining oil on the stick, but I did not detect coolant or fuel. Oil appeared normal upon drain, only a lot of bearing metal in the pan.

Originality is not my pimary concern, as I do plan to work this truck a bit. Heck, I was starting to line up work for it this summer!

The best option in my mind at this point is to repower as Rob suggests. I already have 2 donor trucks out back, now to choose which one to part out.

Gregg

I got a great idea!! "Rob" the engine out of the B model and give me the remainder; Yeah, that's the ticket!!

The spare engine I know of is in western New York state if what remains of my feeble mind serves.

Rob