Crank had better days

[donbj]

I wonder what this saw sounded like when this happened? Maybe I should use it and see
- YouTube

[DHansen]

Surprised the connecting rod didn't break at the crank strap.

[donbj]

For sure. Must have been a few stray forces going on in there. This was in a 372 parts saw I came across.

[sawguy21]

That one got mighty hot just before things went south. I wonder what the p & c look like. :

[donbj]

Yes it must have got pretty hot as it's blue around the crank bearing end. There was no cylinder with the saw. The piston actually looked good, no scoring or damage.

[donbj]

That one got mighty hot just before things went south. I wonder what the p & c look like. :

Here's the piston. Just some very light scratches barely felt with a finger nail. Rings are rusted as the saw sat in a damp shed. Got some good parts from it though.


 

[Al_Smith]

FWIW just so you know discoloration around the crank bearing could be due to the fact that at assembley the crankshaft halves most likely were ran through an induction heater during assembley process .
 

[donbj]

FWIW just so you know discoloration around the crank bearing could be due to the fact that at assembley the crankshaft halves most likely were ran through an induction heater during assembley process .

That's a good point for sure. That would affect the crank itself though. The discoloration is on the con rod and looks like it was overheated pretty bad. Here's two identacle cranks. The bad one on the left.


 

[Al_Smith]

It's a forged rod .You can tell that by the marks from the forge  hammer dies .As such it has been induction hardened which will "run the colors ". If it were powdered metal I doubt that bluish color would be present .
Trying to be a detective IMO what we have here is just a bearing failure which could have been caused by either the mix oil or more likely from a lean mixture ratio  over time .Depending on the steel alloy used for the rod the hardening temps should be from around 1600 to 1900 degrees F which would be orange to yellow in color .
I'm not going to argue about it as it's just my opinion . ;)

[donbj]

No arguement intended at all, just interesting information. The significant difference in colour between the two identical rods has me curious

[Al_Smith]

The only two crankshafts I could find were Stihl 200T's .Looks to me because of no hammer  die marks those were powdered metal .

[sawguy21]

I would think they are castings, I can't see powdered metal lasting very long in that application but I'm not a metals expert.

[ehp]

you better check everything out very close , that rod bearing went somewhere and most times the piston get hit bad as the rod bearing tries to come threw the transfer port so the top of the piston catches it as it goes up past the port , also check the top of the cylinder up by the sparkplug to make sure none of the needle bearings are stuck in the roof of the cylinder , would be a waste to bolt the cylinder onto another crankcase then those pieces fall out of the roof and ruin another piston and stuff

[donbj]

you better check everything out very close , that rod bearing went somewhere and most times the piston get hit bad as the rod bearing tries to come threw the transfer port so the top of the piston catches it as it goes up past the port , also check the top of the cylinder up by the sparkplug to make sure none of the needle bearings are stuck in the roof of the cylinder , would be a waste to bolt the cylinder onto another crankcase then those pieces fall out of the roof and ruin another piston and stuff

Thanks. The saw didn't have a cylinder or carb goodies with it.

[Al_Smith]

Again perhaps another  point of debate .I retired almost 4 1/2 years ago from a Ford engine plant .Those engines made  at that time used sintered metal connecting rods that had pressure cracked rod caps .Fact Summit racing sells sets for small block Chevys to the tune of over $500 for 8 others might get nearly $100 a pop .
I had heard McCulloch used cracked rods on some models,perhaps the 125 but I can't find it nor do I remember having had a few apart . Trivia which doesn't have a thing to do with the topic .What happened to the bearing ? ???