Dirty neglected filters and bad cranks

[Hydro74]

So I’ve received 3 saws two oem 660’s and an 034. All three had the big main bearing in the cranks broken. The two 660’s from one owner and the 034 another owner. The one thing I noticed with all three saws were that the air filters were completely packed with fine dust and looked like they had never ever been cleaned. Would this cause catastrophic failure in all the main bearings....?


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[Little Al]

Very possibly if the fines were getting through the air filter check carefully in the crankcase for "crud" the fact of the filter being fouled wouldn't help

 

[alexcagle]

Constant chitty air filtration usually kills other things first.
Bazillions of revolutions from all day every day use can do it too.
That or someone had the squish too tight, and the piston got hammered like a hooker.

 

[pioneerguy600]

Lack of lubrication is the worst contributor followed by too high of RPM. This doesn`t mean there was no oil in the mix but often not enough for the load and RPM the crank is subjected to. As far as brand of oil I have seen no conclusive proof one is better than another as I have and have worked on plenty of chainsaws that were run on plain 30 wt crankcase oil for mix. This was all there was back in the 50`s into the late 60`s for mix oils. The saws from that era did not reach high RPM like modern saws but crank failure was not an issue then, more often carbon buildup in the top end was. More modern saws do rev higher and require better cleaner burning oils , to keep my own personal saws from experiencing crank damage I run a mix of 40 - 1 in them due to them turning at 2000 rpm higher than stock.

 

[Hydro74]

Good points taken, but there was definitely crud in the bottom of the cases, the saws are tuned with clean air filters on them so you’d think with filters on them that are so dirty and almost useless somethings gotta give...


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[pioneerguy600]

A dirty clogged filter will cause a saw to run rich as long as that filter is still not breached and letting debris through it. Works same as partially applying the choke so there should be more lubrication for the crank with a clogged filter than a clean free flowing filter. In gestation of debris can damage crank bearings but I have seen far more cases where debris has contributed to premature wearing and scoring of the intake side piston skirt until failure but the cranks were still fine. I have repaired many saws that had been run for many years with poor to no airfilters on them, the piston skirts broke off and stopped the saw but the cranks were not damaged, new piston and cylinder in most cases put them back to work. Couldn`t really rule out debris killing a crank just not what I have seen in the 56 years I have been wrenching on them.

 

[Hydro74]

So maybe then the culprit could have been improperly mixed fuel without enough oil content, both 660’s had no piston scoring at all, the 034 had a little you’d figure if the carbs were tuned improperly or the there was an air leak causing a lean condition the piston would have signs of that?


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[alexcagle]

+1 @pioneerguy600
My guess is they replaced the cylinder and pistons not knowing what the real problem was......
Wow, @pioneerguy600 , you're pretty good with your tech and typing for an older gentleman.
You don't even mispelt nothin'.....lol
- I'm young compared to you.

 

[alexcagle]

They have decent aftermarket cranks at HL Supply.

 

[pioneerguy600]

+1 @pioneerguy600
My guess is they replaced the cylinder and pistons not knowing what the real problem was......
Wow, @pioneerguy600 , you're pretty good with your tech and typing for an older gentleman.
You don't even mispelt nothin'.....lol
- I'm young compared to you.

Always a possibility the top ends were changed but one never knows the hours packed on a saw that comes around with no history attached to it. Milling saws come in with little cosmetic damage, look very low hour but are worn out internally. Beat near to death saws show up that have quite pristine interiors but were just abused by their owners, left out in the elements year round often sliding around in the bed of a pickup loaded with tons of other nasty tools,chain, cable,winches,jacks etc. Once the damage is done there is not much left to do but decide to repair it or toss it into the parts bin.

 

[Hydro74]

Nope both saws were all original not rebuilds, the 660’s are used commercially in a processing mill 8 hours a day 5 days a week and the 034 was used at firewood processing facility what brand are the hl supply crankshafts


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[pioneerguy600]

Commercial worked saws are the worst for diagnostics as they are often used by many different operators. I was repairing chainsaws for firewood buckers that really abuse saws since these saws were company owned. The guys were leaning the saws out to rev as high as possible and grinding or filing the chain depth gauges right off down to the tie straps. Took me several saws to catch them as usually only the powerheads came in for repair, I asked the owner to send me the next one complete with chain and bar. The bar was put on by me brand new and only 2 weeks old but came back with the nose sprocket bearings totaled, bar tip spread and that new chain`s cutters almost filed to the witness marks along with the depth gauges filed off. They also run the chains with used crankcase oil, cheaper than chain oil, just another expense they figured. These were 066`s using 24" Stihl bars and chain, clutches and clutch side bearings were most frequent breakdowns for them.

 

[pioneerguy600]

+1 @pioneerguy600
My guess is they replaced the cylinder and pistons not knowing what the real problem was......
Wow, @pioneerguy600 , you're pretty good with your tech and typing for an older gentleman.
You don't even mispelt nothin'.....lol
- I'm young compared to you.

Ok for a guy that never went to school , eh....LOL

 

[Hydro74]

Before I tore the 660’s apart I pressure and vacuumed tested both positive for no leaks


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