Plastic caged crankshaft bearings?

[Fordiesel69]

I never paid too much attention to this until I purchased my Husky 555, I noticed both Stihl and Husky are using plastic caged crank bearings on their chainsaws. I was wondering why this is? Husky seems to have a lot of crank bearing failures on the 562XP models with the rev boost feature on the clutch side. Also a lot I have seen on stihl. What is happening is the operators use a dull chain, transfer lots of excess heat into the crank shaft (from the clutch) and it basically destroys / melts the bearing cage.

If they used metal caged bearings, yes you can still turn them blue and damage them, but it would sure take a lot of effort.

Curious, there must be some reason they are using these.

 

[gman2304]

$$$

 

[ARCOgraphite]

Metals cages are "plastic" stamp-able steel but I understand the heating concern with a two stroke. NO fuel oil = no lube if it isn't oil injected. Likely a high temp TPFE polymer or substitute.

 

[thastinger]

I don't know why, buy if you want a metal ball bearing retainer plate then just cross reference the specs for this bearing, not difficult to find the same bearing but with a steel cage.

 

[Greasymechtech]

Worked really well with some Toyota manual transmissions, and guessing others too

Keep your chains sharp, your fuel premixed correctly, and keep logging away.

 

[wag123]

Maybe they had problems with the steel cages disintegrating (coming apart) and filling the crankcase with metal pieces at high RPMs, destroying the engine. The bits of plastic will not destroy the engine.

 

[Fordiesel69]

Maybe they had problems with the steel cages disintegrating (coming apart) and filling the crankcase with metal pieces at high RPMs, destroying the engine. The bits of plastic will not destroy the engine.

I genuinly want to beleive this. I would not take a new saw in warranty and strip it down before failure. But what happens if the plastic cage comes apart will the balls eject and shoot up into the top end?

Normally the failure mode I have seen with regualr steel caged bearings, is the bearing will get pitted or galled from heat or corrosion, then it will begin to have alot of play. The play will very quickly wipe out the seal and create an air leak.

 

[wag123]

I genuinly want to beleive this. I would not take a new saw in warranty and strip it down before failure. But what happens if the plastic cage comes apart will the balls eject and shoot up into the top end?

IDK. Maybe the plastic caged bearing's failure mode is to always melt.

 

[IndyIan]

I assume these would be phenolic resin, like brake pistons?, and stable up to 300-350C. Maybe the actual bearing surfaces overheat because the phenolic cages don't transmit a lot of heat? I'd think there might be less friction and cage wear with plastic cages as well?

 

[Exhaustgases]

Reason ? 1 Plastic is easier to work with than metal. 2 Plastic will be destroyed long before metal. 3 Plastic and assembling it is way cheaper to do.
4 Plastic will hopefully mess it all up and require some expensive work and parts, or the purchase of a new engine or saw or what ever they are using them in.

 

[jeepman3071]

Plastic is used because it is cheaper, and in most applications if the saw gets too hot the piston and rings will fail first.

 

[Mike72]

The use of a plastic cage in a chainsaw ball bearing could be for lubrication. The plastic cage might trap and hold more oil from the fuel mix and some ball bearing plastic cages have a lubricant mixed in with the plastic. It probably was a engineering decision. Regardless, I always preferred needle bearings in a two cycle engine, for the crankshaft and at both ends of the connecting rod..