Stihl 066 Engine Case Differences Poly vs metal flywheel

[Detri Mental]

Good day folks,

I was wondering if I get a new style poly flywheel, crankshaft and bearings for my 066, will it fit in my case that has the old all metal style flywheel and crank? I don't see anything that says Stihl changed the crank case between these flywheel and crankshaft upgrades.

Thanks much!

 

[w8ye]

Early 1994 - Thin cylinder base ( Red light etc) changed to "thick base". Base screws changed from M6x20 to M6x25


Mid 1994 - Beefed up crank - Crankshaft BIG end changed from 12 to 13 roller pins from serial number 129 588 002. At the same time, the cylinder base gasket changed to rubber coated Steel (so quit using the junk aftermarket gaskets!).


Early 1995 - OHSA (NOT EPA) forced the discontinuation of the Dual port Magnum muffler from serial number 131 960 509. HP dropped to 7.2


Mid 1996 - decomp valve fitted on all 066 from serial number 131 960 509


Early 1996 - Poly flywheel installed and crankshaft bearing increased in size from 13.5 to 15mm from serial number 131 917 066

Early 1998 - shrouds and filter box changed from squared to "rounded " type. Limiter caps on carbs and EPA labling...


Early 2002 - Name changed from 066 to MS660.

 

[w8ye]

In 1996 they went to the polymer flywheel which had its own coil with a advance curve instead of straight line advance.

The flywheel side bearing is bigger - the crank end on the flywheel side is larger diameter and the bearing was different.

Flywheel oil seal seat diameter was increased to 15mm from 13.5mm

So this answers your question? That the cases are different for the poly flywheel chainsaws.

 

[Detri Mental]

So this answers your question? That the cases are different for the poly flywheel chainsaws.

Yup this certainly tells me that the flywheel side bearing and seal is larger in diameter on the newer style cases. The best I could hope for would be that I could chuck the flywheel side case half up in the mill and bore it out to the larger size, but I dont know if the casting is thick enough on the old case to do that, and for that amount of research and effort to make that happen I might as well just find a good used newer style case.

Thanks for the information w8ye!

 

[Jacob J.]

The flywheel side bearing is the same size. It's the seal that is a different size, but the bearing itself and the bearing seat are unchanged. The bearing has a different part
number because Stihl changed suppliers and the 'style' of the bearing (non-shielded phenolic cage style vs. shielded style) but the size is exactly the same. Same thing with the PTO side bearing- the style changed but the dimensions are the same and it has a different part number.

 

[w8ye]

Stihl gets good money for these special bearings

 

[Jacob J.]

Stihl gets good money for these special bearings

That's why you don't buy the flywheel side bearing from Stihl. The FAG/SKF flywheel side bearing for most Stihl saws is $30 from Stihl or the same bearing
at a bearing/industrial supply house is $10. Unfortunately the PTO is proprietary and pretty much has to come from a Stihl dealer.

 

[PogoInTheWoods]

So with the exception of the cylinder base threads and the flywheel side seal, the cases are actually the same?

:msp_confused:

 

[pioneerguy600]

The flywheel side bearing is the same size. It's the seal that is a different size, but the bearing itself and the bearing seat are unchanged. The bearing has a different part
number because Stihl changed suppliers and the 'style' of the bearing (non-shielded phenolic cage style vs. shielded style) but the size is exactly the same. Same thing with the PTO side bearing- the style changed but the dimensions are the same and it has a different part number.

The guys with the greasy, oil stained hands are the ones that know what swaps/interchanges, compared to what a service bulletin states.

 

[Jacob J.]

The guys with the greasy, oil stained hands are the ones that know what swaps/interchanges, compared to what a service bulletin states.

Yep. I never follow the advice of a sales rep with milky, soft hands. I always talk to the mechanics with club fingers and dirty fingernails...

There's a few sales reps out there though that spent a lot of years turning wrenches but they're few and far between.

 

[Jacob J.]

So with the exception of the cylinder base threads and the flywheel side seal, the cases are actually the same?

:msp_confused:

Ok, here's the deal-

The bearing seats for all of the cases are the same. The flywheel side seal pocket for the poly-flywheel cases is larger for the larger seal.
The cylinder base mounts on all of the cases (066/660) are the same.

The poly flywheel case is wider than the metal flywheel case. This is why you cannot put a poly flywheel crank in a metal flywheel case
even if you machine out the flywheel side seal pocket for the larger seal. You've have to make a case gasket that's 4mm thick and that
isn't feasible. The poly flywheel crank is 4mm wider than the metal flywheel crank. Clear as mud?

 

[Chris-PA]

Plastic flywheels? No kidding!