Plastic crank case?

[vavaroutsos]

Can someone enlighten me on the whole plastic crank case issue? I have looked at a couple of saws that forum members claim have plastic crank cases, but it looks more like a metal crank case and plastic covers to me. Take the Husqvarna 455 Rancher lower crank case for example.

It looks to me like the lower half is all metal around the bearing journals, crank, etc.. The plastic part looks to be molded around it and has bosses for attaching the handle, covers, etc.. So why is this so bad?

~petev

 

[sawinredneck]

I think it's much ado about nothing, like everything, if you get a lemon, you get a lemon, you get a good one, you get a good one.
I have a Husky 350 with a "plastic" crankcase that I have beat the snot out of for better than six years, it runs better now than the day I bought it.

 

[04ultra]

parted out a 455 that jumped a chain and put a crack in the case...It ran for a year till it developed a bad vacuum leak......I posted pictures on here after the crack started............


The 455 is more of a clamshell motor ......The one I parted out had a crack in the lower pan in the right upper side of your picture of the metal tray......It came from abuse ......




.

 

[Streblerm]

"plastic crankcase" is a misconception. Just as you have found, the crankcase is metal. I don't know of any saws that have the bearings and crank suspended in a plastic housing. Pro saws tend to have all metal cases, not just a metal crankcase surrounded by a plastic housing.

A more correct description is "clamshell" as 04Ultra pointed out. In this design, the crankcase splits horizontally, around the crank pins, and the cylinder is cast as part of the crankcase. this makes for a cheaper build with less machining

On the pro saws, generally the crankcase/sawcase splits longitudinally and the bearings are pressed in place. The cylinder bolts to the two bottom halves of the crankcase/sawcase. This makes top end rebuilds easier, and arguably a stronger saw.

It all boils down to what you need in a saw. If you make your living, day after day, with a saw. You probably want a pro model. If saws are a hobby, for yard cleanup, or a little firewood, then a clamshell design saw should fit the bill.

There are well made saws in both designs, nothing about the design itself is inferior IMHO. But the pro saws tend to be of the two piece crankcase with a bolt on cylinder, while the less expensive saws tend to have the "plastic crankcase"

 

[04ultra]

"plastic crankcase" is a misconception. Just as you have found, the crankcase is metal. I don't know of any saws that have the bearings and crank suspended in a plastic housing. Pro saws tend to have all metal cases, not just a metal crankcase surrounded by a plastic housing.

A more correct description is "clamshell" as 04Ultra pointed out. In this design, the crankcase splits horizontally, around the crank pins, and the cylinder is cast as part of the crankcase. this makes for a cheaper build with less machining

On the pro saws, generally the crankcase/sawcase splits longitudinally and the bearings are pressed in place. The cylinder bolts to the two bottom halves of the crankcase/sawcase. This makes top end rebuilds easier, and arguably a stronger saw.

It all boils down to what you need in a saw. If you make your living, day after day, with a saw. You probably want a pro model. If saws are a hobby, for yard cleanup, or a little firewood, then a clamshell design saw should fit the bill.

There are well made saws in both designs, nothing about the design itself is inferior IMHO. But the pro saws tend to be of the two piece crankcase with a bolt on cylinder, while the less expensive saws tend to have the "plastic crankcase"

Ever take a 350 Husky apart?? I'll take pictures this week ........


Found some on ebay...

.

 

[04ultra]

One this that needs to be mentioned is always make sure muffler is tight.....If not it has been known to burn a hole through the plastic oil tank....





.

 

[grantwolland]

just depends on the failure IMO...

the only issue I've had with a plastic "crankcase" is my buddies husky(huskulon) 141 that had an exhaust leak behind the muffler and melted a nice hole in the top of the oil resevoir causing a flood when the saw was set on it's side. Magnesium wouldn't have done that just burn the paint. I figure i could weld magnesium with the tig but plastic doesn't flow so well lol! I had to replace the entire fuel tank assembly but even that wasn't so bad. the plastic they use is pretty durable especially for the intended target user -non professional.

 

[Rookie1]

This has been discussed quit a bit before. Im not real familiar with Husqvarnas,more of Stihls. The clamshell motor saws are timecomsuming to take apart. They require removing lots of screws and parts to get to the engine. So if you dont work on your own saw the dealer charges for time to disassemble and reassemble. The split case saws are much easier to take apart. Especially the cylinder,top cover muffler,carb boot and off it comes. Split case engines are easier to port and modify also. Hope that helps.