Dumb question.... Clamshell

[Jon1212]

No that was a 3300 maybe?, with an 038 mag top end. That was a cool build.

That's right, it was a Craftsman 3.3

 

[Fubar]

I could see how it would be advantageous for the homeowner who wants a low cost and is going to be a low hour saw to be a clamshell. He won't be tearing into it when it started loosing compression. Doesn't want to have it vibrating his hands too sleep... All the features of a small homeowner saw produced as economically (cheaply) as possible.

i have both , and i haven't seen any evidence that a split case lasts any longer or is more durable than the clamshell design , but then again i don't use a saw every single day ,i have a 18 year old craftsman which is just a poulan that belonged to my uncle that still runs like a new one and it's hard used , and i have a 4 year old poulan pro pp4218 avx with about 60 cords under its belt that i paid $150 on sale cause i just needed a extra saw so i figure it paid for it's self the first year , but i liked its lighter weight and smooth , tame cutting disposition so it wound up being the saw i use the most ,and yeah when the motor is toast on a clamshell i just buy another saw , i only use my pro saws for felling and bucking the big logs , i figure i save some wear and tear on them and me by sacrificing a poulan or two .

 

[Franny K]

If a clam shell is an engine module with bottom cap bolted into a plastic case then saws where the bottom of the engine is actually a casting (forging or whatever) that contains the bar mount is what?

 

[Chris-PA]

If a clam shell is an engine module with bottom cap bolted into a plastic case then saws where the bottom of the engine is actually a casting (forging or whatever) that contains the bar mount is what?

It starts to get less clear then, doesn't it? Generally those are horizontal engines, like some of the McCullochs. If you look at something like a cheap McCulloch 3200 homeowner saw, you see that it is a classic clamshell, but horizontal and the bar suds are on an extension cast into the bottom cap, just as you describe. It's very strong.

Stihl extended the bottom cap forward enough to pick up the rear bar bolt on the MS290, but this was primarily to make up for their mistake of having bar mounts thread into plastic.

There are also clamshells like the Partner 400, where there is no separate bottom cap - rather the bottom cap is the plastic chassis. Husqvarna continued this approach, and still uses it today, but now they mold a metal insert into the plastic case.

A clamshell has a lot of advantages:

• There is less sealing surface to worry about (no center case partition)
• There is less machining during manufacturing
  
• Bearings are easy to replace without pullers
• The engine is a self-contained unit that can be manufactured separately from building up the saw (Husqvarna's approach prevents this)

There really are no inherent performance disadvantages for a stock engine, it only makes modifications more difficult.

The European Partner 5200 saw uses a clamshell engine in a magnesium chassis.

 

[Franny K]

I was thinking about the Husqvarna top handle t435 currently available and the 338/339 and prior series, horizontal cylinder like you state.

The passages would seem more complicated to create or create with twists and turns in the clamshell or design where the case splits at the main bearing as opposed to a cylinder base. I see removable transfer covers on some of the pictures on here can't say I have seen any on the clamshell variety but that would allow more port passage complexity one would think.