What is a clamshell design?

[Philbert]

This is a Homelite I did some work on: has an air leak somewhere (?).

But it shows what a ’clamshell’ engine looks like: totally self-contained, and mounted inside a plastic (usually) case / housing.




P.S. - I run this one 100:0 on WD-40

Philbert

 

[Wizard]

Vertical split CCs require gasket surfaces to be mostly congruent with each other at the cyl base, and mixing and matching parts might be troublesome. There might also be a consideration of axial alignment of the crank (I think, haven't delved that deep yet, just thinking).

 

[AlphaTech]

I'll stick with what I said, which was in regard of to the strength of the engine itself. You can make the argument that a plastic chassis is weaker than a magnesium alloy chassis, but that is a different claim. There is actually no requirement that a clamshell engine be placed in a plastic chassis, although this is the typical implementation.

Actually some echo saws like my cs-440 were a clamshell design with mag engine case and removable cylinder. So yes you 100% correct just because it's clamshell doesn't mean it will always be housed in plastic.

I'll stick with what I said, which was in regard of to the strength of the engine itself. You can make the argument that a plastic chassis is weaker than a magnesium alloy chassis, but that is a different claim. There is actually no requirement that a clamshell engine be placed in a plastic chassis, although this is the typical implementation.

 

[Okie]

If you open one up and find Pearls inside, especially little round metal pearls it might be a Clamshell.

 

[ladnar]

I like this explanation of "clamshell" engine design.

 

[Armosh]

Here is a picture of a clamshell in a chassis. You can see the horizontal split line at the crankshaft centerline. There is only a small metal cap at the bottom. The engine is a self-contained unit that can be built (and tested?) separately and bolted in the chassis at a final assembly stage, rather than having to be assembled as part of the build up.

Some Husqvarna models don't use a metal lower cap, rather have the plastic housing from the bottom of the engine, while newer ones mold the metal lower cap into the plastic housing as an insert.

As has been pointed out, clamshell construction isn't much different than the way many older horizontal engines were made.
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I just sold a Craftsman/Poulan like that. Good saw despite what you might hear.