Picked up a new Stihl chain saw

Actually, the case I was referring to is the crankcase itself. Yes, your 450 Rancher has a 'clamshell' design with the lower case half being made of the same plastic you see from the bottom of the saw. The crank, journals, etc. are metal, and the cylinder head is metal, but the lower case itself is plastic, same as with all the 440, 445, 450 models.

The 450 Rancher does NOT have the same engine as the base level commercial series. The CS Rep either lied or was clueless. The 450 Rancher has the same basic engine as the regular 450, which is also the same as the 440, 445, 455, and 460 with variations in the displacement.

Like I said, there is nothing wrong with that. It is a design that has been around for 30+ years and most people never have a problem with it. It will probably last you a lifetime of normal use. However, it is not the same build as Husqvarna's commercial models and it is not as easy to rebuild compared to the commercial models.

Basically, there are two main design types: Clamshell and vertical split case.

-Clamshell has the upper half of the case integrated into the cylinder head. It is attached with a horizontal split between that top half and the lower case which is usually made of plastic (some older models have a separate metal lower case that fits in the plastic housing). You can't remove the cylinder head without splitting the case. This is the typical construction of a homeowners/consumer saw in today's market.

-Vertical split case has a two piece case that is split vertically perpendicular to the crank with a separate cylinder head that can be removed without splitting the case. This is the typical construction of a commercial grade saw in today's market.

The difference in Husqvarna models can be seen if you compare the 450 with the 550XP model (their comparable 50cc professional saw)

450, Lower case on page 12, cylinder/top case on page 18
http://www.husqvarna.com/ddocdownload/HUSI/HUSI2015_AAaa/HUSI2015_AAaa_450_2015-09.pdf


550xp, Split case on page 14, cylinder on page 20.
http://www.husqvarna.com/ddocdownload/HUSI/HUSI2017_AAaa/HUSI2017_AAaa_550XP_2017-09.pdf

Yes, all saws can be rebuilt, but the commercial saws with a removable cylinder are much easier to do minor repairs (ring/cylinder/piston replacements). If it comes down to a full blown rebuild with new rod/crank/bearings/etc., then they both require about the same amount of work.

When I say case, I am very much referring to the engine itself.

The Crankcase. Yes, your Husky has a plastic crankcase bottom. As I clearly said, there is nothing wrong with that. It will probably outlast you, but the sales person was full of it.

Explanation below.

Modern chainsaws typically have one of two engine designs:
-Split alloy (magnesium) case with a screw on jug (cylinder). The cylinder jug on these can be easily removed without splitting the case. ,
or
-"Clamshell" case design where the actual lower crankcase is plastic (lined with metal crank journals) and the cylinder head not easily removable (without splitting the case).

Some reading here: https://www.arboristsite.com/community/threads/clam-shell-motors.129640/

You can also see in the IPL for the 450 model here:

http://www.husqvarna.com/ddocdownload/HUSI/HUSI2015_AAaa/HUSI2015_AAaa_450_2015-07.pdf

Page 12 shows the bottom crank journals are built into the outer case (that includes the oil tank and handle mounts. Page 18 shows the cylinder/top case which is one piece and includes the top crank journals. The two pieces clamshell together.

Compare to the IPL for the 545, which is their lowest professional model:
http://www.husqvarna.com/ddocdownload/HUSI/HUSI2017_AAaa/HUSI2017_AAaa_545_2017-09.pdf

See page 13 and 19 for case and cylinder view. Definitely not the same.

I know what you mean about the heavy saw. My Jonsey 630 Super II is no lite weight either but it's easy to maintain/repair and I have yet to be let down. Usually it tires me out at about the right time to quit cutting for the day anyways.