McCulloch muffler reed valve - what does it do?

[asulliv2]

I inherited a Pro Mac 700 from a friend - first attempt at chainsaw rebuild (regretting this endeavor at the moment. I noticed that a significant portion of the muffler reed valve was cracked off (part# 71 in diagram below). Can someone tell me a.) what function this serves and b.) if I need it, what the fix options (if any) other than buying the replacement part from Randy's or Old Mower Parts, etc.?

Many thanks to Mark (heimannm) for previous help on air tank seal!

http://www.searspartsdirect.com/model-number/promac700model60011604/0684/1503200.html

 

[dougand3]

I think it's noise attenuation. Saw will probably be much louder w/o it. And if it's cracked, I'd be worried it may crack more and metal pieces find their way into exhaust port. I'd make another one out of similar thickness sheet metal.
Ask this ? in the McCulloch sticky thread - Mark and others will know for sure. They may pull them, tune richer and go at it.

 

[Chris-PA]

Interesting, I had never heard of that before. McCulloch was quite innovative at one time, and I wonder what they had in mind with that.

 

[ironman_gq]

Maybe it was to reduce exhaust reversion into the cylinder? You can usually make new reeds with the same thickness spring steel shim stock or stainless shim stock.

 

[a. palmer jr.]

I would assume it's to keep the muffler from sucking back on the intake stroke. That might help to keep carbon out of the combustion chamber...just a guess..