Mac 1-71 air leak

[NPKenny]

Preface: This is the first large McCulloch I have worked on. 1-71 3360 block.

When pulled over slowly, I hear an air release sound at compression, almost like a decomp. I can’t see a manual decomp. I have consistent, weaker spark and cannot get it to start with mix prime down the carb. It is much easier to pull over than it should be.

Question: Does this saw have a decompression valve or similar release? Where are likely leaks before I dig into it?

This is a removable head saw (which I have not worked with before) and the piston and rings look great through the exhaust port.

Thank you!

 

[jacob j.]

Is it the thin-ring piston motor? Usually with those the rings are just worn down.

 

[Chainsaw Jim]

Does this model have a removable head like the 1-70?

 

[NPKenny]

It looks like a removable head to me.

I don’t know about thin ring or not... two rings and one looks stuck upon further inspection.

 

[Lee H]

Check the head gasket. It's easy enough to remove the head.

 

[NPKenny]

The head gasket is certainly damaged and it looks like mix was able to escape the cylinder.

Bore ID is 53.68mm and gasket thickness is .055” - .060”.

Where do I get a replacement gasket or can I build an aluminum / Yamabond .020” gasket?

Thank you!

 

[NPKenny]

The combustion chamber on this thing is awesome. Talk about a wide, flat squish band.

 

[Chainsaw Jim]

There is an abundance of mcculloch head gaskets available.

 

[NPKenny]

There is an abundance of mcculloch head gaskets available.

Where? My usual search course kept showing out of stock or unavailable. I need a good McCulloch parts source. Thank you.

 

[Chainsaw Jim]

I went to Ebay and searched mcculloch head gasket. Quite a few popped up.
Many of those parts are only listed as mcculloch with no parts or model info. You have to get good at eyeballing parts to match them up, and send a few messages to sellers asking for measurements.

 

[Al Smith]

If it helps any the stock number is 51339 .Most of the head gaskets on flea bay are for kart engines .Now if one of those would fit I have no idea .

 

[Al Smith]

If you are good at cutting gaskets and if you can find soft aluminum sheeting it might be possible to cut out a gasket .In the mean time I'd clean the head,block and gasket and grease it up and tighten it to torque,it might hold .