Reviving an MC-91 engine

[Michael Drechnowicz]

I am working on an MC-91A engine that has been sitting on a shelf for many years, at least 6 but probably longer. Looking thru the exhaust port, the cylinder looks really good and the engine has good compression. From the research I have done, a major concern about using an engine that has been sitting is that the bearings on the piston pin could be stuck. Is there any way to ensure they are free or to free them up short of removing the piston and replacing the bearings. Any suggestions would be greatly appreciated.

Thanks,

Michael

[Terry Bentley]

Remove ignition coil and unbolt that boost port cover.. Puts you right there at the piston pin to lubricate. Something like Marvel will help loosen up the dried oil. I have some Macs sitting for 40 years and not any problem with loosening them up. Mac chainsaws sitting for 60 years rarely have failure on those bearings. Hopefully castor was not used for the oil mix. It tends to gum up and dry out bad. Sometimes even rust.

You can also remove stuffer and pour in gas marvel mix then let sit for a while. Shake up and rotate engine over. Doesnt need much to coat everything.

[Michael Drechnowicz]

Remove ignition coil and unbolt that boost port cover.. Puts you right there at the piston pin to lubricate. Something like Marvel will help loosen up the dried oil.  I have some Macs sitting for 40 years and not any problem with loosening them up. Mac chainsaws sitting for 60 years rarely have failure on those bearings. Hopefully castor was not used for the oil mix. It tends to gum up and dry out bad. Sometimes even rust.

You can also remove stuffer and pour in gas marvel mix then let sit for a while. Shake up and rotate engine over. Doesnt need much to coat everything.

Thanks for the suggestions. I will try them.

Michael