How often can crankcases be reused?

[mb4]

Hi!

I’m wondering about rebuilding vintage saws that are no longer in production. I know the cylinders can be re-lined indefinitely, but what about the crank case? If you’re careful splitting the cases when you rebuild them, can they be reused indefinitely or do they eventually crack or not seal? I was given a beautiful vintage saw that I want to keep for milling and would like to keep it running as long as possible.

 

[Bob Hedgecutter]

Well, it kind of depends- make and model of saw and the use it sees between rebuilds.
My rule of thumb- once a saw has done two sets of main crank bearings- it is usually due for the bin.
But a lot can depend on how it was used and treated in the meanwhile, milling can be hard and hot if the operator is not up to speed with exacting chain sharpening, fuel mix ratios and how hard the saw is pushed.
Logging saws can lead a hard life and the cases suffer accordingly.
288XP's used to get stress cracks under the bar plate on the PTO case half.
Eventually magnesium threads tend to become brittle and strip easily.
Saws that spend time sitting on concrete floors, or cutting palm, or being run with less than ideal bar oil can develop mag rot.
Some saws are bad for having bearings spin in pockets- thats a case killer.

You just have to judge condition at each rebuild and yeah or neigh it.

 

[mb4]

Well, it kind of depends- make and model of saw and the use it sees between rebuilds.
My rule of thumb- once a saw has done two sets of main crank bearings- it is usually due for the bin.
But a lot can depend on how it was used and treated in the meanwhile, milling can be hard and hot if the operator is not up to speed with exacting chain sharpening, fuel mix ratios and how hard the saw is pushed.
Logging saws can lead a hard life and the cases suffer accordingly.
288XP's used to get stress cracks under the bar plate on the PTO case half.
Eventually magnesium threads tend to become brittle and strip easily.
Saws that spend time sitting on concrete floors, or cutting palm, or being run with less than ideal bar oil can develop mag rot.
Some saws are bad for having bearings spin in pockets- thats a case killer.

You just have to judge condition at each rebuild and yeah or neigh it.

Thanks. It’s a Stihl Contra. Why do they crack as opposed to other 4 cycle engines that just get rebuilt?

 

[Bob Hedgecutter]

Thanks. It’s a Stihl Contra. Why do they crack as opposed to other 4 cycle engines that just get rebuilt?

I guess because most 4 stroke engines have lumps of cast steel for crankcases and are designed to be bolted to something with wheels and not carried by hand?