Chainsaw excessive compression

[JackDWaller]

I saw a tread but now can't find it. Can anyone make a suggestion.

I was given (estate) a small McCulloch chain saw and it started and ran great. Replaced the chain and did some serious cutting and was so pleased. Now it has sat since the last use and I went to start it and it turned over maybe three times and the compression went so high I can't possibly pull start it (I'm sure the rope would break first). After sitting a day, gave it a pull and got about one rotation and the compression again went so high. The chain is free and I'm 99% positive it's a compression issue not a mechanical problem. This happened once before but after some days it started (a pretty hefty pull) and I thought it had to do with me inadvertently having the protection bar flipped to the forward position but seems that's extraneous.

Could something be leaking into the cylinder?

Thanks in advance for any ideas.

Jack

 

[Barry 1]

Remove sparkplug,pull rope and blow it out. Carb is probably leaking fuel.

 

[JackDWaller]

Thanks, I'll give it a try. Seems the plug is conveniently hidden somewhere .... oh well.

Jack

 

[JackDWaller]

Well, good news. The spark plug was hidden in the recess of the handle and once out I pulled hard and a considerable amount of oil?/gas blew out. I blew off the plug and away it went. Worked great for a good two hours. So, not wanting to start looking for the cause of this problem, I now have a simple solution.

I'm wondering if there is any way bar oil could find its way into the cylinder?

Jack

 

[David_Kb7uns]

Some of the old saws had a crankcase port with check valves to pressurize the tank, the cheaper saws do not have oil pumps.


David Kb7uns

 

[JackDWaller]

David, I'm not sure I understand. Are you suggesting that oil or gas could be finding its way into the cylinder by this means? The problem only seems to exist when time has passed after use. When refilling it started up just fine and its performance seems fine, but I'm not an experienced chain saw guy.

Jack

 

[xyz123]

Saws that had duck bill valves could be leaking into crankcase or a gasket could be leaking.

I've had bar oil leak by gasket in front bar oil tank into rear fuel tank on a dolmar 166. Was ruining my $30 a gallon nitro alky fuel .

 

[RandyT]

If it is the saw that I think it is, the fuel and oil tanks are on the bar end of the saw. I would also say that the carb is leaking into the crankcase. You have two options. Either blow out the say before each use or run the saw until empty. The carb repair kits are obsolete.

 

[JackDWaller]

Thanks guys, that is almost certainly what's happening. This saw came from an estate and had very little use and then sat for a few years. It's not a big deal to pull the spark plug, so now I know the solution, that's what I'll do. And if it's convenient I'll run it dry before storing it. Case closed. Thanks again!

Jack

 

[Deprime]

Does it look similar to this saw? If so there is a crankcase pressure operated bar oil pump that is leaking bar oil back into the saw when it is sitting. Draining the oil tank when not in use should minimize the amount of oil that makes its way into the crankcase.

 

[JackDWaller]

Thanks Deprime, That's it, except mine had a shapener gismo that I removed when I replaced the chain. I believe you have hit the nail on the head. Also, I didn't mention it, but when the saw sat, I had topped up the bar oil and it ended up running onto the floor. I'd say this is an issue I can live with now that I understand it, since the saw seems to perform very well.

As a new member I have to say TBN has an amazing amount of collective knowledge and I sure appreciate the helpfulness of everyone!

Jack

 

[xyz123]

My dad bought one of those little macs to trim with years ago. Dang thing likes to vapor lock when hot.