Swapping Oil Pump pistons

[Brawnschweig]

Idea: to swap out an oil pump piston on a MS390 for one built for a MS441 (Leaving the housings intact on their respective saws) Purpose: Gain more oil output. I've read the post where the Control Bolt (controls the output by turning the screw), and the pump piston were modified to increase the volume of bar and chain oil. Easy to say; hard to do. I'm wondering if the pistons are similar enough so that a person could change one for another and by that change, can increase the flow. The pistons look the same in those fuzzy diagrams on the internet... they seem to have the same shape... Are the bores the same? What is different between the two? My guess would be that Stihl probably used the same basic housing design and the only difference (other than the housing shape) is the piston travels further in the MS441 than the MS390 by using a greater eccentric on the piston and corresponding match on the control screw.
I have tried to max out the control screw by putting a grind on the 'stop' ... I succeeded in that task... not too hard. It's the piston that is a real bugger... I can't seem to make a half decent grind that is worth a darn. It's really hard to do!!! I destroyed one already.
So, does anyone know if I can interchange pistons and control screws successfully between the two pumps? Your help would be greatly appreciated.

 

[Junkwrencher]

Idea: to swap out an oil pump piston on a MS390 for one built for a MS441 (Leaving the housings intact on their respective saws) Purpose: Gain more oil output. I've read the post where the Control Bolt (controls the output by turning the screw), and the pump piston were modified to increase the volume of bar and chain oil. Easy to say; hard to do. I'm wondering if the pistons are similar enough so that a person could change one for another and by that change, can increase the flow. The pistons look the same in those fuzzy diagrams on the internet... they seem to have the same shape... Are the bores the same? What is different between the two? My guess would be that Stihl probably used the same basic housing design and the only difference (other than the housing shape) is the piston travels further in the MS441 than the MS390 by using a greater eccentric on the piston and corresponding match on the control screw.
I have tried to max out the control screw by putting a grind on the 'stop' ... I succeeded in that task... not too hard. It's the piston that is a real bugger... I can't seem to make a half decent grind that is worth a darn. It's really hard to do!!! I destroyed one already.
So, does anyone know if I can interchange pistons and control screws successfully between the two pumps? Your help would be greatly appreciated.

 

[Junkwrencher]

Not to my knowledge. While not an expert I have handled everything you spoke of profusely. (Lots).

 

[windthrown]

The oil pumps in the 1127 saws and the parts in them are not interchangeable with other lines of saws. Few oil pumps are interchangable outside of their series, really. The 361/362 will interchange with the larger output 460, but that is the only swap of that type between series that I am aware of as they have the same oil pump housing in them. The 1127 series clam shell engines are completely different than the pro model engine designs. You need the same pump housing to change the control bolt and other parts in the oil pumps.

 

[windthrown]

You can also run thinner winter weight bar oil (10wt) to get more flow. Or run soybean oil which is a lot cheaper and thinner than regular bar oil (30wt). I have found that Soy oil works better than canola oil, as it has a higher flash point and does not gum up as much when they are not used. It is also cheaper. $4.50 per gallon at WalMart (called vegetable oil). Its also completely non toxic.

 

[Brawnschweig]

Thank you very much. I did some looking and the bores are different sizes... rats. I'm going to try and do a piston head modification... again... Another idea was to take a different oiler and try to make a base plate for it, but that idea has some problems right from the get-go.
Thanks for the advise on Soy and Canola