Engine goes off when the hand guard pushed for break

[alsayyed]

Hello fallas yesterday I have made service to my MS 650 chainsaw I installed a new oil pump and it is working well. I started the chainsaw I have observed some strange phenomena with the chainsaw whenever I push the hand guard toward the bar the chainsaw stops or the engine go off. Then I start again and it works well again when push guard lever for break stops. My question has anybody run into this problem before and what could it be.

[JimBuis]

I apologize if I am misunderstanding your question. On most modern chainsaws, there is a safety lever or guard in front of the chainsaw handle. This lever operates a brake mechanism. If for any reason the operator's hand pushes that lever, the spring loaded brake mechanism is activated and it instantly stops the chain and sometimes the engine as well. If the engine does not totally stop it will at least slow down as the brake stops the chain from moving.

From your description, the chainsaw is operating as as designed. Simply pull the guard back towards the handle and the saw should be operational again.

Jim

[alsayyed]

 Thank you for your reply. I agree with you but when I purchased this MS 650 whenever I push that guard the chain stops of moving in the bar BUT the engine keeps idling when I push the guard back the  chain is moving again

[Zundapp]

Hi

Sounds like a clutch problem. Either one or more clutch sping is broken/missing, or the drum is bound up on the roller bearing. You mentioned you installed a new oil pump. Did you remove the clutch assembly to do so?

[joe_indi]

This sounds very much like a washer problem.
I think you have installed the protective washer between the clutch and oil pump wrong side up.This restricts the independent movement of the worm gear, which in causes the same to happen with the clutch drum.The result is the clutch drum is constantly locked to the crankshaft and if the brake is put on, the engine stops.
The Remedy?
Remove the clutch, re-install the washer with the Stihl logo facing towards the oil pump.
Make sure that the clutch assembly is free of too much wear and does not have any missing parts or damaged parts.Also ensure that the part of the drum which goes onto the crank shaft does not have too much wear.To check this, fit the sprocket needle cage and drop the drum onto the shaft wrong side up.Check if the drum tilts too much on the crankshaft, if yes, replace the drum(not available by itself, but as part of the rim sprocket kit)
Refit the clutch assembly and clutch drum.
Rotate the drum by hand to ensure it is running free of the crankshaft.
Start the saw without the bar and chain, with the brake in 'off' position.
The drum should come to a stop easily at idle speed when you use a finger against the outer edge of the drum.
If this is possible, your saw should  not stall in idle with the brake on.

Joe

[alsayyed]

This sounds very much like a washer problem.

Joe

Let me tell you thank you and thank you . the moment  i have read the statement which is shown above immediatly went and dismenteled  everything and reversed the wash and started perfect. very good Joe

[ladylake]

Good going Joe.  Sure is nice when you hear back that the problem is solved.   Steve

[dancan]

great diagnosis , however did you figure this out ?

[sawguy21]

That is one of those little nuggets that comes from experience and is filed away for future reference. Good job Joe. 

[joe_indi]

Thank you  Sawguy, Dancan & Steve for the compliments,
Actually,Sawguy  is right.This sort of thing comes from experience.
I have to confess that this was one of my early goof ups, so it was easy to understand the cause of the problem.