MS 441 cuts out then wont start

[MATTMOSS]

I have an MS 441 that starts ok an will run and cut for a short time then cuts out and will not start again.

 

First thing that i thought initially was the coil breaking down as it got warm and loosing spark.

So i attached my ht lead with the indicator window on it which showed a strong spark.

Then it occurred to me that the compression felt poor when pulling the starter cord.

I havnt got a pressure tester so cant do that but It miserably fails the test of holding it up with the cord- the saw falls down quite easily.

So I am now thinking piston rings.

 

So the question being: Can worn piston rings/ low compression give these symptoms of not starting when warm?

In my mind I would have thought that with such an issue it would be hard to start when cold, then if you did manage to start-- the compression would improve as the piston warmed and expanded.

 

what are your thoughts please

Matt

[Rich2484]

Comp will drop when warm.

 

Have you tried all the usuall stuff. You've done spark but is there fuel? Is the plug wet when taken out after trying to start??

 

Need to comp test it. Does it start again when cooled down??

 

Probably me being thick but where abouts are you in country. I know it's Oldham but not sure where that is.

[MATTMOSS]

Yes there is no fuel issue- plug is wet.

 

Oldham-Manchester

 

I am going to have to buy some more tools--- oh no!!

 

Im gonna need a bigger shed

[Rich2484]

I've always said halfords do a gunston tester for 25quid mine hasn't let me down and had a couple of years. Best investment I have made as its the first thing I pick up and use on any engine.

 

If its getting fuel and has spark that only really leaves comp.

 

Could be a carb issue but it should run with fuel getting in even if it will be rough running.

[burrell_]

hold the saw by the pull cord and see how long the saw takes to drop from compression to compression

should be about 10sec first one is always fast

god im starting to sound like my mentor :lol: the dark lord

[Stubby]

Dieing when warmed up amnd not restarting is typical of low comp . Take the exhaust can off and have a look to see if there is any scoring to the piston .

[spudulike]

The saw dying when warm, being impossible to start and then starting again when cold could well be a sign of low compression.

 

Compression is best tested with a gauge, anything above 140psi is OK but 150psi is about right for a used saw and aroound 170psi on a low use one.

 

The compression will be less when warm due to the fuel/oil around the piston being less viscous when hot.

 

Like Burrell said, hold the starter handle, make sure the decomp is out and drop the saw, you would expect the saw to pretty much stop on each compression stroke and take tha 10-15 secs to fall to full extension, a rapid drop is bad.

 

Taking the muffler off and checking the piston on the exhaust side is a good quick check - it is possible the saw has had a light seize:thumbdown:

[Al Smith]

I might add a little something here .I've had 3 441's that for reasons unknown have a tendency for the spark plugs to work loose .Why I have no idea but if they do unbeknownst they start hard .

 

They go over looked I think because of the way the spark plug boot is made you about have to remove the boot to check the plug .One example amusingly the guy bought another new one because he had thought it had burned a hole in the piston .Took me about 3 minutes to fix the problem .

[MATTMOSS]

I might add a little something here .I've had 3 441's that for reasons unknown have a tendency for the spark plugs to work loose .Why I have no idea but if they do unbeknownst they start hard .

 

They go over looked I think because of the way the spark plug boot is made you about have to remove the boot to check the plug .One example amusingly the guy bought another new one because he had thought it had burned a hole in the piston .Took me about 3 minutes to fix the problem .

 

Good point Al, fortunatley I have already experienced this and checked first.

I am sure my problem is low compression, probably down to light seize as mentioned above.

Going to strip down over xmas and fit new rings if its recoverable.

thanks

[spudulike]

Good point Al, fortunatley I have already experienced this and checked first.

I am sure my problem is low compression, probably down to light seize as mentioned above.

Going to strip down over xmas and fit new rings if its recoverable.

thanks

 

Just make sure the bore is clean on reassembly otherwise it will kill your new rings:thumbdown: