Stihl MS391 suddenly lost power.

[spudulike]

Damn, it almost looks like I know what I am talking about...... my original post....."It sounds like the spark plug or decomp valve may have come out as even a seized engine will give slight compression enough to tension the starter."

 

One bit of advice and that is to check the plug tightness regularly to make sure it doesn't happen again - it often does. I hope the plug was just loose and hadn't actually popped out as when they do, they often take a few threads with them and that can lead to the thread failing completely. You need to do it up to finger tightness and then compress that sealing washer by half so you get a good grip.

 

Anyway, good result, the dealer should have fixed that every day of the week. Glad it is sorted...Happy Christmas

 

[spudulike]

3 hours ago, Rich Rule said:

I think you owe Spud a beer.  Sounds like he diagnosed exactly what you experienced.

Pass it on....do a favour for someone else or help someone on their way, and pass on the message, it may make the world a better place.

[adw]

If that plug has been loose for a while I fear it may well have damaged the threads and will end up blowing the plug out, I am seeing more of this since manufacturers using 10mm spark plugs, anyway chalk another one up Steve, how many more before you are nominated for a knighthood? or at least the prestigious gold chainsaw medal.

[spudulike]

It gets pretty easy the longer you do it. I did have a weird one earlier in the week, big fat spark on the spark tester - jumping at least 7mm + and after swapping out all the main components, turns out to be the HT lead so the plug must have not been sparking under compression.....that was a first and took hours as I had discounted the HT lead being the problem!

This one in comparison...piece of p£$s!

Your thoughts are the same as mine, the blow-by of combustion gasses around the plug hardens and breaks down the aluminium thread which can then strip out hence what I said earlier about making sure the plug is kept tight.

I think you need the award doing the job you do, at least I can abuse my customers....they love it;-)

[Paddy1000111]

On 10/12/2020 at 18:33, Paddy1000111 said:

check the spark plug

I get no credit 💔

 

In all honesty the real question here is how the stihl tech said there was compression but it's the gasket at the top but didn't tighten the plug? 😂

Edited December 16, 2020 by Paddy1000111

[Moose McAlpine]

27 minutes ago, Paddy1000111 said:

In all honesty the real question here is how the stihl tech said there was compression but it's the gasket at the top but didn't tighten the plug? 😂

 

He was too busy trying to locate the head gasket.

[spudulike]

27 minutes ago, Paddy1000111 said:

I get no credit 💔

 

In all honesty the real question here is how the stihl tech said there was compression but it's the gasket at the top but didn't tighten the plug? 😂

TBH I wasn't sure if you were saying the plug could come loose or the insulator may blow out or something else.

The guy fixed it, that is the main thing and it didn't cost him anything.

I had a saw sent in once with the exact same fault. In my case it took me about 30 seconds to find the fault hence what I said!

We still love you😉

 

[Khriss]

On 11/12/2020 at 16:07, Moose McAlpine said:

 

 

There's no gasket at the top of the piston. 😕

.... Its a Stihl dealer ... 😆 K

[Khriss]

25 minutes ago, Moose McAlpine said:

 

He was too busy trying to locate the head gasket.

Couldnt find his arse if you superglued his fingers to it.  K

[Moose McAlpine]

1 minute ago, Khriss said:

.... Its a Stihl dealer ... 😆 K

 

'Nuff said. 😬