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As a Briggs master technician ( I can see your impressed Steve ) you use a leak down tester to check valve leakage, cylinder and piston wear etc. check it out it’s a good bit of kit.

Leak down test will give you a good idea of the health of the engine internals.

So here we have good and bad.

Sorry I got the carb settings round the wrong way, L = 1 3/4 and H = 1 1/4 sorry I had a moment. I can take some pictures of the cylinder and manifold if it helps.

You can look from the r/h side between the covers, you will see the the back of the cylinder, you should not see a gap where the manifold is not fitting tight to the cylinder, just measure the distance between x torq ports on the original cylinder and compare with the new one, the impulse tube runs from the top of the carb to a connection on the inlet manifold.

The K760 is very bullet proof so there has to be some fairly obvious wrong with it, so to start, look at where the alloy inlet manifold connects to the back of the cylinder, it hooks under a plate on the back of the cylinder, there should be no gaps here it should fit and seal firmly on the cylinder, next make sure the impulse hose is connected, next have you fitted a genuine metering diaphragm? the after market ones do not have the additional hole to feed the compensator, next the rubber gasket between carb and air filter box, is it in good condition and aligned correctly? next did you fit the piston the right way round? this is very important as this saw has a ex torque cylinder, next if this is an after market cylinder make sure you have the correct inlet manifold because the cylinder ports were widened on the latter cylinder, carb settings are L 11/4 H1 3/4

I must confess I have not seen many big end bearings, plenty of main bearings though, these saws really suffer with the flywheel side seal leaking like a hole in a bucket, could this have been a factor in this failure?

The Husqvarna back pack blowers are from zenoah Japan, good engines but as with all this type of machine, cables and plastic shoot wear and tear, can’t really comment on the Stihl machines.

Let’s start with is it a mark 1 or mark 11? stating the obvious if there is no spark it’s never going to run, so start by removing the ignition switch and diss connecting the wires, check again for a spark, no spark and you may be replacing the coil, I will not kid you it’s a near strip down to do this.

I guess from what you say something is causing a drag on the crank journal, so worn sprocket bearing, or worse wear on the crank journal allowing the drum to pull sideways when the chain is tension, this in turn allows the back of the clutch to drag on the inside of the drum, just as a short experiment space the clutch out with a suitable washer and try again.

The armature on a corded saw is much larger and heavier than a battery saw so there is much more inertia there when the power is switched off, we used to strap a single leg from a pair of type one chainsaw trousers to a dummy leg, then run a saw into it to show how many layers it penetrated, we had to stop using a corded saw as it could penetrate more layers than the petrol equivalent

I am a little bias so would choose the Husqvarna, that’s not to say it’s better than the Stihl just my personal preference, just do not buy either mail order or you may regret it should you have an issue with it.

I guess it does sometimes come down to price, but bear in mind weather the local dealer is Stihl or Husqvarna for service back up, also check if the Stihl has those god awful filler caps, if so you will hate them after they have poured fuel or chain oil down you legs, just saying.

In answer to the original question, no the mk11 dog will not fit the mark 1 , the shape, and hole spacing are completely different.

I do not think you should/or need to put bigger dogs on a 550 sir.