spudulike

I would slap in a Meteor £40 piston, do all the ancillary work I mentioned earlier and put some hours on it. Big engines suffer a lot less from this sort of thing compared to smaller engines. You should be able to delete the base gasket as well which should help but check the squish first.

I would stick a new piston in it. I think you will be surprised with how well it will work. The damage under the port looks light and is much less likely to cause issues than the inlet side which would cause lots of blow back and leakage on crankcase primary compression. If you haven't, lightly hone it with a rotary hone and see if you can get a Meteor, Hyway or Golf/Vec piston in that order! Engines don't see that the bore isn't visually pleasing. They just work on compression made hot and cold etc. Make sure you pressure and vac test then service the fuel system and tach the saw a bit rich to let it all bed in!

Just make one with 0.5mm gasket paper! It may have been deleted to up the compression, especially if there was liquid gasket used!

Sharp wood chisel on the old gasket. My money is still on old oil causing Mega compression, seen that before. It is usually this or fuel in the crankcase causing a lock. Just reassemble after cleaning the bore with WD40. Use no oil and try it again. Reckon it will be back to normal!

DB Schenker, I used to use a company called Bax Global to ship in to Dell Limerick many years ago when in my former job. They got taken over by DB Schenker...reminded me of Michael Schenker of UFO fame! Bax Global were good, not used Schenker for many years!

I am going to retire and do all those things I have been meaning to do for a while....like inspect my navel fluff!!

It should have a cylinder base gasket as standard or at least be sealed with liquid gasket which would raise the compression and seal the engine as it should be. No gasket or sealing compound would cause an air leak giving running issues but not your symptoms.

Probably a fluid lock....fuel mix in the bottom of the crankcase. Pull the plug, turn the unit upside down, pull it over hard a few times and see if the engine kicks out fluid. If nothing comes out, it may be just old oil on the bore making the compression super high. If it isn't this, it may be one of the bolts holding the cowel on catching the back of the flywheel which is common to Stihl blowers but the plug being in or out shouldn't matter. Unlikely to be the plug as it is a CMR6H and they are pretty long anyway and am not sure you can get a longer type!

I have used DHL for many years and they have been pretty good!

A nice simple one, glad it is all OK now.

Most couriers do a damn good job, working long hours and getting paid peanuts. I have had fair exposure to this getting in parts, personal stuff and shipping as a business and most do a damn good job. I always use a 24-48 hr service and that is generally what happens. I would suggest your supplier has used a discounted..."deliver sometime service" as it is cheap but not cheerful in my experience! If you pay the going rate to a commercial courier company for a 24-48hr service, in my experience....they deliver just that!

Bugger, the link - https://www.stihl.com/p/media/download/uk-en/STIHL_Chain_Saw_Safety_Manual.pdf

Most saws are pretty much the same, use 50:1 mix in the FUEL tank, chain oil in the OIL tank, make sure you tension the chain correctly, understand how the chain brake works and how and when to use it. Understand the dangers of using a chainsaw and that will give you some chance of protecting yourself. Never carry a running chainsaw with the brake off, never cut anything with the tip of the bar unless you want to damage yourself. This may be of use if you are in to reading but the important thing to do is UNDERSTAND the dangers and how they can happen and use the correct methods to avoid them happening. I am sure someone will now wax lyrically now about PPE?

One thing I do know, they are damn good at getting a bonfire going well....or a fire pit!!

I ported mine, deleted the base gasket, opened up the ports and a light MM. Pulls 1-2Krpm more now on the top end and is noticeably better. Leaf blowers are a good bit of kit, raking leaves can give you a jippy back, all that twisting motion, not good. Never tried one before I got one as part of a job lot of busted kit and it changed my opinion. Before anyone asks.....bugger off, I am not going to port your blower!!!!!

I would do what I suggested first, probably just a build up of congealed oil!

Saws that have been run on an oil heavy fuel mix when left standing evaporate all the fuel from the cylinder bore leaving oil. This can REALLY seal a healthy engine. You may have this phenomena. A few squirts of WD40/GT85 down the plug hole and pulling it over hard a few times will help dissipate it and then try it again. I can't help but think it is this. The only other thing left is something has come loose and is catching between the flywheel/clutch and the casing/engine but would have thought that this would also happen with the plug out as well. The last thing to note is as you pull the starter, is the engine jamming up as the piston comes up past the exhaust port to create secondary compression or is it random or another part of the cycle? This can help a diagnosis.

The crank is manufactured out of damn hard steel and is very unlikely to get damaged or form any sort of "lip" etc. I just fit a new key and then crank the flywheel down pretty damn hard - the exception being some of these lighter modern flywheels that can crack if you torque them too hard. The 660 is fine, it has a steel boss!

Pull the plug out, turn the saw upside down so the plug hole is pointing downwards and pull it over hard for 5-10 times. You should get a fair bit of fuel mix running out of the plug hole. Let it dry out and try again.

Not being funny but the OPs remit was for cleaning saws and pumping tyres and the no tank design will do that just fine.?

I agree with Stubby, there is no issue with a no tank compressor for air gun applications. Sure, you cant run a rattle gun off them but they are very suitable for cleaning saws - just switch it on and go. We aren't making it up, it is what it is and it works!

I started with a pump only compressor so no tank, you just turned it on and the pressure was generated against the gun so you just kept pulsing the trigger. It worked just fine and did the job until it pretty much wore out! Any compressor is better than none and you could use it to pump tyres etc. It wouldn't power a staple gun or rattle gun though!

The 660 coil and flywheel are pretty robust and rarely go wrong. The flywheel has a steel taper and it is rock solid and can take a lot of torque on the location nut. Backfiring is a sign that the ignition timing has shifted which is strange. Best to pull off the flywheel, check the key and then reset the flywheel again and tighten - not sure how you locked the crank in place to do this but you should use the Stihl double ended plastic stop for this IMO. Not sure how the original flywheel "spun off"????? They usually need a damn good whack once the puller is fitted, to get them off! Are you in the repair game?? If the key is OK - I suspect it has sheared again as I don't reckon you are tightening it enough and am guessing you had removed it before......it is possible the flywheel coming loose has hit the coil and either damaged the internals or the flywheel impact has damaged the magnetism in the flywheel. I have seen this before - the magnetism loss in a MS461 so very much like the 660 flywheel but this one lost its spark! In order, I would say Key, Coil, flywheel would be the most likely issues. Is there any other history to this machine?

I feel let down?

I am taking it that the screw hole goes straight in to the inner crankcase same as the 372. If so, helicoil the hole carefully and fit a new bolt - may need a little sealant around it to ensure it is airtight.