MS880 - no spark with new coils

[Bob Murphy]

Hi, new member here.

 

I have three Stihl chainsaws (and five other makes), my most recent being a brand new MS880 with a 48 inch bar (I have some large trees).

 

This thing is driving me crazy, it was running for a while but was very difficult to start - it would kick back so violently it was hurting my hand. I fitted a mitten starter grip from a snow blower and a different (Stihl) decompression valve. Eventually it wouldn't start or fire at all. Investigation showed no spark.

 

I have bought a few cheap Chinese coils (reputedly for the 880) but no joy. A couple of them have showed a weak spark when testing in a dark room but it won't run. I put a new flywheel on in case the magnets on the original were weak, no joy there. At last I decided to bite the bullet and bought a genuine Stihl coil - for £222.06 ! It is as dead as the others. I have checked the nasty plug cap fitting, tried a variety of spark plugs, put the original flywheel back on, tested the continuity between the coil mounting screws and the cylinder head but still no sign of a spark. I am setting the coil up with a 6-thou (0.006") clearance, the coil poles are not touching the magnets or any part of the flywheel.  

 

I am not new to engines of all types and it used to be said that "if Bob can't get it to run then no-one can" - cars, motorcycles, mowers, chainsaws, outboard motors I am familiar with them all - but this 880 is trying my patience.

 

To be clear, I am removing the plastic covers, making sure that the spark plug is in good contact with the head, I have tried unplugging the earthing stop cable in case it is shorting somewhere and pulling the starter rope fast in a dark room - no spark. I have tried putting it all together and starting it as a normal saw in case I'm not seeing the spark. Same result - no life. There is loads of compression, the decompression valve works . . . 

 

WHAT AM I DOING WRONG ??

 

Its not a timing issue and spinning the flywheel magnets past the coil poles should produce a spark at the plug, but that isn't happening.

 

Any bright ideas? Is there someone somewhere who can test coils in isolation?

 

I don't have any hair or I would be pulling it out.

 

Bob Murphy, in Central Scotland. 

[Botty Cough]

Broken wire?

[Muddy42]

So multiple new coils, spark plugs and flywheels and no spark. Are you sure you dont have a wiring problem elsewhere, is the on off switch disconnected?

 

Can you describe your multimeter and continuity test in more detail?

[woody paul]

Switch would be my guess. 

[spudulike]

Blimey, "broken wire" really

I am guessing that your saw has the OEM poly flywheel? I once had a MS461 in with a similar issue and assumed the same as you...coil and it transpired that there was slight impact damage to the magnet and, this being a steel laminated type on the poly flywheel, had decided to lose most of its magnetism and as such, it didn't spark. 

You say you have fitted a new coil...my thinking is that it is extremely unlikely this is a bad new OEM part. The kickback you mention - I have had this on MS660s where the gap between the coil and flywheel has been too little. The reduced gap advances the ignition and my thinking is that your flywheel may have been too close to the flywheel and if it clattered it a bit, the flywheel may have failed during the period where you got kickback.

Checking the continuity between the spur plug connector and the coil laminates proves the coil and HT cap are connected OK - I think you have done this. 

Closing the gap up between the magnet and coil can sometimes work on weak flywheel magnets - I have used typical printer paper before to set the gap just to get a decent spark - as I mentioned, this will advance the ignition and it may kick.

If you remove the kill wire from the coil, you only have the coil and flywheel that can be wrong!

The last thing - some saws need a bloody good tug to get a spark, the 660 is one of them and probably the 880 is the same so look for the spark in subdued light....they are often weak at low flywheel speed.

My guess is the flywheel magnetism is shot...unless we are missing some info or some of your tests/assumptions are incorrect.

[Bob Murphy]

Thanks for the comments - some replies:-

 

The continuity test used the buzzer on my multimeter connected between the cylinder head and the machine screw holding the coil. That obviously uses a battery and I didn't want to run voltage into the body of the coil in case there were some electronics inside.

 

I haven't tried a test between the plug cap and the coil laminations I'll do that and report.

 

Its nothing to do with the kill switch as I ensure its in the run position and have disconnected the kill wire at the coil in case it was earthing to the earth wire in the wiring sleeve. This is just a coil with a plug on the lead and a flywheel magnet. Nothing to do with timing or anything else - I'm just looking for a spark.

 

I also have a Stihl MS461 - it can certainly kick back and can be difficult to start but its nothing compared to the brutality of the MS880 which is a beast. What annoys me is that I have seen videos of people (in America) using 880s where they appear to start with a casual pull on the rope. Mine has only done a couple of hours work so maybe when they are old and worn they become easier to live with, I may never know!

 

I'll try widening the gap between the coil pole faces and flywheel magnets. I set it up with a feeler gauge so its easy to use 0.015" instead of 0.006". 

 

I have tested this in my workshop with the lights off (its dark) and have spun it furiously with the plug connected and resting on the head - no sign of a spark. When I do this with the 461 and the 181 I can see a good spark.

 

The saw has only run for a couple of hours so everything is like new but I bought a new flywheel in case the magnets had lost their strength. There was no difference so the original flywheel is now back on.

 

I'll keep plugging away at it (sorry for the pun !). I don't give up easily and "the truth is out there".

 

Bob.

 

[roys]

Hate being Captain Obvious, but you have tried a different spark plug?

[GarethM]

Isn't that the m tronic variant?

[Muddy42]

27 minutes ago, GarethM said:

Isn't that the m tronic variant?

 

I think the 880 was the last non mtronic, but that's a good point to confirm as this would be a totally different problem. 

 

Regarding your 461 and 880, they may have different screw patterns, but you could try swapping the coils? Or testing the working 461 in parallel.   Yes do test from coil to the plug cap and test the continuity between the case near the cylinder and the case near the coil. 

 

My 088 is a beast to start.  Some people say it helps to get beyond the compression stroke then pull?  Pulling with no spark plug fitted gives you an idea of what is mechanical and what is compression.

Edited February 29 by Muddy42

[Botty Cough]

I'm still going with broken wire and most likely in the spark plug connector...🤺😬

Edited February 29 by Botty Cough