No Spark

[Stump Shot]

Other than I would have set the coil air gap at .2mm with a Stihl tool for the job, I can't say that .25mm is a deal breaker, but stranger things have happened, might be worth a check.
Can recall having a run of bad luck with Chinese made AM coils to where it just became not worth my time. Last saws I put new OEM coils in went back to a running condition without fail. Yes it cost more, but only paid just the once too, so...

 

[Stuart]

Hi Bob – Stump Shot, Thanks for your patience,
Sorry for the slow reply but I was trouble shooting one of our water transfer pumps….Fixed.

Well, I’m considering hooking up the saw to the tractor and dragging it around a paddock….or digging a hole, bury it and end the frustration.

Bob, Took onboard your idea of the one commonality, the plug, Pulled the definite ok one from the 310…no spark.

See Attached:

The ground / contact wire is only grounded at the coil, as in the Figure 1 diagram attached, wire 2. Wire 1 is the short circuit (kill) wire, the other end of the kill wire goes to the kill arrangement in the Figure 2 diagram attached and operates via the ground / contact wire spring arrangement making contact with the kill wire terminal when the run lever is in the off position. The wiring arrangement is installed correctly, and I have continuity on both wires.

I did wonder (not being an expert and clutching at straws) if the JB Weld Red Hi-Temp RTV Gasket Maker And Sealant I used between the crank case and cylinder was impeding continuity (I know but clutching) as the coil is located on the crank case but I’ve checked continuity between the 2 components and it’s good.

As I mentioned before….3 coils with questionable readings??? So, I’m now going to remove the coil from the 310 and see what readings we produce.

If inconclusive, I may consider hurling myself off the roof and rely on reincarnation

Cheers……Stuart

 

[Stump Shot]

@Stuart before reincarnation is implemented, take and check continuity between the coil frame and the crankcase and while you mentioned it, between the cylinder and the crankcase. Coil can't work with a bad ground for sure.

 

[Bob Hedgecutter]

All starting to sound a bit suspect to me and the only common variable I can find amongst all the swapped out parts and combination of parts- yet still no spark from a proven good plug is the human factor.
So the only thing left is the fact once removed from the cylinder to test for spark, the plug body is not sufficiently grounded to enable spark to occur.

 

[Stuart]

Hi Guys,

I think I’d better make this the last appeal for assistance, cause I’m sure by now you must be finding the whole scenario somewhat tedious…..to say the least.

Stump Shot, I checked the continuity between the coil base and the crankcase…it’s good.

Bob, I’ve just checked the grounding on the plug body scenario, I even secured it with a cable tie ensuring a good/solid seating against the cylinder head and gave the pull start some serious wellie…No spark.

What I’ve also done, is check the resistance/continuity parameters on the 310. The only place I’m getting any significant variation between the 2, is on the HT lead. With the meter set at 20k ohms, I’m getting 2.2 on the 391 and 12.1 on the 310 !!

The confusion I have, is that I’m led to believe that lower ohms indicate a good connection and less chance of a short issue. Am I wrong? If yes, then I guess I need to buy another original coil ??

Cheers……….Stuart

 

[Bob Hedgecutter]

Hi Guys,

I think I’d better make this the last appeal for assistance, cause I’m sure by now you must be finding the whole scenario somewhat tedious…..to say the least.

Stump Shot, I checked the continuity between the coil base and the crankcase…it’s good.

Bob, I’ve just checked the grounding on the plug body scenario, I even secured it with a cable tie ensuring a good/solid seating against the cylinder head and gave the pull start some serious wellie…No spark.

What I’ve also done, is check the resistance/continuity parameters on the 310. The only place I’m getting any significant variation between the 2, is on the HT lead. With the meter set at 20k ohms, I’m getting 2.2 on the 391 and 12.1 on the 310 !!

The confusion I have, is that I’m led to believe that lower ohms indicate a good connection and less chance of a short issue. Am I wrong? If yes, then I guess I need to buy another original coil ??

Cheers……….Stuart

Right we might be getting somewhere!
Remember I said way back there were two different air cleaners that signified two differing models of coil?
I am willing to bet the two Chinky dink ones you bought are incorrect for your flywheel and your original has a broken HT lead.

We might have to do some investigating and see if the HT lead can be unscrewed from your original coil and replaced with a generic length from Supacheap Auto or some such.

 

[Stuart]

My word Bob, you got me excited there…and I still am…tried to unscrew the HT from the original (not easy, used pliers) and it snapped at the base, tried the same with one of the “red” ones and it easily just pulled out or broke (I think) inside the coil housing.

Re-tested the original from the stub, end as it were…..Same 2.2. Which I guess suggests the coil itself has issues?

In any event, now only 1 way forward….Buy a new original coil and see what unfolds. As you probably know, you get very little off the shelf in WA, so, unless I’m lucky and get one local, I guess we’re looking at 10 days.

If it’s ok with you, I’ll give you a shout, when and if, some form progress is made.

Cheers……Stuart

 

[Stump Shot]

Hi Guys,

I think I’d better make this the last appeal for assistance, cause I’m sure by now you must be finding the whole scenario somewhat tedious…..to say the least.
Cheers……….Stuart

Not to worry, this is how the process goes sometimes, by finding out over and over what is not the problem, until the problem can eventually be found upon. Keep your chin up, you will get there.

 

[Bob Hedgecutter]

Right we might be getting somewhere!
Remember I said way back there were two different air cleaners that signified two differing models of coil?
I am willing to bet the two Chinky dink ones you bought are incorrect for your flywheel and your original has a broken HT lead.

We might have to do some investigating and see if the HT lead can be unscrewed from your original coil and replaced with a generic length from Supacheap Auto or some such.

Ask a few Stihl dealers if they have any trashed 391 or 311's on their rack of saws that are uneconomic repairs- you know, saws like yours that someone has straight gassed, taken to the shop and been told it is an uneconomic repair, left it there and bought a new saw.
That will gift you a lot of spare parts and is probably cheaper and faster than finding a new OEM coil.
Or look on Aussie fleabay for a parts 311 or 391.

 

[huskihl]

Not familiar with a 391. But being a clamshell, the body of the saw that the coil mounts to… Is it plastic? You need to have continuity from the cylinder or base pan to the coil mounting bolts

 

[Bob Hedgecutter]

Not familiar with a 391. But being a clamshell, the body of the saw that the coil mounts to… Is it plastic? You need to have continuity from the cylinder or base pan to the coil mounting bolts

Neither am I- but are they not single wire earthed- the green (?) wire with the ring terminal at both ends- one end to coil mount bolt, other up to a bolt on the manifold mount or similar?

 

[huskihl]

Neither am I- but are they not single wire earthed- the green (?) wire with the ring terminal at both ends- one end to coil mount bolt, other up to a bolt on the manifold mount or similar?

That could definitely be his issue. I saw earlier where he said the coil was making contact with the case. But if the case isn’t grounded to the motor, it’s not going to work right

 

[Stump Shot]

That could definitely be his issue. I saw earlier where he said the coil was making contact with the case. But if the case isn’t grounded to the motor, it’s not going to work right

Which is why I asked to check continuity between the cylinder and the case, I didn't read where that got done, just the coil frame and the case.
I would hazard a guess that if the cylinder retaining bolts were gooped up with sealant it could be possible.

 

[Bob Hedgecutter]

That could definitely be his issue. I saw earlier where he said the coil was making contact with the case. But if the case isn’t grounded to the motor, it’s not going to work right

I did ask this very question much earlier in the conversation- but my asking, whilst clear in my head- may not have been interpreted at the other end. I mean we are talking a Brit living in Aussie....... an easily confused combination!

 

[Scott kunz]

i didn't read the whole thread. is the coil grounded to the cylinder? the early 039 had this problem. the coil needs to be grounded to the cylinder because it's mounted to plastic.

 

[Scott kunz]

it could be a bent ground strap that you didn't put back in when you rebuilt it.

 

[Bob Hedgecutter]

My word Bob, you got me excited there…and I still am…tried to unscrew the HT from the original (not easy, used pliers) and it snapped at the base, tried the same with one of the “red” ones and it easily just pulled out or broke (I think) inside the coil housing.

Re-tested the original from the stub, end as it were…..Same 2.2. Which I guess suggests the coil itself has issues?

In any event, now only 1 way forward….Buy a new original coil and see what unfolds. As you probably know, you get very little off the shelf in WA, so, unless I’m lucky and get one local, I guess we’re looking at 10 days.

If it’s ok with you, I’ll give you a shout, when and if, some form progress is made.

Cheers……Stuart

Remember where I said investigate? Not twist and pull till it breaks!
Oh well, possibly ruined a perfectly good OEM HT lead and rendered the coil unusable.

Seems at least 3 or 4 of us have at some time mentioned the grounding of the coil to the crankcase/cylinder- and with these being the largest version of a Stihl consumer saw- a very real possibility still.
Rather than multi meter testing, I would be rigging up a temporary earth from a coil bolt to a cylinder bolt (muffler mount bolt if easier) and seeing if spark suddenly reappears from the unmolested Chinese coil.

 

[Fabz]

1) Disconnect wire / lead from primary tab - this will eliminate any switch/wiring problems. 2) use spark plug method to test coil , if spark occurs then coil MAY BE good , if no spark then replace coil. On STIHL saws I’ve noticed they will crap out when hot and then “rejuvenate” when let cool. I built a China doll 372xp for a gent and the coil went south after around 60tanks of fuel … A replacement coil was installed and he’s back in business