372 clone, no spark, any ideas.

[Old Greenhorn]

So I have this 372 clone, it's certainly no gem, but there is no point in having a saw that doesn't run, so I am trying to fix it. The last time it ran, it quit on me in the middle of a job ad would not start. I tossed it and grabbed another saw to finish the job. It had failed on me several times or various reasons, that last time I put it in the corner of the shop. 2 years later and it's time I either fix it or burn it. 

 What I found is I have no spark. I checked the kill switch and it is functional (this is the third one I have had in it, the first two failed). I even disconnected it. No spark or change. Looks like I have to tear this saw all apart to get at the coil. Before I do that, can you folks share some ideas on other things I should look for? This saw has very low hours on it, probably around6-15 hours. It's dirty but the wear is minimal on any parts. I don't mind tearing into this stuff, but I am no expert. Any leads would be appreciated.

[Old Greenhorn]

Kind of responding to my own question, which is weird, but I never thought to check the gap on the coil. If the screws were loose from the factory, which would not be a surprise at all, it could have moved. I'll check that first thing in the morning. I think it's .010" but does anyone know for sure?

[CJ154SG]

0.012" - 0.014". A standard business card usually gets you in that range.

[Old Greenhorn]

Well I checked it this morning and I can't get a .012 business card in there no how. But there is no rubbing or contact either. I took it out just to clean it and have a look.
 Does this look right t everyone?


 Note the folded over lamination on the lower right and what appears to be ground away laminations on the upper left. There are no witness marks on the flywheel to indicate contact or rubbing. Is there anyway to test these things? All the same I think I am going to look for a replacement. This Chinese workmanship continues to disappoint, but I should have expected it.

[leeroyjd]

Maybe try a new plug? What brand did the clone come with?

[Hilltop366]

Besides eliminating the plug boot and plug wire from the equation about the only thing you can do is test with a ohm meter.

To eliminate the kill switch I always remove the kill wire from the coil not the switch as this also eliminates the kill wire shorted out to engine.

I linked a video that seems to go over it pretty good, the only difference I would do when testing the secondary side is leave the plug wire and plug cap on first then if it test open or really high resistance remove the cap and test directly to the wire then if same remove (if removable) the wire and test directly to the coil. That way you may find a bad wire or cap connection.

The best test is to put on a known good coil.

[Spike60]

Try the coil from the project saw. The wire will be a little longer as it's from a XT.

[Old Greenhorn]

Well I messed with it a bit this morning but am not sure I trust the numbers exactly. I just ordered an AM coil. Didn't really want to take apart a saw I just built up, but yeah, I guess that will really answer my question so I'll give that a try next. That will clinch it for sure.
 I had gotten inv0lved in doing something I have wanted to do for 5 years now and finally made time for it. (I'll post that in my running thread later.). That's pretty much done now, so I will pull the saw off the hook and pull it apart and make the swap after comparing the numbers.
 Oh yeah, and the first thing I did was put in a new Champion plug. Some saws and small engines burn through plugs it is ALWAYS the first thing I try.

[Old Greenhorn]

Ok I think it's figured out. I took the coil out of a 372 project saw and compared the resistances. The Chinese coil is low on both values.  I put the husky coil in the clone saw and it sparks up. Seems a bit weak, but it sparks. So I put the husky coil back on the husky saw and will wait until the new coil shows up in a few days.

 Thanks for all the advice guys.

[Hilltop366]

I will mention that I was taught that a spark will not jump as far of a gap under compression as it will in the open air so some coils will have enough spark across the normal plug gap but won't in the cylinder. A spark tester should have a larger gap than a plug. I just keep a plug with the side electrode straightened out or cut off for a spark tester. I also try to do this with a plug that the top terminal unscrews so I can test both types of wire caps.

From  AI so it must be true! 

No, a spark will not jump as far under compression as it would in open air.The increased pressure in the cylinder of an engine, for example, makes it more difficult for the spark to jump across the gap. This is because compressed air is a poorer conductor of electricity than air at atmospheric pressure. 

Here's why: 

• Higher Pressure, More Resistance:
  When air is compressed, the molecules are packed closer together. This creates a more challenging environment for electrons to move and form a spark.
• Increased Voltage Needed:
  To overcome this increased resistance, the ignition system needs to produce a higher voltage to force the spark across the gap, according to DENSO Global.
• Spark Plug Gapping:
  For optimal performance, spark plugs in high-compression engines or those with forced induction may require a smaller gap to ensure ignition under the higher pressure.

[Old Greenhorn]

Well if AI says so, then it must be so.
 Actually I knew that.... but had completely forgotten it a while ago.  I'll wait for the AM coil and see how it goes. I also ordered a 4 pack of NGK plugs because I am getting low and I like to have spares in my bags for an easy swap.
 
 This particular saw was never anything special and was never dependable at all. I suppose if I keep after it with all these failures, eventually it will be more usable. I only bought it because I needed a 70cc saw and could not afford a new 372, nor could I find a used one that somebody wasn't asking a stupid price for. As I said, Spike predicted it would be a 'project saw' and he was right. Bottom line... never trusted it. It failed me almost every time I used it and I had to use another saw. Now I just about finished building a real 372 project saw that is a runner. So this one I am just trying to get running so it's usable. If it fails again, I'll fix the next thing again, and move on. But that real 372, I'll dress that one up nice and keep it ready to rock and roll. Best saw I think Husky ever made.

[Old Greenhorn]

Well the new AM coil arrived today and it's dead. Its a flat open circuit between the plug wire and the primary coil. Somedays I can't win for loosing.

[Spike60]

Maybe. I Honestly don't even know how to test a coil with a meter. I just move things around and inspect  everything.  Try going the other direction and put the new coil in the projet saw. Wire will be a little short, but you can still test for spark. Unusual for one to be dead out if the box.

Eire from switch to coil can short to the case in 2 spots.  1st is where it passes through the case back by he switch. Slso make sure they didn't pinch it when they screwed in the short grounding wire. 2nd place is where th long wire passes OVER the collide and is held in place by the air conductor. Running it under the coil wire can cause it to short to the case.  Especially with AM coils which often have a fatter wire than original.

[Old Greenhorn]

I agree Bob. I rechecked it several times and checked that there wasn't a meter issue. Hard to believe. But I could compare it to another coil just to confirm. Only thing I can figure is that the plug connection (on this one it is a spring type thing) and it may not be properly connected to the wire. I can't slide that boot back to get a look at it like you can with the sheet metal ones. I sent a note off to the seller, but no reply yet. He should know how many of these he sells and how many failures he's had.
 Checking with the meter is fairly easy, there is a you tube link in this thread above. I have already taken the coil out of the project saw and put it in this one and that works. I don't know if I want to take that project saw apart again, especially since I get no readings at all on this coil, nothing, nada, el zippo.
 Guess I'll order another coil.

[Old Greenhorn]

Well color me stupid, I just ordered another coil from a different seller. This one says it's been 'tested'. It's a crap shoot with these things. I'll hang the saw back on it's hook and wait another week. It's just a clone, but I like my stuff running. Not sure, have a bunch of irons in the fire right now, but maybe I'll get back on the project saw tomorrow.

[old2stroke]

I have given up on buying AM coils, most of the time they don't work.  Unfortunately, due to the electronic package that controls the primary current, there is no valid test you can perform on the primary. About all you can test with an ohm meter is the secondary path from the plug cap, through the secondary to ground at the cylinder.  Many of the coils will give a good spark but the timing is too far off (too retarded) but if you have enough patience and a timing light you may be able to make them work by relocating the flywheel.

[Old Greenhorn]

Yeah, I hadn't thought about the timing and relocating the flywheel seems like a pretty difficult thing to do given what  have to work with these days. Sure would be nice if one could move the coil instead.
 But what I don't get is that I have the same OEM coil back on the (running) OEM saw it came off of and it's not working now. I can't imagine I mislocated it when I reinstalled it, but I will pull it apart again and re-check everything. It's a project saw so I will just keep at it until I get lucky.

[DHansen]

One thing at a time, don't create multiple issues and not know what caused the change.  Stick with just swapping coils and find out why the one that was working has stopped.  Air gap I can see but moving flywheel or coil mounting in attempt to change timing I would avoid.  Spark should occur regardless of timing.  Timing will affect performance, or no start, but will not cause a no spark condition.  As long as the primary is producing flex lines and the secondary is not open or shorted it should induce spark to the secondary windings. 

[Old Greenhorn]

Agreed, I would need a lot of convincing to even think about moving the timing.

Just to re-cap, this conversation started with regard to my 372 clone which has sat dead for a couple of years. I also have a 372 (OEM) project saw I am building up from almost all old parts. That saw was running just fine when I started working on the clone. But I borrowed the coil from the OEM to try in the clone. UI did get a spark and stopped there thinking I just needed a new coil. I put the coil back in the OEM and now that too will not start.

 So, this morning I pulled the coil out of the OEM and checked everything again. Tested with an Ohm meter best I could and that looks fine too. Put it back in and I have a spark with the plug out of the cylinder. But no way will it start or even burp. I know I have fuel, I can see it with the plug out. Hard to believe something else could have failed in that short time. I checked all the basics, spark, fuel, air, all the carb to cylinder connections (not sucking air), cylinder head and just about anything else I can think of.

 Meanwhile, the (2nd) new coil showed up for the clone today, so I put that one in and I can't get spark. I tried 3 different plugs just to be sure. I am loosing my mind at this point.

 Anybody know just how sensitive that coil gap distance is? I use a business card (about .014") but it's very hard to pull it out when set and there isn't much adjustment room on the coil mounting holes.

 Now I have 2 dead saws and I am about at the end of my rope.

[Spike60]

Just since posting in this thread, 5 of my saws will not start. It's a virus of some kind!

Dave is right. Let's be careful and not add multipliers in the discussion. Changing the timing is an example of that. And such things should not attempted as a guess without knowing the timing is at fault. Which it isn't. 

IMO, there' is something we haven't seen yet. No way statistically that you are dealing with 3 bad coils. Maybe it's the business card. Maybe use the meter to be sure the kill wire isn't grounding out

[Spike60]

 Don't know numerically what the coil gap is. I just use the plastic Husky gauge. It may have the gap printed on it but I'm not home right now. It's pretty thin and allows the gap to be set consistent with the curvature of the flywheel. I'm thinking  you might just have 3 good coils.

[Old Greenhorn]

What confounds me is that the project saw coil was working fine until I put it on the clone and now I can't get the project saw running again.

I have never had a problem with a chainsaw coil in my life, and now I have 3 bad ones?

I just put in another session of testing everything with an ohm meter and eliminating the kll wire for now. Everything seems correct. My head hurts. Is it too early to start drinking?

[Spike60]

No, of course not. I've already started.

You don't have 3 bad coils. Just hit the reset button and we'll get it sorted out. 

[DHansen]

I do not have a 372XP but I went and measured the air gap between the flywheel and coil on my 272XP it is at .012" So if you are in the .012" to .014" that will be fine.  So that will but the air gap question to rest.  I would say verify you have spark from the OEM 372XP with the coil that was originally in that saw.  Then put one of the new coils into the OEM saw and also check for spark.  This will eliminate coils and air gap as to being an issue.

[Hilltop366]

I always used a brass feeler gauge that is in a set it has a regular one the same size. Not 100% on the size but for some reason I think it is a 10 thou.