Coil exploded

[Taboogs]

Finally got around to getting an mot for my 79 gs850g - it passed this morning after running fine.
On the way home it started struggling and died. Diagnosed failed coil relay - quick rewire and running again. . For 4 miles anyway, when 3 things happened one after the other...
First, loss of power and backfiring on throttle (later found to be the main jet fallen out in carb 3 vm26ss)...
Second, a major pop as spark plug 4 flew out (any advice on rethread kits)...
Third, a few seconds after the plug ejected, the coil for 2/3 exploded leaving a burnt plasticky goo over the frame and top of engine. Also found that the battery electrolyte plugs had all blown off (yb14la2).
Needless to say, the gs850 isn't going anywhere soon - will be trying to sort this out first.
On my urgent list is New battery, 3ohm coil with twin leads, spark plug repair kit. On my wishlist is dyna ignition (to replace points) and dyna coils.
Would my reg/rec be ok or would that be fried too and how can I check. (No fuses blew). . Am assuming something wrong electrically due to coil issue, but going to give a complete check throughout.

[fastbysuzuki]

I guess the carb problem is now fixed maybe a good idea to check all carbs for general jet tightness.
As for the spark plug thread my preference would be a time/thread sert I personally would not use an helicoil for your problem. Either way I would take the head off to do the fix as it's very difficult/ impossible to stop any metal getting into the cylinder and causing a disaster.
This months Classic motorcycle mechanics has a good piece on time Serts being used on a Cyinder head.
As for you electrical problems a thorough check on the stator and rectifier are required along with all the wiring/connectors and a fuse box cleanup.
maybe an idea to fit a series rectifier SH775 seems to be the choice on here.

[AMK]

" Either way I would take the head off to do the fix as it's very difficult/ impossible to stop any metal getting into the cylinder and causing a disaster."

This sounds like the disaster has already happened. I agree with you on the advice against the Helicoil.

[Nessism]

A solid spark plug insert can be installed with the head on the bike. It's done every day. You use grease on the tap and catch the chips. A few random aluminum chips that may fall inside the cylinder will get burned up or expelled.

If your bike has points that means you need 4.5 ohm coils. 3 ohm coils are good with the Dyna S though. Seems strange to pop a coil and blow up your battery. Sounds like your charging system is over charging.

[geol]

I was going to suggest you fire your mechanic but I suppose your day hasn't been that bright, at this point. Good luck with the fixes. Actually not all that terribly difficult I suppose. Use a solid insert on the plug thread vs a coil insert. Best of luck as you haven't had much of that recently and DO POST A PIC OF THE COIL... never have personally seen that little bit of fun!

[bwringer]

A solid spark plug insert can be installed with the head on the bike. It's done every day. You use grease on the tap and catch the chips. A few random aluminum chips that may fall inside the cylinder will get burned up or expelled.

If your bike has points that means you need 4.5 ohm coils. 3 ohm coils are good with the Dyna S though. Seems strange to pop a coil and blow up your battery. Sounds like your charging system is over charging.

Agreed on all points. The insert can be safely installed without removing the head -- just follow the instructions exactly, take your time, go slow, keep everything straight, and see if you can find a helper with some experience in this. I would add that you can vacuum any remaining chips out of the cylinder with a piece of fuel tubing duct taped to a vacuum nozzle.

[Taboogs]

Thanks for the info, am going to take a closer look tomorrow -
Is a 3 ohm coil ok to run on points and then upgrade to dyna, or is a 4.5 ohm coil ok to run with dyna at a later date - would like to save having to buy more coils in the near future. (Expense prohibits buying coils and dyna together)

for those that wanted to know what an exploded coil looks like - have attached pics -










This went with a loud bang - there is now a crack running lengthwise.

[Nessism]

The Dyna S is designed to work with the stock coils but the instructions state that 3 ohm minimum coils are also acceptable.

http://www.powercommander.com/downloads/Support-Released/Dynatek/Manuals/DS3-1_3-2.pdf

[roeme]

Wow, how did everything fail this catastrophically? How can a spark plug blow off? (Genuinely interested, I'm a noob).

Would my reg/rec be ok or would that be fried too and how can I check.

Do you have a separate R/R on this bike? If so, the regulator should clamp between 14-15.5V (exact value may vary, that's what I found in my manual at least).

The rectifier can be checked through measuring each of it's internal diode, refer to the schematic for the wires' colors. Google will give you plentiful information on how to measure a diode.

If it's a combined unit – I'm sure someone of the old-timers around here can help out (I don't have the schematic at hand).

[Taboogs]

Wow, how did everything fail this catastrophically?

Guess I was having a lucky day!!

How can a spark plug blow off?

I'm guessing the compression is good on that cylinder - plug thread in the head is knackered tho.

The R/R could be from anything - PO was a bit like that, as long as it worked at the time, it would be ok (have found this out since getting the bike and doing my own maintenance - he didn't even know about the secondary gear oil on the shaft!)

I'll check out the R/R when I get my multimeter back next week.

[geol]

Wow... the internal windings shorted I guess and got real hot and built pressure internally. Oh, by the way, my experience with coils is the Dyna green coils listed as 3 Ohm coils will normally measure about 4.2 Ohms new and are pretty good about staying in that range. I have always felt that most OEM coils for points or IC Igniter ignitions are not fussy about the coils except they be about 4.2 Ohms. The only exception I know is Kawasaki large 4s in 79/80 were engineered with 2 Ohm coils and they put a ballast resistor in line with the power wire to get the total up over 3 Ohms. Why? Dunno as it seems stupid and an extra complication and the ballast resistor resistance creeps higher and higher as the bike ages and I have seen them at 7-8 Ohms (which is added to the nominal 2Ohm coils). Strange stuff.