spark plug failure

[Charles]

Hi,

on my way to work my KR1S suddenly turned into a single cylinder
As I removed the failing rhs spark plug it looked like this :


It's a BR10EIX plug fitted about 250miles ago. I last checked it 50miles ago (looked like new then), when I had a helicoil fitted into the spark plug opening.

The lhs spark plug looked like this:


Think that one looks ok, just a bit too rich. I have fitted 140main jets at the moment, and the needle jet one clip richer as I didn't want to risk a seizure with my new lomas exhaust just fitted.

What I've checked so far:
- carbs are synchronized accurately, I've just cleaned them (ultrasonic).
- oil pump functions properly.
- no blockages in fuel lines, swapped the fuel lines at the fuel tap.

Got some new plugs (BR10EG) at work and came home safely. But now these new plugs look like this:

RHS:


LHS


Can anyone tell me what's wrong with the RHS?
Could it have anything to with the R6-coils I use?

thanks,
Charles

[Charles]

Could it be that the helicoil insert impedes the heat transfer from the plug to the head that much that it destroys the plug? Before fitting the helicoil insert I had no problems whatsoever

[TwoStroke Institute]

The failed plug shows signs of pre-ignition, a quick look at the piston would be in order also.As you might find erosion on the crown directly under the plug.
Could well be the steel of the heli is glowing causing the pre-ignition.as pre-igniton is usualy a heat related issue.
The plug second from the bottom is an odd colur too.

[Charles]

The failed plug shows signs of pre-ignition, a quick look at the piston would be in order also.As you might find erosion on the crown directly under the plug.

Piston still is ok, took the exhaust off yesterday and checked with a torch.

The plug second from the bottom is an odd colur too.

That's what I thought too, same cylinder (the one with the helicoil insert), new plug after 20km ride.......

thanks,
Charles

[the-elf]

The RHS one looks well nuked and the second one looks like its running very eweak. Have you got an air leak or something? When I had one nuke like that it was a crackcase leak allowing the engine to suck in frsh air.

[Charles]

Have you got an air leak or something?

I covered the whole of the engine in brake cleaner fluid but couldn't notice any change of revs. Checked the carb once again, it's fine.....

As I took the plugs out after this run, the helicoil came out too. It covers only a small portion of the plug thread, could this be the reason for the overheating of the plug?



Charles

[alanw]

Charles, plug third picture down has combustion marks down the threads
! as if the plug were to long ( hot ) which it is not ????? Alan.

[mgtkr1]

looks like the plug isnt sat air tight thus pulling air in on the downstroke causing a mega lean combustion process=excess heat therefore pre ig??? do you have a spare head? i have one you can use until your sorted if your stuck. std so you can just bolt it on if your barrels/pistons are std height. also have a low milaege piston you can have but personally id use new piston/rings/little ends ect for peace of mind if your piston need replacing. i definitly put that down to an air leak and all the evidence points toward the helicoil.

[kwackman12]

Think thats an "insert" not a Helicoil Charles, If you cant get it repaired I have a helicoil set for spark plugs, I could repair it while you wait when you come over this month, as long as the hole is not to big?
Stan Stevens didn't repair it for you did he?

[scooble]

If the helicoil only goes halfway down and the plug isn't making contact with metal at the combustion chamber end, then I would think that it may not get the oppertunity to disscipate heat, thus got too hot etc. Also possible I guess what has also been suggested is that it could not be airtight. Might also be worth sticking a compression tester on there to see what you get

[mgtkr1]

heads/pistons ect arent such a pain if there buggered although ideally theyd be perfect. however barrels are very hard to get these day's so hopefully they shall be unaffected. what scooble just said makes sense aswell. i think its the insert for sure. too much of a coincidance besides kr's are super reliable if all is well. 140 mj doesnt add up to causing a conventional lean seizure so it must be further along the process, for want of a better phrase. sorry folks its friday!!!

[symtec23]

I have also had a simular issue this year, not as bad as that though, but mine was caused by a tiny split in the carby rubber on the engine side of the oil line. I would be checking to make sure that the plug is sealing up,if not, replace the head. The biggest problem is that melted plug could be through out the motor, a potential time bomb if not sorted quickly. In my motor, there was deposits stuck to the top edge of my ring and piston was pitted to hell .

[Charles]

Hi all, thanks very much for your replies!!

plug third picture down has combustion marks down the threads

yes, it has. That's because just as scooble wrote:

the helicoil only goes halfway down and the plug isn't making contact with metal at the combustion chamber end, then I would think that it may not get the oppertunity to disscipate heat, thus got too hot etc.

The insert doesn't even go halfway down the plug
I guess combustion is now taking place around the plug instead of under the plug, thus impeding the plug to disscipate the heat to the cylinder head.

The plug/insert were however airtight. I checked them by spraying brake cleaner onto them while running. No change in revs whatsoever.

Checked the piston by looking through the exhaust, it still is fine.

Will fit the spare head I got and check everything by taking the barrels off.

thanks again everyone, this forum is great =D>

Charles

PS will report on my findings next week, as I unfortunately must accompany wife and kids for a week at the beach in Holland. I'd rather fix the bike, is the weather on the other side of the channel great as well?

[Charles]

Hi Gary,

Think thats an "insert" not a Helicoil Charles, If you cant get it repaired I have a helicoil set for spark plugs, I could repair it while you wait when you come over this month, as long as the hole is not to big?
Stan Stevens didn't repair it for you did he?

No it wasn't Stan, just his evil twin brother who lives next door here.

I thought it was a helicoil, a local motorbike garage fitted it for me, I'd never worked with inserts/helicoils before.

If you could try to repair the head that would be great! I'll bring it with me (when I've checked it and it's worth repairing) we can then see if you got the time to repair it.

thanks very much for the offer

Charles

[Charles]

heads/pistons ect arent such a pain if there buggered although ideally theyd be perfect. however barrels are very hard to get these day's so hopefully they shall be unaffected.

That's what I hope too...... I do have two sets of freshly replated KR1-barrels but I'd rather leave them for future use, when necessary.

too much of a coincidance besides kr's are super reliable if all is well.

I hope mine will be reliable as well, had nothing but bad luck with my RD350s, hope the KR1S will be better..

cheers,
Charles