OH NO, exploded spark plug!

Well,
If you havent been by the new members page lately, I am the proud new owner of a 76 kz400d3:

The previous owner had it running at high rpm and all of a sudden it lost power and had a bad rattle in the top end... I have a feeling I know why:


It seems like the end of the spark plug literally just exploded, leaving a craterlike surface on the plug. And theres definetly some serious shrapnel in the cylinder. So heres my question - what now?
I imagine its going to involve me reading my clymer manual that (luckily) came with the bike quite a bit.

Ouch - really no way around pulling the head to remove the shrapnel and check if there´s any damage to piston and valves.

In addition to your manual you´ll find a lot of info and help at KZ400.com , probably the best resource there is for your bike.
Odd Ivar, who runs the site, is a really nice guy and knows just about everything there is to know about the 400s/440s.

Post edited by: OnkelB, at: 2007/11/09 12:34

Gawd! That bites! Well, you might try this...

Get the piston at TDC so both valves are closed, stick a shop vac on the plug hole and hope it sucks up all the debris. Rotate it a few times to make sure you get everything. There is probably some damage to parts in there, but maybe, just maybe you have some luck and can clean it out, stick a new plug in and get running again! You could do a compression check afterwards to get an idea of how healthy that cylinder is compared to the others.

Of course, make sure there is no fuel or vapors in the system! You could blow up your vaccumm or start a fire.

Good luck!

Matt in TX

Looks like the spark plug hole is torn up also! You may have to heli coil or install an insert. Sorry to see a bike damaged. Let us know!

KZJerry wrote:

Well,
If you havent been by the new members page lately, I am the proud new owner of a 76 kz400d3:
The previous owner had it running at high rpm and all of a sudden it lost power and had a bad rattle in the top end... I have a feeling I know why:
It seems like the end of the spark plug literally just exploded, leaving a craterlike surface on the plug. And theres definetly some serious shrapnel in the cylinder. So heres my question - what now?
I imagine its going to involve me reading my clymer manual that (luckily) came with the bike quite a bit.

Sorry, but the head will have to come off to "begin with"! I would suspect from your description you broke a rod or wristpin and the piston smacked the plug. Take a flashlight and look down in the hole. I suspect you will see more damage. Sorry for the bad news.

Yep, Modprod hit the nail on the head.

That's not an exploded plug (plugs don't explode),
That's damage caused by the piston smacking
it with considerable force.

Not specifically in a KZ but I've seen a dropped/broken valve drop into the cylinder and become a bouncing ball jamming-up and smashing-up anything that gets in the way.

No two ways about it, the head (at least) should be pulled off. Most likely shards of stuff will be jammed into the rings and any operation of the piston will only cause more damages to the cylinder walls - assuming the rod or wrist pin didn't let go too.

Check the ring lands for the top compression ring are not pinched or jamming if anything was "eaten" by that ring.

It's a bummer all the way around man.
The Plus side?
You're going to become intimately familiar with your KZ's engine operation soon :whistle:

allrighty then - thanks for the replies - I definetly agree with pulling the head and lookin at what ive got... so are there any special tools that Im gonna need past the usual array of sockets, screw heads, hex heads, etc to pull the head off? Ive been pouring over my clymer manual and checked out kz400.com (awesome site btw, thanx!) and it seems fairly straightforward, as long as ive got the manual within arms reach at all times.:dry:

on a positive note, everything else seems to be good - clutch, brakes, electrical... so hopefully it'll all be mechanical issues cause goddamn I hate workin on electrical!:pinch:

-wrenchmonkey,
thats exactly why I bought this bike - it didnt run, but is in decent condition and very cheap so now I've just got me a really big complicated lego set to work on in my free time!

Post edited by: KZJerry, at: 2007/11/10 17:02

Hi Jerry,

I haven't had to pull the head on the 400 yet, but I have had to chase gremlins in my carbs and electrical system. I'd recommend trying to get the factory service manual for your 400. I have both the Clymers and the Factory manual for mine and while the Clymers is ok, the Factory manual has always had more information in it.

Most of the other guys have already mentioned pulling the head and I'd agree. It may be obvious, but I'd look at pulling the oil pan too and cleaning out any metal that ended up down there. Check out Z1 Enterprises for gaskets too before you pull anything.

Sorry for your loss

wrenchmonkey wrote:

Not specifically in a KZ but I've seen a dropped/broken valve drop into the cylinder and become a bouncing ball jamming-up and smashing-up anything that gets in the way.

Yes, It could be a dropped valve too but "something" in that cylinder "hammered" that plug, no doubt about that

Post edited by: modprod, at: 2007/11/10 21:30

OnkelB, thanks for the tip - kz400.com is crazy awesome, I've already started on the disassembly based on Odd's step by step engine rebuild pics, I'll let yall know what I find...
so if the cylinder walls and piston heads and rings all are ok, then all I need to do is clean all traces of shrapnel out of cylinders (and clean carbs while theyre off) and reassemble, right?

me - o - my - o - jambaly - o - crawfish pie - o - etouffee


:sick:
well that bike is toast!

as several of you mentioned, it dropped the valves and beat the piston beyond submission and into dust. metal dust.

anyone lookin for a 1976 KZ400D3 parts bike?

also, anyone sellin or know someone who is sellin a running KZ? cause I really dont think its worth my time and money to fix this bad bad mess...