So I've got a blown head gasket. Aaaaaaaargh

Last ride coolant blew out, temp was only on 4 bars. Bleed coolant system and refilled. Started with cap off and everything was fine until thermostat opened then coolant starts bubbling out, if I rev it it belches out all over the show.

This is the flippen 4th bike I've blown a head gasket on, I don't know what's with me and head gaskets!!

Anyway has anyone got any tricks for working out which cylinder it is without any specialized tools? The other bikes were inline four or single cylinder so no need to diagnose which one needed replacement.

There's no oil in the water and no water in the oil, looking at spark plugs doesn't seem to help as the coolant's not getting sucked in, just pressurized out.

990 or 1290? If its a 990 its pretty easy. Even easier if it the front cylinder as you can do it without moving the engine.

Are you sure it's the head gasket?

2005 990, it just the amount of strip down I have to do that sucks! I could a single cylinder in a couple of hours. That's why I'm hoping its the front so less tear down, just need to find out how to diagnose whether its front or back.

Pretty sure its the head gasket. I chased the other 3 bikes all over the place but in the end I've never found any other scenario that blows coolant out the radiator cap directly related to revs. If you have any other suggestions to try though I'm all ears, I'd love for it not to be be a head gasket! I've never even heard of an LC8 blowing a head gasket, just my freakin luck.

It sounds like the head gasket. If it is blowing bubbles out of the coolant, even more so when you rev it I'd say it is the head gasket.

Do you have a compression tester? If so whip both plugs out and test it on turn over. It might work better with bike hot and thermostat open. Or whip thermostat out.

No don't have a compression tester, was thinking maybe I could try somehow sealing a hose from the compressor on to the spark plug hole and see if bubbles come out the radiator. Good tip about the thermostat, I didn't even think about removing that before testing!

So I reckon I'm just gonna replace both head gaskets while the bike is stripped down, the rear has a slightly leaking base gasket anyway so I'll do base and head gaskets.

I'll have to order everything I need in one go because ktm New Zealand won't have anything in stock if I'm halfway through and forgotten something!

Let me know if I've missed anything obvious

2 x base gaskets
2 x head gaskets
8 x stronger studs (is there a little one that needs upgrading also?)
2 x copper washers for cam chain tensioners
2 x piston circlips
Do I need new head bolts/washers?

Just glanced through that walk through. Damn I wouldn't fancy doing that again. Especially as the bloody thing dropped a valve 350 miles later and destroyed the rear cylinder, piston and head Still lesson learned, at 52k miles the valves were probably due to be changed and I was cheap and didn't change them.

Just a thought but will the engine start/run with just 1 spark plug in?

If so pull one plug out and run the engine with the rad cap off, if you don't get bubbles it's likely is that one.

Run engine up to temperature, disconnect each coil pack and run engine in turn.

It won't run on one cylinder. Without a compression tester you are going to struggle to find out with cylinder it is. Even with one it might not be down by a large amount. You will probably need to remove the thermostat as well as I'm guessing it opens somewhere around 80c. It won't take long for the coolant temp to drop back down and the thermostat to close. As you'll be turning the engine over coolant will continue to circulate through the rad cooling it.
If I was you I'd just bite the bullet, whip the engine out and change both. You have to change the base gaskets as well as the cylinder is held in place by the same bolts that hold the head on. It isn't that difficult. That walkthrough was way more complicated as I was changing the timing chains as well. Just make sure you have the engine in TDC for each cylinder when you remove the cams and put them back. Oh and either buy or make yourself a locking bolt. I can't remember what the bolt size is now, just needs grinding to a point on the end you insert into the engine.

Both of mine have run, reluctantly, on one.

Have all the parts and finally about to start this job but was wondering if there's a way to remove the oil tank with the oil still in there or does it have to be drained first?

Drain the oil tank.

So got the beast back together, only a 50km test ride (in stinking hot weather so a good test I think) and all seems good so far.

Few things I found in the process.
For the most part its pretty easy to work on but a couple of things were a real bitch, especially the piston clips (worst I've ever dealt with) but I must have worked out a technique in the hour I messed around with the first one because on the second piston I popped it straight in. (stabbed a screwdriver through my nail on the first one too)
I had to bleed the coolant twice, first time I only had the bike raised about 40cm so that may have been why, second time over 50cm worked.
Only one valve was out of spec at .32 (exhaust)
I put a very thin bead of three bond sealant on the valve cover gaskets as the front looked like it had leaked slightly and I didn't have new ones available to replace them.
Couldn't get the proper KTM adapter so I used a shorty 13mm ring spanner with a 1/2" drive torque wrench in the open end for the outer head nut. Tried first at 90 degrees with the same torque value but wasn't 100% convinced so used an online calculator with it straight on and clicked at the same point.

Anyway this is the order I removed parts & it seemed fairly efficient.

-Seat, shrouds, tank, belly pan.
-Water reservoir
-Throttle cables at throttle body
-Throttle bodies/airbox/breather/sensor
-Radiator (after draining coolant system)
-Oil tank (left oil in)
-Exhaust headers (left akra's in place)
-Battery
-Loosened battery box and left in place under bike
-Front engine mounts
-Coolant hoses (just 2 hose clips by heads)
-Starter motor (now a real good clean around the base of the cylinders so no crap falls in when lifting)
-Removed 2 screws holding hard oil line running past right side of front cylinder so it would move out of the way while lifting the head
-Spark plugs then fitted the engine lock bolt (home made from threaded rod) at top dead centre for front cylinder.
-Checked valve clearances then lifted the barrel/head and replaced head/base gaskets and studs and reassembled all as per workshop manual

With that buttoned up moved to the rear which needed tilting forward in the frame
-Gear linkage off the engine
-Rear wheel
-Swingarm pivot bolt (supported engine first with tie down around front barrel, frame supported on stands under rear sets)
-Front wheel/guard
-Lowered engine at front till room for the head to come out (at this point maybe 500mls of engine oil came out of the crank locking bolt hole/ I should've rotated it to tdc rear and put the bolt in before tilting and I probably would have lost bugger all.
-Replaced gaskets etc as per manual

Wrote this list as I went then just ticked them all off in reverse for reassembly, also rotated engine a few times and rechecked valve clearances before throttle bodies and spark plugs were re-installed.

Good on you man! Oddly satisfying and frustrating working on our beloved beasts. I think the sense of satisfaction once you are done fixing it has to tickle or primal instincts and make us feel like manly man. And its typically a learning experience and saves us money at the same time.

And in my case I'm thinking "I'd like to get something new, shiny, different. But I've done so much work on this bike already, bought the special tools, I know exactly how it's been maintained and repaired that might as well keep it"

Nice writeup