KZ750b Head Gasket

Since I bought it, my bike has always had a slow oil leak where the cylinder block meets the head (on the front of the engine), the crankcase is also pressurized (you can feel strong air pulses from the oil filler cap). So I am assuming the head gasket (at least) is blown). I have a lot of mechanical experience from working on everything from old ferraris to heavy machinery, but pretty much none on motorcycles, so I am hoping to hear any advice on the subject to help make things as smooth as possible.

I have done a search and heard some info on the subject, I heard somewhere that it wasn't the headgasket that usually failed, but some sort of o ring? Besides adjusting the cam chain, I won't need to do any other adjustments when I reassemble, correct?

Before I had to quit riding it (for fear of engine damage) I was putting an average of 600 miles on it a week. So If there is anything I should do (cheaply and easily) while I have it apart to improve the reliability, I'd be interested to hear about it.

I appreciate all the help

Kelly
Lawrence, KS

Part number 92055 is the o-ring known to leak. But that just causes oil leakage. There's typically some pressure going on in the crankcase, just like their would be in a car engine. I mean, there's a lot of heat and a lot of stuff moving quickly. I don't know if I'd be able to tell what was abnormal pressurization by holding my hand over the oil filler cap. Once, when I was younger, I tried pouring some oil into a running engine, none of it made it in, just got blasted everywhere by the pressure from the inside of the engine, and that engine was fine (this was on an old truck I had). If you're worried about cylinders leaking, run a comrpession check or a leakdown test.

Also, are you on a 750 two or four cylinder. Kaw called them all KZ's, but they're a lot different. Let us know the year and all. I've been assuming 4 cylinder, cause that's what I know about. The head-gaskets on these are pretty tough, when I got my bike, one of the cylinders was venting out the gap between the cylinder block and head, so I retorqued the head, and then it was fine, if that gives you an idea of their durability. That said, if you remove the head, you'll still probably need a new gasket, but other than that and the properly timing the cams, I can't think of anything else that you'd really need to do for reassembly. If you're going in anyways, I'd check valve clearances, since you'll be messing with the cams anyways, and it seems like everyone always ends up needing to redo them when they first get their bike.

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Incidentally, Kawasaki has parts diagrams like this for all their stuff on their website. And they show part interchangeabilities and what's still in production too, good stuff.

Thanks for the replys, my KZ750 is a twin. It is interesting what you said about crankcase pressure. Just leaving the thing running leaves everything near it with a light coating of oil. It really is hard to explain how much pressure there is coming from the crank, but the pulses are strong enough to cause me worry? Hopefully someone with experience with the twin will chime in, since I could see a lot of pressure being built due to both pistons moving up and down together.

kro10000 wrote: Since I bought it, my bike has always had a slow oil leak where the cylinder block meets the head (on the front of the engine),

FYI, every Kawi 750 twin I ever saw seeped oil there including mine...... for 30 years. And that was new from the factory, first valve job, second valve job, and last rebuild. If you look close you will usually see a scum trail where the oil seeps out there and blows backwards on most any 750 twin.

I roll up a heavy duty paper towel and stuff it in between the fins to keep the seepage from running backwards.

kro10000 wrote:
the crankcase is also pressurized (you can feel strong air pulses from the oil filler cap).


leaving the thing running leaves everything near it with a light coating of oil. It really is hard to explain how much pressure there is coming from the crank, but the pulses are strong enough to cause me worry?

I think that's normal, you NEVER run it with the filler cap off.

Where is the oil spraying from?


Is the breather hose at the rear of the engine still OK? If that fails it will blow oil there.

Any reason why it's terrible to run with the cap off? I mean, obviously I wouldn't be running down the street, things could get in, but it seems like it'd just let it vent, which is what the breather does, so I don't see why it would matter.

For what it's worth, I never do run it with the oil cap off, the oil spray only happens with the cap off, I was just trying to explain the amount of crankcase pressure.

Hmm, well I just about have the whole bike apart, I may consider reassembling and going to buy an air compressor to do a leakdown test. Parts for these aren't easy to come by, nor inexpensive, so I might be better off doing some more diagnosis before I get any further.

Del_Herring wrote: Any reason why it's terrible to run with the cap off? I mean, obviously I wouldn't be running down the street, things could get in, but it seems like it'd just let it vent, which is what the breather does, so I don't see why it would matter.

All I know is, I stupidly forgot to put the filler cap one time after doing an oil change and started the engine...... :ohmy:

That's how I learned never to do that again. :laugh:

Del_Herring wrote: Any reason why it's terrible to run with the cap off? I mean, obviously I wouldn't be running down the street, things could get in, but it seems like it'd just let it vent, which is what the breather does, so I don't see why it would matter.

The movement of the piston up and down causes a positive and negative pressure pulse in the crankcase. The breather is there to keep it from spewing oil.

kro10000 wrote: For what it's worth, I never do run it with the oil cap off, the oil spray only happens with the cap off, I was just trying to explain the amount of crankcase pressure.

Hmm, well I just about have the whole bike apart, I may consider reassembling and going to buy an air compressor to do a leakdown test. Parts for these aren't easy to come by, nor inexpensive, so I might be better off doing some more diagnosis before I get any further.

New piston/ring sets ca be had for a decent price (like $50 each ballpark). Rebuild gasket sets are about $80.