TOPIC:

I spent the last two years on/off rebuilding from the frame up a 1974 KZ400. 9,000 original miles, last on the road in 1984. I took it down to the crank. Cleaned everything. New cylinder base O-rings, OEM head gasket and all other gaskets replaced with new. Followed the rebuild specs to the letter, right down to bolt torque values and tightening sequence. I fired it up today for the first time ... it started right away, ran on two cylinders, idled ... then started to ooze oil out of my nice new head gasket. Grrrrrrr ....
I've read on numerous sites the early KZ400 models were notorious for leaking oil. Has anyone here found a way to make a KZ400 engine stay oil-tight? Silicone? A brand of gaskets? Prayers? I would like to know if there's hope or if these early motors are just trouble. I LOVE this little bike and really, really want to see it back on the road.
Any suggestions, products or vendors that have something that would help me, I greatly appreciate the input!

Rebuild after only 9k miles? Why? (inquiring minds wanna know)

OH, and did you get a genuine Kawi gasket set? ...or 3rd party?

don't know about 400, but the 750 twins have several10mm bolts that go up through into the head to help hold it. Make sure you didn't miss any small bolts.

I did a rebuild as the bike had not been run since 1984.

I did not neglect any of the nuts/bolts/fasteners when i did the re-assembly. I used OEM Kawasaki gaskets. The head gasket I special ordered through a local dealer: $120.

I had a 440 that leaked at the cylinder head and the base gasket. I replaced the head gasket and the base gasket quit leaking when I torqued it up. Common issue with the small twins.

You need to re-torque the head after you heat cycle the engine, if you haven't done that then give it a try it may solve your problem.

How did you prepare the head and cylinder surfaces, did you check with a straight edge to ensure they were still flat?

I spent two days carefully cleaning all the old gasket material off the cylinder head and all other surfaces. Checked for flatness. The first start-up of the bike it ran, didn't leak or give a sign of trouble. That was maybe a five-minute run at idle speed and some low- to mid-rpm throttle. Came out the next day and it was dry of oil. The second start-up/run session is when things went south.

I did fill the thing with oil right to the top line of the sight glass. Overfill? Would that cause too much pressure and it would find the weakest area and push oil out?

barquirt wrote: I spent two days carefully cleaning all the old gasket material off the cylinder head and all other surfaces. Checked for flatness. The first start-up of the bike it ran, didn't leak or give a sign of trouble. That was maybe a five-minute run at idle speed and some low- to mid-rpm throttle. Came out the next day and it was dry of oil. The second start-up/run session is when things went south.

I did fill the thing with oil right to the top line of the sight glass. Overfill? Would that cause too much pressure and it would find the weakest area and push oil out?

You MUST re torque the head gasket after the first run cycle. When I checked mine after I first ran it, the head nut torque had dropped to about 1/2 of what it was at assembly.

Oil to the top line is not over full, I always did that on mine.

I thought some KZ440's came dry-blocked. So you might be able to do the same on the 400. I'll see if I can find any photos.

Item 14 is an oil pipe. I assume this means there is no pressurized oil going through the block, so that should help reduce oil leaks at the head and base gasket.

Not sure if it's doable or what it would take.

Loudvhx on the 440 the oil pipe supplies oil to the head, oil still returns through the cam chain tunnel and passages in the cylinders.

leaks at the top and bottom of the cylinders seem to be a common problem on the 400/440's. My guess it's that since the pistons move together in phase that the studs suffer from some resonant frequency ridding riding that work things loose.

A friend of mine had a 400 that leaked at the base and cylinder head gaskets. He asked me about replacing them after I had done the job on my bike. I told him to bring it by, when he did we just re-torqued the head and the leaks dried up.

I don't know if the bigger twins are the same way, maybe the studs are larger and its not a problem like the 400s.

Yes, but my point was about "pressurized" oil. The return oil is not under pressure. My buddy's 400 had a leak near the pressure passage feeding oil to the head. I think an external line would have eliminated that particular leak.

I went to the KZ400 introductory factory school. Kawasaki claimed that their use of Orings in the head will prevent the oil leaks that plagued Honda engines. Oh the Irony !. Some of the original Kz400 had the entire sealing kit replaced several times. One point of leakage was the inside cylinder studs in the back. We had to pull these studs and locktite them to seal them. It was a real problem child of an engine. The 440 with the overhead oiling was the answer but by that time the Kawasaki small twins had a bad reputation...

Tyler wrote: Loudvhx on the 440 the oil pipe supplies oil to the head, oil still returns through the cam chain tunnel and passages in the cylinders.

leaks at the top and bottom of the cylinders seem to be a common problem on the 400/440's. My guess it's that since the pistons move together in phase that the studs suffer from some resonant frequency ridding riding that work things loose.

A friend of mine had a 400 that leaked at the base and cylinder head gaskets. He asked me about replacing them after I had done the job on my bike. I told him to bring it by, when he did we just re-torqued the head and the leaks dried up.

I don't know if the bigger twins are the same way, maybe the studs are larger and its not a problem like the 400s.

My 750 twin has leaked oil from the head gasket since it was new. Right now it's on it's third headgasket (two rebuilds) and every one has seeped oil worst at the front. I have never seen a picture of a 750 twin that didn't have the greasy scum line around the head gasket where the oil seepage gats blown back. My "solution" is to roll up a really good paper towel and stuff it between the fins at the front around the sides to suck it up. After a couple of months, I replace it. Mickey Mouse but I gave up trying to get the leak to stop.