TOPIC:

1976 Kz900 Bored to stock +.50mm. Rebuilt 18 months ago with new pistons, rings, valves recut and I thought all new valve guides. Rebore and valves were farmed out to local motorcycle machine shop. Does tend to smoke a little/lot until totally warmed up and at fairly hard acceleration. I think maybe not all the new guides were actually put in by the shop and I failed to chech as the whether my new stem seals were used?

Rode to 7 from Birmingham (400 miles)last saturday and used 3 quarts.

Have put about 2500 miles on since the rebuild but have now sprung a healthy oil leak coming, i think, from the front left corner of the base gasket. Probably going to tear it down again when the weather gets too cold to ride.

Any thoughts/ideas on the "smoke" and the leak? Thanks.

Bummer. Were the gasket surfaces on the cases and bottom of the jugs cleaned well prior to install? Cleaning those really sucks, but it's important if you don't want to have leaks down the road.

A compression check, oil in cylinders and the usual tricks should determine if it's rings or valves...

If you're running higher than normal compression, then maybe you should be replacing the studs. Also you should periodically check torque, and remember to retorque after the engine has been running a bit. Seem to recall that the standard torque was 25 for the 900 and 29 for the 1015, but you'll need more with higher compression. How much more is a good question - maybe 40-44 with heavy duty studs and nuts - getting this right affects the stability/rigidity of the entire motor, including cases.

Nothing in the valve train would make you use 3 qts of oil in 400 miles. You have ring issues. Probably, the new rings didn't seat. I would try compression testing then test with a drop of oil in each cylinder to verify. If the base gasket is leaking, verify this before ripping into the top end, but I suspect you will want to look at the cylinder bores and pistons carefully. Check to see that the rings are on correctly (not upsidedown) and check the bore diameter and piston diameter to ensure that the clearance is not out of spec. I know that a shop did it but you need to double check. It is possible you have a broken ring or broken piston. It happens and this can cause oil loss and smoking.

...also if the ring gap locations aren't staggered this might occur. Compression test on a warm engine with the throttle open, and then do the squirting of a little oil in each cylinder before testing, for the possibility of a ring issue. Of course you know all of the spark plugs should be removed before this compression test, right?

Good luck, and let us know what you find.

Thank you for all the great suggestions so far. I think a compression test is in order. I'll try to get to it this weekend and report back when I have some readings.

I was aware (only through reading on this site) that the throttle should be fully open when I do the compression test but was, until now, unaware that ALL the plugs should be out. Is this a safty issue or is there a reading difference if the other three plugs are left in?

Assume I just remove all plugs, screw in the tester to one of the pots, opem the throttle and crank using the starter? how long should I crank to obtain the correct reading?

Thanks.

Here's some ideas why...
Taking all the plugs out makes it easier for the starter to crank the engine.
If you do a leakdown test, you can hear air out another spark plug hole when there is a head gasket leak between cylinders.
If you had that leak, I suppose there is some chance the compression test might be different with the other plugs in vs. out.

Crank until the gauge doesn't go higher, usually 3-6 compression strokes. But you should do the same # of strokes with each cylinder.

My compression gauge has a disconnect in its hose, so I can disconnect it to thread the end in the plughole. I take my air hose and connect it to that, blow air in the cylinder, and see if it comes out the exhaust, intake, or oil filler.. The regulator on the compressor has a line pressure gauge; the difference between what the reg is set to and the psi the cylinder can hold is the leakdown.

Barney-, looks to me as so one or more rings have been assembled onto the piston(s) the wrong way around. There is always confusion with Z1000 & Z900 rings! This would explain your excessive oil consumption. I would not discount Wg's broken ring theory.
Regardz

Definately sounds like a ring problem. Could be from incorrect installation, incorrect finish on the bores, etc. This will result in cylinder pressure filling the crankcase, and the base gasket is usually the first place the pressure escapes.

If you have low compression, then use a good leak-down tester and perform a leak-down test. If it has over 10% leak-down, you will be able to hear it. Listen in the oil filler, if you can hear it there, it is rings. Listen in the pipes, if you can hear it, it is exhaust valves. Carbs = intake valves.

How did the three quarts get out? Blue/gray smoke from the exhaust, or thru the oil leak?

If you have to take it back down, send the cylinder and pistons to someone who can make sure they are correct. And you might want to put heavy duty studs in it. I know someone makes those, it just excapes me at the moment;)

Jay
www.kzzone.com

Post edited by: APE Jay, at: 2005/11/05 15:54