Burning oil

[DavidZ1R]

Now then, on my little Z250 project which I completed 18 months ago, and ran very well and done 900 miles with no probs, in the last 50 miles or so its started smoking a fair bit, took out the plugs and one is very wet with oil, so took off the head, replaced the gasket, new 'o' rings, checked the valve seals, all seemed ok, put it back together, bugger me still doing it, what would be the most likely cause? Also in the last two lots of petrol I have put in a stabliser, if that makes any difference.

[z1bman]

worn bore or worn /broken rings? have you done a compession test?

[DavidZ1R]

No tested for compression, but the pistons and rings were new and the cylinders were honed? could the rings break in place?

[AERIAL0]

Have you done a compresion tester check? If not you can get one on flea bay for £25 with all adaptors. Got one myself to test out the Z1300. Sounds as though blowing past rings. If valves. Smoke goes after a short while of riding

[z1bman]

rings can break in the bore but would have to be badly worn. did you check the piston to cylinder clearance & piston end gap before you fitted the piston & rings

[DavidZ1R]

No the damn thing smokes from start up and continues for a couple of miles, but smokes most of the time, sound like it could be rings? I ground the valves again when the head was off, and did a test with oil to see if they passed, but all was tight after an hour or so.

[DavidZ1R]

rings can break in the bore but would have to be badly worn. did you check the piston to cylinder clearance & piston end gap before you fitted the piston & rings

No but the engine had done only 10k when I rebuilt it.

[jphaynes669]

A compression test is your next job,.....looks like a rebore and piston kit is on the cards though.

[DavidZ1R]

Compression tester bought, will see what that tells me!

[jimmock]

Compression tester bought, will see what that tells me!

Screwfix do a not too bad compression tester with adaptors.
But I see you've bought one already.

Might be worth running it in for a couple of hundred miles first?

[z1bman]

is there any oil running down the back of the valves?

[Z1Boy]

Blue smoke I take it?

[Garry.L]

David...

It's a Z250 not a KH250 so you don't need to put oil in the tank.....

[sid123]

A compression test won't show if the oil control rings are faulty - it will show condition of compression rings

First check oil level is not over full ( oil whip from crank creates oil mist which is drawn through breather )

Take bike for a run go at speed then close throttle - then open up again if smokes will be valve stem seals / guides -- ( high vacuum created in inlet manifold draws oil past faulty seals )

Also on run load the engine up hill and look to see if smoking if so rings / bore issue.

How many parts are there in the oil control rings ? if three part rings check they are correctly installed ( ends not overlapped)

To confirm stem seals run engine till hot let stand and remove carbs and exhaust look closely at the valve stems to see if any trace of oil running down - is anything this will confirm stem seals -

SID

[DavidZ1R]

Thyanks for the info guys, keep me busy for a while, would not be bothered if it was a KH Garry !