Z1 as a project?

[royhall]

It's the piston to bore clearance that's important. You need to measure the skirt of each piston then measure the corresponding bores. Not unusual for pistons to be slightly different sizes so each bore should be honed to it's specific piston and numbered. You need to find the Kawasaki stated piston clearance in the book, but it should be around 2 thou. If the guy that bored it was used to iron barrelled Triumphs he may have done them too big. Whilst your in there, have a push and pull on the gudgeon pins to see if they are moving in the small ends. If in doubt take the pistons off the rods and give them a good clean with solvent, then re-oil and try the pin in the small end. It should be free to slide.

[Bryanj]

I agree the clearance is critical but when we used genuine kit i never found a variation in piston size they were always spot on, maybe todays pattern kits are not so good but even those on the honda ones ive used have not varied

[royhall]

Mine have.

[Bryanj]

For which bike Roy and by how much?

[royhall]

CB350F genuine pistons had slight differences. Trigger did the rebore and made a bloody good job of it.

[MrDavo]

One of these things is not like the other....



I'm not sure if I should be worrying about the two pistons with NO carbon, or the two that have coked up that much in only 375 miles. Either way its not right, I'm glad I pulled the head off, I'm sure it wouldn't have lived a long and happy life like that. As far as I can tell I didn't have an air leak from the inlets, everything was tight, the rubbers are new. The plugs were pretty much like the pistons, pale and weak looking on #2 and #4, sooty on the other two.





Until I borrow some calipers, I can't accurately measure the bore to piston clearances. The piston thrust faces are lightly polished, as are the honing marks in the bores.

I'm wondering about the head gaskets. I had been intending to retorque the heads at 500 miles when I did a service, but when I took the head off I was surprised how untight the head nuts were, it didn't take much force to undo them. could the gasket have 'settled'? could oil and/or air have been getting into the bores around the gasket? That could explain both the air and oil where it shouldn't be? Air could get into the 'clean' cylinders (there was a whistle but I assumed it to be induction noise from the airbox), and or oil from the feed studs into the bores. Or it could just be the valve seals, which seemed to be hard and not a great fit around the valves, which had black burned oil deposits on them (they were new).

By the way, Saturdays test ride has produced my first Notice of intended Prosecution for speeding in many years. I saw the van, but too late, it must have been set to long distance looking down the hill I was coming up. At 42mph in a (deserted) 30mph limit, I just qualify for a Speed Awareness course, I looked up the limit and it is up to and including 42mph. Hopefully, it is up to plod's discretion.

[royhall]

Sounds like it wasn't torqued up in the first place which is worrying.

[K2-K6]

It does look like the clean cylinders have been running oil through them, from whatever source.

You get an odd effect depending on combustion temperature as the oil doesn't burn effectively and reduces the notional compression ratio. 
If you saw blue smoke (which you didn't) it would indicate it was getting the oil close to burning but still not quite,  hence the blue haze on two strokes as you don't want the oil to quite burn in making it effective as lubrication.

In much quantity, engine oil in the compressed cylinder takes away it's ability to burn the conventional mixture and acts like a fire damper to slow the process and you may be below the temperature that would make carbon deposits.

[royhall]

From the burning on the head and barrels it's looking a bit like a head gasket issue.

[K2-K6]

Forgot to add, it may have sounded "off beat" when running as the two soft  chlinders wouldn't match the other two for percussive output and couldn't be balanced out with carb synchronisation as it wouldn't affect the vacuum to a significant degree.

[hairygit]

I would certainly check the head for flatness, as it doesn't look like it's been machined since the factory, and if it was that loose, if it wasn't warped it probably is now running that slack.

Sent from my POT-LX1 using Tapatalk

[MrDavo]

I just checked the head with a straight edge, whichever way I put it there was no gap, so I'm pretty confident I didn't warp it. Worrying though.

[K2-K6]

Strange, as I thought from the pictures it definitely didn't look warped as the contact all seems consistent with being flat regardless of whether it's been skimmed.

Looks fine from this distance.

[MrDavo]

I may have found the smoking gun. The head gaskets weren't cleaned or wiped when I took the head off, they went straight into the parts tray.

First photo is the left side, you can see oil going from the stud, top right in the photo, across the gasket (and under the head) to #2 cylinder (the lower one )



This photo you can see a similar trail, from the front right stud to cylinder #4.



2 and 4 are my two 'wet' cylinders.

The oil feed to the cams comes up the rear outer studs. There don't seem to be O rings to stop it leaking in the parts book.

[royhall]

I thought so. You need better head gaskets they are crappy gasket set things.