Z1b smoking on start up

[Kennyboy]

I bought my Z1a around 6 months ago, it was smoking, blue smoke from the exhaust when first started up. the smoke goes away once she is warm. My first thought was valve guide seals letting oil into the combustion chamber whilst stood. I changed the seals and lapped the valves, fitting good quality seals from Z power but this made no difference.

So yesterday I decided to strip the top end with a view to rebore and new pistons. However, at first glance there is no evidence of 'blowby' past the rings and the pistons look to be very good. Next stage is to get the bore and rings measured.

I have attached pics of the piston crowns, these were cleaned around 1,500 miles ago when I changed the valve guide seals. As you can see all 4 are now carboned up with oil residue.

My thoughts are that oil is getting into the bores from the head when stood. Could it be the valve guides themselves that need replacing ?

I also noticed that one of the 73mm bore O rings is broken, between the liner and crank case (see photo), I not sure that this could be causing smoke on all cylinders though.

I will get the bore, pistons and rings checked this week so will either find the problem or eliminate these components.

Once the engine is warm it runs fine, and without smoke.

Has anyone else experienced this ? any suggestions welcome.

T I A Kenny

[warren3200gt]

Are you sure it's not just Condensation in the exhausts?
Hot exhausts when left cool and any humidity in them condenses on the metal skin. When you restart it it evaporates as steam and exits the tail pipe mixed with rich choke emissions would come out as blue. Or it could just be choke enriched exhaust emissions.
How long does it smoke for after you turn the choke off.
You may be looking for a problem that isn't there.

[Ultim8pc]

Are you sure it's not just Condensation in the exhausts?
Hot exhausts when left cool and any humidity in them condenses on the metal skin. When you restart it it evaporates as steam and exits the tail pipe mixed with rich choke emissions would come out as blue. Or it cod just be choke enriched exhaust emissions.
How long does it smoke for after you turn the choke off.
You may be looking for a problem that isn't there.

What Warren said

[zapo]

My A4 has smoked on cold start ever since I brought it 6 years/13k miles ago. It clears within 1/4 mile of riding and way before choke is off. Bike runs great and 50mpg so I've just ignored it.

[Kennyboy]

I would say it's definitely oil smoke, deep blue and smells like a 2 stroke. Normally gone within a few hundred meters of riding. It only does it when the bike has been stood for a long time i.e. overnight. Which makes me suspect oil getting into the combustion chamber via the head, once it's burned off it runs great with no smoke.

Believe me when I say it smokes it really does puther out, not just vapour.

[Gray17]

Hi been through this myself on my own Z900, in my case it was bore ovality that caused the smoke on start up. Have you done a compression check, what are your results? If any low try squirting a teaspoon of oil in then re test. If pressure increases def bore wear or cracked ring. I Had rebore new pistons, rings etc, now no more smoke on start up or running, however it could also be other things too eg possibly running rich, Whats your plugs like?
Choke plunger seals gone allowing the rich mixture. valve guides.
Unfortunately its a case of checking everything is within tollerance to prevent re building and ending up with same symptoms.
How do i know, Dont ask but should have done rebore 1st time round save a lot of headaches, time wasted and cost.

[Kennyboy]

Thanks for all of the suggestions guys, it's definitely thick blue oil smoke. I could almost live with it but its like a smoke grenade has gone of on my street when first started, need to sort it really.

A friend is checking the barrels with a bore gauge on Friday, maybe bore ovality as Gray17 suggested. I suppose I will either find the problem, which would be great, or eliminate the bores and move onto the head.

I don't suppose anyone knows what wear limit is acceptable for my bores ? its had a rebore at sometime and running with 0.5 oversize pistons.

I will let you know the results.

Thanks Guys, Ken

[warren3200gt]

Service limit is O. 1mm over bore size. So if its 0.5 over then service limit is 66.6mm.
A borescope isn't likely to tell you much you need accurate measurements not a visual inspection.
Measurements should be taken both L to R and F to B at three height positions.

Screenshot_20240910_083105_PDF Reader - Hi Read.jpg (73.23 KiB) Viewed 3048 times

[Kennyboy]

Warren3200gt, Thanks for the info. I did mean a bore gauge, not borescope. Either a typo or I had a blond moment

Ive edited my post.

Cheers, Ken

[Kennyboy]

I got the cylinder bores measured and they are well In tolerance. there was a stain on one bore, looks like it had been stood for a while and probably got moisture in through an open exhaust valve. Bores re honed very lightly and they are looking mint, no staines marks or scratches.

As the bores are in tolerance and looking good my next step was to fit new rings. Problem is the pistons are ART and I am unable to source any rings for them. It looks like I will have to replace the pistons as well, maybe IMD ones at £228 for 0.5 oversize.

The question I am asking myself is, if I'm going to spend £228 on a new set of 0.5 oversize pistons to replace the ART ones, should I get the 1mm oversize ones and get a re bore done done while its stripped ?

[warren3200gt]

Talk to Andrew at IMD. His pistons and rings are from the same company that the big four used originally. Art was the major supplier of pistons and rings back then to kawasaki so if his rings don't fit he should be able to advise where to get some.

[DeadZedDave]

Hello Kenny and welcome to the club forum.

Your own analysis in your o.p. seems logical and matches experience.

No evidence of blow by on the ring lands - normally you would expect to see some burned oil deposits if you had a cylinder bore / ring issue. (none visible in pictures)

Did you check the valve guides - as you mentioned ?
You wrote "My thoughts are that oil is getting into the bores from the head when stood. Could it be the valve guides themselves that need replacing ?"
Your thoughts could well be correct and this might well be the cause.
It would be good to think a new set of valve guide seals would solve the problem but from experience, this is not always the case.

As you have the motor disassembled again already it would make sense to check the guides - particularly the exhaust side judging by the deposits on the piston crowns.
There is a good explanation of how to check valve guide wear in the factory manual - easily done and maybe the answer ?
(also check for any burned oil deposits accumulating on the back of the valve heads - this can help identify the source of the issue)
Bronze guides in Z1 and 900 heads are known to wear more quickly than the later sintered iron guides used in the Z1000.

If the motor was not already disassembled, I'd have been inclined to go with what Zapo wrote - Back in the 90's I had something similar and aside upsetting the neighbours, no real harm was done (and I generally upset my neighbours anyway - so nothing lost !)

If it turns out that you need new guides then try to make sure the person doing the job knows what they're doing / is experienced fitting guides for old Zed's.
Its all to easy to get it wrong and end up with a list of other issues.

The "o" ring at the base of the cylinder liner should be replaced, obviously, but almost certainly is NOT the cause of the problem.

Dave

[Kennyboy]

DeadzedDave.

Hi Dave, Thanks for your very good comments.

If I can source a set of rings for the ART pistons I will replace them, no brainer for what they cost. Yes I need to check the valve guides and find a good engineer to replace them if necessary, I would be gutted if I rebuilt the engine, installed it and it still smoked on start up, never mind the cost of gaskets, etc !

One other point I should have mentioned in my O.P..... it doesn't seem to smoke when first started if left ticking over, it smokes like like hell though when I blip the throttle, or ride off with throttle open. It's like the wider the throttle the more it smokes. My thoughts would be the oil in the bore needs oxygen to be able the burn, the wider the throttle equals more air/oxygen and the oil burns. Until its gone, then no more smoke until its stood overnight.

Oh well, if a jobs worth doing, better to do it right first time.

Regards, Kenny

[Ultim8pc]

Note:
White smoke especially on over run - rings/bores
Constant light blueish smoke - valve stem seals