Z900 engine problems

[Phil50]

Hi All,

Back after a long break.

I posted some time back about some engine problems I had had. THe bike was totally rebuilt, bored out 0.5mm oversize. By a local chap who actually runs a motorcycle repair shop.

The bike ran fine except the carbs were from a Z1000, so it was not perfect.

A year later I had made enough money to have the bike the way I wanted it.

This involved stripping it down so Mr Smethhurst could do the case cleaning and refurb of all engine parts and boy what a great job he did.

I recommend him most highly.

Even after two winters the only tarnish is a bit of white aliminium oxide dust which washes off with clutch cleaner fluid.

Anyway an aquaintence from the past was requested to do the work of stripping it all down arranging the repainting of the frame and put it all back together.

This he did and the bike looked fantastic. However he seemed to think there was some inperfection with the re-bore I had had done before and had his "expert" re do the work. The resut of this was the bike now pumps so much oil into the carb airbox I have had to fit a small bottle to collect it!!!

The bike is un-ridable except for short trips

The starter motor managed to need new clutch bearings when they were working fine before the strip down

I have finally managed to obtain an original set of z900 carbs and the bike did run perfectly once I set them up myself but the oil and starter motor problem persists.

I would ask members if they have any clue why a z900 would pump huge amounts of oil out of the breather, other than the rebore was screwed up?


The other questions I would like to put to club members are

1)if you pay someone a lot of money to work on your bike and it is returned with two major faults on it do you think the rebuilder has a moral obligation to fix them at his cost and should he ignore reasonable requests for a solution.

2)What is the legal position here?

3)Is it decent or ethical to simply ignore emails and quietly steal away?



regards
Phil

[Garn 1]

Phil50, before looking at legalities...
I would say, if we can find a reason why you are getting oil in the air-box we may be able to find a solution for a fix, this may or may not be expensive!

There must be a reason for this...
Cracked head, inlet valve bent, rings in wrong way around (upside down).
There is another reason that escapes me at the moment, perhaps, someone can suggest it. It may be simple.... Possibly crankcase compression, check to see if oil entering into air-box via oil breather (check by running a tube from oil separator to bottle)

Your second problem .."need new clutch bearings".
Are you talking about the stater-clutch, which consists 3 rollers & springs, rolling on a large gearwheel boss that itself has a small roller bearing? Or the actual clutch bearing, which requires a case split?
The starter-clutch (3 roller) is usually a relative easy fix!

RegardZ.

[StephenW]

Hi Phil,
Sounds familiar, I had an engine rebuilt by a so called expert. The engine would not run. Was kindly resolved by a Z1 member.
Phil donot get dissheartened.
It could be a simple fix, just need a responce from someone more technical that I.
Good luck, it will be worth it in the end.

[weaver]

as far as the oil goes obviously make sure the oil level is not too high,should there be a small gauze type filter where the breather enters the air box? an increase in capacity will increase crankcase pressure,you could fit a breather to the oil filler.

[PAULJAC47]

Have you got a compression tester? if so check your cylinder pressures and post on here,sounds like a bit of a nightmare your having!

[Big Fluff]

2nd ring upside down could cause an oil consumption problem, but not the crankcase pressure problem.
More likely is that that there is now too much piston to bore clearance (through over-honing), resulting in increased ‘blow by’ past the pistons and in turn pressurizing the crankcase, thus pumping oil out of the breather.
Remove the plugs and try looking in the cylinders with a small torch (ideally an endescope) to see if there is any ‘pooling’ of oil on top of the pistons.

4 thou’ piston to bore clearance is really the max allowed.

Good luck, Will

[Mark Tiller]

Hi....how is your oil level? running it at the upper level could contribute to the oil in the airbox

[weaver]

2nd ring upside down could cause an oil consumption problem, but not the crankcase pressure problem.
More likely is that that there is now too much piston to bore clearance (through over-honing), resulting in increased ‘blow by’ past the pistons and in turn pressurizing the crankcase, thus pumping oil out of the breather.
Remove the plugs and try looking in the cylinders with a small torch (ideally an endescope) to see if there is any ‘pooling’ of oil on top of the pistons.

4 thou’ piston to bore clearance is really the max allowed.

Good luck, Will

could you explain the blow by a bit more mate? not questioning your diagnosis just interested to learn! and if this is the case would an extra breather alleviate the problem?
cheers

[Phil50]

Hi and thanks

some interesting comments.
The most promising seems to be the re honing that was done that is the problem.

A compression test seems to indicate 142psi to 148psi on all cylinders.

The oil level has been done on a level road with a spirit level on the top case.

The gauze square is present inside the air box.

The head was not damged before the rebuild nor the valves. The engine was perfect. The only fault the bike had was Z1000 carbs on it which made it run a little weak and it would not red line. The pull was a little strained.

When I fitted the Z900 carbs last year it pulled like a Z9 should!!
However the oil filling up the airbox was a problem.

The starter motor clutch seems to be the problem, the starter overuns a few seconds after start up.

thanks all

regards
Phil

[zman]

Have you done a vacuum test
I have had oil in my vacuum take off pipes recently.Turned out to be very high vacuum.once brought back to correct level not more problem

[z1bman]

compression is way too high which is causing excessive crank case pressure

[HowieD]

what is the compression supposed to be for a Z900 ?? this thread has a range of 128 to 156psi

http://www.z1ownersclub.co.uk/forum/viewtopic.php?p=120307&sid=43625e606249b3f4569e79a1d16afe20

[z1bman]

what is the compression supposed to be for a Z900 ?? this thread has a range of 128 to 156psi

http://www.z1ownersclub.co.uk/forum/viewtopic.php?p=120307&sid=43625e606249b3f4569e79a1d16afe20

standard compression for z1/ z900 is 121 psi

[HowieD]

standard compression for z1/ z900 is 121 psi

Ah ok - maybe a wrong base & or head gasket ? as well as the rings.

Top end strip down required then.

And I think the guys doing the overhaul should pay for it as it hasn't been returned as was expected.

regards
Howie

[PAULJAC47]

MY standard a4 displays 150 psi within a couple of psi across all 4 pots i have seen these motors run at 95 psi with no apparent problems, and have seen one notable tweeked example run at 185psi albeit with oil leakage problems.
though have seen the service bottom limit quoted as 100psi..