The 'build thread' of a Kawasaki Z250 C, a total beginner's point of view...

sham

New Member
Hey teazer - I'm planning on getting a proper leak down test and getting the engine honed - what do you think? Then replace all the gaskets etc.
Not sure if I should just take the engine apart myself as there are a lot of special tools I need ie. to take the piston out, various tools to measure things which I don't have.

I would just replace the gaskets, but I'm thinking while I'm there I may as well? Just to have the piece of mind. There's a mobile mechanic advertised on gumtree who says he'll do any engine work for $100 as long as I supply the parts. Thinking it might be a good opportunity to learn and ask questions?

Managed to replace the fuel tap gasket and "rebuild" the petcock. The leak was from a dodgy strainer, which had come off from the O ring and mangled that as well. For future reference, the fuel tap gasket which fitted my Z250 C gas tank cap ended up being the 51059-008, the same one for Z900/1000's.





Even got new washers!


The crankcase vent.

So its the cam chain tensioner and engine work next. I think I will get a new spring just in case, though reasons for it breaking may have been because I installed it incorrectly resulting in the cam chain being over tightened. Not sure how this may have been as I thought I installed the tensioner in the loosest position.
 

sham

New Member
Can anyone confirm which spring tensioner part I should be using for my kz250?
After thinking that I had ordered the wrong part, as the one that arrived in the mail was 5mm longer than the service limit, I believe that my part number is correct and I was either sent the wrong part, or the microfiches have the wrong part number one them.

The part I believe I should be using is 92081-1105 Spring Tensioner.
 

sham

New Member
Here's the reply from Z1's Rob:

The 92081-1005 spring was originally used as a throttle stop screw spring on KL250-A and KZ400-A, D and S models. On the 81 KZ250-D2 however, the spring was used as a tensioner spring.

Reviewing the 80 KZ250-D1 and 81 D2 cam tensioners on fiche, the tensioner components, except the tensioner spring, are the same between both models. I suspect, Kawasaki was experiencing issues with the 92081-1105 tensioner spring on the D1 model and found the characteristics it was looking for in the 92081-1005 throttle stop screw spring. Hence the change.

Unfortunately, I’m unaware of any documentation providing specifics of the 92081-1005 or 1105 springs. As the 92081-1005 spring is not available through Kawasaki or our network of dealerships, you’ll have to locate the spring through other channels, Ebay, craigslist.org, online parts search of the OEM part number, etc. Once you locate the spring ask the holder if he can provide whatever specs he can of the spring.

If the manual in hand covers the 81 model. The information may be indicating details for the 1005 spring rather than the earlier 1105 spring.


My manual definitely covers 80-82. If its the case that the specs detailed is for the 1005 spring, yet the 1105 spring was used before hand, then perhaps the 2mm excess isn't that big a deal? But my cam chain tensioner did break...

Have looked at the 1005 part for sale on ebay - the number of coils are different from the picture shown in the manual, but I have emailed for confirmation of free length.

If anyone has any additional information that would be much appreciated.
 

sham

New Member
Ok think I have got to the bottom of this cam chain tensioner business.
Looked into putting the new cam chain tensioner on yesterday, and, after a big struggle to remove the tensioner collar (had to sand down a side before tapping it out) managed to put the new one on.

That's when I realised the adjusting bolt was again not fitting properly - this had happened on the original one, but seeing as the hole was kinda messed up, I attributed it to that. Turns out my "adjusting bolt" is just a random bolt which has been cut down to size, with similar threads but not quiet...

So I believe that's the main culprit to the cam chain tensioner splitting, seeing as it wouldn't have been capable of handling the same loads.

Took off the top end and cylinder block today, which was quiet fun. I've gone through the manual looking at the various tools I'd need to disassemble and reassemble, trying to gauge whether to get a mobile mechanic to come do the job or if I could do it myself. It costs about the same to get the tools, but the different procedures for removing and checking the valves seem to suggest that a pro should do it. Also will have trouble tightening the cylinder base and head bolts to the right torque as the torque wrench won't fit...

Regardless, wanted to take the top off to get it to the machinist, to get it honed and leveled. The state of the gaskets and O rings weren't fantastic, and I think that is definitely related to the low compression I'm getting. Found one of the O rings from the cylinder head chewed up and lodged in the bolt passage. The large O ring around the cylinder also had holes through it, though I assume I can check with my new one (I assume I have one in the gasket/o ring set) to see if that's normal. The gaskets between the cylinder head and block, and block to crankcase were also a mess - flaky and breaking off immediately upon removal.

So lots to do in terms of going through the maintenance section and doing as much as possible, getting the block honed head leveled if necessary, and getting a pro to do the rest. Will start by cleaning the carbon off the combustion chamber.

Don't want to get into the crankcase if possible, hopefully the mechanic will look at it.






ps. used the Y shaped attachment from the paddock stand to push out the piston pin. Fit perfectly.
 

teazer

Well-Known Member
DTT BOTM WINNER
Some gaskets stick to both sides and others crack and are reasonably easy to remove. That piston has a ton of blowby. Have someone accurately measure the barrel and tell you if it needs a rebore and new piston or just new rings.
 

sham

New Member
Thanks teazer - had to google what blow by is - its one of the first terms that actually turns up with results. Can you clarify what the signs of excessive blow by are on the piston? Ive read that visually its the excessive amount of combustion gas past the piston rings - is that just the black soot?

By the sounds of it, after checking with the machinist I should also open up the crankcase and have a look then, seeing as the excessive fuel/air from the combustion chamber which has leaked into the crankcase would have affected the motor oil and may have caused damage?

All this makes the crankcase vent seem like a much more important function than I first imagined. Do many people route it back to the intake or is the crankcase vent filter enough. I did read that the issue with these are that once they get clogged there's no where for the exces gas to go...was thinking I'd just check it often enough but perhaps that's not the most reliable idea.
 

teazer

Well-Known Member
DTT BOTM WINNER
I wouldn't split the bottom end unless you have a reason to do so.

You got it right first time. Al that black stuff on the piston that has blown past the rings. That indicates rings that are not sealing. The rings may have lost their tension or the bore may have worn so that the clearance is excessive. A quick way to check is to put the piston into the bore and slip a feeler gauge blade in between the front of the piston and the bore. Stock would be around .002" and wear limit is probably around .006" or so (check the manual).

If yours is more that the wear limit it needs a new piston and rings and probably a rebore. Places like Bert Kingston Honda in QLD used to be good for that sort of service but I have no idea who to go to now. Ask your local dealer who they use for rebores.
 

sham

New Member
Thanks teazer,

I've been in contact with the guy from MMT in Granville, who was recommended by one of the old guys at MCA. Planning to clean up the cylinder head and block/piston a bit and then send it down to him for a check. Hoping I can also get him to check my valve and valve seals.

As for the bottom end, the main reason for opening that up would just to be to check its condition seeing as the information I found relating to blow by said that damage could have been caused? I think there are also a couple seals there which I could replace with the kit I got. Do you think that's necessary? From the manual it looks quiet serious and I don't have access to tools like the rotor puller and holder, but I'm thinking seeing as I have the top off already and planning to do it right, may as well clean out the bottom? If I do so, I'll probably get a mechanic to look at it as well.
 

Erskine

New Member
Mate, you have the perseverance of saint! Just wtf is the back story of the bike? Did the PO strip it and then try to rebuilt it blindfold? There has just been one thing after another.
I would have surrendered and got another engine by now!
 

sham

New Member
Erskine - thanks but you're probably mistaking my slow work rate and inexperience to perseverance :p

Anyways, tried to clean up the piston and combustion chamber a bit today. Scrapped the carbon off with a bit of bark and cleaned it with methylated spirits.





Also checked whether the cylinder head was level or not, and checked the clearance between the bore and piston. Level is fine, but the clearance exceeds the .058mm listed in the service manual...

Will take it to the machinist soon - so rebore and new rings isn't enough? Don't really want to get a new piston...the piston 130011037 is already a discontinued part, but I assume I will also need a larger one?
 

teazer

Well-Known Member
DTT BOTM WINNER
.058mm is a tiny clearance. It's .0015" or 1.5 thousandths and that's really tight. Have your machinist check it with bore gauge and micrometer. If the bore is worn it needs to be rebored to match a new piston and rings.

The head can be stripped and cleaned and it's OK to use a wire brush on it. To check the valve seats you can leave it upside down and pour some kero into the bowl there and wait to see if it leaks down the ports past the valves.

To remove the valves, you need to beg borrow or steal a valve spring compressor. They are not expensive. Read up on that process before you start. Carefully collect all the parts and then you can clean the valves and inspect the seating surfaces. If you machinist quotes you a number to strip and build the head that's less than the cost of the tool, then that's an option.

It's very unlikely that the small amount (relative to the article) of blowby would cause any real damage. if you have to strip the bottom end to replace leaking oil seals that's a different story. Some seals can be removed with a wood screw and pressed back in without a complete strip. Others, like say the gear shift shaft are sometimes too awkward and require the removal of the clutch assembly to get the shaft out. I wouldn't advise you to strip the bottom end unless you either want to or need to do so to fix a known problem on that motor.

If it were mine, I'd strip and clean and check everything, but I have built dozens of motors and I like buying tools. :)
 

4eyes

Active Member
DTT BOTM WINNER
Look on the bright side, now you know, what all goes on inside that engine. ;D
By the time you get it finished, you will know it intimately. 8)
 

sham

New Member
Thanks guys - the bright side wasn't so bright in the end.

I ended up taking the cylinder head and bore to the machinist at MMT, who was a really cool guy, showed me around the workshop and let me watch him work a bit. I asked for them to remeasure the clearance as you suggested teazer, and told them about the discontinued piston. They tried to do a very light hone but in the end, the clearance went to .10. I also left new alive seats with him and he replaced and reseated them - that seems fine.

So all of this is now ready, it cost 275. It seems reasonable but i was expecting less. A hone was only going to cost $10 a hole, but i understand more time would have gone into this. I believe 110 was for the new piston and rings. But for around 80 I could have got a valve spring compressor, rotor puller and holder...

I guess my question now is having spent so much on the top half, is it worth just letting him check out my crankcase just incase? I don't feel like having the top ruined by some random debris that might have fallen in, even though I've covered it with a cloth and glad wrap...there are also the seals I want to replace.

Will call and get a quote. I guess the annoying part of this is that they're only open weekdays so I don't actually get to learn.
 

sham

New Member
So have asked the machinist about the bottom end but he has no time anyways. He's offered to have a quick look at it for me when I pick up the front end but which sounds pretty generous to me. Busy taking the bottom off now - ran into some issues with stripped screws, so I think I'll get a new set for the motor.

Hopefully will have a roller soon. Looks like it's gonna be a long project.

Ps, also found out one of the guys at work has an old DT400. So tempting...
 

sham

New Member
Ok, so even taking the bottom end off the bike is turning out to be a lot more challenging than it first sounded. Another saga of the stripped screw, this time on the chain cover...


Here's it is, before I tried angle grinding a slot into it to fit a flat screwdriver into it...might have to look into using a screw extractor, but I have a feeling its too stripped for that? Might have to get a friend to weld a nut onto it? Any ideas?


Also how do I detach these? I thought it would be like the 6 pin connector on the CDI, but I can't seem to pull it apart? Is it just a housing and I should be pulling on the wires instead?
 

Erskine

New Member
sham said:
Looks like it's gonna be a long project.
A long project? Whole empires have risen and fallen since you started this project .........
all you need to do is add a 'built by a teen' suffix to the title ;) :)

Let's face it, your engine must have been built on a Friday afternoon just before the factory knocked off for a public holiday weekend, by trainees, out of the bin of rejected parts, because the supervisor couldn't be bothered to go to the stores to replenish the racks because he wanted to get off sharpish and beat the traffic?

If only bikes could talk!
Is there anything that has actually been straight forward?
Your dogged perseverance is a triumph of patience over a sledgehammer :)
 

JJ

New Member
G'day Sham.
I've been reading this thread with great interest, I have a Z250C that I did a "quick" rebuild about 5-6 years ago and gave to my old man for a run around.
He has since bought an XVS 650 and handed it back, so now I'm going to "Cafe" it for my young bloke to learn on.
I do all my own work, and it gives you great satisfaction seeing a project you have done yourself.
With that screw, try getting a small cold chisel (cheap as at Super Cheap) and tapping on one side of the head anticlockwise, it should let go fairly easily.
 

akcender

New Member
After stripping multiple phillips screws during my build i started to use an impact driver with a phillips head bit on it, as long as you make sure it is grabbing properly it will take it off with no problems. But dont hit it too hard because then it'll break and you've got an even bigger problem on your hands.
 

4eyes

Active Member
DTT BOTM WINNER
akcender said:
After stripping multiple phillips screws during my build i started to use an impact driver with a phillips head bit on it, as long as you make sure it is grabbing properly it will take it off with no problems. But dont hit it too hard because then it'll break and you've got an even bigger problem on your hands.
^^^^^THIS!!! FYI the screw is not a phillips it is a JAP # something, which is the reason they all get stripped to start with. Get an impact driver and some JAP inserts and it is amazing how easy stuff comes apart.
 

BLSully

New Member
I feel your pain Sham....it's hard enough to work on these bikes without a full workshop, and then you start dealing with soft screw heads stripping, etc.

Other's have already pointed out the impact screwdriver and jap inserts.... I'd like to throw my vote in for a nice set of stainless hex-head bolts for when you put it back together.

Sorry I couldn't find em on Z1... here's an fleabay link though

http://www.ebay.com/itm/Stainless-Steel-Bolt-Set-KZ250-81-NGSS-854-/221139850918?pt=Motorcycles_Parts_Accessories&hash=item337cf656a6&vxp=mtr
 

DTT Bike Of The Month Gallery

DTT Light or Dark

japan.webike.net
www.cognitomoto.com
https://www.townmoto.com
www.speedmotoco.com
www.jadusmotorcycleparts.com
www.lostapostle.ca/
www.sparckmoto.com
Top Bottom