Need to rebore ? (KZ1000ST)

Hello,

I measured the cylinders of my KZ1000ST. I already asked for your opinion about the pistons, in that thread .



Here is a picture of the results:


The pistons are:
#1: 69.97 mm
#2: 69.96 mm
#3: 69.96 mm
#4: 69.96 mm

It's a KZ1000ST, standard bore = 70mm.

Here's what's written in the Kawasaki service manual:


Measuring the cylinders was so long! In fact, I had to take a lot of measures (more than 10 for each measurement), and average them. Some measures are really strange, how could they be less than 70mm?

Anyway, what's your opinion? I think the pistons should be changed, and the cylinders bored, but that costs a lot of money, and I would of course prefer just replace the rings.

The bike didn't smoke, BTW. Here are the compression, taken when the engine was cold :

Cylinder 1: 118 -> 134 psi (with oil)
Cylinder 2: 126 -> 143 psi (with oil)
Cylinder 3: 118 -> 135 psi (with oil)
Cylinder 4: 120 -> 120 psi (with oil)

The pistons aren't very clean...


Post edited by: Conti, at: 2007/04/10 13:20

Conti wrote:

Measuring the cylinders was so long! In fact, I had to take a lot of measures (more than 10 for each measurement), and average them. Some measures are really strange, how could they be less than 70mm?

Wow. :woohoo:

I think that's the most complete lead-in to this question I've ever seen....

The important dimension here is the one I didn't see; whether the bores are way out of round vs. spec.
Bores will wear slightly out of round for a number of reasons, but if they're close, there's a useful - and economical fix.

Anyway, what's your opinion? I think the pistons should be changed, and the cylinders bored, but that costs a lot of money, and I would of course prefer just replace the rings.

Well, you can *always* get new pistons and bore the jugs if that's what you want to do, but you didn't mention a reason why the pistons need to go, unless you do in fact bore it.

However, if the bores aren't way out of round, ball hone the bores, re-ring with new and put it back together.

The money you'd drop in pistons and boring would in that case be better spent on a valve job.

Done right, a ball hone, re-ring and valve job should bring the compression figures back up to in the 160+/-a little per bore value.

It'll run like a top and last a long time.

Conti:

I concur with the flying reptile...change rings and a simple hone to take off the glaze. Should be good for a long time after that:)

I think one of the issues is the use of the snap bore guage, they can lie to you, I would try and remeasuer the bores at 90 degrees part, and down the bore, looking for out of round.
the most wear is going to be at the top of the bore right under the ring pattern, the least is at the bottom of the cyl

That's right, snap bore gauges are really difficult to use. I don't trust them anymore. Unfortunately, I haven't any other tool to measure the cylinders and the out of round. To get acceptables measures, I really did take a *LOT* of measures.

What I notice are some figures (exemple: 70.19) which really exceed the service limit (70.10mm). Moreover, there's more than 0.05mm of difference between the measures.

However, as I said, the bike didn't smoke. I only rode 30km with it since there was a problem with the carburetors. However, I noticed it ran quite well sometimes (when the carburetors temporarily worked fine). I mean, the motor defintely had a lot of power.

Frankly, I would prefer to avoid having the cylinders bored and buying new pistons. Money is an issue here.

I thought it wouldn't be possible to reuse the standard pistons (which seem ok) in standard cylinders freshly honed. On the other side, I now do not trust entirely what is written in the service manual...

Do you think I risk to seize the motor by using it in such conditions? Sorry for the dumb question, but I'm quite new to this.

To bore the cylinders and buy new pistons costs a lot of money. Honing the cylinders, buying new gaskets and new rings cost far less...

Conti wrote:

However, as I said, the bike didn't smoke. I only rode 30km with it since there was a problem with the carburetors. However, I noticed it ran quite well sometimes (when the carburetors temporarily worked fine). I mean, the motor defintely had a lot of power.

Not sure why you pulled the head off in that case - the "...if it ain't broke..." skool of thought.

I thought it wouldn't be possible to reuse the standard pistons (which seem ok) in standard cylinders freshly honed. On the other side, I now do not trust entirely what is written in the service manual...

Service manuals are written to exemplify what is *proper* to do, not what is *possible* to do.

Myself, along with a gang of others herabouts, have done that exact procedure a bunch of times, and it's quite effective.

In fact, if you'd kept track of which rings go to which pistons and where, it's entirely possible to re-assemble the whole mess in reverse order, lube well and expect a reasonable amount of life from the motor.

But, since you're waist depp in the Big Muddy, I'd go for the hone/re-ring/valve job - do it now, do it once, and be done with it.

Do you think I risk to seize the motor by using it in such conditions? Sorry for the dumb question, but I'm quite new to this.

Lube. Loob. LoooooobE.

ADDENDUM:

While you're in there, might as well freshen up the top cam chain guide, rollers and idlers while you're at it. Those are the most abused parts in the top end maintenence-wise, the biggest pain in the neck when nothing else is wrong, and at your stage of the game, the easiest pre-emptive fix to make.

Do it now, do it once, and be done with it.

Post edited by: Pterosaur, at: 2007/04/10 15:23

Thanks for sharing your experience, Pterosaur

Pterosaur wrote:
Not sure why you pulled the head off in that case - the "...if it ain't broke..." skool of thought.

Yep, I already heard about that school.
I opened it to know the condition of the motor. I didn't get any information about the bike when I bought it. The guy who sold it bought it more than 5 years ago, rode with it 1 month, and put it in his garage up till a few months, when I bought it. He didn't himself asked any question to the guy who sold it before. All I know now is that the bike is "legal", I mean, it wasn't stolen at any time.

In fact, if you'd kept track of which rings go to which pistons and where, it's entirely possible to re-assemble the whole mess in reverse order, lube well and expect a reasonable amount of life from the motor.

I carefully stored the parts. I could reassemble the rings at their position. However, I plan to change them.

But, since you're waist depp in the Big Muddy, I'd go for the hone/re-ring/valve job - do it now, do it once, and be done with it.

I'm taking care of the head too.

While you're in there, might as well freshen up the top cam chain guide, rollers and idlers while you're at it. Those are the most abused parts in the top end maintenence-wise, the biggest pain in the neck when nothing else is wrong, and at your stage of the game, the easiest pre-emptive fix to make.

Do it now, do it once, and be done with it.

Yep! I looked at those parts. The top guide was in a bad shape.


However, I was quite surprised to see the other parts are in a very good condition. I'll change the top guide, the chain, and some small bits too.

I'll have some other question about the top head, I'll ask in another thread.

You're welcome, Conti

Looks like you're making the right moves and are well on the way to owning a motor that'll run smooth and long.

Congrats.

Making good measurements is critical. If you are unsure about your measurements, take the block to a machinist and let him give you measurements for the different orientations. They understand cylinder bore ovaling so show them where the suggested measurement locations are and then let him tell you if you are within service spec on the piston to bore clearance. My gut feeling is that you should just re-ring and hone but I like to have good measurements. Your compression readings bear our my gut feelings but if you have the thing apart, let a pro do the measurements if you are not comfortable with your own... especially since you "averaged" the measurements which isn't really good.