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Discussion Starter · #1 ·
I started tearing down the motor last week and one piston is so rusted in that I might have to cut it out. With that in mind i started looking for pistons and went into shock at the prices (not to mention rings and wrist pins).
I might have been looking in all the wrong places but the prices I found are more than I could have them custom cast for me. Is there a place that sells these at a reasonable price?
 

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Discussion Starter · #3 ·
I fully understand aluminium does not rust..and I understand it's the rings to the sleeve. And when the rings rust to the sleeves and mess them up I normally go to an oversized piston. Which is why I'm looking for a source for a good price on rings and pistons.
Based on what I've found it's not worth rebuilding the motor and I hate to just trash any old bike.
 

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Discussion Starter · #5 ·
If the bike was in great condition I wouldn't mind spending bucks to get her running, but it's not. I only have $200 in it (took it off a neighbors hands to see if it was worth fixing). If I were to restore it, it would cost way more than it would be worth.
I've restored a lot of british bikes and harleys and have to admit that I was somewhat shocked to see the prices on KZ's parts. I do have other JAP bikes but I bought those new and I take care of my stuff so I've never had to buy many parts.
I did find the Wiseco and it was a little over $100 per hole and when you add to that another $40 (per hole) to bore it seems like a lot. I did my '65 Matchless last year and the oversize pistons, rings, wrist pins and clips were just under $50 (per hole) - plus the $80 to bore 2 holes. Same deal with my 1972 Triumph Daytona. Got them from JP in AU.
Once I get the pistons out (down to 1 being stuck) I'll see what condition they are in and it might be that I only need rings if the sleeve can be honed or I can have it re-sleeved.
Guess I'm just cheap.
 

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well with as many kz650s as there are, you can most likely find a good running none titled bike much cheaper then the cost of the parts to fix the one you have.
 

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I fully understand aluminium does not rust..and I understand it's the rings to the sleeve. And when the rings rust to the sleeves and mess them up I normally go to an oversized piston. Which is why I'm looking for a source for a good price on rings and pistons.
Based on what I've found it's not worth rebuilding the motor and I hate to just trash any old bike.

Sorry man, misread your post, guess I had one too many last night.

As for the stuck piston I´ve heard of people having good luck with filling the cylinder with diesel oil and let it sit for a couple of days or more, it´s worth a try.

Or how about this on ebay.
 

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Discussion Starter · #8 ·
No prob. onkelb. I managed to get it to break free last night. Lots of PB Blaster for the last month and since I knew it was on the downward stroke I made a press (like a wheel puller) and had pressure on it for the last few days. I'll pull the jugs tonight and see how the sleeves are. I also called a friend who has a small bike repair shop and he has some jugs from a 78 KZ650 that he said looked good.

I appreciate the link. I never have luck on ebay but I might give it a shot.
 

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The Cruising Gunsmith
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I fully understand aluminium does not rust..and I understand it's the rings to the sleeve. And when the rings rust to the sleeves and mess them up I normally go to an oversized piston. Which is why I'm looking for a source for a good price on rings and pistons.
Based on what I've found it's not worth rebuilding the motor and I hate to just trash any old bike.
index

I just bought oversize pistons/ring sets for my 1979 KZ750 for $36 per set piston and ring (which is about 1/6 OEM price). Parts look exactly like OEM and had Kawi part numbers on the boxes.
 

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Discussion Starter · #10 ·
index

I just bought oversize pistons/ring sets for my 1979 KZ750 for $36 per set piston and ring (which is about 1/6 OEM price). Parts look exactly like OEM and had Kawi part numbers on the boxes.
Thanks. I emailed them and just received a response that none are available. Just my luck.

But I took it apart tonight and the sleeves look great, only 1 piston had compressed rings. So it looks like all I'll need are rings and clips. I'm impressed by how clean the bottom end is, guess Kawa makes some good stuff. Now if I can just hunt them down.
 

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The Cruising Gunsmith
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Thanks. I emailed them and just received a response that none are available. Just my luck.
Bummer. I checked their site and found ring sets only for the 650, didn't find the sets with both pistons and rings. The pistons you have might be serviceable?

Just looked again, they do have ring sets for the 650 but they are the "third over" size, not standard size. That is a size about 0.015" diameter larger than stock. If push comes to shove, it is possible to use oversize rings by filing the ends off a bit until proper end gap is obtained. The ring will "size itself" to the inner wall of the cylinder. Using oversized rings to tighten up compression in a worn engine is an old trick used many times, but you must trim the ends to get proper end gap (typically about 0.012"). You just set the ring inside the cylinder sleeve and check the gap with a feeler gauge.

But I took it apart tonight and the sleeves look great, only 1 piston had compressed rings. So it looks like all I'll need are rings and clips. I'm impressed by how clean the bottom end is, guess Kawa makes some good stuff. Now if I can just hunt them down.
If you absolutely can't find stock ring sets anywhere, you may have to go with oversize rings cut to fit. The third over sets are listed as: CW58-2220

vintage pistons
 

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Discussion Starter · #12 ·
If it wasn't for bad luck, I wouldn't have any luck. Found some rings on ebay, outbid at the last second (actually 3) by $2.50.

I started looking for some oversized pistons and rings and thought I had them, from a dealer in Indiana. Got a call from them today and they were wrong, they didn't have them.
The guy told me that Kawasaki has a strict 10 year rule. Nothing is made for bikes after 10 years. Scares me a bit when the manufacturer thinks their bikes are crap after 10 years - they could be right.

There are a bunch of big bore kits out there but the price is much to high for this bike since it needs so much to make it right.
 

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The Cruising Gunsmith
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If it wasn't for bad luck, I wouldn't have any luck. Found some rings on ebay, outbid at the last second (actually 3) by $2.50.

I started looking for some oversized pistons and rings and thought I had them, from a dealer in Indiana. Got a call from them today and they were wrong, they didn't have them.
The guy told me that Kawasaki has a strict 10 year rule. Nothing is made for bikes after 10 years. Scares me a bit when the manufacturer thinks their bikes are crap after 10 years - they could be right.

There are a bunch of big bore kits out there but the price is much to high for this bike since it needs so much to make it right.
Actually, it is federal law that mandates vehicle manufacturers must make parts to keep them going for at least ten years. That doesn't mean they stop making parts then, they just aren't required to. I just saw a 750 twin valve cover gasket at the dealer which could not have been more than a few years old, and those bikes have been out of production for about 20+ years. You'd be surpised what parts are hanging around, and the good news is: metal parts don't age and go bad like rubber parts and gaskets do.

Before you get too depressed... my 750 twin is 29 years old, and they made a lot fewer of the twins than the four bangers. Even so, I just found another new set of +0.50 pistons and rings on e-bay for it.

The KZ650 was pretty popular and I would not be surprised if there are NEW piston/ring sets around. But, given your cost limits, a bore might be too expensive. My shop charges about $75/hole, so about $300 to punch four sleeves. You might not need that.

I don't know the condition of the pistons you have, they might be servicable if you clean them up. They are aluminum so vertical ring groove wear is their wear point. If the bike is relatively low mileage, they might be OK to use. use some chrome polish and a toothbrush and give them a rub.

The cylinder walls are another issue. If they are rusted, and if it's only surface rust. It's possible you could hone the cylinders and install a new ring set and run the engine a whole bunch of miles.(?) I couldn't tell you how many cars have gotten the "ring rebuild" to get another 30k out of them before they get junked.


If you want to check the cylinder walls, get some #400 and #600 wet/dry sandpaper and light oil and sand them a bit and see if they clean up. If so, a hone might get them good enough to run again. JC Whitney had a nice little hone for about $20.
 

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Discussion Starter · #14 ·
Thanks bounty. The cylinder walls look good, I have a hone but I don't have a bore gage to properly check it. The pistons don't look bad and cleaned up very well - except for 1 that I can't get the top ring out off (yet). And I picked up the '78 jugs from my friend.

I normally like to go up to the next size piston when I do a rebuild.
I guess I'm just spoiled from all the Brit bikes I've done. No problems finding pistons for them (I just finished a 1940 last week) and the prices are so much better. Come to think of it I didn't have a problem with my 24 year old Honda.

I'll just keep looking for a "deal" until it comes along.
 

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The Cruising Gunsmith
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Thanks bounty. The cylinder walls look good, I have a hone but I don't have a bore gage to properly check it.
You can check the wall wear by finger feel, slide your finger down the inside until you reach the end of the area where the rings ride and you will see the ridge. It's probably not bad. Engines will tolerate a fair amount of play between the cyl wall and the piston, as long as the rings are good and fit the piston grooves well (That's where most of the blow by actually occurs). You can probably give it a hone and roll.

The pistons don't look bad and cleaned up very well - except for 1 that I can't get the top ring out off (yet). And I picked up the '78 jugs from my friend.
You may want to check the manual and see what the clearance specs are on the ring to groove, that fit has to be tight. That's how you will know if the pistons are worn. They are probably OK.
 

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Discussion Starter · #16 ·
Bounty,
Several people have mentioned buying larger rings and filing them down to work on standard pistons. I can't wrap my head around this. I found some s 1.00mm (4th over). Is this possible?
Thanks
 

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The Cruising Gunsmith
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Bounty,
Several people have mentioned buying larger rings and filing them down to work on standard pistons. I can't wrap my head around this. I found some s 1.00mm (4th over). Is this possible?
Thanks
It is definitely possible and is done often. The added 1mm is an extra diameter of about .040"

That means the ring's length will be about that number (multiplied times pi) too long when the cylinder compresses the ring into a circle. So, you would need to file about 0.12" off the end of each ring. The proper "end gap" on a piston ring is about .003" - .004" PER INCH OF PISTON DIAMETER. So, a 2" diameter piston will need a ring end gap of about .006" to .008". This gap is essential to allow the ring to expand as it gets hot. You just file the end, set it inside the cylinder and keep trimming until the end gap is right.

An oversized ring will be a little looser fit on the piston when free and out of the engine, but will be forced down to the same size when inside the cylinder. I doubt there is a whole lot of added stress by squeezing it an additional .040"

You might have to take a little more care when you compress the rings to install them since they are larger and might snag an end on the piston. Compress the strap by hand until all the rings are set well in the grooves and then clamp on the holding pliers.
 

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Discussion Starter · #18 ·
Thanks Bounty. I ordered the oversized rings and will give it a shot. The good thing is a buddy of mine has a ring file that I can use - he builds race motors. The better thing is, he is such a perfectionist that I know he will insist that he file them for me - he also owned a machine shop for 20 years.
 

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The Cruising Gunsmith
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Thanks Bounty. I ordered the oversized rings and will give it a shot. The good thing is a buddy of mine has a ring file that I can use - he builds race motors. The better thing is, he is such a perfectionist that I know he will insist that he file them for me - he also owned a machine shop for 20 years.
Good deal, when I did my engine rebuild last month my only allies were my droplight and my shop manual.

The only thing I would say to take extra care when installing the cylinder onto the pistons. Hopefully, your buddy has ring compressors. That's the only dangerous part of the operation as rings are made of very hard (brittle) steel and I somehow managed to break one. But, two sets of hands will make it MUCH easier because you have to wrangle the compressors, pistons and lower the cylinder onto them all at the same time.

If you have an experienced cohort, success seems inevitable.
 
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