Piston/rings 1985 kx500

[Zack]

Hello again guys

Things are going well with my transmission/ shift drum issues. I will be updating that thread here soon.

I am currently looking for a piston for my 1985 KX500. It seems I have read somewhere that the 1983/1984 pistons were very similar to the 1985 piston. Maybe the difference was a couple extra oiling holes? Anyway, can anyone confirm this info? Would be nice since it seems parts are rather scarce for the ‘85.

https://www.ebay.com/itm/NOS-Kawasaki-1983-1984-KX500-Standard-Piston-Kit-Set-05-6941-w-Rings-Pin-Clips/190840376679?epid=869556976&hash=item2c6ef90d67:g:vzgAAMXQuu9RlCCV

The piston that was in my engine was a RC brand. I see there are a few of these brand pistons available on eBay. Some even as a kit. Is this a piston that would be appropriate for a recreational-use KX500?

https://www.ebay.com/itm/KAWASAKI-NOS-ROCKY-PISTON-KIT-KX500-STD-1985-05-6949/372685290769?hash=item56c5c63d11:g:iFAAAOSwEZdZ~Uqt

I am considering a nos oem piston as well. There are a few available on eBay for $150ish. But rings seem to be hard to come by. Do some aftermarket rings fit the oem piston? Suppose the best way to tell would be to compare measurements?

Thanks for your help.

[KXDINO]

Dont get it if you cant get a replacement ring saparate as you need to change the ring  sooner than a 2 ring design otherwise grenade it self ,on my kx125 08 i do a change of ring at 9 hrs then at 18hrs a piston and ring to keep the bore in good shape and that useing a wossner piston .Of course you can double that on a 500 with a piston kit for recreational use but i be keeping a close eye on it , warm it up slowly and make sure you use at least 95 or more octane fuel and have no pinging what so everThere can be differances between oem and aftermarket rings so be carefull ,83-84 engines were air cooled and 85 water cooled so even if they fit there could be differances in material etc etc.

[sandblaster]

A Wossner 86-04 KX500 piston will work but it has a smaller dome than the 85 piston.
To fix the issue you can change the head squish and combustion area to a modern design.
Tom Morgan Racing in the USA has a head cut that is perfect.

On the drum, did you find that 83-85 are the same?

[Zack]

This eBay ad explains a little about the interchangeability of the ‘83-‘84 piston and the ‘85 piston.

https://www.ebay.com/itm/KAWASAKI-NOS-PISTON-STD-SIZE-13001-1199-KX500-1983-84-85-A1-A2-B1/193366087574

To save you guys the trouble of opening that link, the seller says in the description
“ N.O.S Standard Size Piston  13001-1199 .. Prior  13001-1088 .... FITS KX500-A1/A2 & B1  The Superssesion -1199 Replaced the -1088 and dose not have the small hole in the Skirt   R1/4R”

So is this may be factual information?

I think I would prefer to install a cast piston for longevity purposes. Again, this is a kx500 for recreational use.

I have emailed Tom Morgan about cylinder head modification as a backup plan. I am currently waiting for a response.

[sandblaster]

I have a old 85 piston in storage.
I do not think that it has a hole in the skirt.
The 85 does have holes in the wrist pin boss area and the Wossner does not,
However, the wossner has oiling grooves in the boss area making the holes redundant except under extreme conditions.
I drill holes in the boss as well as in the skirt.
But I have been known to be abusive at times... 

[Zack]

I suspect one could use the ‘83-‘84 piston in the ‘85.

For my ‘85 KX500 I did decide to swap to the ‘88-‘04 piston. My cylinder is bored to .5mm oversize already so my hope of installing a standard size cast piston is a no-go. My cylinder is being cleaned and plated for a .5mm oversize wiseco piston and I am expecting things to work out just fine.

I did contact Tom Morgan about the suggested modifications to the engine when swapping to the late KX500 piston and he priced the work at $129. Tom told me he needed only the cylinder head to do the work. I have heard of guys doing this piston change without doing the head modification and never missing the potentially lost power. Since it is only the cylinder head to remove, I believe I’ll try it as-is and make a judgement after I ride it- if I need more power I intend to send the cylinder head to Tom.

 Anyway, the cylinder and piston should arrive in a couple weeks, I expect to ride the big kx again shortly thereafter.
I will keep you guys in the loop.

[sandblaster]

I think that the guys who said it did not affect the power had worn out engines.
I've seen that statement more than a few times.
With a fresh bore, piston, and rings I'm sure it felt just fine.
Let's look at Approx piston dome cc's.
Wiseco 3.25cc
Wossner 3.9cc
Stock 86 double ring 18.5cc
Stock 85 single ring 14.5cc

You can swap any of them around with the correct head and or cylinder cut.
But to think you can drop in a 3.25cc piston dome in a bike that was made for a 18.5cc piston dome and not loose any power...
Well... I could find some bridges to sell you 

[Zack]

Thanks for the piston dome cc!

Well lost power to be sure.
I wonder if a recreational rider would ‘miss’ said power though.

If the cylinder head mod is only to mill down the head to restore lost compression (~11.25cc worth) then I could likely perform that job myself.
I thought the job might Include setting a squish band angle on the head as well as fix lost compression.

Does anyone know what the cylinder head mod actually consists of?

[sandblaster]

Yes, the squish and dome has to be completely re-done.
Every .010" of height you remove from a 86mm bore is approx 1.5cc

[Zack]

Update

I got my engine back together. It is currently assembled with the 86.5mm wiseco piston.
I opted against the cylinder head modification for a few reasons, the main reason being impatience.
The engine runs great! Engine compression is on the low side of useable- 130 psi. But certainly much better than the 100psi it had before the rebuild
I honestly can’t complain about the engine at all. Starts pretty easily, idles nicely, revs out nicely, plenty of power.
I still have the cylinder head mod in-mind for later, maybe late this year. For now, I intend to enjoy my kx500.