1988 & older VS. 1989 - 2004 : Engine Performance | Output Shaft Nut | Swingarm

[manco]

If this is something already covered I am sorry to bring it up again. I did some reasearch and haven't found as much engine performance charcteristic comparison info as I was hoping for. If anyone has any solid input I would appreciate it.

I have recently found myself in possesion of two KX500s. One is a 1987 the other is a 1998. The 87 has the older motor, the 98 has the newer one of course. I have ridden the 98 at the track a bit and it runs pretty good. I just aquired the 87 and haven't had a chance to take it out yet. When fired up in my shop the 87 seems to sound a bit meaner though. It could be the sound characteristics are that my 98 is running lean with an airbox, stock carb, Fatty pipe & a freshly packed FMF TurbineCore while the 87 is running rich with a Mikuni, no air box, a rag for an airfilter & a stock pipe with a performance silencer that needs repacked.

When I get both bikes out for a spin I will have a better overview of the two engines. In the meantime I was interested to hear what others thought on the two different motors. Is one better suited &/or does one outperform the other under various conditions? MX track vs trails vs drag strip? Is there much difference between the two motors?

Another few questions I have are about the output drive shafts on the two motors. The 87 has the old lock nut style output shaft and the 98 has the newer snap ring to hold the front sprocket. The reason I ask about the output shafts is that my 87 is missing the obsolete drive sprocket lock nut. A custom nut could be made I am sure though I would rather purchase one if something is avaliabele. Is there a known readily available nut that can be purchased to fit the 87 output shaft? I am also wondering can the output shaft in the 87 be swapped with a snap ring output shaft from a newer motor?

Also once the suspension changed to the newer style without the rod is the swing arm interchangable then from 1987 - 2004?

Thanks for any info you have.

[manco]

I found the info I needed on the output shaft sprocket nut here at this thread. http://www.kxriders.com/forums/index.php?topic=11819.0 I am gonna go see if the hardware store has a M24x1.0 that will work.

Still wondering about swapping the output shafts between motors.

[RoostiusMaximus]

i've checked the assembled lenths and the -1988 set is wider than the 89+

[dave916]

i've checked the assembled lenths and the -1988 set is wider than the 89+

I guess u mean  pre88 is wider than 88+ as 88 has circlip

[manco]

i've checked the assembled lenths and the -1988 set is wider than the 89+

Can you clarify what you mean by "...set is wider" Are you talking about internal differences or external differences?

Externally the 1987 & older shaft is approx 15.3 mm out from the case while the 1988 & newer is approximately 10.3 mm out from the case. The extra external length is what holds the nut on the 1987 & older. The loss of 5mm on the 1988 & newer is because the clip takes up less space then the nut. The sprocket positon/space itself is the same on both shafts with approximately 5.3 mm of space. Below are pics of my 1987 & my 1998 showing these measurements.

Does anyone have 1983-1987 and a 1988-2004 output shafts loose in their shop? It would be great too see some side by side pics of the the two shafts.

[manco]

Another few questions I have are about the output drive shafts on the two motors. The 87 has the old lock nut style output shaft and the 98 has the newer snap ring to hold the front sprocket. The reason I ask about the output shafts is that my 87 is missing the obsolete drive sprocket lock nut. A custom nut could be made I am sure though I would rather purchase one if something is avaliabele. Is there a known readily available nut that can be purchased to fit the 87 output shaft? I am also wondering can the output shaft in the 87 be swapped with a snap ring output shaft from a newer motor?

Here is my update on this M24x1 nut:

They are impossible to find. M24x1 is not a standard nut size. It is a custom thread found on a handfull of applications including flywheel puller threads, the honda stem mentioned in the above linked thread & yamaha YZ & WR stems from roughly the early ninties all the way up to current models. The aftermarket offers aluminum & titanium nuts for these stem nuts. The new and used market appears to offer steel versions of these nuts. I have opted to try a used Yamaha stem nut. The one I ordered appears to be steel. I will update on it when it arrives.

I did also check with hardware stores, looked online and checked with a custom nut maker. Only coarser thread M24 nuts could be found. M24x1.5 and M24x3 seem to be pretty common. There are M24x1 taps available for machinists. Most nut makers don't have these taps in there collection thus most nut makers won't be able to make m24x1 nuts. However since the taps are available all a custom nut maker needs to make the nut is to buy a $40 tap and get busy. Search google for m24x1 tap for more info.

[manco]

...I just aquired the 87 and haven't had a chance to take it out yet. When fired up in my shop the 87 seems to sound a bit meaner though. It could be the sound characteristics are that my 98 is running lean with an airbox, stock carb, Fatty pipe & a freshly packed FMF TurbineCore while the 87 is running rich with a Mikuni, no air box, a rag for an airfilter & a stock pipe with a performance silencer that needs repacked.

I should also give an update on this. Turns out my excitement in aquiring an new to me 1987 KX500 muddled my head. I had the chance to fire up both my 1987 & 1998 side by side the other day. The 1987 runs great but the 1998 just crushed it even on the stand. It had just been a while since I had fired the 1998 up last fall. When I did yesterday the 1998 was clearly pissed off at being considered tamer then the 1987. When the 1998 roared to life I darn near wet my pants. The ground started vibrating, windows rattled, dogs barked and a child next door began crying. I tried to be cool putt putting around the block on the 1998 so as not to arouse the neighbors further. Unfortunately when I took off out of my driveway and rolled unto the throttle I forgot that I needed to be sitting with the gas tank cap under my butt when riding a KX500. Yep, I gently rolled unto the throttle and proceeded to wheelie right past my neighbors house. Oops.  

[yeomans]

The nut from a cr 80 output shaft will fit the 87. Same measurements, also try running the part number on ebay. I find them there sometimes.
The 86 and 87 output shafts are completely different lengths as well and different part numbers. Not sure how they compare in length to the 89-04 but ill have to check it out on my 91.

[manco]

The nut from a cr 80 output shaft will fit the 87. Same measurements, also try running the part number on ebay. I find them there sometimes.
The 86 and 87 output shafts are completely different lengths as well and different part numbers. Not sure how they compare in length to the 89-04 but ill have to check it out on my 91.

Great info. Thanks for clarifications on shafts. I did notice the part numbers were different in schematics. Differing part numbers can be misleading sometimes though. There are quite a few differing number parts that are integchangable in various makes models years of bikes. The shaft looks similar but it is just a drawing of cousre but that dosen't mean much. I also noticed last night that newer output shafts have only snap rings between the gears on the shaft while the 1987 & older have snap rings & circlips. Mabe this effects the physical differences in shaft out design.

[manco]

What about top end swap? Will the -1987 top end swap to a 1988-?

I am also thinking of messing with some power valves. Has anyone ever yanked the power valves out and run straight ports? I figured it would just kill some of the low rpm tune & give the bike an overall higher rpm power curve.

[manco]

Keep bumping into this Dirt Bike KX500 article when looking into big bores recently. Finally took the time to read it through. The article brings up the engine changes in the early nineties. It also mentions the ignition change that year. I have found other mentions on the net of these changes but not really any specifics. Does anyone have info on the ignition curves & crank specs before and after the change over?

THE LIFE & TIMES OF THE KAWASAKI KX500

"1992, the ignition and crank were changed as an unofficial acknowledgment that the KX was being used more for off-road riding than motocross."

http://dirtbikemagazine.com/industry-news/the-life-times-of-the-kawasaki-kx500

[manco]

Totall Bollocks. The yamaha stem nut arrived & fits well. Too bad it turns out to be aluminum though. The nut will work for test riding around the block but will need to be upgraded to steel for regular use. I am gonna try to find a cr80 nut next.

[manco]

I just looked into a cr80 nut. There is no nut on the output shaft of any year CR80 that I can see. All of them use a plate with two nuts to attach the sprocket to the output shaft as shown in the below picture. If any one can offer any other info on this nut whether CR80 or otherwise let me know. Thanks.

[manco]

Here is some more info on the output nut.

I was concerned that replacing what I beleive is a steel nut with an aluminum nut would not allow the aluminum output nut to be tightened enough as aluminum is softer then steel. I did some digging though and found that my concern is probably unwarranted. The torque specs for the output shaft nut in question are 58 ft-lbs. The torque specs on the aluminum yz250 nut are 105 ft-lbs. So the nut should tighten up properly to 58 ft-lbs without issue. I am no machinist so don't take my word on all this though. I guess I will use the aluminum nut tightened to spec and see how it goes. Below is a pic of torqure specs for the KX500 output shaft & YZ250 stem nut.

Here is some more info on this rare output shaft nut:

The nut was used on 74-79 kx250, 79-80 kdx400, 81 kdx420, 82 kdx450, 83-87 kx500 as well as a few other older kawaski models.

If you look on ebay right now there are three of these used nuts for sale ranging from $10 w/ s/h for a crappy one up to $40 w/ s/h for a nice one.

I have found that recently Triumph has used M24x1.0 nuts on there new America & Speedmaster bikes. It is part number t3350680. It sells for $4 new. I do not know what the nut is made out of. I am guessing it is either steel or aluminum. I am gonna stop by the local Triumph dealer and check one out sometime. Here is the nut on line http://www.2wheelpros.com/oem-parts/triumph-nut-flgd-m24x1-0-t3350680-part.html

Here is the torque specs on the kx output shaft & yamaha stem nuts.

[Actionman]

These are great threads! These detective-style threads are always fun to see what can be repurposed when the "proper" part is unavailable.