Motor Comparison by Year

[Senator]

Hello gang,

To keep with proper form, I have first exhausted the search option to the best of my ability on this topic.  The search tool, by the way, has been ultra helpful for me in every other instance.  I have come to understand that 88-04 are basically the same but I'm trying to find more information about how the 87 motor fits into the mix, specifiaclly mountability.  Topics like this one

http://www.kxriders.com/forums/index.php/topic,2758.0.html

have titles to get a fella excited about possibly finding answers but lead only to another deadend.

[don46]

Actually it's the 89-04 that are pretty much the same, 86-88 are the same.

[cutting torch]

Hello gang,

To keep with proper form, I have first exhausted the search option to the best of my ability on this topic.  The search tool, by the way, has been ultra helpful for me in every other instance.  I have come to understand that 88-04 are basically the same but I'm trying to find more information about how the 87 motor fits into the mix, specifiaclly mountability.  Topics like this one

http://www.kxriders.com/forums/index.php/topic,2758.0.html

have titles to get a fella excited about possibly finding answers but lead only to another deadend.

I am so glad you asked this question, since I just picked up a donor '87 KX500 for a hybrid project, and I was wondering about the interchangeability of jugs, KIPS, KIPS drive and linkage, ETC.

I have a few pics of mine after I ripped the heart out of it today:

Reed side:



Exhaust side, where you can see the head, which appears to have munched on something for a while:



Carbon-loaded power valve:


Senator, if I am hijacking your post, let me know and I will cease and desist immediately!

torch

[tobys 2 strokes]

From my limited expereance the 88 lower end is the same as the 89 up they were just short the guilitine style center Powervalve they only had the 2 like the 86 87

[don46]

cases are different as well, might be some other issues to.

cutting torch, if the power valve drums are that gummed you may have issues the teeth on the drums, they were aluminum and prone to the teeth going away, an un fortunately they are no longer available.

[tobys 2 strokes]

For the life of me I canot see the diffearance I have a set of 93 cases right next to my 88 and other than the smaller early flywheel and PVs they look exactly the same the late cyl fits as does all the covers (clutch and flywheel) the sprocket is held on with a snapring like the later ones and both ends of the crank are the same.
I would sure like to know for sure.

[Senator]

Toby, you sir, are the man.  My question stems from the price differential that seems to increase significantly between 88 and 87 motors.  The inference I have identified for myself here, is that there must be some interchangability concern as the years begin to precede 1988.  Will a complete 87 motor bolt into the later frames?

[cutting torch]

cases are different as well, might be some other issues to.

cutting torch, if the power valve drums are that gummed you may have issues the teeth on the drums, they were aluminum and prone to the teeth going away, an un fortunately they are no longer available.

I yanked the jug today, and they seem snug with the rack. I just held the valves and tried to detect lash at the rack, and I couldn't feel any. They do move freely, though.

This engine has been gotten into in the past. It has a Hot Rod in it. The shrapnel that beat up the head (likely a piston skirt) does not seem to have stayed in the bottom end for long. I was pleased to see that the scarring on the cases was minimal.

The rod big end seems pretty tight, too. I'll verify that once I have a manual.

torch

[don46]

For the life of me I canot see the diffearance I have a set of 93 cases right next to my 88 and other than the smaller early flywheel and PVs they look exactly the same the late cyl fits as does all the covers (clutch and flywheel) the sprocket is held on with a snapring like the later ones and both ends of the crank are the same.
I would sure like to know for sure.

maybe you have an 89 or newer, the 88 only has 2 holes for the power valve drums 89 and newer has 3, take a picture and I can tell you for sure.

[tobys 2 strokes]

This is my new parts bike and it does have the 3rd hole for the PV end.It didnt come with a cyl.
I was asuming that it was a 88 due to the air box not having the vents and the differant chain adjuster on the swinger. is there another way to tell the YR. the numbers have been removed from the frame at one time.

[kwakman]

senator,
          as mentioned, 85 is a stand alone year.86 thru 88 are same apart from port duration.(see the port timing thread for specs)89 onward has a 3 stage powervalve.the only difference on the cases between 86 - 88, and 89 on is a different bearing and the hole for the centre valve drive.there are no changes on the mounting points so an 86 will fit a 04 frame and vice versa.HTH.

[cutting torch]

senator,
          as mentioned, 85 is a stand alone year.86 thru 88 are same apart from port duration.(see the port timing thread for specs)89 onward has a 3 stage powervalve.the only difference on the cases between 86 - 88, and 89 on is a different bearing and the hole for the centre valve drive.there are no changes on the mounting points so an 86 will fit a 04 frame and vice versa.HTH.

That was helpful!

Which bearing(s)?

And..... can you tell us the difference in power delivery between the '87 and '89?

torch

[kwakman]

Torch,
        The different bearing is one of the gearbox ones if i remember correctly. The pre 89 engines tend to have awesome low end and midrange is wqicked and downright dangerous to know in equal measure.As with the cr500, the early models have 'issues' and left alone, they will bite the heads off fluffy bunnies given half the chance.The 89 on models were tamed slightly to make them easier to ride. There's no real difference in power output, just how and where in the rev range the power is made.

                            My 86 is coming to the grave with me......

[cutting torch]

More helpfulness. Thanks, kwakman!

I have an '87, and I'm planning to put an '89-up jug on it, since the parts availability is better. Plus, I could sell the '87 jug to someone that needs it more.

torch

[cutting torch]

I think so. The case needs to have a pilot hole drilled for the power valve idler gear, but I think the rest will work fine. Of course, you will need all of the appropriate parts that are jug-specific....

torch