Kx100 - Wrist Twisters
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post #1 of 46 Old 09-11-2013, 01:52 PM Thread Starter
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Kx100

I bought a locked up 100 2t as I was unloading at my house the engine unlocked. Changed oil. New plug cleaned carb and no compression and no spark. So I ordered a coil and am watching a piston and crank assembly. Any thoughts.

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post #2 of 46 Old 09-11-2013, 02:47 PM
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No compression means you need to do a leak down test, investigate the head gasket, Valves, and piston rings.

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post #3 of 46 Old 09-11-2013, 02:56 PM
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Yeah I bet the problem is that you don't have any valves. :P

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post #4 of 46 Old 09-11-2013, 03:00 PM Thread Starter
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What's the easiest way to do that without a smoke tester

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post #5 of 46 Old 09-11-2013, 03:07 PM
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Being a 2 stroke engine, I would think it just needs a top end rebuild. I've never done one myself but I know it's a common thing to do. I also understand that they're easy.

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post #6 of 46 Old 09-11-2013, 03:41 PM
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You have to take it apart and inspect/troubleshoot before ordering parts.

I raced two-stroke MX'ers and they are very easy to work on. We did rings every two races and piston/rings every four races, so the motor was apart twice a month. It's really easy stuff.

Seat off, tank disconnected, tank off, pipe off, cylinder head off, carb off, cylinder off, immediately stuff a clean rag in the crank case hole so nothing falls in, inspect.

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post #7 of 46 Old 09-11-2013, 03:45 PM Thread Starter
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Lol I can't find my valves. Im gonna do crank and up

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post #8 of 46 Old 09-11-2013, 04:07 PM
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What Ottawa said....2 strokes easy to do.

Top end is very easy to rebuild -- bottom end requires a bit more - but really not difficult. It is a bit intimidating to split the cases for the bottom end until you've done it once.

Don't buy any parts until you tear it apart.

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post #9 of 46 Old 09-11-2013, 04:09 PM Thread Starter
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Well I just bought a crank assembly what's it like splitting the case will I have to rtv it back together

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post #10 of 46 Old 09-11-2013, 04:13 PM
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post #11 of 46 Old 09-11-2013, 04:20 PM
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take off the top end before you figure out if you even need to break the bottom....if the top is the root cause...you'll know right away.

Then you can try to turn the bottom with the crank -- but be sure to do like Ottawa said (except to troubleshoot it) KEEP THE BOTTOM END COVERED and don't let anything drop in there. If there's any looseness in the crank (you'll be able to feel if the crank feels loose....or it will be locked up) -- then you need to split them.

On the one side you'll have to take out your magneto and stator...and the other side you'll have to free up your clutch .....then split the case with a hammer and chisel to release the crank....at least that's how I remember it.

check out some videos
Dirt bike bottom end rebuild - splitting the cases

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post #12 of 46 Old 09-11-2013, 04:23 PM Thread Starter
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There is definitely some bearing noise coming from the bottom

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post #13 of 46 Old 09-11-2013, 04:33 PM
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It shouldn't make noise ...and even though there can be a tiny bit of right to left play (because it will be locked in place by the wrist pin bearing)...since you have the top torn apart and the parts already for the bottom....seems like your path is already decided.

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post #14 of 46 Old 09-11-2013, 04:35 PM Thread Starter
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It is but I guess I can replace the top end first then try again then if still nothing go to the bottom. I'm betting after the top rebuild it will run and then throw a rod or something like that

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post #15 of 46 Old 09-11-2013, 04:43 PM
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btw....haha
Transfer ports 1, part 4.wmv - YouTube

If you want to have some fun with trying to gain horsepower watch some 2 stroke porting tips..... a SMALL bit of cleaning will make extra horsepower...GENTLY.

http://www.youtube.com/watch?v=vZf7HrW9RtI

just a couple examples.

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post #16 of 46 Old 09-11-2013, 04:47 PM
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Quote:
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It is but I guess I can replace the top end first then try again then if still nothing go to the bottom. I'm betting after the top rebuild it will run and then throw a rod or something like that


Have to watch the surfaces...you really shouldn't try the top end...and expect to go get the bottom end later....waste of gaskets and time..and you'll probably need to do a ring and hone it again if you have to back into it (otherwise you run a risk of blowing the top end if you open it again, and close it without replacing all the gaskets and honing again)

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post #17 of 46 Old 09-11-2013, 05:40 PM Thread Starter
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If I don't break the gaskets why can't I reuse them

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post #18 of 46 Old 09-11-2013, 05:55 PM
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You maybe will have luck if you try it. I suppose I cant recall ever trying it.

The base gaskets and head gaskets don't use any kind of sealant. The head shouldn't need to be removed, but the base gasket will need to come off.....and I just don't believe its worth the risk of having it fail because it didn't seal properly. It only needs to be in the slightest way different, and it could not exactly match the way it was put on the first time.....they're kind of a one time use item from my experience.

Also the rings and cylinder wall get "seated" together after you replace the rings and hone the cylinder -- if you break that "bond" between them, you could get some loss of compression. Again, same as the gaskets - not worth the risk.

I recommend a second opinion though...I was probably being extra careful because I didn't want to earn a DNF.

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post #19 of 46 Old 09-11-2013, 05:57 PM Thread Starter
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So just go ahead and do it all

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post #20 of 46 Old 09-11-2013, 06:08 PM
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If you took the top end off...and when you turn the crank you have play or hear noise -- that's a problem. You need to open it up and find the problem....while you're there I would check everything very close.

I actually twisted a shaft in the transmission into two parts one time....it was such a clean break that I couldn't figure out what was broken and had to take the pieces into the shop. Before Al Gore created the internet.

Maybe something has changed over the years and its not a problem to reuse base gaskets. You'll probably be able to find some great online resources with more current advice.

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post #21 of 46 Old 09-11-2013, 06:46 PM
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Quote:
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Looks like an '81-82 RM125. Ahhh, the good old days. Huge transitions right there, like the first liquid cooled and Kawasaki, Suzuki and Honda going single shock. Those first few years of the Suzuki Full-Floater suspension blew everything away.

By the way, 10 years later most of the MX bikes used O-rings as head gaskets and they are reusable. I suspect this KX has them too.

Death Barrel, I wouldn't do more than you have to. Take it one step at a time and assess. Keep us posted.

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post #22 of 46 Old 09-11-2013, 06:50 PM Thread Starter
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image-2760972935.jpg



image-3148915618.jpg

Dug this far and bought this

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post #23 of 46 Old 09-11-2013, 06:58 PM
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1986 RM125. First race of the PacWest Series that year.

But yeah...there were some changes from earlier years. Here's my 1977/78 RM50


I absolutely agree with not doing more than you need to. Good luck on the rebuild! I look forward to a video hearing that 2 stroke run.

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post #24 of 46 Old 09-11-2013, 07:03 PM Thread Starter
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So what's the final recommendation top end then try it out. Then bottom if need be

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post #25 of 46 Old 09-11-2013, 07:32 PM
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You need to trouble shoot your three symptoms:

- seizure (now seemingly unseized). You need to find out why is seized. You can rule out a top end seizure with your top end inspection. Could be the crank.

- no compression. This is an odd one. There should be some compression, even with blown rings. There could be a loss of seal in the crankcase so that the cylinder isn't getting air through the transfer ports during the exhaust stroke, I guess.

- no spark - need to inspect the ignition system. Get a service manual.

You have 20 minutes of work to get the cylinder off. Next step.

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post #26 of 46 Old 09-11-2013, 07:41 PM Thread Starter
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There is some slight compression but it does not hold which could only be rings( or piston or cylinder wall)

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post #27 of 46 Old 09-12-2013, 09:21 PM
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sounds like theres a hole in your piston... seen it happen many times on the 2 strokers.

Speaking of top ends on smaller 2 strokes.... this kid probably goes through alot... his parents need to feed him large doses of ritalin.

Too Much Red Bull for Biker Kid - YouTube

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post #28 of 46 Old 10-11-2013, 10:49 AM Thread Starter
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If you google kx100 bottom end rebuild this thread is like the fifth return. Soooo the cases are split and now I gotta get them back together anyone know how?

image-989625984.jpg

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post #29 of 46 Old 10-11-2013, 01:29 PM
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Make sure you grease up your bearings well....you may find some suggestions in places about "freezing the cases" and/or heating bearings..... I DONT RECOMMEND EITHER suggestion - but thats just my 2 cents.

Gently but firmly put the cases together with either a rubber hammer, plastic mallet, or use a block of wood and gently tap them in place -- making sure the alignment pins are all lined up....watch for the thrust washers, make sure the bearings completely seat.....I used to use a 3M forma gasket liquid extremely lightly to the case halves so LITTLE/NONE squeezes out while the halves join...you dont want any sealant to fall off inside the case halves.

Put the shifter on and make sure its in neutral and the trans shaft shouldnt stick -- dont keep putting it together if it doesnt feel right.....make sure you get the transmission together right before putting the top end on.

You can find other videos of putting together 2 stroke cases....they're fundamentally the same.

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post #30 of 46 Old 10-19-2013, 06:24 PM Thread Starter
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Guise I can't find where this goes

image-3707028759.jpg

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post #31 of 46 Old 10-20-2013, 07:15 AM
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Quote:
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Guise I can't find where this goes

Attachment 35378
Thats the bushing that goes on your counter-shaft (the shaft your front sprocket mounts to). There should also be an o-ring or seal that goes behind it.

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post #32 of 46 Old 10-20-2013, 09:33 AM Thread Starter
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Thank you you the best

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post #33 of 46 Old 10-20-2013, 12:38 PM
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Almost looks like a wheel/axle spacer, too.

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post #34 of 46 Old 10-20-2013, 02:21 PM
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This is where it goes. #92027 replaces #92152
Attached Images
File Type: png KX100trans.png (128.0 KB, 8 views)

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post #35 of 46 Old 10-20-2013, 09:02 PM Thread Starter
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Sweet

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post #36 of 46 Old 10-31-2013, 03:34 PM Thread Starter
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Which way does it go

image-4146497607.jpg

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post #37 of 46 Old 10-31-2013, 03:43 PM
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Quote:
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Which way does it go

Attachment 37050
Install with the top flat part of the piston facing up in the bore, you are holding it sideways right now for some reason.







J/K ----- arrow goes towards the exhaust port in a two stroke.

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post #38 of 46 Old 10-31-2013, 03:45 PM Thread Starter
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Nice trolling hahah

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post #39 of 46 Old 10-31-2013, 05:04 PM
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Arrow forward, if I recall correctly. The small holes bleed crankcase gases into the exhaust port during part of the stroke or something. I used to know this stuff, but it was long ago.

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post #40 of 46 Old 10-31-2013, 05:10 PM
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Quote:
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...The small holes bleed crankcase gases into the exhaust port during part of the stroke or something....
TWSS

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