Crank and Flywheel mystery

[RubberSalt]

Does anyone recognize this crank or flywheel?

233960 233961

[atc300r]

Either 86 atc or 86-89 trx 250r.

[The_Steve_Man]

^^^^What he said. Looks like liquid cooled 250r 85-89.

[RubberSalt]

The flywheel fits. It looks like a TRX250r flywheel. No doubt about it.
The crank doesn't match any liquid cooled Honda that i can find.

This Ebay post has plenty pics to show.

http://www.ebay.com/itm/1985-89-Honda-ATC-250R-Crankshaft-/111817183517

The splines look closer to a KX250 crank.
http://www.ebay.com/itm/1992-Kawasaki-KX250-KX-125-250-Engine-Crankshaft-Crank-Shaft-/111958191568?hash=item1a113a6dd0:g:6lAAAOSwYGFU0r0 J&vxp=mtr

[The_Steve_Man]

I can't see the splines.

Sent from my MotoG3 using Tapatalk

[atc300r]

Can you post your crank at different angles.I was able to blow it up on my phone it looks to have some holes in it.

[RubberSalt]

Once I get to the house this evening, I'll take some better pictures.

[DohcBikes]

Measure the stroke, it will be a very good clue.

[RubberSalt]

I'm having a difficult time measuring the stroke on this guy. It's somewhere between 60-70mm.
233969 233970

[DohcBikes]

Oh cmon man! I wish i could reach into the screen and measure it for you...

Set the point of one jaw of your caliper at the center point of the crank pin hole on the outside of the crank and the other at the center of the bearing journal on the shaft. This will give you the throw. Double that, and you have the stroke. Obviously its going to be slightly approximate but your eye can see .003" so it shouldn't be that far off. Be sure to hold your caliper as close to a 90 degree angle to the imagined line that would connect the crank pin hole and the shaft centers. I wish there was a better way to explain this very easy procedure, frustrating. If you can get the stroke measurement within 1mm, the identity will become obvious.

ok here's a rudementary diagram. Center circle represents crankshaft, outer hole represents crank pin hole. Need the measurement of the line.

233971

[RubberSalt]

I didn't measure it, but it's a 64.9mm stroke. .

There goes the fun lol. Anyways, I figured out this combination last night. I was more surprised when the flywheel looks like it'll clear the cases and fit the stator perfectly. What gets me is this... Why hasn't anyone else documented this or mentioned anything? For a while, there was no flywheels for this machine being made, leaving ricky stator as your option. I'm not able to find one of them, so I started sourcing alternatives. I've got a list that is ridiculous.

In order to make this work with the oem set up, it will need to be clocked. Unfortunately, I don't believe there is enough room in the case to fit the pickup coil from the honda. But the trx stator could be adapted to fit.

[DohcBikes]

I didn't measure it, but it's a 64.9mm stroke. .
How do you know? I added a picture above, drawed it m'self

[jeswinehart]

Hey Gabe, i thoght i would post up the difference we spoke about earlier in week.
Hopefully you can veiw my little cheat sheet in background.
Both flywheels share same magnet size, BUT,,,, the 2 magnets with north polarity are where south polarity magnets are.
If the 86/87 kdx200 flywheel magnets was rotated 1 spot it would have same magnet placement as all years tecate 3 + 4 wheeler.
Kxt housing is thicker,,,, just heavier for more low end grunt.
I might add that the 86/87 kdx200 4 magnet flywheels are imo many times harder to come across in usable shape then kxt flywheels.

[RubberSalt]

I need to check the polarity of the trx flywheel, see if it matches.

Only 1 magnet position correctly is required to make it fire on time. These things fire atleast 4 times per revolution it seems.

My guess is that it just doesn't fire until it's under the correct compression and stoichiometric ratio.

[jeswinehart]

With tecate (or kdx) you can have the magnets in any combination of wrong ans still produce a fine spark,,,, just at the wrong time

[RubberSalt]

Exactly. The cdi uses blocking diodes to only fire for 1 magnetic pole. This leaves it to fire 4 times per revolution. Currently, it fires once every 90 degrees. I'm not sure which polarity makes it fire.

[RubberSalt]

This is for DOHC. It's my measurements and formulas I used.
233981

[DohcBikes]

This is for DOHC. It's my measurements and formulas I used.
233981Neither of those formulas bring you to 64.9

[RubberSalt]

Sorry, it was tired when I posted that. Im sure you figured it out, but that's the throw.

For those who haven't, multiply by 2. Forgot to add that in.>.<

[DohcBikes]

Sorry, it was tired when I posted that. Im sure you figured it out, but that's the throw.

For those who haven't, multiply by 2. Forgot to add that in.>.<I did multiply by 2. It still doesn't add up to 64.9.

The reason i'm continuing to discuss this is because if your measurements are correct, the stroke of your crank is not 64.9, and it's not the crank you think it is. The right diagram shows a stroke of 66.87mm. This is why it's easier to just measure center to center, even if the caliper must hang out in space a little to get the approx. number, and multiply by 2.

Although I do agree that it appears to be a tecate crank, just wanna be sure its not a +2mm stroker crank or something else weird. Judging by the placement of the crank pin in relation to the milling marks on the crank, it does look to be stock.

No big deal, but maybe the convo will help others in the future.

[RubberSalt]

Center to center is tricky to line up. Imma double check them when I get home.

I honestly hope your right with the math and my measurements were right.. stroker !! :-D

[RubberSalt]

I redid the math with the number's provided. I received 64.97 and 64.87 for the 2nd one.

I'm not sure how you received 66.87.


I feel let down now. I need to get ahold of an offset crank pin. There's my stroker!

[sixpackrt]

83 84 kx250 crank or a 84 85 tecate crank