1992 YZ250 lockdown-teardown- completed with start up video

Chance1216
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Chance1216 6/23/2020 8:07pm
6/23/2020 8:07pm
sandman768 wrote:
First time with an older Yamaha YPVS ... so figured I drop cylinder on without piston installed to test power valve operation. Everything has been decarbonized...
First time with an older Yamaha YPVS ... so figured I drop cylinder on without piston installed to test power valve operation. Everything has been decarbonized and polished. New left side powervalve holder. Moves very smooth in the cylinder. With linkage hooked up it opens up nicely but does not return all the way on its own, no real spring tension closing it ... not sure if that’s how they are? The spring & first actuation arm have some wear. I just ordered a new tension spring, it was only 5$. I will put a dab of weld on the arm wear spots & then file back down to flat.




Oem Yamaha base gasket . Fits water passage better
It seems OEM gaskets are always the way to go over aftermarket. A couple of water passages were completely blocked on a buddy’s 87 CR 125 using aftermarket. eBay became his best friend since OEM gaskets can be tough sourcing for older bikes.
sandman768
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Saratoga Springs, NY US
sandman768 6/24/2020 3:33am
6/24/2020 3:33am
Chance1216 wrote:
It seems OEM gaskets are always the way to go over aftermarket. A couple of water passages were completely blocked on a buddy’s 87 CR 125...
It seems OEM gaskets are always the way to go over aftermarket. A couple of water passages were completely blocked on a buddy’s 87 CR 125 using aftermarket. eBay became his best friend since OEM gaskets can be tough sourcing for older bikes.
If OeM is available, I will use it every time. I have had good luck with Athena aftermarket gasket kits on some bikes where OeM is no longer available.
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Chance1216
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Chance1216 6/26/2020 4:23pm
6/26/2020 4:23pm
Chance1216 wrote:
It seems OEM gaskets are always the way to go over aftermarket. A couple of water passages were completely blocked on a buddy’s 87 CR 125...
It seems OEM gaskets are always the way to go over aftermarket. A couple of water passages were completely blocked on a buddy’s 87 CR 125 using aftermarket. eBay became his best friend since OEM gaskets can be tough sourcing for older bikes.
sandman768 wrote:
If OeM is available, I will use it every time. I have had good luck with Athena aftermarket gasket kits on some bikes where OeM is...
If OeM is available, I will use it every time. I have had good luck with Athena aftermarket gasket kits on some bikes where OeM is no longer available.
Yeah, now that I’m thinking about it,
Cometic was what he had issues with.
sandman768
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sandman768 6/27/2020 3:10pm
6/27/2020 3:10pm
Rebuilt rear caliper & master cylinder installed & bled.... new Oem rear caliper mount bolts


3

The Shop

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sandman768
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sandman768 6/29/2020 12:04pm
6/29/2020 12:04pm
I ordered a new powervalve spring & actuator arm. While I wait for the parts I decided to take the assembly apart again and see if I could do anything about the wear on the valve where it hits the stopper. As you can see in this photo this is where they become worn and can over rotate.
The bought a new Oem stopper but the valve itself is NLA and anything used will be just as worn. The valve was not over rotating too bad, when they are very worn, they can rotate too far into the cylinder & actually hit the piston. I just wanted to give the valve & stopper a good flat surface To contact each other, very similar to contact points on transmission gears. I used a high temp, oil/ gas resistant epoxy that hardens like steel. I prepped the valve & used masking tape to make a form. Once the epoxy setup, I removed the tape form & rough shaped with a razor blade, then after a full 24hr cure, I filed down to the desired thickness. Now I have 2 nice flat mating surfaces and the open & closed positions of the powervalve Are perfect.


1
sandman768
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sandman768 6/29/2020 3:31pm
6/29/2020 3:31pm
Picked up a Boyesen Rad valve from a 94 YZ250 for cheap, I test fit it without the reeds in... wouldn’t you know it, the reed stopper screws hit the intake on the cylinder...wish I had performed the test fit with the rad valve assembled! Would have been easy to grind away a little material to make the screws clear the intake... not going to happen now with the top end installed. The stock intake & reeds are in good condition and will be used....
sandman768
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sandman768 6/30/2020 4:19am
6/30/2020 4:19am
If anyone has a 91-92 that can take a few photos of how the CDI box, coil & spark plug wire & related wiring are mounted/ routed, It would be appreciated! Think I have it sorted pretty good but want to see how it is supposed to be. The previous owner had the wiring & cables all wrong.
sandman768
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sandman768 7/1/2020 1:22pm
7/1/2020 1:22pm
Working on these older bikes really makes you appreciate new bikes... the radiator hoses are a cluster... they redesigned the radiators & hose routing on the 93 model. Good move👍

sandman768
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sandman768 7/1/2020 1:23pm
7/1/2020 1:23pm
Honda radiator overflow tube...KTM pipe to silencer rubber...
sandman768
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sandman768 7/1/2020 6:20pm
7/1/2020 6:20pm
New OEM shifter, kick start & pipe mounts....it’s nice when things are tight👍


1
sandman768
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sandman768 7/1/2020 6:24pm
7/1/2020 6:24pm
Poor design with mag cover holding clutch cable... very sloppy, causing poor clutch feel at the lever. I fabricated a sleeve out of hard nylon to take up the slack when mag cover tightened down, no more sloppy cable mount.
Stock chains rollers on these older YZ”s did not have bearings or just on one side of the roller. New UFO rollers have sealed bearings on both sides of the rollers.
3
sandman768
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sandman768 7/2/2020 4:10am
7/2/2020 4:10am
Brian_Bowles wrote:
Looking great! Keep it going!
Thanks Brian. Bike is in the home stretch... if not for having to get the shock recharged it would be done. I had the shock body vapor blasted & it was taken apart but when reassembled the shrader valve leaked for some reason... I have it sorted now, just need to visit my suspension guy for Nitrogen charge...looking forward to firing her up to check my work😭
sandman768
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sandman768 7/3/2020 8:12am
7/3/2020 8:12am
Ktm silencer rubber works good
Pipe is very close to water pump and hose...seems like a disaster waiting to happen....

Pit Row

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deccr250
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GB
deccr250 7/6/2020 9:21am
7/6/2020 9:21am
Great work on this build sandman, attention to detail is awesome. Looking forward to seeing the finished product Smile
sandman768
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sandman768 7/6/2020 10:25am
7/6/2020 10:25am
deccr250 wrote:
Great work on this build sandman, attention to detail is awesome. Looking forward to seeing the finished product Smile
Thanks deccr250... Chipping away....
1
sandman768
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sandman768 7/7/2020 2:20pm
7/7/2020 2:20pm
Shock recharged and installed along with airbox & filter.

Leaky petcock rebuilt...passed the test!
2
bonseff
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bonseff 7/7/2020 3:15pm
7/7/2020 3:15pm
This thing is gonna be so show room fresh
Rickyisms
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Rickyisms 7/8/2020 10:34am
7/8/2020 10:34am
Remarkable work. Super impressive. I would not have the heart to get that thing anywhere near dirt if I were you.
1
sandman768
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sandman768 7/8/2020 12:05pm
7/8/2020 12:05pm
Rickyisms wrote:
Remarkable work. Super impressive. I would not have the heart to get that thing anywhere near dirt if I were you.
Thanks Rickyisms.....I will take it out on a good condition day to make sure everything works.... but sounded great at initial startup and no leaks!
sandman768
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sandman768 7/8/2020 12:06pm
7/8/2020 12:06pm
deccr250 wrote:
She’s a beauty sandman. Great work 👍
Thanks deccr250... this one was a challenge at times but pretty happy with the way she turned out.
NiekL
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NiekL 7/8/2020 12:14pm
7/8/2020 12:14pm
Congrats with the build💪

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