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Question 73 MX250 fixer upper- part 2

  • hackman101
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Replied by hackman101 on topic 73 MX250 fixer upper- part 2

I remembered from another comment in my posts here, about the airbox joints leaking, letting unfiltered air into the engine, took that out, drilled out the rivets, and removed the foam gaskets. I will clean it all up with Dawn, and silicone it all back together when it gets pop riveted back together.

Another week down.

    
1973 MX250
Past rides 45 years ago (and longer)
1964 Honda 50cc C110
1960s Yamaha 65cc scooter
1960s Honda 65cc w/ 90cc engine mashup
1971 DT1-E modified to MX kinda...
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28 Nov 2021 18:30 #51

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Replied by RT325 on topic 73 MX250 fixer upper- part 2

Thanks for the progress reports. Look forward to when she fires up as i'm sure 'you do'. I'll just mention with the mag rotor, [sounds like you're all good] but if ya ended up stuck you could run it minus the crank key. It'll never slip so long as done up tight & lined up over the keyway as don't have enough inertia like a flywheel to eat the key easily. Anyway you're past that point so all good.
Also, good sealing air filter boxes was never Yamaha's strong point & a real shame as many a motor would have been compromised by that downfall. Good that ya onto it!!. Had same issue with my YZ250B when about one season old. Local panelbeater who raced motocross with us had some good stuff in the squeeze gun that worked great, silver grey smelly stuff.
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Last edit: 28 Nov 2021 19:36 by RT325.
28 Nov 2021 19:27 #52

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  • Sneezles61
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Replied by Sneezles61 on topic 73 MX250 fixer upper- part 2

A thought on sealing up an air box... There is a product that the tin benders use to seal up duct joints.. Its water based and like an almost spread-able paint.. grey in color.. Manufactured by Duct-Mate and its called Pro Seal... Maybe a good coating all inside?
Sneezles61 
29 Nov 2021 04:46 #53

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  • hackman101
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Replied by hackman101 on topic 73 MX250 fixer upper- part 2

Yup I am familiar with it since I am in the construction trade. It is ornery stuff, works good
1973 MX250
Past rides 45 years ago (and longer)
1964 Honda 50cc C110
1960s Yamaha 65cc scooter
1960s Honda 65cc w/ 90cc engine mashup
1971 DT1-E modified to MX kinda...
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29 Nov 2021 06:22 #54

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Replied by hackman101 on topic 73 MX250 fixer upper- part 2

@ RT325. The grey smelly stuff sounds about like silicone. Yup I am anxious to get it together too. The time and funds needed so far is well beyond my original expectations, but I am in it for the long haul now. The plan and still is to get it running well, a complete bike, hopefully all original, but that has had to go by the wayside because of the shock and control cables, maybe even the carb and gasket. When all is done for this stage, and ride it for a while, I plan to disassemble it and restore the rest of the bike to look like some of the beauties on this forum.
1973 MX250
Past rides 45 years ago (and longer)
1964 Honda 50cc C110
1960s Yamaha 65cc scooter
1960s Honda 65cc w/ 90cc engine mashup
1971 DT1-E modified to MX kinda...
29 Nov 2021 06:29 #55

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Replied by hackman101 on topic 73 MX250 fixer upper- part 2

It has been a while, being a self employed carpenter, work got the best of me, really busy, working long hours and saturdays too for a while but now it has toned down for now.I still got a little done in the "in-between" hours. I brought my cylinder and crank to a local shop and shown him what I had. He said the ring gap that I seen was way too big.... was way to big. Everything had a lot of wear. I think he said the ring was probably worn a lot extra by the lack of chamfer on the ports. I had him bore the jug and I got a Wiseco 4th over piston, rings, wrist pin and upper bearing from Amazon.The airbox is back together but not mounted yet. Everything is back together, assembled with silicone caulk, replacing the foam that was removed. 

 
1973 MX250
Past rides 45 years ago (and longer)
1964 Honda 50cc C110
1960s Yamaha 65cc scooter
1960s Honda 65cc w/ 90cc engine mashup
1971 DT1-E modified to MX kinda...
23 Dec 2021 20:01 #56

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Replied by hackman101 on topic 73 MX250 fixer upper- part 2

The air filter I got from Uni that was supposed to fit my bike, which was nowhere near doing that was disassembled and remade so it hopefully will.  

    

I forgot to mention, that while the crank was in the shop, the guy offered to check the alignment, I went for it, he said it was out .003, now it is only .001. Maybe there is supposed to have another "0" in there, but it is 3 times better than it was. He also ordered me another nut for the main gear since the threads on the original nut were trashed. It would run up only halfway by hand on the crank. He had me try the nut the other way and would not even start. So that might have been the reason it was so hard to get off.
 Got the new tire on the rim too, with new rim locks since the old were trashed out how they were installed which made it necessary to cut the tire off.

That's it for now until next time
1973 MX250
Past rides 45 years ago (and longer)
1964 Honda 50cc C110
1960s Yamaha 65cc scooter
1960s Honda 65cc w/ 90cc engine mashup
1971 DT1-E modified to MX kinda...
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Last edit: 23 Dec 2021 20:15 by hackman101. Reason: Added more info
23 Dec 2021 20:13 #57

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Replied by hackman101 on topic 73 MX250 fixer upper- part 2

Been really cold out there, colder than the usual winter. That got me to thinking, since I am now ready to set the crank and join the halves.... I need the crank to be cold, the bearings to be warm, this cold snap my be of great help. Yesterday I put it to the test. It was 20 degrees out, I already had the trans in the case with the other half set on top loosely without the crank in place, since I just wanted to give everything a dry run so to speak. I had at first was working from the left side but upon asking the shop owner who did the bore on my jug what was his approach was, he says he prefers the right side build. Going off of that, I flipped the lower end over onto the right side and removed the left side case. It come off like a breeze. Inspected everything, looked good. Even tried the crank in the bearing to see if it was a slip fit.... not quite, I probably could have tapped it in with a wood block and hammer, but wasn't about to try, since cold and heat on the install of the bearings had become my friend.

Got out the heat gun, heated up the bearing evenly, including some of the surrounding case so all of the heat was not pin pointed, set the crank in place at it dropped in with a decisive thud, shim in place and all. Cleaned all the gasket surfaces one last time since some of the assembly oil had dripped out onto the other case. Using brake cleaner sprayed onto a paper towel and wiped all surfaces making sure I did not shred the paper in the process, changing the wiping face regularly.

Bought a set of artists brushes....twice... uuugh. The first set fell off /out of the other items I carried from Walmart since I did not put everything in a bag. Back to get another set brushes, since they were only sold in a pack of 4 at the cheapest (4 bucks). Set the Yambond in place, carefully spreading a thin layer with the brush on both case halves.

Moment of truth. Heat applied to the left side until the bearing was quite warm. Raised the case above, doing what a could to keep from touching the gasket surfaces, lining everything up and lower the case onto the other half. SWISH! It came down onto the other side, I thought the sealant was going to shoot out the sides.... just kidding,,,, but it did go on readily. Tightened up the Allen screws. Cases assembled ready for for stuff to be added. What a relief.

Till next time.
1973 MX250
Past rides 45 years ago (and longer)
1964 Honda 50cc C110
1960s Yamaha 65cc scooter
1960s Honda 65cc w/ 90cc engine mashup
1971 DT1-E modified to MX kinda...
The following user(s) Liked this Post: Scootern29, MarkT, Sneezles61, adguy2112, Mike P
Last edit: 01 Jan 2022 10:38 by hackman101. Reason: Fixed typos
01 Jan 2022 10:27 #58

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Replied by msavitt on topic 73 MX250 fixer upper- part 2

I love your colorful updates,...I can almost smell the burning tire, the tin sealer and the ice cold!  Soon it will be warmer and you will be riding around!
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02 Jan 2022 11:50 #59

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Replied by hackman101 on topic 73 MX250 fixer upper- part 2

Been a while again with just a little going on. I did get the case halves joined, I thought the trans might have had an issue and posted about it in the general forum, but when I figured out that i had the shift sequence backwards, the way the spindles acted made more sense. So onto setting the clutch and other related parts....or not. Looking at the way the clutch friction rings looked, remembering the way they were all stuck together pretty bad to the discs, measuring them with a micrometer (and the springs too) if found the dimensions were all over the place on the friction rings and the rust (I guess) wasn't worth trying to reuse any of them. So another order was made and now waiting for them to arrive.

 

With that set to the side I moved onto the carb rebuild. That went well enough.... to a degree.... I dipped the parts in the recommended carb cleaner endorsed by YE, it did the job I guess. It was cold still, about 40 degrees, perhaps it did what it was supposed to do. I will find out in time. Anyways, when I took apart the carb, it was pretty clean inside since I took it of the bike 40 years or so ago and drained it out then. The rubber seal on the choke was difficult to get off since it was so stiff, the plan for that is to treat it with wintergreen oil along with the rear wheel seal, kill switch button (really needed it cause it was hard as a rock) and the carb to airbox boot. Got the carb all back together except for the choke, so it was time to treat the rubber. 

I looked online to refresh my memory of what I had seen before of the many times I went through various ways of treating rubber with wintergreen. I settled on one that seemed a sure fire way to do it. Gave great detailed instructions.  motofaction.org/mechanical-101/how-renew...asket-o-rings-seals/
I got the water boiling with the oil in it before I put the parts in so it would be easy to time, boiled the parts for 6 minutes and turned off the heat. (I used the gas burner on my BBQ grill) and let it cool just like the instructions said. I poured off the solution and was saddened by the results.

 

All of them were swelled to an unusable size. The worst of them was the kill switch, since there is only one that I can find on Ebay and I think the guy wants over $200 for it. I'm not gonna do it. There must be some way to shrink it back down a least to a useable size??? The carb boot, did ok, but evidently the water that covered the boot wasn't enough to get the whole thing softened, there is a ridge along its length that is still quite stiff, stiff enough to make it difficult to get the boot onto the carb, but it does go onto the airbox ok.
I am considering finding a way to shrink the kill button somehow. That is my next project, till next time.
1973 MX250
Past rides 45 years ago (and longer)
1964 Honda 50cc C110
1960s Yamaha 65cc scooter
1960s Honda 65cc w/ 90cc engine mashup
1971 DT1-E modified to MX kinda...
The following user(s) Liked this Post: Sneezles61
Last edit: 15 Jan 2022 20:09 by hackman101. Reason: Added picture
13 Jan 2022 22:02 #60

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