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1971 yamahonda at1/250 swap

23 May 2020 19:31
Yamahonda
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1971 yamahonda at1/250 swap #1
I may be shunned but I am building a bike out of parts, I plan on doing a long desert ride on. It is a 1971 at1 with a 1986 xr 250 engine in it I have put a lot of miles on it on and off road but I feel the front suspension is not adequate especially off road. I have not rebuilt the forks yet but I think dt 250 forks and a 21 front wheel will be better? I also was wondering if anyone had any other ideas to help the off road handling like extending the swingarm. Help me make my junk handle!

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23 May 2020 22:19
Yamahonda
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1971 yamahonda at1/250 swap #2
I also have these shocks I don't know what they are

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23 May 2020 22:38
MarkT
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1971 yamahonda at1/250 swap #3
You need to flip the shocks over. They are not designed to run upside down like that. They are Yamaha Thermalflows from a later model. They look longer than stock so should be a good match to the 250 front end.

You can swap the front end from a 250 onto your bike. You need the whole thing... triple clamps, forks, and wheel. Service Manual in Tech Library has a parts swap guide in the back.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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24 May 2020 06:17 24 May 2020 06:18 by Makotosun.
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1971 yamahonda at1/250 swap #4
The 250 fork swap is, as noted, a direct bolt up. Easy easy and will add Tornio all stability. Given the tech, they’ll be sturdier, but not necessarily “better”. The 21” wheel will be good.

I have a friend who extended his swing arm an inch or so along with the fork swap, and swears by the handling improvement. Pic below. He is running aftermarket shocks on the rear. He races it in VMX successfully.


IF it isn't one thing, it's another.

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24 May 2020 08:02
Yamahonda
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1971 yamahonda at1/250 swap #5
Thank you! I will flip them as soon as I can. That bike is awesome, it looks like he extended the swing arm in front of the shock mount correct? Now I need to find a new front end :)

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24 May 2020 08:06
Makotosun
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1971 yamahonda at1/250 swap #6

Yamahonda wrote: Thank you! I will flip them as soon as I can. That bike is awesome, it looks like he extended the swing arm in front of the shock mount correct? Now I need to find a new front end :)


Correct. He added an insert after cutting the swing arms.

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24 May 2020 08:09
Yamahonda
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1971 yamahonda at1/250 swap #7
Ok, I have An extra swing arm that will be put under the knife later; do you know what he is running for the chain guide?

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24 May 2020 17:36
RT325
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1971 yamahonda at1/250 swap #8
That's a "very" interesting combo. Must be a tight squeeze in an AT1. One of my DT or RT1 frames had a 3TA triumph in it once.

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25 May 2020 09:35
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1971 yamahonda at1/250 swap #9
Do you have a picture of the bike? No one said you can't cut the frame to fit, but you do have to remove the engine to pull the valve cover

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25 May 2020 21:39
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1971 yamahonda at1/250 swap #10
Before I cut up my swing arm to extend it I I'm planning on extending it one inch in front of the shock mounts does that sound like a good idea for handling and suspension travel

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