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Lt2/AT1

  • bhepp15
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Lt2/AT1 was created by bhepp15

Was digging into my LT2 for the first time last night. Bought it without spark. Dug into flywheel and metal shaving everywhere and bolt was not even hand tight. Yep crank key sheared off.. oh well I have a new one on the way. But what I noticed when looking at the engine vin is that it is actually an AT1 engine in the frame which was cool I guess, probably a nightmare to title. Anyway, the seat has a new cover and looks like a kdi cover but they didn't get new foam so it looks bad. Just wondering if there are any seat foams on kdi that will fit on the pan. Maybe an JT or AT? Another question.. the at1 engine still has the LT2 exhaust on it, or at least the chrome 100 plate. Will that be a big performance issue, I dont really need it to be a performance machine as it is only a 125 and probably won't ride it much but would like it to run well. Gotta check to see if it has the right carb as well.
23 Sep 2022 09:38 #1

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Replied by RT325 on topic Lt2/AT1

An interesting combo by the sounds of it. Don't think the pipe will matter on a std motor, if it fits it'll be good if its clear & not blocked. If ya super keen to see if it runs i'd just line up the flywheel over the crank key slot & tighten it super tight then give her a kick. I get impatient haha. You say AT1 but does it have reed inlet, if so it'll be an AT2 or 3 so even faster--better.
23 Sep 2022 14:13 #2

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Replied by bhepp15 on topic Lt2/AT1

I actually have to look because the vin says at1 but I completely forgot that doesn’t mean it IS an at1 because looking at my rt3 vin this weekend it starts with rt1 as I believe all rts did. So I will go look and see what it is. 
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25 Sep 2022 15:32 #3

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Replied by bhepp15 on topic Lt2/AT1

Just looked, it’s an AT2 engine. The key doesn’t come untill Tuesday but I’m pretty busy this week so I’m going to end up waiting. 
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25 Sep 2022 16:34 #4

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Replied by bhepp15 on topic Lt2/AT1

Does anyone know the size of the magneto bolt on the at2? the one in there seems to be a standard thread someone forced in and I can’t find the spec for the bolt anywhere. Thanks 
26 Sep 2022 15:48 #5

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Replied by MarkT on topic Lt2/AT1

Okay...  I was wondering what you had.

Sounds like someone jammed a magneto onto the original AT2 generator crank stub?  It can be done though it's a little hokey.

Magneto models all have a nut holding the flywheel to the crank. 

I think it might be an 8mm x 1.25 thread in crank? 
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
26 Sep 2022 19:14 #6

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Replied by MarkT on topic Lt2/AT1

Here is a old quote from MotoDave0 regarding installing a CT ignition on the original AT generator crank:

"I have done it to 2 bikes and I am currently racing my Trackmaster framed 1970 AT1 in the AhrmaNW Classic 125 Novice class.
All I had to do to the CT1 ignition was to take about a 1/8 of an inch off the bottom of the flywheel and get a shorter bolt."


He also had a more detailed how-to on the now-dead "other" Yamaha Enduro website.  I believe he also had to notch the points rubbing block to about half width. 

On yours you might have the LT ignition...  I think LT ignition is very close if not identical to a CT ignition. 
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
26 Sep 2022 19:36 #7

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Replied by bhepp15 on topic Lt2/AT1

Haha I was wondering why it seemed so weird. Here’s what it looks like. 
26 Sep 2022 20:08 #8

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Replied by bhepp15 on topic Lt2/AT1

One more 
26 Sep 2022 20:16 #9

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