Old early to mid 1970's Yamaha 175cc Enduro

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#1
Yamaha DT175A/B Dual Sport

I recently got this bike for $25. It needs some serious repair, it'll be amazing if the clutch gears arent dust considering it was out in the elements for two years without the head on. (it cranks and seems to clutch atm) adnd I'm in the middle of cracking the case open (using an impact driver to remove some stubborn bolts, I need an extender to remove the engine to get them all off)

Anyway, I thought at first it was a DT175B, but the VIN number on the frame says otherwise, the dealer thought it was a 1973 AT3, but it's a 175CC and the exhaust and the exhaust mount on the frame arent right. I think it could be a '74 DT175A

Anyway, what do you all think?

The VIN is:
AT1-310297

Any ideas? I'd love to fix this thing up and have some fun.
 
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#2
is it possible this bike might be a hybrid? like an AT3 frame with a 175CC engine

or was there a 1973 DT175?
 
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#3
If the frame says AT1-#########, then it is a 1969 to 1973 AT1, which is a 125cc bike. If it has a 175cc motor, then it probably has a motor from a 1969-1973 CT1, which is a 175cc bike absolutely identical to an AT1 in every way other than that it is a 175cc cylinder instead of a 125cc cylinder. Every single part on an entire CT1 is exactly the same ast on an AT1 except for the cylinder. The early Yamaha enduros started out with the DT1, which was first released in 1968 and was a 250cc bike. It was so successful that in 1969 they released the DT1 in a lot more sizes, which continued until 1973. The new sizes were AT1 (125cc), CT1 (175cc), DT1 (250cc), and RT1 (360cc). All of these bikes were exactly identical, but just had different cylinder sizes, and different motor parts. Even if your motor says AT1 on it, there is absolutely no difference between an AT1 motor and a CT1 motor except for the cylinder bore, so if it says AT1 on the motor than you have a 125 motor with a 175 cylinder from a CT1, and if it says CT1 on the motor than you have a 175 motor.

1969-71 models:

AT1 125cc piston port
CT1 175cc piston port
DT1 250cc piston port
RT1 360cc piston port

1972 models:

AT2 125cc reed valve
CT2 175cc reed valve
DT2 250cc reed valve
RT2 360cc reed valve

It is important to note that all 1972 models say AT1, CT1, DT1, and RT1 on their serial numbers instead of AT2, CT2, DT2, and RT2, but merely have later serial numbers to differentiate them as being a later year, not a different model code. You will never see a bike that says CT2 on it because even though it is a CT2, the serial number continued to be printed as CT1. The same goes for all other enduro models.

1973 models:

AT3 125cc reed valve
CT3 175cc reed valve
DT3 250cc reed valve
RT3 360cc reed valve

It is important to note that all 1973 models say AT1, CT1, DT1, and RT1 on their serial numbers instead of AT3, CT3, DT3, and RT3, but merely have later serial numbers to differentiate them as being a later year, not a different model code. You will never see a bike that says CT3 on it because even though it is a CT3, the serial number continued to be printed as CT1. The same goes for all other enduro models.

In short, if your Yamaha dealer tells you that you have an AT3 when they look up your serial number, but your frame says AT1, they are right. All AT3s and AT2s said AT1 on the frame and the engine, as there were no changes in the 1972 and 1973 models from the earlier 1969-71 models other than switching from piston port to reed valve, and switching to a gas tank that didn't have a tank badge. All parts are interchangeable from all years as long as you put them on the same size bike, except for the 125s and 175s, in which you can use any part on either size bike for all years, since an AT1 is a CT1 with a smaller bore. All of these bikes are merely the original DT1 with different engine sizes.

Starting in 1974, Yamaha discontinued the AT1, CT1, DT1, and RT1, and replaced the AT1 with the DT125, the CT1 with the DT175, and the DT1 with the DT250. The first YZs were modified DT1s. The first YZ WAS a DT1 modified for racing offroad, but it was only used in racing from 1969 until 1973, and did not become commercially available as a YZ until 1974, when the YZ125 and YZ250 were introduced commercially.

What you have is an AT1 with a CT1 motor or possibly an AT1 motor with a CT1 cylinder. Are you sure it really is a 175cc motor? If it is, it will say 174cc engraved in the metal on the left side of the base of the cylidner. If it is a 125 cylinder, it will say 123cc at the exact same spot. If you have a reed block, it is from 1972 or 1973, and if you do not have a reed block, it is a 1969-71 model. Hope all this helps.
 
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#4
Now here's the odd part:
The muffler fits like a DT175A/B muffler, and there's even a mount, dunno if they had a universal mount solution or not
Second, the oil tank seems to be like the DT175

In fact, looking at all the schematics and parts at bikebandit and yamaha's site, I think the only thing that makes this bike an AT3 is the frame.

The oil tank is a DT175 tank, the gas tank is a dt75 tank (with key lock) The oil tank has a blue paint job which leads me to believe it's off a DT175B, the bike has the exhaust from a DT175 and the electrical system is for a DT175.
The AT3/CT3 parts have nothing in common with the parts on this bike, the frame seems to be the only thing, and since the DTs are nothing more than renamed AT3s and CT3s, is it possible the AT3 frame can work with the DT175 parts? If not then I have a really REALLY odd bike.

Which begs the question.. are DT175A and DT175B (or possibly even C) pistons and cylinders the same size and bore?

Also, on the DT175 oil injector, it has a gear on it that controls the oil flow, what's a good setting for the oil? and no I'm not gonna go with pre-mixing, namely because if I wanted to fuel up at a gas station, I wouldnt have to worry about mixing fuel at the pump.
 
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#5
lub997 said:
If the frame says AT1-#########, then it is a 1969 to 1973 AT1, which is a 125cc bike. If it has a 175cc motor, then it probably has a motor from a 1969-1973 CT1, which is a 175cc bike absolutely identical to an AT1 in every way other than that it is a 175cc cylinder instead of a 125cc cylinder. Every single part on an entire CT1 is exactly the same ast on an AT1 except for the cylinder. The early Yamaha enduros started out with the DT1, which was first released in 1968 and was a 250cc bike. It was so successful that in 1969 they released the DT1 in a lot more sizes, which continued until 1973. The new sizes were AT1 (125cc), CT1 (175cc), DT1 (250cc), and RT1 (360cc). All of these bikes were exactly identical, but just had different cylinder sizes, and different motor parts. Even if your motor says AT1 on it, there is absolutely no difference between an AT1 motor and a CT1 motor except for the cylinder bore, so if it says AT1 on the motor than you have a 125 motor with a 175 cylinder from a CT1, and if it says CT1 on the motor than you have a 175 motor.

1969-71 models:

AT1 125cc piston port
CT1 175cc piston port
DT1 250cc piston port
RT1 360cc piston port

1972 models:

AT2 125cc reed valve
CT2 175cc reed valve
DT2 250cc reed valve
RT2 360cc reed valve

It is important to note that all 1972 models say AT1, CT1, DT1, and RT1 on their serial numbers instead of AT2, CT2, DT2, and RT2, but merely have later serial numbers to differentiate them as being a later year, not a different model code. You will never see a bike that says CT2 on it because even though it is a CT2, the serial number continued to be printed as CT1. The same goes for all other enduro models.

1973 models:

AT3 125cc reed valve
CT3 175cc reed valve
DT3 250cc reed valve
RT3 360cc reed valve

It is important to note that all 1973 models say AT1, CT1, DT1, and RT1 on their serial numbers instead of AT3, CT3, DT3, and RT3, but merely have later serial numbers to differentiate them as being a later year, not a different model code. You will never see a bike that says CT3 on it because even though it is a CT3, the serial number continued to be printed as CT1. The same goes for all other enduro models.

In short, if your Yamaha dealer tells you that you have an AT3 when they look up your serial number, but your frame says AT1, they are right. All AT3s and AT2s said AT1 on the frame and the engine, as there were no changes in the 1972 and 1973 models from the earlier 1969-71 models other than switching from piston port to reed valve, and switching to a gas tank that didn't have a tank badge. All parts are interchangeable from all years as long as you put them on the same size bike, except for the 125s and 175s, in which you can use any part on either size bike for all years, since an AT1 is a CT1 with a smaller bore. All of these bikes are merely the original DT1 with different engine sizes.

Starting in 1974, Yamaha discontinued the AT1, CT1, DT1, and RT1, and replaced the AT1 with the DT125, the CT1 with the DT175, and the DT1 with the DT250. The first YZs were modified DT1s. The first YZ WAS a DT1 modified for racing offroad, but it was only used in racing from 1969 until 1973, and did not become commercially available as a YZ until 1974, when the YZ125 and YZ250 were introduced commercially.

What you have is an AT1 with a CT1 motor or possibly an AT1 motor with a CT1 cylinder. Are you sure it really is a 175cc motor? If it is, it will say 174cc engraved in the metal on the left side of the base of the cylidner. If it is a 125 cylinder, it will say 123cc at the exact same spot. If you have a reed block, it is from 1972 or 1973, and if you do not have a reed block, it is a 1969-71 model. Hope all this helps.

okay, here's the really weird part, I looked up an AT3 frame, looks NOTHING like the frame I have, there's a big bar that comes down the center on the AT3 frame. this has a DT175 frame on it for sure, is there an offchance they put an AT3 neck on it? is there a possibility a 1974 DT175A might start with an AT1- prefix?

I was looking at misc bike schematics and everything..

Is this something I should call up yamaha service support for?
 
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Oct 18, 2006
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#6
lub 997...i am purchasing a 1969 yamaha at1....if i buy a 1972 rt3 (for parts) will the parts (other than the engine..) be interchangeable?...it was not totally clear in your post whether the interchangeability applies to like models (at1, ct1, etc) from 1969-73 or all models intermixed over that period...thanx!!
 
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#9
Okay, well basically, I contacted yamaha and they told me it was an AT1MX, but it obviously isnt. Did a little more digging and I'm sure it's a 1975 DT175B.

that VIN is most unusual though, but the frame is entirely unlike all the bikes that have been listed, and the most identical frames are the DT175A and the DT175B (1974 and 1975) all other years have too many irregularities to be like my frame.

I'll show you guys some pics (remove the spaces) :

ht tp://img.photobucket.com/albums/v607/acidchat/Motorcycle/100_0757.jpg The bike the night I got it (I sanded the seat pan to get rid of the worst rust, the seat pad and cover are thrashed, I need the rubber foam they use and the material for seat cover to fabricate a new seat..) the exhaust goes out the other side, the white tank under the seat is the oil tank. the original color of this bike was blue.

ht tp://img.photobucket.com/albums/v607/acidchat/Motorcycle/100_0793.jpg picture of the bar that goes between the sides of the frame with one of the 3 mounts. (the engine mounts in a triangular fashion like this: : - (imagine that dash as a dot) ) which is what proves this isnt an AT1MX like yamaha says, which has a big thick vertical bar that comes down.

ht tp://img.photobucket.com/albums/v607/acidchat/Motorcycle/100_0794A.jpg The engine, not a good shot, but I cracked the sides off to check for any major rust damage or oxidization, the magneto seems somewhat oxidized and wobbles a tad, but I dont think that's too much of an issue. the oil that sat in the engine preserved it pretty well to the elements, no major rust damage. just minor oxidization on the surface of some parts that were directly exposed to the elements (such as the connector rod! though its integrity seems to be intact and isnt really rusted out..)


So what do you think?
 
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#10
I have a parts bike that looks identical mine is a 1975 DT175.Could the numbers on yours been restamped? It looks nothing like a AT1 mx I have a 72 and a 73 AT1 your frame and motor are 74 or newer making it a DT. look at the numbers very close someone could have altered it to match their paper work.
 
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#11
pryor said:
I have a parts bike that looks identical mine is a 1975 DT175.Could the numbers on yours been restamped? It looks nothing like a AT1 mx I have a 72 and a 73 AT1 your frame and motor are 74 or newer making it a DT. look at the numbers very close someone could have altered it to match their paper work.

pretty sure, unless, say, the original frame got thrashed and they got a new frame from another country, like say, mexico. I dunno if that'd change the VIN numbering scheme or not...