Other 1978 DT 175 Build Thread

MY-BLUE-BEAST

MY-BLUE-BEAST

I picked up my latest project today its a 1978 Yamaha DT 175. Its in a little rough shape but nothing that cant be saved. The best part of the bike is that it has a clean and ORIGINAL, yes from 1978, title, really cool. The fenders are beyond repair, they can easily be refinished, but the rear fender is smashed and the front seems to have been modified to fit so its not worth saving. Im tearing it completely down including the engine and redoing it from top to bottom. Im going to redo it with white fenders and paint the tank the old school Yamaha yellow. I already found someone who can redo the seat and the graphics. The stator cover is missing to. This is going to take all winter almost, but it will be fun. :thumb:

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MY-BLUE-BEAST

MY-BLUE-BEAST

tore the engine apart tonight, I did everything but split the case. I convinced a co worker to do it for me for a case of Coors-Light :smirk:.
Anyway that will be done on Thursday. I found all the parts to rebuild it and with my discount at the Yami shop I can rebuild it with all new parts for $200, without it its well over $300 for everything. This includes clutch kit, piston kit, crank case bearings, reeds, and all the other good stuff. I have all the parts in little baggies and labeled so I don't misplace them. The clutch plates are worn to nothing so that's on the list to be replaced. The oil was in there for a while so it turned to snot and has to be cleaned out.

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Everything just needs a little cleaning
 
MY-BLUE-BEAST

MY-BLUE-BEAST

quick question, this thing has an oil pump that hooks into the throttle cable. There is an oil reservoir full of 2 stroke oil that runs to the pump. Does this thing need mixed gas? or since its supposed to be a dual sport can you just put gas in the thing since the pump its there?
 
2smoke

2smoke

Yes it is a 2T machine. But it appears that it has an oil injections system. So you have the motor apart and parts on the way. So this is what I would do. Get the engine back together and ready for break in. But you will need to disable or cap off the the oil injection portion for the break in. Find out what the pre mix ratio is supposed to be and mix up a gallon of pre mix. Then proceed with the break in using pre mixed fuel in the gas tank. No this wont hurt anything. Once you have the engine running and mostly broke in then you can trouble shoot the oil injection system. This is pretty easy to do also. Fill the 2T oil reservoir with oil. About half way will be enough. Remove the hose or line that injects the oil into the carb. Start the bike (ensure that your still running pre mixed fuel in the gas tank). Let it idle and observe the oil line to see if it is producing oil. It should make some. Then try it at different throttle positions to see how much oil it is producing out of the oil line. If no oil is produced then the pump isnt functioning. If oil is produced atleast you know its working. But it should produce a certain amount of oil. For example a drop of oil per second. You will only know for sure how much its supposed to produce with a little research or a manual. If you dont want to replace or repair the oil injection system you can totally disable and remove the system. (ensure that you cap off or plug where the oil line injects the oil into the carb.) At this point you can just run pre mixed fuel and know for sure that your piston is adequately lubricated with no worries of damage.

If the injection system is working correctly producing the proper amount of oil. Then yes you will only need to put just fuel into the gas tank, and only 2T oil in the oil reservoir. I recommend running a thin oil synthetic oil. My reason for this is that you dont know how tired the oil pump is. If your 2T oil is too thick it may have problems pumping the oil to the carb resulting in to little or no lubrication to the cylinder. This is mostly a problem if it is cold out side. Unless youve replaced the oil pump. Then at that time you can run what ever you'd like to in the way of 2T oil.

Hope this helps. Ive done something similar to this with a oil injected ATV that I suspected was having oil injection problems. Turns out the oil wasnt the correct type of 2T oil and it was very cold out side and the oil in the injection reservoir was really thick. So I cleaned it out and ran Red Line 2T oil to make sure the pump was working correctly. And we continue to run Red Line oil in that ATV year round with zero issues winter or summer.
 
bobkyle2

bobkyle2

Best way to tell if oil injection is working... Is that it will use the oil.... Run premix for a few tanks, While the oil system is hooked up. If it don't use the oil its not working.
 
2smoke

2smoke

bobkyle2:
Best way to tell if oil injection is working... Is that it will use the oil.... Run premix for a few tanks, While the oil system is hooked up. If it don't use the oil its not working.
Click to expand...

You could also do it the way Kyle described, as it is a little easier and the extra oil wont hurt anything except maybe foul your plug. But.............. that oil injection system is supposed to produce a specific amount of oil at different throttle settings. If you choose to do it the way Kyle described you still dont know if your oil pump is producing the Proper amount of oil. You will only know if it is producing oil or not. The description I posted is how it was explained (roughly) in the manual for the particular engine I was working with. I wouldnt want risk brand new parts on not knowing if that pump is working correctly. Not to mention the fact that your faced with ensuring that the jetting in the carb is correct for your elevation and day time temperatures. So there is something else your gonna need to figure out. But that info is readily available on the web if you look hard enough.

This link might be useful. As I find more info about your system I will post them here.
http://www.dansmc.com/2_stroke_oilpump.htm
 
MY-BLUE-BEAST

MY-BLUE-BEAST

2smoke:
You could also do it the way Kyle described, as it is a little easier and the extra oil wont hurt anything except maybe foul your plug. But.............. that oil injection system is supposed to produce a specific amount of oil at different throttle settings. If you choose to do it the way Kyle described you still dont know if your oil pump is producing the Proper amount of oil. You will only know if it is producing oil or not. The description I posted is how it was explained (roughly) in the manual for the particular engine I was working with. I wouldnt want risk brand new parts on not knowing if that pump is working correctly. Not to mention the fact that your faced with ensuring that the jetting in the carb is correct for your elevation and day time temperatures. So there is something else your gonna need to figure out. But that info is readily available on the web if you look hard enough.

This link might be useful. As I find more info about your system I will post them here.
http://www.dansmc.com/2_stroke_oilpump.htm
Click to expand...



I have access to a manual so ill look it all up
 
MY-BLUE-BEAST

MY-BLUE-BEAST

Update on engine rebuild price. After spiting the case today, instead of thursday, we looked it over and saw that it needed a few extra things. The oil seals of course, the crank bearings, connecting rod, and a few more important things. Luckily the transmission was in great shape. I will get pictures of the motor later but below is the list I need and the price with and without my discounts.

The List, The gasket set is unavailable through new stock so I ordered it from Yambits on ebay from their new old stock.

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Price without discount $522.44

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Price with discount $330.60. That's a savings of $191.84! Pretty damn good.

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2smoke

2smoke

As I mentioned earlier. That is an option and its not going to hurt anything. Just have to plug the hole where the oil gets injected. I did a little bit of reading and found out its not injected into the carb but actually into the cylinder. So the right size screw and a crush washer should do the trick. Not to mention the fact that by running pre mixed fuel you know for sure that your getting what the engine needs. Now you just need to sort the jetting per your elevation and temps and you'll have a fine running bike.
 
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