1978 DT 175 Yamaha Question ???

[JLC1931]

If any of you know anything about these, please, help me out.
I Have a 1978 DT 175. After about an hour, to an hour and a half, of riding, my bike will burn about a 100cc of oil out of the lower cases. What would everyone's first thought on this be...a crank seal??
Thanks... :cool:

 

[XRpredator]

it burns the oil or it just leaks? If it's burning the oil, you should probably re-ring it. If it's leaking, you have several options . . .

 

[2 strokes for life]

The crank seal is bad on the DT and IT175. Or, it could be the drain plud seal is gone.

 

[thorman75]

If its not leaking, its the transmission side crank seal.The same vacuum that draws fuel into the lower end will suck the oil out of the trans if the seal is bad.Rings have no effect in this area(only on a 4/Stroke).Sounds like its time to split the cases and change crank bearings and both seals, tranny and ignition side.

 

[XRpredator]

If its not leaking, its the transmission side crank seal.The same vacuum that draws fuel into the lower end will suck the oil out of the trans if the seal is bad.Rings have no effect in this area(only on a 4/Stroke).Sounds like its time to split the cases and change crank bearings and both seals, tranny and ignition side.

ah yes, you are correct sir. I keep forgetting that even though the two stroke is dead, there are still two strokes out there. ;)

and I truly should have known, as I owned one of these machines.

 

[TimberPig]

If its not leaking, its the transmission side crank seal.The same vacuum that draws fuel into the lower end will suck the oil out of the trans if the seal is bad.Rings have no effect in this area(only on a 4/Stroke).Sounds like its time to split the cases and change crank bearings and both seals, tranny and ignition side.

There's also a slim possibility it could be the centercase seal letting oil into the crankcase, or leaking out as well.

 

[thorman75]

There's also a slim possibility it could be the centercase seal letting oil into the crankcase, or leaking out as well.

not sure what you mean by center case seal.If you mean the gasket between the 2 case halves is leaking you could be right, but if I remember correctly there is no gasket, the cases are a matched set and are lapped together.

 

[TimberPig]

not sure what you mean by center case seal.If you mean the gasket between the 2 case halves is leaking you could be right, but if I remember correctly there is no gasket, the cases are a matched set and are lapped together.

Yes, I was meaning that they can leak at the seal between the case halves. Yamahas don't use a gasket there, they use a non drying sealer (Yamabond). They are lapped together, but they can warp and develop leaks in rare cases.

 

[thorman75]

When I was working at the shop we we're instructed not to use any type of sealer on matched cases.The sealer itself could cause the leak.In any case I'd bet it's the tranny side seal, and it's leaking because the bearing is starting to get loose ;)

 

[djj]

ah yes, you are correct sir. I keep forgetting that even though the two stroke is dead, there are still two strokes out there. ;)

and I truly should have known, as I owned one of these machines.

The two stroke is dead, the two stroke is dead, the wicked witch is dead, NOT IN THE WOODS.
Are you fouling plugs, usually when you start sucking trans oil you are fouling plugs.

 

[XRpredator]

The two stroke is dead, the two stroke is dead, the wicked witch is dead, NOT IN THE WOODS.

I ride in the woods . . . on a 4 stroke :fft:

wish I had a Pro-Tec TT500 to ride in the woods

 

[TimberPig]

When I was working at the shop we we're instructed not to use any type of sealer on matched cases.The sealer itself could cause the leak.In any case I'd bet it's the tranny side seal, and it's leaking because the bearing is starting to get loose ;)

I'd have to agree on the crank seal being the likely cause if it's ingesting the oil, rather than leaking it, although you're going against what Yamaha and kawaski both reccommend for sealing the centercase by not using the sealer. We're talking a very thin layer, not big clumps of it here, so it helps fill any imperfections andseal the cases.

 

[thorman75]

I worked at a Kawasaki,Montesa, Benelli,Puch, shop. I remember this very keenly as I was been taught by the District Service Manager. The Z1's had just been released and the 73 models if you recall were so new the cases were sand cast and we were having lots of problems at first.No bond, permetex nothing, I listened and it was fine.My first bike was a 70 G31M Greenstreak that blew up faster than I could rebuild it.Again no sealer, would it hurt? I doubt it, but just gives you extra work next time, if any, it comes apart. I was at the shop so often with that G3 they actually gave me a job.It was good because I ended up getting to race the owners bike which was much nicer than mine.Puch 175

 

[chicoman]

One other possibility, check where the main bearings press into the cases, the bearings press into rings which are made of a different type of metal. These rings can sometimes come loose causing leaks, even with new bearings and seals. The best cure is to weld them back in. It took me a few rebuilds to find this one on an old IT175 I used to have. To seal the case halves I use loctite 515 or 3-bond.