Crankcase oil seal orientation?

[bosco659]

This question relates to the installation of crankcase oil seals in a 2 stroke engine, but I thought there would be knowledge available from members of this group.
I’m replacing a damaged oil seal behind the flywheel of my ‘78 Yamaha DT175E enduro bike. Took it apart, ordered a new seal and but read on line that I should be reinstalling the oil seal with the lip facing outward and the “flat side” towards the crank bearing inside the crankcase. Now this has

thrown me off because I’ve never installed a crankcase seal in that orientation. I’ve always positioned the lip of the seal inward towards the bearing (with the seal spring located inside the crankcase). The seal I removed had the flat side with the numbers and markings facing outward.
I’ve attached a picture of the old oil seal beside a new one (the new one is a camshaft seal, for the 650) for reference.
Please let me know what you know about this. Thanks

 

[gggGary]

Haven't done this but the two stoker forums say; it depends.
Spring towards the oil, so if the seal separates crankcase from transmission oil the spring faces the tranny side, if it separates crank from atmosphere spring faces in towards the crankcase.

 

[Paul Sutton]

I see your dilemma. The attached video for a Suzuki illustrates the issue well:

Sorry I cannot answer your question.

 

[bosco659]

Haven't done this but the two stoker forums say; it depends.
Spring towards the oil, so if the seal separates crankcase from transmission oil the spring faces the tranny side, if it separates crank from atmosphere spring faces in towards the crankcase.

Thx. In this case we are sealing the crank from atmosphere so I agree the spring should go towards the inside of the crankcase. That’s what I would have done until others say the opposite.

 

[bosco659]

I see your dilemma. The attached video for a Suzuki illustrates the issue well:

Sorry I cannot answer your question.

Video is good but essentially tells you to follow the manual. I have a factory service manual and it doesn’t tell you anything about the orientation of the seal. I think spring inside makes sense. Old one was that way (but leaked lol). Thx!

 

[Paul Sutton]

In the video they show that the right seal can be a very specialist design and then you need the technical manual. The left seal is what I call a plain old ordinary oil seal. With these left seals I consistently see them being removed or fitted with the spring facing into the crank case. In the following link the guy is working on what must be the DT250. He fits the left seal with the spring facing out (See his photos) then acknowledges he did it wrong and states the spring should face in:
http://www.chinonthetank.com/2014/09/replace-yamaha-2-stroke-crank-seals/

 

[arcticXS]

Post your question on 2strokeworld.net.
The crankcase pressure on a 2 stroke varies between partial vacuum and low pressure.

 

[bosco659]

In the video they show that the right seal can be a very specialist design and then you need the technical manual. The left seal is what I call a plain old ordinary oil seal. With these left seals I consistently see them being removed or fitted with the spring facing into the crank case. In the following link the guy is working on what must be the DT250. He fits the left seal with the spring facing out (See his photos) then acknowledges he did it wrong and states the spring should face in:
http://www.chinonthetank.com/2014/09/replace-yamaha-2-stroke-crank-seals/

Thanks, I saw that article. Looks like the old seal was in the other way around too. Apparently, for my bike, the DT175, the seal has a single lip. The IT175 is supposed to be a double lip seal and people put those in “backwards” in the DT175’s. Maybe once I get the seal I’ll flip a coin and make a decision that way.

 

[bosco659]

Post your question on 2strokeworld.net.
The crankcase pressure on a 2 stroke varies between partial vacuum and low pressure.

Let me search there. Another option that I just thought of. I sold a propane heater to a guy yesterday and he told me he was a Yamaha mechanic for many years until the local dealership closed (maybe 15 years ago). I should ask him which way to put the seal in. I’ll report my findings.

 

[Paul Sutton]

Oh yes, you guessed it. I am bored today. I found a 1978 DT175 manual with clear pictures:
Left Seal

Right Seal

Note the spring is visible in the right seal.

These picture were grabbed from the free manual at@
http://www.scrimsmustangclassicyama...k-list-and-service-manuals-free-download.html

Perhaps these will help your decision making.

 

[bosco659]

Oh yes, you guessed it. I am bored today. I found a 1978 DT175 manual with clear pictures:
Left Seal
View attachment 183799

Right Seal
View attachment 183800

Note the spring is visible in the right seal.

These picture were grabbed from the free manual at@
http://www.scrimsmustangclassicyama...k-list-and-service-manuals-free-download.html

Perhaps these will help your decision making.

Great...thanks!

 

[bosco659]

Was in contact with the ex Yamaha mechanic and he confirmed lip pointing in towards the crankcase and flat surfaces with the mfr’s numbers and markings pointing out. Please note that this is for my specific application. Other models and manufacturers may differ.

 

[cra-z1]

If pointed in the other direction you would be pulling oil from the transmission in a short period of time.

 

[arcticXS]

Many 2 stroke crankshaft seals have lips on both sides.

 

[bosco659]

Many 2 stroke crankshaft seals have lips on both sides.

On this application it has single lip with dust seal. I know that a different model with the same engine has a double lip seal. Go figure?

 

[JRay77]

To me the taper towards the hole. Helps the seal go in like a chamfer. I actually take a burr knife and slightly taper holes too. Being careful not to contaminate with shavings.