technical question

[Dale Sonnenschein]

I've been on this site for quite a while now and value the wealth of knowledge here. So while my question is not penton related, it is hopefully general engine knowledge.
I'm working on a 72 suzuki ts250. I split the cases and the right side crank seal had the spring of the seal facing the crank. The seal is inboard of the bearing. I'm not sure if the seal was in correctly or not. Is the back side of the seal (spring side) supposed the face the oil side (clutch cover) or should it face the crank?

[G Ellis]

Yes that would be correct. Just like on the sach's and KTM motors. Spring side to the oil.

[Dale Sonnenschein]

Thank you Gary. That was my thought but I wasn't sure when I saw the seal with the spring side towards the crank.

[Daniel P. McEntee]

Somewhere along the line you will encounter a seal that doesn't have a spring, but the shape of the seal take the pressure from the "liquid" side to make the seal. Look closely at the shape of the rubber and you'll see what I mean. It relies on that shape and pressure in addition to the spring to make a leak proof seal. I had always thought that the spring was there just to help the seal at rest, when nothing is rotating to create the pressure needed to do the job.
   Type at you later,
  Dan McEntee

[Mike Rosso]

From my experience I would say the spring side of a seal usually faces the side of the most pressure or in this situation the crankcase or crankshaft. The spring side of the seal is actually a compression chamber in a sense and a 2-stroke builds pressure as the piston comes down to build pressure to force the charge up through the transfer ports and for scavenging the previous spent charge. If the spring side or compression side of the main seal is on the transmission side then the crankcase pressure can more easily pass through. Fork seals work the same way as the spring/compression side is facing the oil and fork air pressure side. If you flip a set of fork seals spring side out you'll see what happens. The same with the ignition side seal, the spring side is almost always facing the crankcase/crank pressure side. There were a few later model year KTM's that had the transmission side main seal with the spring facing the lower pressure side. This was on 2-stroke engines where the main bearing was inboard and the main seal out board on the pinion gear side. The main seal rode on a very narrow part of the crankshaft outboard of the main bearing. When I asked KTM engineers about this they said that in those engines it was a production issue to quality check that the spring did not come off of the seals during production engine assembly. It was nearly impossible to see if the spring was still on the seal between the bearing and seal with the crankshaft installed unless you went to extra lengths of careful  assembly. The factory decided to not take the time or extra steps for what they considered minimal crankcase pressure loss() I thought that was strange and then told (on the side) that the race team mechanics argued that too and carefully installed the seals with the spring side facing the crankshaft higher pressure side. 2-stroke transmission/clutch cases do not have high pressure like the (2-stroke) crankcase, if they did or do then it's from a failed main seal leaking high crankcase pressure into it. I've always installed seals and especially 2-stroke main seals with the compression (spring) side facing the higher pressure side.

[firstturn]

Great read Mike Rosso. I have always installed the spring side on the side with any or the higher pressure side.

Ron Carbaugh

[Dale Sonnenschein]

Mike, very interesting info. I found a diagram for this bike and indeed it does show the spring, or compression side facing the crank.
Thank you all for the advise.

[Toolsurfer]

The spring creates pressure and causes the seal to retain shape before and after pressurized . technically called energizer spring I believe . Some times Quad Rings use O-rings as energizer . Just saying?

[t20sl]

I do not think all engineers agree on this. There is both negative and positive pressure in the crankcase area.  Bearing location has no affect that I know of.  Puch 125 /175 were originally smooth side against crankshaft.  Then in about 1973 they reversed and put same seals in with springs facing crankshaft.

[G Ellis]

Well I for one know if you switch them around in a Penton/KTM motor. You will be fogging for insects.

[Toolsurfer]

Right on  G. Ellis