Right Crank Seal..Which direction????

chiro972

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Dec 12, 2002
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OK, I'm replacing my right side crank seal on my 1980 RM250 because the bike couldn't go more than 20 minutes without fouling a plug and the jetting was actually a bit lean. Leakdown test showed a bit too fast of a pressure loss from 5 psi.

Anyway, the manual shows the seal with the open side facing the crank. When I got in there, the open side faces the crankshaft gear. Which is right? I know fork seals have the open side on the oil side, so maybe this is right, but I want to make sure before I put this in. Maybe it was installed wrong and that's why it is leaking.

So, Concave side faces inboard or outboard??

Please help if you know!
 

Bunya

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Apr 26, 2007
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The Clymer manual for my 2000 RM250 showed the open side towards the gear. When I got it apart, sure enough, the open side was towards the gear. On the flywheel side, the open side is towards the crank. For what it's worth, looking at the fiche for your bike on YamahaofTroy, it looks like they have the open side towards the crank. You could try calling your local dealer. Also, keep an eye out on Fleabay for the service manual. They pop up on there all the time.
 

whenfoxforks-ruled

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On a 76 rm 125(with no rings)it has the seal open to the gear. the bearing is between the seal and gear,it gets lube from the tranny! My figuring says to match the other side,concave inward! So do the micro fiche's!
 

chiro972

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Dec 12, 2002
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Yeah, the parts fiche is what is throwing me off. It looks like the open side goes inboard. Mine was leaking but the bearing feels fine and I thought maybe the reason it was leaking was that it was installed backwards.

Who knows? I hate to put the new one in backwards and have the same problem all over again. It's a pain in the buttocks. Bike runs great for one moto but it will not start again after that and the plug is totally oil fouled. Putting in a new plug every time I go on the track is getting to be a pain and getting expensive.
 

whenfoxforks-ruled

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I do not believe it would hold a seal for long,that rm125 seal has springs on both sides of the seal lips! Installed correctly should solve your sparkplug issues!
 

chiro972

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Dec 12, 2002
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Wait! I'm missing your point. Are you saying that I should install it with the open side inboard? My seal is outside of the bearing and accessable without splitting the case. There is no spring that I can see on the seal.

So are you saying mine is installed wrong?
 

jason33

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Oct 21, 2006
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i have went through this as well- almost all the bikes i have rebuilt have the spring/ open side to the oil- it gets lube this way-
also if the gear slides under the lip it will not fit properly the other way
suggestion- seal the centercase gasket while your in there-
 

Bunya

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Apr 26, 2007
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chiro972 said:
...Mine was leaking but the bearing feels fine and I thought maybe the reason it was leaking was that it was installed backwards...
It was leaking because it was bad, direction had nothing to do with it.

Normally, the open side of a seal is installed towards the pressure side. Due to the design of the seal, added pressure on the open side will help press the sealing lips tighter against the shaft.

In your case, you're getting oil into the crankcase. In order for this to happen, the oil side must be at a higher relative pressure than the crank side. Because your seal had the open side towards the oil side, it should have been more effective in stopping the flow, not less.

Keep in mind the crankcase experiences both positive and negative pressure cycles so the seals have to work against both. Suzuki for sure has adopted the practice of installing the r/s seals with the lips facing the oil. They've been doing it that way for quite a few years now and there's been no indications that they fail any sooner than seals installed the opposite way.

I suspect whomever did the seals on your bike the last time installed them that way out of habit of working on newer Suzuki's. Since the fiche show the open side towards the crank, install it that way and don't worry about it. Provided the crank is in good condition, as long as the seal is installed square to the bore and not deformed during installation, it will be fine.
 

RM_guy

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Keep in mind too that there is still oil present on the crank side from the fuel mixture so it gets lube no mater what.
 

griffbones

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Sep 12, 2006
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With almost no exception, the open side of an oil seal goes towards the side or cavity holding the oil. I don't care if it is an axel seal in your pickup or a crankshaft seal in your dirt bike. Stator side seals go with the open side inboard toward the crankshaft, right side seals goes with the open side toward the gear case (location of tranny oil) closed side toward the crankshaft.
 

chiro972

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Dec 12, 2002
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Some great posts here, but I'm more confused than ever. It sounds like I can't go too far wrong either way.

I also have no way of knowing if the seals had ever been changed before. The bike is on it's second overbore, but I don't know if the bottom end had ever been looked at. The bike seems to be fairly low hours of total use. The clutch basket looked like new, no notches in the fingers, so maybe that is the original seal. The crank bearing shows no sign of play that I can detect. I grabbed the shaft and tried to wiggle it as hard as I could and felt no play.

I think I'll probably install it the way it is. Interestingly, the seal doesn't touch the crank. There is a spacer around the crankshaft and that is what contacts the inner lip of the seal. The spacer has a rubber o-ring to keep it air and oil tight. For all I know that is what was leaking. Anyway, I have both the seal and the o-ring coming in the mail. Should be here tomorrow.

Gasket might be backordered though. The clutch cover came off mostly intact. Any bets on whether I can re-use it with a little yamabond where it tore and get by until the new gasket shows up?
 

chiro972

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Dec 12, 2002
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76GMC1500 said:
I say the open side goes towards the pressure, not the fluid. Lip seals work off of pressure. The crankcase sees the most pressure.


Thinking about that a bit more, I think that area of the crankcase sees more negative than positive pressure. The combustion pressure all takes place above the piston.
 

Bunya

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Apr 26, 2007
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76GMC1500 said:
I say the open side goes towards the pressure, not the fluid. Lip seals work off of pressure...
That's not entirely true. Yes, increased pressure on the open side will provide greater sealing ability, but a seal will work perfectly fine in neutral pressure. The garter spring provides enough pressure on the lip to maintain an effective seal in the absence of external pressure.

There are hundreds of lip seal designs so it's hard to generalize about them. In this case we're discussing crank seals which are going to experience positive, neutral and negative pressure differentials. With this in mind, I would imagine the seals are designed with 2 lips facing opposite directions and a stiffer garter spring to aid in sealing pressure from both directions.

Another factor that hasn't been brought up is hydraulic pressure on the gear side. Although there won't be positive air pressure on the gear side, the flow of the oil around the gear may impart a hydraulic pressure in the seal area which may be why Suzuki found it necassary to install it 'backwards' from convention in their newer designs. I'll assume that the engineers that design these things know more about it than us and not second guess their design.

This is why I suggested the OP follow the fiche and manual that show it being installed conventionally and put the open side towards the crank.
 

whenfoxforks-ruled

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Put it together like the fiche shows. What about changing the volume of the lower end? Not alot,but it will! There is no amount of figuring to find out why it was installed backwards. As long as your bearing did not cause the seal to go bad. Properly installed,square to the bore,and down to the chamfer in the case.
 

76GMC1500

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Oct 19, 2006
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The crankcase in a 2-stroke sees positive pressure. 2-stroke engines use underpiston supercharging to scavenge the cylinder. That is part of why the bike has reeds, to keep the fuel/air mix from being pushed back through the carb during periods of elevated crankcase pressure.
 

griffbones

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Sep 12, 2006
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I know for a fact that the right side crank seal goes with the open side towards the tranny oil. Besides the crankcase alternates between pressure and vacuum. Show me a manual transmission that has the open side of the lip seal outward on either the input shaft or output shaft! How about an axel seal, a primary drive or tranny seal on a H-D, how about the pinion seal on the rear end of your truck, do I need to go on?
 

chiro972

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Dec 12, 2002
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OK, Thanks for all the advice everyone. I placed it as it was, with the open side towards the clutch. That was at the advice of my mechanic who works on lots of vintage bikes. I'll let you know how it works and if it solves my fouling problem.
 

Bunya

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Apr 26, 2007
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griffbones said:
I know for a fact that the right side crank seal goes with the open side towards the tranny oil. Besides the crankcase alternates between pressure and vacuum. Show me a manual transmission that has the open side of the lip seal outward on either the input shaft or output shaft! How about an axel seal, a primary drive or tranny seal on a H-D, how about the pinion seal on the rear end of your truck, do I need to go on?

The direction seals are installed in axles, transmissions, etc. have absolutely nothing to do with this discussion which is about crank seals on MX bikes. Most bikes have the open side of both seals in towards the crank, contrary to your line of thinking. As far as I know, Suzuki is the only manufacturer which reversed the r/s crank seal and has the open side facing outward towards the primary gear, and that is only on later models. The fiche for his bike clearly shows the r/s seal installed open side towards the crankshaft, as does his Clymer manual. I suspect that Suzuki who drew the fiche, and Clymer who took the same model bike apart and documented it, are probably a more reliable source of information than your experience with completely unrelated items.
 

whenfoxforks-ruled

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griffbones said:
I know for a fact that the right side crank seal goes with the open side towards the tranny oil. Besides the crankcase alternates between pressure and vacuum. Show me a manual transmission that has the open side of the lip seal outward on either the input shaft or output shaft! How about an axel seal, a primary drive or tranny seal on a H-D, how about the pinion seal on the rear end of your truck, do I need to go on?
I am fairly certain all your bikes have the seal open to the crank,when applicable! So either there is confusion,or you are the perpetrator of misinformation and backwards seals! That 76 rm125 is THEE only one I have ever seen,and it was double lipped and the right bearing got lube from the tranny! http://houseofmotorcycles.bikebandi...wSchematic.aspx?deptId=1130318&machineId=3774
 

griffbones

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Sep 12, 2006
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OK, Thanks for all the advice everyone. I placed it as it was, with the open side towards the clutch. That was at the advice of my mechanic who works on lots of vintage bikes. I'll let you know how it works and if it solves my fouling problem.

Seems to me that I am not the only person to have come across this same finding!
My old YZ's had the open side towards the clutch, my '83 CR60 had the open side toward the clutch. Maybe manufacturers have done it both ways? But, most of the bikes that I have opened up have had the open side toward the clutch, most were older bikes though, but not that it should really make a difference. This is just what I have found, I am not trying to give any misinformation, just sharing experiences. I didn't mean to ruffle any feathers fellas.
 
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