Stihl Clam Shell Crank Seal Differences?

[SteveSr]

Hello,

Currently working on rebuilding an MS251. I have 2 engine assemblies and am going to make one good one. I noticed that the oil seals appear to be a different color from the FW and PTO side. This makes me wonder if they are different materials. The PTO side is brown while the FW side is blue.

The IPL shows a technote 44.2010 that changes something. Unfortunately, I don't have access to that TN. It doesn't appear to be included in the 2012 MediaCat.

I also noticed that one of the FW seals had contamination between the outer lip and the inner lip. I can't explain how the contamination got there unless the inner seal was also leaking which may be why the saw burnt up. BTW, one of these engines has a 2014 DOM and the other 2017.

Do any of you have an idea of what is going on here?

Thanks,
Steve

 

[Loony661]

This won’t directly answer your question, but if memory serves me right from my dealership days, there is a different seal used for the clamshell engines depending on whether the seal will be installed as the crank case cover is tightened, or if the seal will be pressed into place on an already assembled engine.. there was a tech note about it on certain models.

As for the different color seals per side, not sure why that would be..

 

[huskihl]

I’ve seen different colored oem seals. Figured they were from different suppliers or older vs. newer stock. I wouldn’t worry about it if they fit

 

[qurotro]

I’ve seen different colored oem seals. Figured they were from different suppliers or older vs. newer stock. I wouldn’t worry about it if they fit

This.
I think the seal supplier CFW? use different color rubber from time to time. I have an OEM 660 seal that is brown from the last year order, the marking is the same as the blue ones. The latest one 660 seal I ordered for my asian bulid is blue again.

 

[DND 9000]

The oil seals in your picture are the soft ones with a snap ring. These rings are used on the closed engine. The hard ones without snap ring are used if the engine is disassembled.

Install the soft oil seal with the snap ring facing outwards and the hard oil seal with its open side facing the ball bearing.

 

[Al Smith]

Regarding colors .It was maybe 10 years ago I noticed the OEM seals from a dealer were a shade of dark blue rather than black .Same with carb rebuild kits .What I think these newer examples might have been more robust in standing up to ever increasing ethanol mixed gasoline .At approx the same time having worked in an automotive engine plant at the time certain seals, o-rings etc. connected to the fuel injection were also changed . Saying that the older seals and carb rebuild kits will still work .

 

[SteveSr]

The oil seals in your picture are the soft ones with a snap ring. These rings are used on the closed engine. The hard ones without snap ring are used if the engine is disassembled.

I think that you got this backwards. Take a closer look at the photos. These are the "hard" OEM seals that came from the factory.

 

[SteveSr]

Well, I did a little research and I think I have a plausible explanation. FCW is Freudenberg and the attached datasheet shows seal color corresponding to seal material type. The blue is regular nitrile whereas the brown is a fluoropolymer. The fluoropolymer holds up much better to fuel and especially heat.

If Stihl has been "cheaping out" and using just nitrile on the FW seals this may help to explain the FW seal failures that seem more common on Stihls. Stihl may have gotten away with nitrile in the past but these new strato engines run much hotter and are harder on seals.