DD 8v71 rear oil seal change out

[mike]

Does anyone have experience changing out the rear crankshaft oil seal on a detroit? How difficult is it to perform? Any tricks or cautions I should know about? I have my transmissions out and it seems like a good time to make the change, any comments/advice is appreciated. Tx, mike

[captddis]

not real hard but you need to be careful. You will probably need to use the sleeve and oversize seal. It is much easier if you have the installer. Do not pound on the sleeve or it will break. The oversize seal is thicker than the original. You need to carefully measure how deep you install it. If you put it flush it will hit the crank, not deep enough and the flywheel bolts will get it.
Also the seals are directional, make sure you get the correct one and that you need a double lip seal for the Allisons. Good Luck,
Dave

[mike]

Dave, thanks for the info. What do you mean the seals are directional? What specifically make the seal directional? I have recently replace the flange seals on my transmissions and seen the same indicator, but could not discern an obvious difference that would indicate direction was an issue. In fact when I asked about it, the answer I got was it did not matter, but I am skeptical about the response. Any insight you have is much appreciated. I don't want to do this twice. The trans shaft seal is easier but still a pain, and the crank seal is a once in a lifetime activity for me I hope. Mike

[Genesis]

Pull the old one and see if the crank looks ok. If the surface is damaged in any way, then you need the oversized one and the sleeve.

You have the flywheel and scuff plate off?

[Nonchalant1]

The simple answer is: to do it right requires special tools, like a seal lip expander and seal alignment/installer, to prevent damage to the seal and to ensure correct installation. You also have to know which things must be lubricated during installation and which must be dry (the teflon and wear sleeve must be dry to achieve teflon transfer).

You probably know that seals have inner flanges (lips) that point in one direction. The lip on a seal is the rubber sleeve that is bent at an angle so the lip of the seal rides against the sealing surface at an angle. The angled lip points towards the "wet" side. On DD 8V71 rear seals, there is a double lip and the inner lip is teflon while the outer lip is silicone. To add to this, DD8V71 rear seals are also directional based on engine rotation, so your port engine takes a different part number than your starboard engine. If installed for the wrong direction, they will fail quickly. You can take your engine model number and serial number and DD can look up your individual engine specs and sell you the right seal for it, including a "wear sleeve" for the used crankshaft. Check for grooves on the crankshaft. The wear sleeve covers the crankshaft to smooth out the groove made by the prior seal. Sometimes you can use a spacer instead to move the oil seal to a smooth part of the crankshaft. A wear sleeve seal is oversized compared to a normal seal used with a spacer.

I know there are those that do it by themselves, and I know they sometimes have to redo it in a few years because it wasn't done right. Because of the large time or expense involved in getting at it, I think the best tool to use for this one is your checkbook. Call DD and they'll bring the special tools and correct direction seals. You already did the big part of getting your gears out, splurge on this smaller, more critical step.

Doug

[MikeP]

Yes, crank seals on most engines are directional as are front cover seals. As Doug explained, installing seals incorrectly will cause early failure because the seal will actually be trying to force the oil OUT of the engine instead of keeping it in. If you look carefully at a directional seal, there are usually tiny grooves in the area between the inner and outer lips. The grooves are angled. You can see that if a shaft bearing against the seal turns in one direction, oil in the grooves will be "pumped" in one direction; if you either flip the seal around or reverse the direction of the shaft, the oil will be pumped in the other direction. Obviously, the idea is to pump the oil back toward the pan, not out the front or back of the engine.

[captddis]

Mike,
The seals are also color coded to make life easier. Orange is RH and green is LH. The installer makes life much easier. Maybe you can borrow or rent one. It can be done without the tool. Just be sure to get the clearance on the seal correct. If you try to tap the sleeve it will split. I have seen some of the local DD factory mechanics screw them up, so paying the bjg bucks is no guarantee of a proper job! Do it yourself and take your time. Dave
PS on a used crank always use the sleeve. And the double lip seal is only used with A llison gears.

[mike]

I will pull the flywheels and give it a try. I managed to install a ready seal on the trans output flange couplers with no problems, but having said that, they came with the correct install tool. I'll let you all know how it turns out. Thanks everyone for the insight and info. mike

[Eufaula]

Mike,
Special rear seal puller can be had from your dealer or maybe borrow one. No one mention anything about pulling the old seal out, heregoes anyway, I drilled two holes on the seal one opposite the other and with the puller or a two tip bend screw drivers will surely get it out of there. Drill only the depth of your front seal face. Take no chance buy the sleeve type and be caut. driveing the sleeve and the seal to the crkshft. Good luck.

[jim rosenthal]

I didn't know 8v71s came in LH and RH rotation!!! I thought the shaft direction change was in the gears!! What do you know....