Datsun Roadster Forum-311s.org

Just wondering if there is a better type of seal for the U-20 two liter motor than the traditional rope style. I figure this works okay when the cars are regularly driven, which mine is not. I have noticeable, but not bad, leaking from the small hole where transmission joins motor after driving, but not while sitting. I’m guessing this must be rear seal, it does not appear to be transmission fluid. I’m also guessing substantial time to complete this repair, after motor is removed. I have not been able to find much info on this in the forum, at least so far. Thanks

Crap shoot on this one. Many swear by soaking in oil overnight before install. I don’t think anyone’s come up with the doughnut style rubber like L-series. Mine failed initially, on second attempt soaked bottom half only and now dry. Had a 50/50 chance that it was the bottom half and it was. Good luck!

+1 on soaking the rope seal in oil overnight. Some have adapted a split neoprene rear seal (although I never have) with reported good results. Once the engine is out it is quite easy to replace the seal.

That being said, I recommend you positively eliminate every other possible leak source first. Anything can look like a rear seal leak since the weep hole is at the lowest point and on a big flat oil drip loving surface

Once the drip has stopped for the day:
Clean the bell housing & flywheel cover VERY thoroughly, and run a pipe cleaner up into the weep hole a few times until it comes out clean(ish). Now, duct tape-off the whole front of the flywheel cover in heavy plastic, top to bottom and all the way from left door to the right one (keeping it well away from the exhaust) and let the plastic extend 4” below the weep hole (not quite touching the ground). Now, drive the car for 10-15 mins (a little hwy time helps) and then park it on a level surface (make sure the plastic is hanging down straight and not folded over - Wait a couple hours.

When you check it, if only the front of the plastic has most of the oil dripping down it, it’s not the rear main seal.

When many people regularly drove gravel roads
Like in the 60s the dust & grit of the gravel drifting up and getting between the rubber and wearing the crank way down quick , the rope shielded it more
The rope swells a bit as it gets full of oil

Thanks for the feedback, guys. I've already begun process of engine removal, so I can't try Kai's method to isolate fluid type, but appreciate your input. I guess I was thinking crankshaft would have to be removed to access that half of the seal? Not looking forward to that.
Thanks to all.

Yes the crankshaft MUST be removed to change the upper 1/2 of the seal. (front cover off, chain off, etc).

The rear seal design itself is not a problem, so there is no good reason for another type of seal. Rope seals just like these were used on MILLIONS of cars without issues.

If they leak, they are simply worn out from miles, were installed incorrectly, your crankcase ventilation is not under vacuum or is too restrictive, or your rings are shot-very common-(causing excessive crankcase pressure).

hope this helps! j

Maybe you’ll get lucky and find the break in the lower bearing cap (if it’s actually the rear seal causing the leak). If not that lucky, it can still be done in a weekend if the engine is already out and you have all the seals and gaskets … maybe a bit longer if you take the opportunity to also install a new clutch whilst things are apart
Let us know.

It would really make more sense to change the complete rear seal assembly, not 1/2 of it.

It's lots of time and effort to pull the engine. Suggest you do it right the first time.

It would be nuts not to change the clutch (disc at very least) at the same time...

I agree with that advise JT68, got to embrace the “as long as you’re in there” mantra. I will see this through and return this car to the road with renewed desire to drive it more often. Removed the solex carbs that made it a little wild and loud and led to it not desirable, especially with wife in tow. SU setup will return it to more civilized experience. Will be selling the solexes soon if anyone is interested, although they are the early style. I am going to check in to the venting requirements mentioned earlier to insure it is properly done.
Thanks all

I strongly recommend viewing a video entitled "replacing rear main seal on Holden V-8". Watch it three times and take notes. I have done a few seals on old farm tractors in addition to my roadster. I found this video to be comprehensive in the details that are so important for the job to be successful. I will also emphasize to others investigating leaks to embrace the advice offered by Bwk2000.

Link below:
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Holden V8 Rear Main Seal Installation
...at least I believe this is correct