Datsun Roadster Forum-311s.org

Hi All,

Has anyone had luck replacing the rear main seal or at least the bottom portion with the motor still in the car.

I'm trying to address an oil leak without having to remove/rebuild the engine.

Thanks

You have a 50/50 chance that it’s the bottom half and can be done by pulling oil pan and rear bearing cap. Some people have had luck with additives but I think that’s for hi mileage cars. Think many of us live with it till engine pull time.

I'm in the same boat on my new motor. I simply did not follow the rules (namely soaking over night in oil) and she's still leaking. I've built several engines over the years and never had one leak. My bad. I had set aside a day to build the bottom end, and forgot to put the seals in oil the day before. Went ahead, paid the price. Lesson learned. The engine has about 6-8000 miles on it now, and it's reduced but still there, and I'm hopeful it will stop (I had one go for a while then stop before). It may be the switch back to 20/50 weight oil helped.

I've reviewed the factory manual procedure, and while it may be possible I think it would require a lift and at least one full time assistant. Without those two things I don't think it's feasible. Even then I think it's 50/50, maybe better if you're zen about it (really take your time). The alternative is to pull the motor, which having done it many times is far easier than trying to do it in car and some thing I can do myself. I don't have a lift! But to really do it right (and to make all the effort worth it, eh?) you need to pull the crank, and that means the front crank bolt, front cover, etc, so it's really some disassembly required. And retorquing, and now we're into more gaskets etc etc... hmmm.

I think with the in car method, the hard part is having to turn the crank while working in the upper seal, when we all know there's very little room to fit in a compression style rope seal. This would be the point where failure is most likely to occur I think. But if you could pull it off it would save having to remove the engine and trans, retorque all the mains and rods, pull the carbs, front cover, drain the rad, remove the grill, remove the hood, etc. Wow, as I think about it, LOTS of work. Doing it in car will require two able people though. One to turn the crank and the other to guide the seal. I'm going to continue to monitor mine, but if I do this I'll post how it goes.

Do you have a copy of the factory manual? If not I think one is on this site.

It is possible that it could be one of the side seals too. They can be really tough to get right. You would know when you pull the rear cap.

I was lucky that the side seals were leaking on the ends, not the main seal. A couple of small dabs of rtv sealant cured on the ends of side seals did the trick for me. I also checked beforehand to make sure there wasn't a notorious tach cable leak dripping down into the transmission bell housing.

Cheers
Ray B.

itsa68 wrote: Thu Mar 26, 2020 5:45 pm I was lucky that the side seals were leaking on the ends, not the main seal. A couple of small dabs of rtv sealant cured on the ends of side seals did the trick for me. I also checked beforehand to make sure there wasn't a notorious tach cable leak dripping down into the transmission bell housing.

Cheers
Ray B.

I'll consider that! Thanks!