Main seal?

[srankin]

Sorry I am picking this up and haven't keep up with all possible threads you have posted.

In the case of the oil getting on the clutch there are only two places it could come from. The rear main seal or oil pump housing. I may be picky but anytime I have the transmission out, I replace the rear main seal and oil pump ring. Sorry I am to sure if you have done this at any other point in your rebuilding.

FYI. I have installed at last rebuild a clutch kit I got from EME. Knock on wood it has been very good and was reasonably priced.

As to the mysterious uneven wear, I don't have a clue except to check the flywheel for true. Good luck, St.

[Jim D 5112]

If you repair with the Heli Coil or a Time Sert either one will be superior to just an oversized threaded hole in the aluminum casting. Especially important when it’s a fastener that you will be removing and retighten occasionally. Plus you will retain the original size supplied when new.

[flyingtpot]

From the pics, the majority of the threads are gone/toast, so 'cleaning up' or rethreading the current M12 threads with a tap is not feasible.

I do that repair by installing Time-Serts. It makes for a robust quality repair. Heli-coils are weak for the application and the depth is not ideal for using them. Tig welding and tapping is another repair process. Yet it is cumbersome, time-consuming and not forgiving to any impurities that were not removed from the casting.

Tapping to the next size common/standard drain plug will be M14 threads. The problems with that are the M14 thread major diameter is not optimized for this thread location. Often times that factory FD casting boss has the original M12 thread through hole off-center, whereas positional placement of that size is critical in this application. Also, standard M14 drain plugs have a longer length under the head than the M12 plug. That needs to be monitored. Along with the fact that the M12 drain/fill plugs are damaged from 'misuse'. The use of a M19 socket/wrench on a M14 drain drain plug in this application is asking for more problems.

Also, there is a reason that M12 Time-Serts are made......To fix damaged M12 threads.

[srankin]

I have to laugh at fate sometimes. I just watched a Youtube video on a fellow testing ten different methods of thread repair.

Time serts was high on the best list but very expensive. It was impressive how well they hold up under stress of torque and pull.

Looks like I will be getting a few different sizes for my tool box in the future. St.

[toolmandoug]

This is how I have repaired stripped threads. I use a heli-coil. Timeserts are better, but heli-coils are stronger than what came from factory. I clamp my jig on the drill press table, the housing is strapped to the jig. After drilling I leave jig clamped and put the tap in the DP to start it square to the housing. If hole or threads are not square to housing, neither option will work.

[San Arthur]

Thanks for the suggestions! I’ll be using either Heli-Coils or Timeserts to repair the threads. I appreciate the detailed tip about keeping the threads square to the housing—really helpful advice.

I was about to remove the final drive to check the source of the leak but decided to first check the bottom of the engine for any play in the rods. If there’s an issue, I’ll need to overhaul the engine, which means removing and reinstalling the main seal, oil pump seal, and flywheel. I’d rather check everything now to avoid doing the job twice.

[srankin]

Don't get too worried about the overall engine condition. It is a good idea to check rod clearance but unless the engine has a lot of mis or was starved for oil, the crank bearings, cam bearings, and big stuff are very bullet proof and last a long time.

I have over 200K on my R80RT and now am the owner of a R100Rt with over 200K. Neither have ever had to have any major engine work done on the rods or cranks.

LOL, the only time I ripped my R80RT down to bare block was when I foolishly soda blasted it and the soda crap got inside and gummed things up. I couldn't get all of it out without a complete tear down and good flush out, other than new seals it all went back together with all parts other than seals.

Rear main seals in older bikes were prone to wear. The new replacement seals are supposed to be better.

I did have to replace the jugs, pistons and have the heads redone on the R80 due to wear of the rings a long time ago. Connecting rod bearing were good. That is another story.

Have fun with the restoration and more importantly riding it when done. St.

[San Arthur]

Thank you for any insights!


Thanks for sharing your insights—it’s great to hear how durable these engines can be when they’re cared for! The confidence you have in the crank and rod bearings is reassuring, especially since I’m not seeing any red flags in those areas on my R90S.




I’ve been thinking about how to tackle the carbon buildup in the combustion chambers on mine. They’re pretty loaded with black carbon, and I’m debating between just cleaning it by hand with some elbow grease or going ahead and fully disassembling the heads to check the valve guides while I’m at it. Under the valve covers, everything looks nice and clean, so I’m leaning toward just cleaning things up and leaving the internals untouched for now.




The cylinders also look good—no scoring or major marks—and when I had the bore measured at the shop, it came out to 90.099 mm and 90.100 mm. The pistons are marked 89.965 mm, which is well within the factory tolerances, so I’m pretty sure this is all original and in decent shape. I’m planning to clean everything, replace all the gaskets (I had some leaks at the tappet guide seals), and put it back together.




While I’m at it, I’ll also paint the cylinder fins and blast the head and valve covers for a fresh look. It’s been a fun project so far, and I’m looking forward to getting it back on the road. Thanks again for the advice—your mileage stories are inspiring!



My plan is to clean and reassemble the engine, replace the clutch, and remove it from the frame to address fatigue cracks that need welding and to repaint the frame.

[srankin]

The good thing about your bike is it is not in the age group of bad valve seats as my R80RT was. I would do the same if I have heads off, it doesn't take much to inspect the valves. Good news about your jugs. As for the carbon, what I see is normal for ridden bikes. It doesn't hurt to clean things up with elbow grease.

You should see the "project" bike I have now. I was going to just convert it from an RT to a naked bike but as I get working on it the picky part of me decided to do a frame up restoration. It is a lot of fun to have a great project for the winter hours.

Nice writing to you, this is what can make the forums fun. Good luck on your project I can't wait to see the finished pictures.

St.

[San Arthur]

Thanks for your thoughtful reply! I’ll definitely take the time to check the valves and guides as you suggested. I did notice a little smoke coming out of the right exhaust, which had me wondering. When I drained the engine oil, I ended up with more than 2.5 quarts—could this be from oil finding its way into the combustion chambers after sitting for a while? I’d love to hear your thoughts on that.

Also, I noticed the fins on the right cylinder head are darker and harder to clean compared to the left. Not sure if that’s normal or something I should dig into further, but it caught my attention.

Have you uploaded pictures of your project bike? I’d love to see how it’s coming along! It sounds like an incredible transformation, and a frame-up restoration is a big undertaking.

Thanks again for chiming in—it’s exchanges like this that make the forums feel more like a conversation between enthusiasts and less like a monologue. Looking forward to hearing more about your project and seeing some pics!