What is making the noise I can't say, but obviously the new flapper valve is sealing VERY well. The old one was probably allowing some air back into the engine, so there was no noise. Now, with the stronger seal, there's a greater vacuum inside the engine.... which is what you want.

Wobs,

Thanks for the reply. Your comments echo my thoughts, exactly. Just trying to get some feedback if there was any reason for concern.

Update:

After a 2 day 500 mile ride, I've got a sheen of engine oil on the transmission shelf. Most likely from the Rear Main Seal, less likely from the oil pump. Both seals were replaced in the past two months.

Issue started with the "fart" after the engine was shut off then worsened to now seeing oil on the shelf.

I did a leak down test, both hot and cold and found R side blowing air thru the oil filler and a 20% leak down. No air thru intake or exhaust.

L side showed less than 5% leak down, no air thru intake or exhaust but some hissing thru the oil filler hole.

Thinking I have blow by at the rings causing excessive pressure and the RMS to weep.

All this happened after I replaced the breather valve with the updated version about 3 weeks ago. RMS and oil pump seal are new and were replaced about 2 months ago.

Questions

1) Should I also do a compression test?

2) Replacing rings, I would do both or just the one side? I would err on the side of both

3) Rear main seal or oil seal compromised and need replacing? I would err, again, on the replacing.

4) Breather installed incorrectly? New breather valve was installed just below flush with the crank case and with the reed opening at 5:30 to line up w. the vent hole on the housing. Used existing housing and a new gasket. Not sure this is the culprit but after I installed it, this is when the farting and oil leak appeared. Normal oil flowing thru the breather and vent hose on the R side. Not too much, seems normal from my experience.

I have not opened up the engine to see where the oil leak is coming from but the shelf reveals a sheen of engine oil.
That plus the farting and air movement from the engine when it is shut off seems to indicate the oil leak is coming from the RMS and a result of bad rings and excess crankcase pressure from the right cylinder.

1) and 2).....
I would certainly do a compression test before I tore the top end off to replace rings "on a whim". Meaning low compression would be positive evidence that the rings actually needed replacing.

Thanks for the note Wobs. I concur with your comments. Turns out the oil was from the trans input seal. Just changed the trans oil so it was clear/clean and appeared to be from the engine. There is a small nick in the seal housing. Going to dress that up and install a new seal, carefully. I may have cocked it on install.

I did use a puller to remove the old one but may have compromised the housing?

Either way, I know where the oil is coming from. RMS and OP are dry.

Still have the air suction at the RMS to figure out.

Thanks for the note Wobs. I concur with your comments. Turns out the oil was from the trans input seal. Just changed the trans oil so it was clear/clean and appeared to be from the engine. There is a small nick in the seal housing. Going to dress that up and install a new seal, carefully. I may have cocked it on install.

I did use a puller to remove the old one but may have compromised the housing?

Several ideas to mull over and consider....

1) What type and brand of oil did you put back into the gearbox ? I have had problems with some brands of gear oil. A lot of oils are now "doped" with synthetic modifiers, and purely synthetic oils are a lot more common place. Oil seals do better with the older straight mineral oil. Apparently in synthetic oils, the makers need to add "seal softeners" to keep oil seals working.

My brother purchased an R1100 one time and the seller was so proud he had paid extra at the last service to have the gearbox and final drive converted to Mobil-1 synthetic. Within 200 miles (the ride home) the rear wheel was soaked in oil. I drained that and installed Valvoline gear oil and and the issue very nearly went away. So my point is before I would do a lot of extra work, try changing the gearbox oil. (Disclaimer: I'm not saying Mobile-1 is "bad", simply that it didn't seem to work in this particular situation.)

2) I'm not so concerned about how you removed the old oil seal out as I am with how you installed the new seal. New seals can sometimes be a bear to simply get into the case. Forget about getting it in straight or seated correctly, or centered, or bottomed out.

A suggestion... Next time you install ANY oil seal, I want you to use a fairly new product called P80. When the case is all clean and ready for the new seal, you wipe this liquid all over the surfaces that touch the aluminum case. Then, using only your fingers, you can push the seal "home". Because the installation force is reduced to the point where you're allowed to seat the seal using only finger pressure, the seal goes into the case completely straight and seated exactly square to the shaft. This is simply amazing stuff. Fork seals that I used to spend 15 minutes pounding in with a hammer now push all the way home with the pressure of 2 thumbs in 10 seconds. It's simply amazing !! Click Here

Hope these ideas help.

Great tip on the p80, will be a good addition to the garage.

Standard 80/90 castrol on the gear box

actually there appears to be a small nick in the seal housing where the oil leak emanated. I need to dress it up a bit before installing another seal.

Wondering if there is a product (like Hylomar or Three Bond etc...) that I can use with the new input shaft seal to make sure the nick in the housing seals good?

It would need to be more than a "nick" to leak like what you're describing. More like a gouge. No, I'm fairly certain that your oil seal was not centered and square to the shaft to be leaking that badly.

One other thing to check.... the bolt that holes the ground cable and speedo cable in place... that's the g/b vent. If some idiot swapped out that bolt, then heat could make oil ooze out of strange places. The correct bolt is drilled out (hollow) so that gas can vent from said enclosure.

Indeed, it's reasonable that I may have cocked the seal on install-maybe even drove it too deep.

See the damage to the housing in the attached picture

Vent bolt is in place on the transmission.

• That nick is nothing to worry about

• Did you moisten the lip of the seal before installation ? Put some grease on the shaft maybe ?

• It's got to be the seal, the shaft or the oil !! 😛

Appreciate your comments.

Seal went in dry but noted on grease and moistening this time around.

Cheers

Follow up on a few things here:

1) I noticed the trans breather bolt had become blocked with grease? Why?
I was over zealous in packing the speedo cable boot with grease, as I have frequent water crossings. Water proof grease has kept water migration at bay on my G/S in the same way but....it appears after some spirited riding on the 90S the grease warmed and migrated from the boot into the housing where the trans vent bolt sits. It was clogged and probably prevented proper venting, thus oil leaking from the IPS seal? I'll be replacing the seal and installing, as noted this time around. Oil leak was exclusively from the trans IPS seal, none from OP or RMS.

2) Breather and engine farting:
Upon further review it appears the brass tongue that sits atop the breather reed may have been pushed down too far, not allowing the reed to properly move and vent. I peened the small screw that holds the assembly together before installation. In that process the brass colored tongue was forced on to the valve. I've reopened the tongue to allow better ventilation on the reed and hoping this was the issue and will allow the engine to breath better. Will report back once all is together.

Turns out you may have been spot on with the vent bolt not venting, causing the leak.

Turns out you may have been spot on with the vent bolt not venting, causing the leak.

One would hope that a high level of pressure would be able to push grease out of the way ! At best, my level of involvement in both cases was only supplying ideas, so no thanks needed. The main thing is that ideas spurred action, which may get you back on the road in a quieter and more leak-free fashion.

All the best.