A call out for experienced advice! I'm not an airhead guru. I'm getting ready to button up the top end on my '94 GS. When I pulled the jugs off the old girl I noticed the factory used a small amount of sealant on the jugs...no o-ring or gasket. the fiche shows an o-ring, which I bought when I ordered my parts. The Haynes manual, with pics based on older models, shows a base gasket. The barrel is clearly machined to accept a ring, and the mating half in the case appears ready as well. I don't recall Snobum saying anything about this. What do you regular builders say??
Should be O ring only, but a PO may have fitted decompression spacers, but even with them, the O ring should be used on the pot side. BTW, there are three O rings per pot, a big one for the barrel base, and two small ones for the top two head studs, they are Viton or silicon high temp ones, DO NOT repalce with cheap butyl rubber ones, or you will get good at pulling the barrels The main problem here is the top two head studs are the oil feed to the rockers, so an ample slather of wondersnot will stop this oil as well as the leaks, not good. If the bike has been pinging, then fit lower compression pistons, and bin the compression reducing spacers (a /5 and /6 holdover BTW) and fit the O rings. If you do decide to go the wondersnot path, use Loctite 515, NOT stag or any other hardening sh1t.
Thanks Andy! Yes, I'm hip to the rest of it. I just wondered about the base o-rings v. sealer. this bike has never been apart, so the factory used sealer, not a ring. If everyone puts them together with the ring, then I'll proceed with that plan. I have all the proper BMW pieces. Also, for elastoeric sealing rings and the like I use Dow silicone grease...really helps in every way.
BMW has used a few methods for sealing the base. Including at one time no gaskets or orings just sealant. I would use the o ring as long as the groove is there and I've found dipping it in motor oil just before installation will help it seal. Maybe they were out of orings that day, frankly wouldn't suprise me!! I should have mentioned I do use a thin smear of sealant also. Orings and sealant, something like hondabond. By thin I mean as thin as you can possibly make it!
I've used a VERY thin skin of Hylomar or similar on the jugs. Making sure that there are no blobs or excess near the upper studs where the smaller O-rings go. I have had sealing success with and without the big O-rings, but I do lube the O-rings before assembly. No sealer on the pushrod seals as they need to be able to move in place.
My advise is sealer and o-rings. I use a flat bladed Exacto knife to spread a very thin layer of Durko on the cylinder base. I use just a tiny spec on the stud o-rings to get them to stick into their recesses. I double check and insure that they have not fallen out of their recesses right before the cylinder is synched all the way down. I have found MANY cylinders permanently F'ed up for those stud o-rings falling out on assembly and getting pinched. That rubber WILL move metal! I lube the cylinder o-ring with a thin coating of Tri-Flow. I otherwise make ALL the surfaces absolutely oil free. I install the push rod tube seals dry. I do rub of the seal's release agent off with Scotch Brite. I adjust rocker arm end play with a modified ViseGrip C clamp. It REALLY helps getting that play right down to zero.
My 1978 R100S Engine didn't have base o-rings or base gaskets, just the pushrod tube o-rings. No grooves for o-rings that I can see. My parts supplier (Huckys) tells me that there are no base gaskets that will fit that year engine.(?) A knowledgable BMW mechanic tells me that some year engines used nothing but a sealant... I assembled it with a tiny bit of sealant and now the right side is leaking.....back apart it will come when I get tired of the oil drip it's leaving. I bought a pair of base gaskets which I will attempt to fit when I tear it down. The slightly lower compression shouldn't hurt anything.(?)
Supershaft - I saw the "push rod seals" (not the pushrod tube seals) on the breakdown, but my bike doesn't have any. The quantity on the breakdonw has an "x" in the box. What are these about? I'm hip to the pushrod tube seals. The referemce fiche was at Max BMW's site.
I have a '94 R100R, no O ring on the left side. Never had the right side off. Look at the cylinder base. If it needs an O ring there will be a grove there. If not don't put one there, just use a sealent. Check out Ted Porter's website he hs a photo of how much to use. Ed
The barrel O ring just sits in the corner between the barrel spigot and the base, there is a chamfer on the outside of the case bore that the O ring seats itself into, nice and simple. But it is the lack of this chamfer that stops you using O rings on older cases, and the lack of the machined recess on the top stud holes that stops the use of O rings here on early barrels, but old barrels on new cases (why would you?) could run the base O rings only.
O-rings were added...when?...in the 80s? Base gaskets are not for sealing, rather, they were added to lower compression on /6 era motors that started pinging when gas went south.
I am guessing 78/79? /5's and /6's have base gaskets for sealing. You could order special thicker gaskets to reduce pinging and a lot of people did but a R90S that has 9.5:1 has base gaskets.
I have had good success recently with loctite 518 flange sealant. It is red, gooey, and supposedly won't clump up in your oil. dc
And there's your winner! I used the Loctite...perfect application for it. I also used the o-ring and coated it with a film of silicone grease, as I did with the pushrod tube seals. It went together nice! I assembled the piston w/rings into the jug first, then slipped the wrist pin into the piston with the barrel slid halfway on. Worked pretty good.
...1978 R100/7, did not have o rings on the base. Ditto, the aluminum base 'gasket was for lowering compression to help with pinging. There are conflicting opinions weather to use or not to use sealant on the jug base, but it's not going to hurt anything if you do. Ditto thin, ditto no goobers on the to studs at the o-rings there. It's got an oil passage.
Looking this situation over, it was apparent to me that the factory found it cheaper to use sealant. Since they can assemble very quickly, they probably weren't very concerned about sealant starting to cure before clamping, etc. But my thought was, knowing that the o-ring would seal fine on its own, a film of sealant between the surfaces would be a good thing as a barrier to corrosion. So I went with both.
