It’s a 1976 R90/6 - had it for about 10 years. Tired of the push rod seals leaking, so I’m going to do that again and use some Gascacinch this time. While I’m in there, I’ve never done rings and I wonder…
Problem. My buddy said the left side was smoking. On the road, fully warmed up, going along and he said the one side was smoking. Not just after starting up, but under way. Carbs in good tune. Oil level is fine. Can’t think what else it would be.
I assume if I pull the barrels back to do the push rod seals, I could just pop off the old, tired rings and put in new ones? Would that be the most likely reason for the smoke?
thanks
Hi -
Some things you ought to know....
1) The crankcase breather vents into the LH carb, and that could be the source of oil that the engine is breathing. Excess oil could be coming out the breather because...
• The air filter needs replacing
• There is a mouse nest under your starter cover
• The oil trap in the crank case breather is overflowing because the drain hole is clogged
• The one-way breather valve is badly chipped needs replacing
• Wrong grade of oil being used
• Piston rings are worn out
So some investigating is due, because piston rings are way down on the list of possible suspects. Snowbum thoroughly explains about Points #3 & 4.
2) No, you cannot simply slip new rings onto the pistons. The cylinder walls need to be honed to break the glaze of baked on oil that is there now, so that the new rings can "seat" or "bed-in". Honing uses specific grit size and is applied with a specific cross-hatch pattern.
Then the rings are inserted into the cylinder (without the piston) to check the "ring end gap" because the rings grow under the heat of combustion. A prescribed amount of room for thermal expansion must be present before being installed... or the rings will self-destruct. Additionally, the rings have a surface that must face Top (the combustion chamber) when being installed onto the pistons.
Not exactly rocket science, but you do need to take those minimal steps.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Super helpful – Thanks!
I'll report back when I know more. Appreciate your help.
No problem.
• Knowing your odometer reading would be a big help.
• I'm not aware that BMW offers a "top end gasket set" like other manufacturer's. And the job is just difficult enough where you don't want to trust it to third party suppliers who may offer the same. Just bite the bullet and get on Max BMW[/b]'s on-line parts catalog and order all the gaskets, o-rings, rings and push rod tube rubbers from the fiche. https://shop.maxbmw.com/fiche/PartsFiche.aspx
• You'll also need a good torque wrench.
Do one side at a time. It's fairly straightforward as engine work goes. Work slowly and carefully laying out all your parts. If you've got a lift and full selection of hand tools you can do it. Working by yourself, allow about 4 hours for the first side and maybe 2-1/2 for the second. Or, maybe make a special arrangement at your next local Tech Day.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
No problem.
• Knowing your odometer reading would be a big help.
• I'm not aware that BMW offers a "top end gasket set" like other manufacturer's. And the job is just difficult enough where you don't want to trust it to third party suppliers who may offer the same. Just bite the bullet and get on Max BMW's on-line parts catalog and order all the gaskets, o-rings, rings and push rod tube rubbers from the fiche. https://shop.maxbmw.com/fiche/PartsFiche.aspx
• You'll also need a good torque wrench.
Do one side at a time. It's fairly straightforward as engine work goes. Work slowly and carefully laying out all your parts. If you've got a lift and full selection of hand tools you can do it. Working by yourself, allow about 4 hours for the first side and maybe 2-1/2 for the second. Or, maybe make a special arrangement at your next local Tech Day.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
The crankcase breather vents into the right carb, not the left. Just a FYI.
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