Engine oil in the Primary

Tangozulu · Oct 1, 2021

So, my 1971 Commando recently developed a rather prodigious oil leak, somewhere behind the primary. The oil did not stink of the gear oil I use in my tranny, nor had the somewhat sticky feel of the ATF I use in my primary, but was of the viscosity and sliperyness of the RedLine Motorcycle 20-50 synthetic I use in my engine. I leveled the bike, checked the tranny, fluid level OK. On a hunch I opened the drain plug on the primary and oil flowed out. I drained the excess and measured it: 200cc! I have an Alton starter (love it) but apparently the excess of oil overwhelmed its modest sealing. So, here's the question: What is the most obvious source of a relatively sudden leak of engine oil into the primary?

APRRSV · Oct 1, 2021

Tangozulu said:
So, my 1971 Commando recently developed a rather prodigious oil leak, somewhere behind the primary. The oil did not stink of the gear oil I use in my tranny, nor had the somewhat sticky feel of the ATF I use in my primary, but was of the viscosity and sliperyness of the RedLine Motorcycle 20-50 synthetic I use in my engine. I leveled the bike, checked the tranny, fluid level OK. On a hunch I opened the drain plug on the primary and oil flowed out. I drained the excess and measured it: 200cc! I have an Alton starter (love it) but apparently the excess of oil overwhelmed its modest sealing. So, here's the question: What is the most obvious source of a relatively sudden leak of engine oil into the primary?

The drive side main bearing oil seal. Item #9 in the screen shot.

Ed

Derek Wilson · Oct 2, 2021

Definitely the source stated above, but where on the primary was it leaking from?

My experience with synthetic oil is it will find a place to leak out where non-synthetics won’t. So everything has to be absolutely perfect to keep it from leaking - a state that is typically temporary at best - lol!!

I switched back a long time ago and run non-synthetic 20w50 plus Lucas oil stabilizer, along with an oil pressure gauge, an AWS valve and a reed style crankcase vent.

Change my oil every 2000 miles.

Tangozulu · Oct 2, 2021

Yeah, I suspect the main bearing seal as well. I presume this buger can be pried out and replaced w/o engine disassembly. I certainly did that with a bunch of seals on a '68 Honda CB350 I recently restored. However, one would think that the failure of a seal would be gradual, whereas my impression is it happened relatively suddenly. In response to Derek's Q about the primary leak, the Alton setup has a seal around the transmission shaft that is mounted in a large, flat circular aluminum disc that fits snugly against the inside of the back primary case...but not that snugly. I suspect all of that excess engine oil overwhelmed it. My forensics continue. I'm down to clutch removal.

maylar · Oct 2, 2021

Tangozulu said:
Yeah, I suspect the main bearing seal as well. I presume this bugger can be pried out and replaced w/o engine disassembly. I certainly did that with a bunch of seals on a '68 Honda CB350 I recently restored. However, one would think that the failure of a seal would be gradual, whereas my impression is it happened relatively suddenly. In response to Derek's Q about the primary leak, the Alton setup has a seal around the transmission shaft that is mounted in a large, flat circular aluminum disc that fits snugly against the inside of the back primary case...but not that snugly. I suspect all of that excess engine oil overwhelmed it. My forensics continue. I'm down to clutch removal.

You will need to remove the alternator and everything else on the crankshaft. Standard procedure is to drill 2 small holes in the seal and use small self tapping screws for something to pull on. Last time I did that the seal fell out in my hand.

Tangozulu · Oct 2, 2021

Thanks. Down to the sprockets on my disassembly. I like your suggested technique for pulling the seal

DevonNorton · Oct 2, 2021

I'd suggest using a bradawl (hope that transalates) to start the hole for a self-tapper.
I've found a drill can stray and there is the possibility of damaging the surface of the shaft.
Just my view.
Andy

Tangozulu · Oct 2, 2021

Ah yes...a pointy thing

cliffa · Oct 2, 2021

DevonNorton said:
I'd suggest using use a bradawl (hope that transalates) to start the hole for a self-tapper.
I've found a drill can stray and there is the possibility of damaging the surface of the shaft.
Just my view.
Andy

That's what I do. Mine has a wooden handle but the shaft passes through it to a domed end, so you can normally give it a thwack with a hammer and it pierces the steel of the seal. Drywall screws are perfect for the extraction as they are very sharp and hardened. Works on fork seals as well, but slide the hammer along the stanchion so you don't dent it.

baz · Oct 2, 2021

Tangozulu said:
Yeah, I suspect the main bearing seal as well. I presume this buger can be pried out and replaced w/o engine disassembly. I certainly did that with a bunch of seals on a '68 Honda CB350 I recently restored. However, one would think that the failure of a seal would be gradual, whereas my impression is it happened relatively suddenly. In response to Derek's Q about the primary leak, the Alton setup has a seal around the transmission shaft that is mounted in a large, flat circular aluminum disc that fits snugly against the inside of the back primary case...but not that snugly. I suspect all of that excess engine oil overwhelmed it. My forensics continue. I'm down to clutch removal.can push the oil seal out

Starting the engine when it has wetsumped can push the seal out

gortnipper · Oct 2, 2021

Also, use some blue silicone gasket maker on the three hex bolts that affix the inner primary to the crank case, as they are known leak spots as well.

Do one at a time and make sure the crankcase is empty of oil before you start.

Engine oil in the Primary

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