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Lots of oil when removing spark advancer cover on 79?

millsmobile

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Recently acquired the bike in non-running condition, but it was running a few weeks ago. First job was fixing the alternator rotor which was completely toast and had no continuity between the copper rings. Did that and took off the spark advance cover today and it started pouring oil / fluid as soon as the 3 bolts were loosened. The manual made no mention of this, so I quickly tightened them down and got a bucket to catch it before taking the cover completely off. In total somewhere between 2-3 quarts of fluid came out. Wasn't quite all oil, seemed thinner like it might have had fuel in it also. The really interesting part is after all that fluid came out the dipstick still reads full. What am I getting myself into here? I've found a couple older threads on this, and one mentioned like 1/2 cup of oil behind the cover and consensus was that's a lot. This was way more lol. I see there's an o-ring, and also a crank seal that may or may not be replaceable with the bottom end together. Please help, thank you!
 

brettp

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I asked this same question a bit ago, but I had less oil than that. I would bet (but I'm not 100% positive) the oil seal can be replaced without getting into the crank case. Curious to hear what the experts say.
 

millsmobile

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I'm looking at gasket kits and the 78 and before show a right and left gasket, the 79-82 kits do not list a gasket for the left side. I've got the 1979 manual, and am also looking at hondapartshouse diagrams and I can't find a gasket for that side in the pictures either. Sure looks like one should be there when looking at the crankshaft section.

This post says that it is open to the crankcase in there. https://www.cb750.com/threads/1980-cb750f-ignition-housing-oil-seeping-in.4858/

If there's supposed to be oil in there, how could that much come out and the dipstick still read full?
 

Biebs

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you have gas leaking into the engine from carbs needles leaking. Make sure the fuel petcock is turned off when not running!!

drain the oil and refill with fresh oil.
 

brettp

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you have gas leaking into the engine from carbs needles leaking. Make sure the fuel petcock is turned off when not running!!

drain the oil and refill with fresh oil.
Needles leaking into the oil from the carbs? I am far from the most knowledgeable, but....no. the float valves not sealing causes bowl overflow drains to drain. Or in some bikes it will end up in the air box. The only way fuel is ending up in the oil is if it fills up the intake boots then drains into the cylinder head and slips past the rings. None of that explains oil behind the timing cover.
 

dirtdigger

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Recently acquired the bike in non-running condition, but it was running a few weeks ago. First job was fixing the alternator rotor which was completely toast and had no continuity between the copper rings. Did that and took off the spark advance cover today and it started pouring oil / fluid as soon as the 3 bolts were loosened. The manual made no mention of this, so I quickly tightened them down and got a bucket to catch it before taking the cover completely off. In total somewhere between 2-3 quarts of fluid came out. Wasn't quite all oil, seemed thinner like it might have had fuel in it also. The really interesting part is after all that fluid came out the dipstick still reads full. What am I getting myself into here? I've found a couple older threads on this, and one mentioned like 1/2 cup of oil behind the cover and consensus was that's a lot. This was way more lol. I see there's an o-ring, and also a crank seal that may or may not be replaceable with the bottom end together. Please help, thank you!
The iginition side on the dohc is open to oil. Your crankcase was obviously over full, you cant drain 3 quarts out and then have it still at the full mark. It had to be 3 quarts overfull to begin with. If you didnt overfill it with oil and seemed like it had gas in the oil as you stated then the needles are leaking running over into the cylinders as suggested by others. It could happen and its easy for fuel to leak past the rings if fuel does get into the cylinders. It happens very easily in automotive engines with carbs on top of the engines...normally it never gets to that point on older bikes as they are side draft carbs and the overflow normally drains before getting into the engine as designed. But with out seeing all the tubing etc on your bike I cant say for sure as some people do some pretty odd things to hoses and such on bikes. As you said you recently got it so who knows what the previous owner plugged or blocked or what have you. Bottom line is if you drained 3 qts and it still shows full then it was 3qts overfull to begin with whether it is oil or fuel.
 

millsmobile

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Here's where I'm at - put new plugs in it, fresh gas all the way through, bike started right up but it's kind of rough. I let it warm up just a bit and then shut it down to change the oil and put a new filter in. It was definitely not still full of oil, I'd say the balance came out. So if on the DOHC it's open to oil in there, would it be normal for that much to come out? And what on that left side would I replace if it isn't? Based on the rest of the oil I don't think there was much if any fuel in there.

I also compression tested it, 150 150 120 and 90. The #4 sounded like it was making a bit of a clack when it ran, previous owner was into the valves so I'm going to check those out and retest. There was also oil coming out of the seal on the right side exhaust cam cap at that same cylinder.
 
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