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CB77 Superhawk spits raw oil out of left muffler

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GG
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Posts: 138
Joined: Tue Apr 13, 2010 10:45 pm
Location: Costa Rica

CB77 Superhawk spits raw oil out of left muffler

Post by GG » Sun Jul 10, 2022 4:34 pm

Hello all - My well cared for 1966 cb77 Superhawk has begun to blow at lot of smoke and raw oil out of the left muffler, so much that fresh oil drains out of the muffler when parked! Compression is even in both cylinders, and the left spark plug is not oily, nice and tan, "normal". I also seem to be getting oil out the breather hose that comes off the top of the head and goes down behind the transmission. It would appear to be a blown head gasket, but how can I have decent, even compression? I wanted to try to pinpoint the problem before tearing everything apart. The bike has been very well cared for (by me, for 35 years), and not abused. Any ideas will be welcome! Thank you! GG

Geoff Hastings
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Posts: 323
Joined: Wed Feb 22, 2017 2:59 pm
Location: Epsom, Surrey

Re: CB77 Superhawk spits raw oil out of left muffler

Post by Geoff Hastings » Thu Jul 14, 2022 12:32 pm

One way you will get an even compression between cylinders is if the head gasket is blown between cylinders. A worn exhaust valve guide could cause your symptoms with no loss of compression.A broken oil control ring will give similar symptoms if the compression rings are still ok but I would expect an oily plug on that cylinder.

GG
honda305.com Member
Posts: 138
Joined: Tue Apr 13, 2010 10:45 pm
Location: Costa Rica

Re: CB77 Superhawk spits raw oil out of left muffler

Post by GG » Thu Jul 14, 2022 3:25 pm

Thanks Geoff - yes, these are basically my conclusions. I've pretty much ruled out a worn valve guide - this happened rather suddenly, and the bike has been maintained well. I guess the top end is coming off. (sigh)

Have a great day!

GG

Geoff Hastings
honda305.com Member
Posts: 323
Joined: Wed Feb 22, 2017 2:59 pm
Location: Epsom, Surrey

Re: CB77 Superhawk spits raw oil out of left muffler

Post by Geoff Hastings » Fri Jul 15, 2022 12:51 pm

Not such a big job, once you put your mind to it you’ll have the head off in about an hour. Hope it’s not too expensive.

GG
honda305.com Member
Posts: 138
Joined: Tue Apr 13, 2010 10:45 pm
Location: Costa Rica

Re: CB77 Superhawk spits raw oil out of left muffler

Post by GG » Fri Jul 15, 2022 6:10 pm

Update on Superhawk - it was the head gasket. An inside piece pretty much disintegrated, which explains why it was pressurizing the crankcase so much. There is a very small scratch in the cylinder where the piston sucked the piece of gasket in and it rubbed up and down for awhile. But honing will clean it up. Everything else looks good, except huge amounts of carbon from the oil burning.

Have a great day, all!

GG

Geoff Hastings
honda305.com Member
Posts: 323
Joined: Wed Feb 22, 2017 2:59 pm
Location: Epsom, Surrey

Re: CB77 Superhawk spits raw oil out of left muffler

Post by Geoff Hastings » Sat Jul 16, 2022 8:34 am

That’s good news, thanks for the update.

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