CL72 or 77

Snakeoil · Post by **Snakeoil** » Thu Aug 05, 2010 9:32 am

One of the bikes I looked at and was supposedly a CL77, could have been a CL72/77 mix now that I've read a few of the technical posts here. The fenders were aluminum, front and rear. The engine had two small barbed fittings just below the intake ports. I looked at a later 305 engine and those barbed fittings were not there. Could that have been a 250 engine and not a 305? Do the two engines look very similar?
Thanks,
Rob

davomoto · Post by **davomoto** » Thu Aug 05, 2010 2:33 pm

Rob, check engine and VIN #s. The barbed things are intake valve guide vents, and were eliminated by Honda in later production. Engines are identical, with the exception on 247 or 305 on lower front of cylinder, and engine #s

Snakeoil · Post by **Snakeoil** » Thu Aug 05, 2010 8:41 pm

Intake valve guide vents.... I've been around a lot of engines and that's a new one on me. What is the purpose? Are these a form of crankcase ventilation?
regards,
Rob

LOUD MOUSE · Post by **LOUD MOUSE** » Thu Aug 05, 2010 10:48 pm

They are vents from the intake guides and were on all the early engines and deleted with the 1967 issue engines. .......lm

Snakeoil wrote:Intake valve guide vents.... I've been around a lot of engines and that's a new one on me. What is the purpose? Are these a form of crankcase ventilation?
regards,
Rob

teazer · Post by **teazer** » Fri Aug 06, 2010 12:14 am

I always believed they were there to reduce oil being sucked down the intake valve guides. There were no seals on the guides.

The barbs connect to teh air filters so that the motor didn't suck in any dirt to the guide.

Whether they really needed them i can't say, but it's an ingenious fix for the 1950s

LOUD MOUSE · Post by **LOUD MOUSE** » Fri Aug 06, 2010 8:51 am

Rather than oil I believe HONDA meant them to suck moisture from that area into the combustion chamber.
I've worked on many head assy. (all 250/305) and the only guide problems I've found was a couple of intake guides with the top broken at the vent groove.
Once again HONDA dropped the design in 1967. .........lm

teazer wrote:I always believed they were there to reduce oil being sucked down the intake valve guides. There were no seals on the guides.

The barbs connect to teh air filters so that the motor didn't suck in any dirt to the guide.

Whether they really needed them i can't say, but it's an ingenious fix for the 1950s

Snakeoil · Post by **Snakeoil** » Fri Aug 06, 2010 9:35 am

So it is a form of positive crankcase ventilation since the head area is linked to the crankcase via the oil return galleries. It is a good idea. I wonder if it lead to premature carbon build up in the combustion chambers?
regards,
Rob