Have been a site member for quite some time but now have an issue I need info on.
I am the newest owner of a 1966 305 Honda Dream (CA77). I live in Pelzer S.C. Bike is very complete, starts easy, runs very well. Compression is 145 psi left/ 147 psi right.
Problem is I could never keep seals from leaking oil, even when new external seals
were replaced. I could not understand why large rubber seal behind drive sprocket
on left side would come unseated from the case. Then by accident I had left the
dipstick just sitting in place after checking the oil (not secured in place) and started
the engine. Was a bit shocked to see dip stack bouncing up and down with each rotation
of the crank. Movement was approx. three inches. Also noted a hissing sound after
engine was shut off and engine had been running with dipstick secured in place. Hissing
was pressure releasing through left side cover bottom seal. Air and drips of oil.
Can it be possible venting through top of head is malfunctioning even though I can
inject compressed air through the vent hose into the engine?
Is it common to have that much blowby with such good compression?
Should I stop riding till problem resolved?
Just as an experment I drilled a small hole through the dip stick to release some of
the pressure, and sure enough seals stopped leaking and engine seemed to run
much quieter, less mechanical noise.
Thanks for any responces.
Tim
Piston Blowby?Looks like you're in my neck of the woods. I live in Simpsonville S.C. . My 67 305 dream had a problem with oil being blown out the vent pipe on the head after the engine was rebuilt. It had alot of crankcase pressure for at least 3-4 hundred miles. After that the rings seated and everything has been perfect. Check the vent pipe from the head while its running to see if has a good volume of air coming out. You should have air and a little oil coming from that pipe.
Nice to find someone so close. Output from vent tube much less than it had been
when first rode the bike. I have replaced the tube/ hose as it was broken at head and blowing oil over engine. I had also connected the vent tube to a reserve, small container I had used with a vacuum pump to bleed rebuilt brake systems and set it inside the frame behind the battery to let the crankcase vent but collect the oil instead of having it over lube the drive chain.Had been after about a fifty mile ride it would have collected a little less than a teaspoon of oil. Now after a similar ride, just a few drops of oil. We have another dream owner that's on this site that lives in Asheville N.C. . I've been working on my CA-78 for about 3 years off and on. It took a while to get all the bugs out of it. I've been through about everything on this bike at least once. Sure is fun though. We will have to get a few people that are close to us together and go for a ride in the hills.
A get together could be fun!! Preformed a small test. Held the end of the vent tube to my cheek
and at idle abundant air can be felt. but as I increase rpm it becomes less and less, until at about 3000 rpm almost none is felt at all. The entire time the loosened dipstick dances up and down about two inches from piston pulses from the crank case, seems to me vent tube output should at least remain constant or increase with increase in rpm. Just thinking out loud I guess. Think I'll lower the engine and remove the top portion of the head to look at the venting system.
A get together could be fun!! Preformed a small test. Held the end of the vent tube to my cheek
and at idle abundant air can be felt. but as I increase rpm it becomes less and less, until at about 3000 rpm almost none is felt at all. The entire time the loosened dipstick dances up and down about two inches from piston pulses from the crank case, seems to me vent tube output should at least remain constant or increase with increase in rpm. Just thinking out loud I guess. Think I'll lower the engine and remove the top portion of the head to look at the venting system.
Removed the cylinder head cover. While upside-down on work bench injected compressed air through vent tube into cover. Out put of air was less on the left vent hole in the breather shield than on the right vent. Then noted breather shield plate gasket was depressed somewhat into the head cover. Once all covers and gaskets were removed and air once again injected, output
seemed less again on the left side. Cleaned inner vent port channel with brake cleaner and compressed air, now both sides equal output. Ordered new gaskets with hope that small obstruction in cover port channel and original breather shield gasket maybe causing partial blockage that perhaps got worse when rpm's increased. Question: Found breather vents toward rear of cover, is this the correct orientation? Thought I would try this first before thinking more serious thoughts.
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