Engine seizure/advance repair

[redblk63]

This episode began years ago on a ride to Death Valley. I did not make it. My 1963 CB77 seized while pulling a long desert grade into Randsburg. I pulled in the clutch and coasted down to about 20 MPH. Hoping the cylinders had cooled, I dumped the clutch. Unfortunately, the pistons were stuck tight and the rear tire just skidded.

After cooling off for a few minutes, I rolled back down the hill to bumpstart, and was able to cautiously ride the last 1/2 mile into town. Shamefully, I was passed by 2 souped up Vespa scooters! The photo below shows a melted electrode (far right) from my RHS cylinder. (Oops, my pictures are "not valid files," sorry) Looks like things got hot in there.

The next picture shows me after turning back, pulled over on a bright desert highway. Using my Swiss Army knife and tool roll, I retarded the ignition to cool down the combustion temperatures. This allowed me to make it 120 miles back home, including over the challenging Angeles Crest range.

With the help of several on this forum, and using my timing light to observe dynamic ignition timing, I could see that when the static timing was right on, the max advance was about 11 degrees past the marks. This is caused by wear in the advance mechanism, in particular, the neoprene ring on the advance limiter pins were worn away. A member of this Forum, Tim Miller, has engineered a fix for this. About two weeks ago I sent my cam sprocket to him for repair. This was done in a few days for a very reasonable $125, and featured a rebuild of the old mechanism with improvements in several areas, especially a hardened steel replacement for the stock neoprene-covered advance limiter pin.

I reassembled the head lastThursday, and installed the motor Friday. As usual with these projects, I took the opportunity to make other repairs along the way. The motor fired up after a few kicks, and I am very happy with the results. The power and response is much better now starting from a stop, and driving around at moderate RPM. For now, I'm enjoying a transformed bike, the way a CB77 should run.

I'll see if I can send pictures from my iphone.

Tim, you do great work. Thanks!

Larry -Pasadena
63 CB77, 66 CT90K0, 69and 71 Matadors, 71 SL350, 75 CT90K7

[redblk63]

I’ll try to add photos of the bike near its breakdown spot, and the beautiful advance mechanism along with the world’s most complicated camshaft assembly.

[Tim Miller]

Thanks Larry!

I’ve been modifying these for 15+ years and it’s by far the best performance modification you can do.
It also fixes the loose rivets/gear problem.
When I first tried this I was concerned about excessive noise when the bob weight stops made contact with cam gear, but there’s no noise. I suppose Honda’s eager engineers back in the day though the rubber was necessary to keep the weights quiet or just not to bounce? but it’s not necessary, there’s no evidence of erratic timing visible with the strobe light and there’s no noise.

If you want help with this contact me via email, this site doesn’t advise me anymore when a PM is sent and I don’t visit much anymore.

1964honda250@gmail.com
Tim

[redblk63]

Tim,

Yes indeed, the engine response has been transformed by your rebuild. I can now detect some small adjustments needed to carburetion which were previously masked. And I could not hear any additional noise.

I admit I was surprised at the violence needed to remove the sprocket. I don't like hammering on ball bearings to remove them. There are 4 bearings supporting the cam, and for some the removal force is transferred through the balls, which I always thought was a no-no. My advice to others is to plan on replacing at least some of the bearings if you do this.

I may have been doing it wrong, but can see no way to avoid the hammering.

Cheers,
Larry

[redblk63]

Ok, after about 100 miles it’s time to recheck the valve clearance. While I’m in there I’ll check whether the problem with excess maximum advance has been solved.

Done. Thought I heard some excess clatter. One intake valve was a bit loose. Now they are all 0.004”. I don’t know if it’s just me, but I find it very tricky to set the gap, and to measure it accurately. It’s awfully easy to shove a 0.005 Or thicker gauge into a 0.004 gap with just a bit of extra drag.

The good news is Tim’s rebuilt advance was right on the mark at maximum advance. Thanks again Tim.

Larry

[Tim Miller]

Thanks Larry, and you’re welcome.

In the last couple months, I’ve rebuilt quite a few advancers. People can’t believe how much better they run once the timing is corrected.

If I can help anyone else email me at:
1964honda250@gmail.com

Tim