Hi all,
I wanted a winter project and I think I may have gotten more than I asked for!
Got a '65 CB77 in parts, and the engine looked ok from the outside, but as I'm tearing into it, the evidence that it sat unprotected out of doors is apparent. Seized pistons, rusted cam chain, rusted clutch, etc.
So while I've got it soaking and I'm building a stand for it, I was wondering what my best plan of attack would be rebuilding it.
At this point, I've got good cases, and that's more or less all I can say for sure. What are some good swaps/mods that can be done on the *relative* cheap? The boxes included Kenig High-comp pistons, 61mm, so if the cylinders can be bored, I'll probably try and run those. I've heard they need some cleaning up, and I'll try and smooth the tops and balance their weights.
My carbs are heavily corroded, and the floats are eaten through. I've thought about rebuilding them, but does it make more sense to try and pick up some CB450 carbs instead? I have to mention at this point that I will be getting new exhausts, as the originals are destroyed, so there will be increased airflow throughout.
Not sure I want to go there, but if anyone could point me to info on the CB450DOHC head swap I'd appreciate it. In particular, how the new head bolted up (lots of welding?)
Also, the '68 CB350 transmission is a possibility, and I'll probably go with electronic ignition.
Other ideas? At least one rocker is broken... I figure if I'm going to be replacing so many parts, why not upgrade. Probably foolish, but what isn't about rebuilding a 45 year old motor?
Thanks!
weathered engine into performer??
Welcome.
CB450 carbs can be fitted and back in the day that was done because there weren't many alternatives. Today that makes little sense. If you want bigger carbs, think Mikuni or CB750. CB450 top end can be fitted with a little work. The crankcases need to be welded up and studs moved etc. Pete Rhodes in the UK did one. And teh frame has to be modified of course. CB350 trans doesn't fit but again with enough weld and machining anything will work. The choice of champions is the CB360 trans which also requires pounds of weld and days of machining. I have no personal experience with kenig pistons, but they are not the best. For a mild street bike I'd go with stock (oversized) pistons and maybe skim the head slightly, or 350 kit pistons from Les Barker. I machine CB350 pistons to fit, but they are heavy and require a lot of machining to work. If you are thinking of a different cam, Megacycle offer several grinds, but stick to their mildest street grind or else you will lose all the bottom end. Electronic ignition is a good upgrade. It doesn't make the bike much faster but it eliminates points and that's always good. time to start posting pics so we can see what you are dealing with. What's the advantage of using the CB450 or 750 carbs on a rather stock engine? Is a K&N filter enough to open up the flow and balance things out?
Current restoration: 1962 CB77
http://www.flickr.com/photos/1962_cb77_restore/
I tried Mikuni VM26's on my bike and they didn't work. At least with the Mikuni's that I tried (and had custom-machined mounts to fit), they weren't meant to be bolted directly to the head. There should be a spacer between them and the head to allow the gas enough room to atomise, but you can't do that with a stock tank/petcock configuration. Here again, this is merely what I experienced -- maybe others have had better luck!
Vince - thanks for that info. I suppose an adapter could be made up to fit almost any carb to the head. Have to see if I can get a CB450 carb in for cheap and see how bad an adapter would be.
Probably won't use the stock tank/petcock as I don't have one. Spargett: It's a bigger carb so more air and fuel. And rather than getting a special aftermarket one, it's a Honda and it's relatively cheap and easy to find. Right now I'm still trying to get this motor apart, so still planning ahead. Vince:
There's a couple of possible reasons why that Mikuni may not have worked. It seems like a PW26 Keihin should be the same size as a VM26 Mikuni but that isn't necessarily so. They are somewhat larger as I'm sure you know. Those carbs come pre-jetted with a primary type 2 stroke needle jet and it it does not atomize the fuel very well. To work on a 4 stroke they don't need any particular spacer or gaps, though they would generate some turbulence and that would aid in atomizing the fuel into smaller droplets. They are not as bad as an Amal for that but still not very good. We use those carbs on a 240cc CL175 sloper motor (racer) but had quite a time getting the carburation right. What we saw on the dyno was the correct air" fuel ratio (eventually) but very high unburned hydrocarbon levels. that told us that there was a lot of unburned fuel, When we modified some 4 stroke type needle jets, had a bunch of air jets machined up to tilt the fuel slope and modified a pair of needles to change the fueling at part throttle, we finally got it close enough. now that bikes is dead smooth from teh basement to the top floor and that puppy revs hard. It takes time to make them work. Chris: The idea is to get more fuel/air mixture into the head but that assumes your motor can use it and has sufficient gas velocity to atomize the fuel. Bigger carbs only help if that particular motor needs more gas or if it's constrained by the gas velocity exceeding 55% of the speed of sound at which point a pressure wave forms and choke the flow. Psyche: Making CB450 carbs work is not a simple task when it comes to jetting those odd ball CV carbs. Seriously, there are better carbs out there, but I'd love to hear how you get on with that conversion. Mounting them is easy and somewhere here I still have an article on those on a CB77 but I think it was a full house 350. It's worth noting that CB450 CV carbs are way easier to jet than later Honda carbs with primary and secondary main jets.
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