CA77 and CB77 pistons.

Scooter trash

Been Around the Block
I'm building a 305 Dream to do the ton, and have some fun on the Harley rides. I've had 305 Superhawks up to 110 mph with some high compression pistons, I was using a Dream crank to get that Triumph sound, after reclocking the cam. There is a high performance Yoshimura kit for a whopping $1900.

Anyone have a connect for high compression pistons?
 
You need to know 3 things if looking for non-stock pistons. Bore size you want, piston pin diameter and crown height (distance from centre of pin to 'flat' above top ring)
Measure what you have and post numbers
 
crazypj said:
You need to know 3 things if looking for non-stock pistons. Bore size you want, piston pin diameter and crown height (distance from centre of pin to 'flat' above top ring)
Measure what you have and post numbers

I found a set of 10.2-1 on ebay, they use the newer 075 rings rather than the 266. Reclocked the cams from a CB77, should make about 29-31 hp. The extra overlay and the higher compression, should let me pull a gear high enough to reach the ton.
 
The deck height is a bit shorter by .070" which is a lot. Will have to use dental impression putty, Coeflex, to see how much room there is in the cylinder head dome.
 

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Too long since I looked at a CA77, but CB77 pistons match a "squish band" machined into the CB77 head ( unlike a CB72). I like CB350 pistons for a 77 because I can machine them to get a squish angle I like and machine chunks off the block and head to get it all to work. There are other ways to do it though.

Those look like Italian CB77 high comp pistons and they tend to self destruct because they are apparently made of some sort of recycled cooking pots or old shoes or something but they tend to break off in chunks with a coarse granular structure. That doesn't mean they are all bad but they do have a reputation.

If you stay with a single carb, try to clean up that inlet tract and upsize the carb. I like CB750 carbs. They have the same 26mm slide as a CB77 but a taller throat so they average out to the equivalent area as a 28mm and still have a small diameter at small throttle openings for tractability.

To get 100 mph you will probably need a better cam and will need good valve springs to avoid valve bounce which happens at fairly low revs with stock springs. Lightening the rockers and valve caps also helps as does lighter valves - See Pops Yoshimura old tech sheet/hop up notes for more details.

BTW, a 360 degree crank makes more mid range torque than a CB77 180 degree crank but loses out at the top end, big time. Fit a CB crank or re-phase the dream crank for better top end.
 
teazer said:
Too long since I looked at a CA77, but CB77 pistons match a "squish band" machined into the CB77 head ( unlike a CB72). I like CB350 pistons for a 77 because I can machine them to get a squish angle I like and machine chunks off the block and head to get it all to work. There are other ways to do it though.

Those look like Italian CB77 high comp pistons and they tend to self destruct because they are apparently made of some sort of recycled cooking pots or old shoes or something but they tend to break off in chunks with a coarse granular structure. That doesn't mean they are all bad but they do have a reputation.

If you stay with a single carb, try to clean up that inlet tract and upsize the carb. I like CB750 carbs. They have the same 26mm slide as a CB77 but a taller throat so they average out to the equivalent area as a 28mm and still have a small diameter at small throttle openings for tractability.

To get 100 mph you will probably need a better cam and will need good valve springs to avoid valve bounce which happens at fairly low revs with stock springs. Lightening the rockers and valve caps also helps as does lighter valves - See Pops Yoshimura old tech sheet/hop up notes for more details.

BTW, a 360 degree crank makes more mid range torque than a CB77 180 degree crank but loses out at the top end, big time. Fit a CB crank or re-phase the dream crank for better top end.
These are made in Italy, and are predispositioned for pre ignition. A burned hole in the dome, is the most likely failure. Squish is extremely important to distribute the charge evenly in the combustion chamber. These are begging for a hole. The CB77 crank is smoother, but doesn't have that cool Triumph sound. Pulling a few degrees in timing, cooler plugs, a little on the rich side, and Octane booster will tell. Getting a good charge spread with high domes is dicey, just the physical surface makes for trapped gasses. Thanks for the input!
 
I like modified CB350 pistons that I have machined with the squish angle I want and then have the block and head machined and machine a squish band into the head at an appropriate angle. Valves still have to be pocketed and gas flowed to suit as well as new pockets in the pistons. Someone that I supplied a cam to years ago was upset that their new motor with high dome pistons would not rev, so they stripped it and machined down the crowns and it revved higher so they repeated that process until they had a low enough dome with adequate compression and great flame propagation.

With high crowns don't be surprised if you end up using more than 50 degrees of ignition timing. Honda 6s used to be 60 degrees IIRC.
 
High dome pistons in XR750 Harley use up to 68~70 BTDC degrees to allow them to rev
 
That's coz they are Harleys and everything is bigger on them things.....

68 degrees is ludicrous though. Is the inlet valve even closed by then?
 
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