Ct70h cylinder head comp.
- Thread starter Silentshredr
- Start date
Not being a contrarian here...
It is possible to use a ball bearing (a.k.a. 12v) head on a K0-`81 motor. But, it's a can of worms...and then some. You'd need either a custom piston, to match the 6v (short rod) compression height and the smaller combustion chamber of the 12v head, or a 12v crank...along with the entire alternator assembly, CDI, wiring conversion, bulbs & battery. Sound a little expensive and nightmarish? For a stock-type rebuild, it is.
First step is a complete teardown, so that you can figure out exactly what this motor needs. It'll probably need new shift forks, in addition to the usual stuff (timing chain, roller, idler, tensioner cap, gaskets, seals etc) and there's a chance that the crank is worn. Anything beyond ~0.018" side clearance at the big end of the rod, any radial slop that can be felt, or any looseness that can be felt at the small (wrist pin) end and the crank should be rebuilt, or replaced. It may be possible to rebuild a 6v crank, using a 12v rod...but...IDK if the crankpin diameters are the same and that's critical. Fact is, H-model rebuilders get a lucky break, $70 repop cranks from dratv, less than half the cost of a crank rebuild.
Frankly, for a stock rebuild, I'd want to repair the head, if possible. There's a good chance that there's still enough metal to use an M12 Timesert. I'm not fond of using a 12mm plug in these but, at this stage it'd be clean, inexpensive, and the threads much tougher than the aluminum casting. If there's not enough metal left, the spark plug hole could be welded, then re-machined...back to the original M10 x 1.0; that's strictly pro work, requiring both a machinist and a skilled welder. I'd estimate $70+/-, all-in. That'd preserve the original casting numbers...if you're a purist. If not, any K0(`69) through `81 CT70 head can be used, plug & play. And those are not rare.
It is possible to use a ball bearing (a.k.a. 12v) head on a K0-`81 motor. But, it's a can of worms...and then some. You'd need either a custom piston, to match the 6v (short rod) compression height and the smaller combustion chamber of the 12v head, or a 12v crank...along with the entire alternator assembly, CDI, wiring conversion, bulbs & battery. Sound a little expensive and nightmarish? For a stock-type rebuild, it is.
First step is a complete teardown, so that you can figure out exactly what this motor needs. It'll probably need new shift forks, in addition to the usual stuff (timing chain, roller, idler, tensioner cap, gaskets, seals etc) and there's a chance that the crank is worn. Anything beyond ~0.018" side clearance at the big end of the rod, any radial slop that can be felt, or any looseness that can be felt at the small (wrist pin) end and the crank should be rebuilt, or replaced. It may be possible to rebuild a 6v crank, using a 12v rod...but...IDK if the crankpin diameters are the same and that's critical. Fact is, H-model rebuilders get a lucky break, $70 repop cranks from dratv, less than half the cost of a crank rebuild.
Frankly, for a stock rebuild, I'd want to repair the head, if possible. There's a good chance that there's still enough metal to use an M12 Timesert. I'm not fond of using a 12mm plug in these but, at this stage it'd be clean, inexpensive, and the threads much tougher than the aluminum casting. If there's not enough metal left, the spark plug hole could be welded, then re-machined...back to the original M10 x 1.0; that's strictly pro work, requiring both a machinist and a skilled welder. I'd estimate $70+/-, all-in. That'd preserve the original casting numbers...if you're a purist. If not, any K0(`69) through `81 CT70 head can be used, plug & play. And those are not rare.
Silentshredr
New Member
Lots of info, appreciate it. I'll just save the 12v stuff for the next bike and source a new head with the other needed items I run into with the tear down.