cbsavage
CB750 Enthusiast
I would like to know which is the better and and has less problems also easiest to work on.
Which is better sohc or dohc
- Thread starter cbsavage
- Start date
amc49
CB750 Guru
Not as simple as that, one makes more power but the other is simpler to work on, along with 50 other offsetting reasons that work or bite either way.
The SOHC is becoming harder to find good parts for, you can find DOHCs everywhere, I was given 3 of them. The much more complicated carbs really kill lots of desire to work on them. But then, like so many others, that's an operator rather than bike issue. Then the operators twist that into being a bike issue since they don't have the knowledge to do the work correctly.
No insult intended at anyone at all but it is what it is.
The SOHC is becoming harder to find good parts for, you can find DOHCs everywhere, I was given 3 of them. The much more complicated carbs really kill lots of desire to work on them. But then, like so many others, that's an operator rather than bike issue. Then the operators twist that into being a bike issue since they don't have the knowledge to do the work correctly.
No insult intended at anyone at all but it is what it is.
Dave
CB750 Junkie
Carbs aside (I'd like to monkey stomp the idiot who thought of using engine vacuum to open the throttle) the earlier bikes that come with the SOHC engine are still easier to work on and are more reliable.
The DOHC engine makes more horsepower but require more maintenance.
The DOHC engine makes more horsepower but require more maintenance.
cbsavage
CB750 Enthusiast
I've had four cb750's in the past. Fortunatly I never had to work on them. I just rode them and sold or traded them. This one, is a '79 cb750k that has been sitting outsde since 2002. When I got it, the carbs were off and some body parts missing. I dont know what the previous owner was doing befor he abanded it. I cleand the carbs and bench synced them, bought new oem carb boots and air box intake boots. I'm leaning more about thi bike, thanks to the help and advice from this great site.
amc49
CB750 Guru
The carbs come off first because most people think they can understand those. Not really though. And commonly the actual issue was the valves leaking due to never setting valve clearances as they involve shim changing and even the shops commonly overlooked doing that 100% correctly.
The valves commonly close up instead of getting looser like most expect. Then engine leaks at valves and owner blames carbs since it seems to be that sort of a problem. The carbs add to that since the idle system is so complicated and VERY easy to stop up as well as be dead sure you've got it 'all clean' and you are SO wrong.
Get with the times, almost all engines now use CV type carbs, they are able to make them bigger (what the customer thinks he wants) yet they work in such a fashion as to detune a lot of the potential of the motor, important to keep rider lawsuits at bay.
The valves commonly close up instead of getting looser like most expect. Then engine leaks at valves and owner blames carbs since it seems to be that sort of a problem. The carbs add to that since the idle system is so complicated and VERY easy to stop up as well as be dead sure you've got it 'all clean' and you are SO wrong.
Get with the times, almost all engines now use CV type carbs, they are able to make them bigger (what the customer thinks he wants) yet they work in such a fashion as to detune a lot of the potential of the motor, important to keep rider lawsuits at bay.
cbsavage
CB750 Enthusiast
Point taken, compression and valves are my next step. Thanks again fot the help.
Dave
CB750 Junkie
I forgot about those shims. I was given a 79 in perfect condition (except it wouldn't stay running) after the owner replaced the timing chain. He didn't realize those were shims and just re installed them in random spots.
A few hours of shuffling and gap checking and I managed to get them all back in the correct places. That one had kitted carbs and a very short (very loud) 4 into 1 hooker pipe on it. Very fast, like a bullet. Yeah, like a bullet, didn't like to turn or stop! LOL
amc49
CB750 Guru
The stupid silly issue with DOHCs is that the cam cap to camshaft clearances are looser than the valve clearance spec and then the cams move around up and down to then fool you when checking valve clearances. What you get is NOT real world numbers at all and why Honda's spec there sucked. The possible .002" minimum actually can have the valve held open to run like crap, my first engine burned several valves in 5K miles when I mistakenly though I was keeping the valves close and quiet. Measure one at .002" and then move the cam ever so slightly to not be on ramps, rather still solidly on the cam base circle and the next reading can easily be off .002" from the last one. That's flaky and what they do. If cams were held down correctly you should find a long stretch where the valve clearance stays the same but not on these. Why Honda again gave the wonky setting marks and then modded them again when the first set didn't work. Surprise! NONE of them work. Best thing to guarantee long running there is to go up to a minimum of .005" and then the engine starts running very reliably along with long periods between having to set valves again. Many people set the valves on TDC compression since that is the point at which you will lose the most power if they are off where you can't tell how far they are real world.
madmtnmotors
CB750 Addict
SOHC are best 
amc49
CB750 Guru
A lot of people thumb their noses at MAC pipes but they look good there.
Nice clean bike.
Nice clean bike.
