SOHC vs DOHC learning thread for newbies

Hichhkrjo

Hichhkrjo

Been Around the Block
Hi all,

I hear a lot about SOHC being better than DOHC and then vice versa. "It's easier to do this on this one," that sort of thing. I've done a little research, but engines are still a little beyond me sometimes. I'm not looking to buy one or the other, or get into a debate, or anything of that nature. Just for pure learning, can any of you more experienced guys (or gals) on here give a basic run down on the two? What are the advantages and disadvantages to both? What are some good bike examples of each? maybe even the history of them..? I'd love as much input from as many people as possible, cuz I want to know as much about this as I can. Maybe more people than me will learn some stuff.

I'm really just curious and want to learn, and it'd be sweet to have this more of a learning/teaching thread than opinion thread. If this has already been covered and you know of a good thread on here to read, by all means, point me in that direction.

Thanks!
 
SOHC and DOHC? I'm assuming you mean the CB750 series, if so, then here's a few things:

1: SOHC were 736cc's, DOHC were 748cc's.
2: SOHC have kick start and push button, DOHC's only have push button
3: DOHC's made about 8hp more than SOHC's
4. The DOHC frame is wonky as shit, has a piece that's even removed for engine removal, and has a dipped seat area and raised rear frame rails. SOHC seating area was almost completely flat with the rear rails.
5: SOHC engines are GORGEOUS, DOHC'S are their somewhat cute second cousin.
6: Because of the kick start option on the SOHC's, you can run it without a battery/extremely small battery, which cleans it up nice. DOHC's take a big ol' honkin' battery to turn over.
7: Both of them are heavy, like 500+lbs heavy and generally have soft suspension from the factory.

There's tons more, these are just some general factoids. Someone else, who probably knows way more than I, can chime in and fill in the blanks.
 
I've got a 1980 CB750C which is a DOHC. Having a DOHC is better for engine performance just due to the geometry of the cylinder and piston, but I think there are better reasons to go for the SOHC. Jewbacca laid it out pretty nicely of the differences between the two. For a personal opinion, I would have gone with the SOHC looking back.

A kickstart would have been nice. My battery is HUGE and it takes a lot of juice to turn the engine over. The flat seat area would have been nice to have to mount a cafe seat. Now I'm stuck with trying to carve a foam mold that will take the uneven shape of the DOHC seat area but still look sleek and not all cruiser-ie.

I have yet to open up my engine, but I'd imagine that working with one camshaft would be easier than two.
 
great stuff! thanks!

As a coincidence, I've got a CX500, which also has that dip in the seat area. It is definitely a serious pain in the ass trying to put a nice flat seat on there.
 
Hey Hillsy,
Which years would you suggest for for the GS750 and do those years come with a kickstart?
Thanks
 
The SOHC is the godfather of the modern sport bike. The DOHC is its younger awkward brother.
 
I have a 1972 Honda CL450 DOHC that has a kick starter. I am confused about the SOHC=kicker, DOHC=no kicker statement. I know that 'every rule' has its exception is often correct. The side covers say DOHC, I guess in 40 yrs they could have been swapped out.
No flames meant or suggested, just confusion on my part. So, what's what? I guess this would matter more if I had the bike running.
 
redbiker said:
I have a 1972 Honda CL450 DOHC that has a kick starter. I am confused about the SOHC=kicker, DOHC=no kicker statement. I know that 'every rule' has its exception is often correct. The side covers say DOHC, I guess in 40 yrs they could have been swapped out.
No flames meant or suggested, just confusion on my part. So, what's what? I guess this would matter more if I had the bike running.
Click to expand...

When people talk about CB's being SOHC or DOHC they are referring to the 750's.
 
Yeah, the cb/cl450 and cb500 twin motors were a 60's bastard child. They are the sexiest of all the DOHC engines though
 
The Suzuki 4 valve DOHCs (80 and on called TSCC), had adjustabe rocker arms while the earlier SOHCs were shim and bucket.
 
Please explain why you said this? I don't understand.
**Yeah, the cb/cl450 and cb500 twin motors were a 60's bastard child**. I have heard the360, 550 and 650's were were made to be the transition bike until the 4 cylinder bikes took the lead.

Really doesn't matter, I have a bike that's been on my 'bike list' for a very long time. Actually, I have a couple of them that I need to get running before we get snowed in.
 
Hoosier Daddy said:
The Suzuki 4 valve DOHCs (80 and on called TSCC), had adjustabe rocker arms while the earlier SOHCs were shim and bucket.
Click to expand...

Suzuki never made an SOHC engine (apart from their singles). Otherwise, you're correct ;)
 
How about some less superficial aspects..
SOHC engines are lighter. They have fewer moving parts. Less complicated systems, works great on simpler engines. Requires use of rocker arms. Unable to produce the power potential of a DOHC. Spark plug can not be in center of cylinder thus uneven ignition and less efficient burn.

DOHC requires more parts which makes it heavier. More complicated system. more moving parts. This system is much more efficient though. The engine has 2 extra valves per cylinder so it can move more gas and air in and out. Improved high end performance. Higher rpms can be accomplished. Centered spark plug, efficient, even combustion.
 
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