1974 V 1978 Counter Shaft Sprocket interchange

[gimpy]

Newer member, Gimpy in Palm Beach Gardens Fla. I bought a original Green 1974 CB 750 with only 12,000 miles from the original owner on craigslist this past summer. The owner barned it for years and the engine is now froze. I will restore it at  a later date. However I want to ride the 74 soon. I purchased a 1978 CB 750 engine that I want to install in the 74. I read that all the parts are the same, interchangeable or so I read. However, after digging in I see the drive primery sprocket shaft is different. The 74 has I guess the chain oiler with small set screw and retaining nut with lock tabs, the 78 has a bolt/washer and the shaft is shorter. The 18 tooth gear looks to be the same and slides on the shaft. However the retaining bolt/washer on the 78 doesn't look correct, anyone know what I need? Wanna ride asap. Gimpy AKA Rick in PBG, Fl.

[Lucky 1]

Th 1978 engine had about 21 changes.

It had no chain oiler.
No oil leaking all over the place.
The 4th and 5th gears in the trans of the 1978 were different too.
The 1978 had more width in the cam chain tower, that COULD cause some exhaust alignment issues.

I do not know if you can get the rear chain to line up without a special countershaft sprocket.
Cycle-x sells those but It is for wider rear wheels. Maybe flip it over?
Some members will chime in and give you a better answer.

I would have just rebuilt the 1974 engine. Then the serial numbers match, and no wiring problems.
All you did is create a bunch of problems and they will all have to be undone to use the 1974 engine. Of course you will probably never rebuild that engine.

Do not throw the 74 engine in a dumpster. Many people need that engine and those parts.

[gimpy]

Well live and learn. The original bike/engine on the 74 only has 12,000 stored in a barn since the early 80s. I got the bike on craigslist @ a yard sale. I got the bike for real cheap. I did inspect the bike good and saw the one cylinder that had moister entered the #4 cyl. And knew the motor was froze. However it was the exact year/color bike I owned back in 1975.
Back in the day I traded the 750 for a brand new H1 500 triple after about a week the ring ding ding of the 500 grew old and I knew I had made a mistake, live and learn. I have been soaking the cylinders with Kroil since I purchased the bike back in mid june, still froze. I checked on the upper rebuild kit, however I was told all the sohc engines were the same execpt for compression/cam specs. So that's why I bought the 78 engine. I only paid 200.00 I thought they were all  interchange, I see nope, not true. I wanted to ride so I traveled all around the state looking for running CB. I found a 1975 CB SS on craigslist. I repaired the charging system wires and have put 1,700 miles on it. But I want to get the 74 going too. I do want to rebuild the top end. I'm a retired auto mechanic so doing all the work is no problem, however you gotta know what works and what don't that's why I'm here. The wiring harness too?? I see a guy/Mark who lives near me in Palm Beach Gardens, who has the exact same bike, Green 74, I have not met him yet and have not seen the bike cruising the streets. I saw his bike here this past summer and wondered if this maybe was my old Green74 750? I'm going to try and post a pic of my 75 SS. I drive around with open 4into1 exhaust it sounds bad-ass.  No tickets yet! Anyone who knows if I can get the engine swaped out or just go for the top end rebuild. I don't like a can of worms.    

[Piute]

   Might wont to read pg.3 Sept 1st also just info is all.
http://honda-cb750-s.456789.n3.nabble.com/Piute-putt-1977-CB-750-F2-td3196204i40.html

[TOOLS1]

The sprockets are the very same, and will interchange. They just have a different way of holding them on. You will need to change the rear cush drive also to use the 77-78 engine since the sprocket was moved out 10mm for the 630 chain.
TOOLS

[Lucky 1]

If it was me I would simply rebuild the 1974 top end and be done with it.

You will save yourself a  lot of hassles.

The bike will be worth more too.

[shinyribs]

TOOLS1 wrote

The sprockets are the very same, and will interchange. They just have a different way of holding them on. You will need to change the rear cush drive also to use the 77-78 engine since the sprocket was moved out 10mm for the 630 chain.
TOOLS

Is that why they moved them out?        is right.

[gimpy]

Now I'm told, in order to use the 1978 sohc engine I purchased on my 74 sohc, all the changes needed is; use the 77-78 swing arm and the rear sprocket carrier/hub, also the axle bolt/nut/spacer cuz the difference with the sprocket/chain alignment, is off by about 1 inch or more.
 I can't believe that's all that is needed. I hear the early sohc's had the 9 1/2 width swing arm V 10 1/2 width of the 1977/78's, and that's the difference between the years. Sounds very cheap and easy fix, however sounds to good to be true. Don't know about this either. Anyone have experience with this??? I'm gonna do more research and education on this, as I have received so much miss information. I wanna ride without spending/wasting money. I'm not the type to buy a project and just start throwing money at it or just take it all apart and never finish it. Just changing out the rear swing arm and hub carrier is no big deal, as its all pretty easy bolt off/on items, and I will save all the original parts so if/when I rebuild the top end of the 74 I can simply reinstall the swing arm and hub. If not if/when I sell the bike later down the road, I will advise everything I did and let all the original parts go with the bike. Then the 74 can be changed back to oem original. If the 78 engine runs out good I'll just ride it like an original bike and leave it alone. Also the difference in the exhaust ports the 74's are deeper inside than the 78's. Can't use the 74 exhaust and spigots. The difference is the spigots V half shell shims and studs, can't use the stock 74 exhaust on the 78 either. The fix just maybe,  to install a nice set of headers mo money mo money. Again don't want to spend any money until I know I can use the parts. I've been known to squeeze a nickel to the Bufflo farts.

[Piute]

<quote author="gimpy">
Now I'm told, in order to use the 1978 sohc engine I purchased on my 74 sohc, all the changes needed is; use the 77-78 swing arm and the rear sprocket carrier/hub, also the axle bolt/nut/spacer cuz the difference with the sprocket/chain alignment, is off by about 1 inch or more.
 
                        Your throwing way to much out at 1 time ,
 
      I do believe that these top 3 lines are right ( keep digging )
     
     from my point of view,OF what I looked into but not tryed
     (was looking at custom longer & wider)
     decided stock would work for now,

     But also means your going to use a 630 chain ,will limit your choices on gearing?

    Just that Lil bit has lots involved THIS is what I mean by throwing to much out there.
 
     I'm with unLucky on this about fixing up the head on the '74' were you can get your money's worth or back to put in the 78 witch I would keep.

   SORRY AFTER READING MORE seem's you on ly have a '78' engine ? right swap the swing arm ,and get complete rear wheel and disc brake set up.Many don't like those parts ,Don't pay those high dollar prices out there on FLEA BAY,hold out for a deal,so you can get it all,there's a lot of parts and could / may run over hundred bucks,Lets say 150.bucks ,HOW MUCH FOR A '74'Head job?

[shinyribs]

Yep. It's that easy. The only thing keeping your 78 engine from working in your 74 bike is the chain alignment. If you use the swingarm form the 78 and all related pieces that go with it, axle spacers, cushion drive... it'll just bolt in.  Don't worry,  it IS that simple! :)

[TOOLS1]

Ditto Shiny.
TOOLS

[shinyribs]

TOOLS1 wrote

Ditto Shiny.
TOOLS

Of course you ditto me. I got that info from YOU!

[TOOLS1]

shinyribs wrote

TOOLS1 wrote

Ditto Shiny.
TOOLS

Of course you ditto me. I got that info from YOU!

LOL.
TOOLS