Honda Twins banner
1 - 20 of 24 Posts

·
Registered
Joined
·
37 Posts
Discussion Starter · #1 · (Edited)
CM450 Engine Swap With Nighthawk SC or Something Bigger?

Hi guys,

So I have got a CM450E which seems likely to need some engine work in the near future. So I have been thinking about swapping the engine with something with more power and adding new disk brakes to tame that power.

I know that CB450 SC's engine is probably the least technically challenging option but for a mere 7 upgrade in horse power, I wonder if it worth the trouble.

Now my question is, whether in your opinion or experience, there is a more viable swap that is achievable with a little bit of extra work put into it? Say a 750 Nighthwak?

Any guidance is much appreciated and thank you in advance.
 

·
Premium Member
Joined
·
24,208 Posts
The SC engine swap is a direct bolt for bolt swap with 1 minor modification. The horsepower is identical for all of the SOHC 450's including the E model so there'll be no actual improvement other than a potentially better engine.
Swapping in a different engine will require figuring out things like mounting points, chain alignment, electrical connections, etc.
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #3 ·
The SC engine swap is a direct bolt for bolt swap with 1 minor modification. The horsepower is identical for all of the SOHC 450's including the E model so there'll be no actual improvement other than a potentially better engine.
Swapping in a different engine will require figuring out things like mounting points, chain alignment, electrical connections, etc.
I was under the impression that CM450 created [email protected] rpm as opposed SC with [email protected] Seems like I could be wrong.

Of all the adjustments that a potential swap would require, I am mostly concerned with chain alignment. To be honest I was hoping that someone would have already experimented with this idea and could steer me in the right direction with specifics such as the engine they used and the tweeks that followed.

Do you think it's a viable thought at all?
 

·
Premium Member
Joined
·
24,208 Posts
The SC counter/output shaft is 4.2mm's longer than the rest of the 450's which places the front sprocket outboard of alignment. This is easily corrected by using a 1" washer, they have a thickness of 4.0-4.1 mm, placed between the sprocket and retainer. 2 holes have to be drilled in it to allow the longer retaining bolts to hold the sprocket.
There's been a lot of confusion on the internet about horsepower and various engines. There are 2 versions of the 450 engine, the earlier DOHC 450 from the late 60's early/mid 70's and the SOHC 450 from 1982 on. There's also a second SOHC 450 found in the CMX/Rebel which is a similar but again different engine
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #7 · (Edited)
AS some around here are fond of saying, with a hack saw and a welder, you can make anything fit. Looking at the frames of the CM450E and the CB750SC, it appears you would need all of that.
Would you happen to know of an alternative that requires less hacking and welding? :)

The only other similar frame I know of is the CX500 but that is a no go.
 

·
Registered
Joined
·
3,538 Posts
Would you happen to know of an alternative that requires less hacking and welding? :)

The only other similar frame I know of is the CX500 but that is a no go.
You could just go get a 750SC and fix that up. About 40 years ago I wanted to build up a fairly new CB360T. I was advised to just go buy a bigger bike. There are some exceptions, CB400F & CB450 DOHC come to mind. My advice is to get the bike going and enjoy it. The 400/450 SOHC were pretty advanced in comparison to other Honda Twins. They are counter balanced so they run smooth, better suspension and are powerful. Summer is coming, get that bike going.
 

·
Registered
Joined
·
2,510 Posts
What's wrong with your current engine?
If it's the top end then doing that may be easier than the alternatives you're considering... Potentially ruining the frame and having a project going years trying to shoehorn a larger engine in, without result.
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #10 · (Edited)
There is nothing wrong with the engine that I know of but that remains to be seen when I take the cylinder head off.

This was my first bike and it was in rough shape when I first bought it with quite a bit of mileage on it. I have since modified it into a scrambler and I have an emotional attachment to it so I don't want to just get rid of it and start another build just cause I would like to have more ponies on the chain. That being said I have started to entertain the idea of keeping all the work and effort that has gone into building it and replacing the engine with something more substantial.

I know it would be much easier to just build up 750SC but what can I say ... I would like to keep this old girl.

And by the way, she's almost ready to be back on the road again :D
 

·
Registered
Joined
·
3,538 Posts
I know about emotional attachment. That is the first stage of becoming a collector. Get the 450 in shape for summer and start looking for the right 750.
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #12 ·
I know about emotional attachment. That is the first stage of becoming a collector. Get the 450 in shape for summer and start looking for the right 750.
I'm looking at the 750 Nighthawks and the shape of the frame and seating position seems almost ready to become a scrambler ... I really should stop buying motorcycles.
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #13 ·
What's wrong with your current engine?
If it's the top end then doing that may be easier than the alternatives you're considering... Potentially ruining the frame and having a project going years trying to shoehorn a larger engine in, without result.
By top end do you mean the power band?
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #15 · (Edited)
Honestly the engine is fine. It does have 33000 kilometers and it runs smoothly but I do see a minor leak around the cylinder head. Could be just the old gaskets but we'll see what it looks like when take the valve cover off once the cosmetic modifications are finished.
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #17 ·
Dude, you wrote in your first post that the engine would need work in the near future.
Oil weep at the cylinder head and valve cover just needs a better gasket seal.
Yeah about that ... we adjusted the timing chain and re-jetted the carbs since that initial post.

I did think about editing the first post, but I didn't. My bad friend :)
 

·
Registered
Joined
·
3,538 Posts
Sounds like you have a good bike. How about sharing some pictures? We love pictures.
 

·
Registered
Joined
·
37 Posts
Discussion Starter · #20 · (Edited)
Sounds like you have a good bike. How about sharing some pictures? We love pictures.
I was going to wait until she was all done and ready but I guess sharing a few pictures from the surgery bed won't hurt anybody:

Motorcycle Motor vehicle Vehicle Chopper Tire
Tire Motor vehicle Automotive tire Vehicle Automotive lighting

Land vehicle Vehicle Motorcycle Motor vehicle Car



Glad you got it worked out.
When rebolting the valve cover, don't over torque the bolts!
Will surely keep that in mind !!!
 

Attachments

1 - 20 of 24 Posts
Top