Topic: Would you put a 650 motor into a 500 or 550 frame, and why? :)

[daewon774]

So, I just bought a CB650.  I got the entire bike for $75.  I was going to rebuild this as a winter project but then I ran across a few threads here and there about putting a 650 motor into a 500 or 550 frame.  I thought this was a badass idea.  I come across an ad in craigslist for this guy that has about a mix of CB500 and CB550 frames/motors.  He's selling them cheap.  My question is, now that I have this idea in my head about possibly doing this motor swap, would you do a swap into a 78' CB550, or a 71' CB500?  Why would you choose one over the other?  Are there any big differences between these two frames/swingarms?

Also, I've read that a 650 fork should go straight into a 550, is this true with 500 frames too?  Same with the wheels I'm guessing?

Thanks in advance!

[Gordon]

I wouldn't, but mainly because I'd lose the kick-start.  I'd sooner go through the process of boring out a 550 and making it into a 650 than do that. 

[Alan F.]

There might be some insurance savings to be had if you can call the bike a 500 or a 550.

[BVCB650]

I wouldn't. Either rebuild the 650 as is, or do like Gordon suggested and use what you can in a 550 motor, but in the end, you are just trying to be a 650, so why not stay true blue?

[Caferacernoc]

I like the idea. Lighter, smaller frame, bigger motor. Less machine work than hopping up the 500 engine to have heads that flow as good as the 650 stock and installing bigger pistons. The 650 cam is used as an upgrade on 550's. This seems way easier. Just use the better engine.

[daewon774]

I definitely understand the loss of the kick, I've been contemplating that for a while, but I also lose the points and pick up CDI, AND get a larger displacement engine.  All this in a lighter and smaller CB500/550 frame.  Plus, no need to bore a 550 engine when I already have a 650 that I can drop/bolt right in.   

This is my first project bike and would rather modify an engine down the road rather than now.  The 650 motor lets me skip over any 550 engine modification.

But, the question I was really trying to ask was, is there a big difference between the 550 and 500 frame?  Sorry, I didn't explain my question well.  The reason I ask is because I am going to pick up one of these frames today after work.  The choice is between one of three 71' CB500 rolling frames or a 78' CB550 rolling frame.  Is there one that is 'better' than the other?  If you were to build up from one of these, which would you choose?

[daewon774]

I wouldn't. Either rebuild the 650 as is, or do like Gordon suggested and use what you can in a 550 motor, but in the end, you are just trying to be a 650, so why not stay true blue?

I thought about rebuilding the 650, but I want to go the cafe route.  The frame I have is a 650 custom frame.  There aren't alot of tank/seat options for the 650.  BUT, the 500/550 has a great supply of parts online! 

[daewon774]

There might be some insurance savings to be had if you can call the bike a 500 or a 550.

niiice... I didn't think of that... 

[Alan F.]

Plus a 71 CB500 is a a K0, it was the first model in the series.  That makes it cooler in general.  Think of it as putting a big block in a small block equipped car...sort of.
Then you can go lightweight with plastic fenders (keep the front brace though) and lighter directionals, plastic H-4 headlight, modern electronics (Pinhead style)
Throw on some alloy rim hoops, swiss-cheese everything, do a 520 chain& sprockets with gearing to suit your needs, you can drop a bunch of weight these ways then add sticky tires like BT45's or Bridgestone S-11's, and the list just doesn't end.  The 500K0 is a way cooler bike to begin with.

I wonder if a 650 engine weighs less than a 500?
-Alan

[BVCB650]

Plus a 71 CB500 is a a K0, it was the first model in the series.  That makes it cooler in general.  Think of it as putting a big block in a small block equipped car...sort of.
Then you can go lightweight with plastic fenders (keep the front brace though) and lighter directionals, plastic H-4 headlight, modern electronics (Pinhead style)
Throw on some alloy rim hoops, swiss-cheese everything, do a 520 chain& sprockets with gearing to suit your needs, you can drop a bunch of weight these ways then add sticky tires like BT45's or Bridgestone S-11's, and the list just doesn't end.  The 500K0 is a way cooler bike to begin with.

I wonder if a 650 engine weighs less than a 500?
-Alan

Around 280# if memory serves me right.

[Alan F.]

Actually the shop manuals have weights listed.
The 650 engine weighs 154.4 lbs.
the 500 engine weighs 152 lbs.

So not too bad of a difference, that kickstart system must weigh a few pounds with the kickstart arm, shaft and that big gear.
-Alan

[daewon774]

Actually the shop manuals have weights listed.
The 650 engine weighs 154.4 lbs.
the 500 engine weighs 152 lbs.

So not too bad of a difference, that kickstart system must weigh a few pounds with the kickstart arm, shaft and that big gear.
-Alan

Wow, thanks for that info.  I was just searching online for the weights.  I didn't realize they were both about the same weight.  Interesting...

[BVCB650]

Actually the shop manuals have weights listed.
The 650 engine weighs 154.4 lbs.
the 500 engine weighs 152 lbs.

So not too bad of a difference, that kickstart system must weigh a few pounds with the kickstart arm, shaft and that big gear.
-Alan

Well as usual, my memory is in the crapper.

[BVCB650]

Actually the shop manuals have weights listed.
The 650 engine weighs 154.4 lbs.
the 500 engine weighs 152 lbs.

So not too bad of a difference, that kickstart system must weigh a few pounds with the kickstart arm, shaft and that big gear.
-Alan

Wow, thanks for that info.  I was just searching online for the weights.  I didn't realize they were both about the same weight.  Interesting...

The difference is probably in the beefed up cam chain of the 650.

[mlinder]

10ish HP difference. That's why I'd do the swap.

[BVCB650]

Actually the shop manuals have weights listed.
The 650 engine weighs 154.4 lbs.
the 500 engine weighs 152 lbs.

So not too bad of a difference, that kickstart system must weigh a few pounds with the kickstart arm, shaft and that big gear.
-Alan

My book actually shows the engine weight at 156.6# for a 650.

[Pinhead]

I definitely understand the loss of the kick, I've been contemplating that for a while, but I also lose the points and pick up CDI, AND get a larger displacement engine.  All this in a lighter and smaller CB500/550 frame. 

But, the question I was really trying to ask was, is there a big difference between the 550 and 500 frame? 

You'll have to keep the CDI stuff (which is actually TCI) from the 650; there is no way to mount points to the 650 motor. Also, the frame weight difference is negligible but the 650 frame is stiffer. It would be a downgrade all the way around.

The only advantage you might gain is style if you don't like the looks of your 650.

[andy120t]

I'm building up a CB550 with a CB650 at the moment - see the thread under "Parts Bin Special" in the UK forum  http://www.sohc.co.uk/

Primary reason is to use up bits I have lying around & to get a unique bike on the road. Benefits are more power in a 'bike that will look more like a 550 rather than a 650 - although will still be different and far lighter than the standard 550 (think Q-bike). One downside, as mentioned earlier, is no kickstart.

It's work-in-progress over the next few months. Currently I've slotted 650 forks (from memory, 35mm - with leading axles) straight into 550 yokes so will have twin discs on this. I'm using 18" CB400/4 wheels front and back so am in the process of sourcing axles prior to matching up bearings for these.

Had planned to use a 400 swingarm but it's narrower than the frame (and shorter than the 500) so am resorting to a CB550 one.

I understand the engine will go straight in. Haven't fitted it yet but no visible reason why it won't & all the mounting brackets I have match the 550 ones exactly. 

Go for it!

[BVCB650]

Not having points is a good thing...no? I thought I would miss a kick start, but so far, not so much. It forces you to actually maintain the bike a little better in the way of a good battery, cables and the actual starter, but that can be benificial as well.

[paulages]

Actually the shop manuals have weights listed.
The 650 engine weighs 154.4 lbs.
the 500 engine weighs 152 lbs.

So not too bad of a difference, that kickstart system must weigh a few pounds with the kickstart arm, shaft and that big gear.
-Alan

there's no "big gear" like on the 750.

i doubt the 650z frame weighs much more than the 500/550 frame, if any, and it does have one major advantage: the right lower frame rail drops out with the engine mounts. makes removing/installing the engine a breeze. don't know about the C frame though. I have a '79 Z frame sitting in my rafters it you're interested in it.

[turboguzzi]

In old air/oil GSXR speak we used to call it a 7-11 :-)

nice beast they were

[daewon774]

Alright, I am officially locked into doing this swap.  Or... at least I'm going to attempt to do this. 

Tonight I picked up a 71' CB500 frame!!!  Along with the frame, I picked up both wheels, front forks, swing arm, rear shocks, and both fenders.  All that crap is sitting in my car since the garage door is blocked by the neighbors car.  It's a bit dark out, so I'll take some pics tomorrow to post. 

Looks like this weekend is going to be all about rust/paint removal and prepping for paint on the swing arm and frame.  I'll also start on tearing down the CB650 I have sitting in the garage. 

[Alan F.]

My book actually shows the engine weight at 156.6# for a 650.

I just grabbed a screenshot of the first weights I stumbled across...

there's no "big gear" like on the 750.

Thank you.
I can remember someone doing this swap back in the greenspun days, but specifically I can only remember reading that the top of the valve cover was very close to the bottom of the fuel tank.
Cheers on your decision, I'm subscribed.
-Alan

[paulages]

My book actually shows the engine weight at 156.6# for a 650.

I just grabbed a screenshot of the first weights I stumbled across...

there's no "big gear" like on the 750.

Thank you.
I can remember someone doing this swap back in the greenspun days, but specifically I can only remember reading that the top of the valve cover was very close to the bottom of the fuel tank.
Cheers on your decision, I'm subscribed.
-Alan

besides my 718cc 650-headed bike, i've done the 650 engine in 550 frame, and there are no tank issues. the valve adjusting covers do ride higher than the 550 cam cover does, but it's not problematic. there are no fitment issues, and the 550 airbox can be altered fairly easily to fit the 650 carbs plenum. i used fiberglass to cover the old hole and cut a new one.

[GoatBaSS]

JUMP IN! It will be your bike for sure........