Topic: 650 top end on 550 is it possible ?

[OZZYSBIKES]

HI

I am new to the forum, just bought my first four cylinder Honda (I have wanted one since I was 12 years old, I am now 58 !), I have bought my favourite one, a 1978 550K, not everyones first choice but I love them,

anyway to my question, can a 650 top end be fitted on 550 bottom end ? I saw an article from this forum on google but it contained lots of photos that were on photobucket that I cannot open so I got a little lost trying to follow the article, I think the answer to the question is yes it can be done but it involves some modification, I have already acquired a 650 top end and I was also thinking of getting a crankshaft,

Any advice or pointers will be much appreciated, the obvious reason for doing it is to give the bike a bit more power and torque for the longer distance runs that the bike is for (I have a 74 and a 89 RD350 for the quick blast)

I am in England, thanks Jeff

[Bankerdanny]

The 650 engine bolts right into the 550 frame,  what you are proposing is a lot of work without much payoff. Just buy a 605 kit and use the 650 cam or find a complete 650 engine.

[DaveBarbier]

You may have read this post by Paulages: http://forums.sohc4.net/index.php?topic=40414.0

Other than keeping the look of the 550 bottom end or to maintain a kick starter, I don’t see any reason to do a mod like this. The 650 bottom end is an improvement over the 550.

I think you’d need the 650 crank, not sure the stroke is the same as the 550.

[Stev-o]

+1 ... If your 550 needs more balls, drop the entire 650 motor in it! Or buy a 750.

Click here for the fotobukit fix.....

http://forums.sohc4.net/index.php/topic,168102.0.html

[nicks2319]

650 cam alone would probably be worth it. Or even an aftermarket one.

[OZZYSBIKES]

HI All,

Thanks for the advice, as mentioned, I want to retain the look of the 550 bottom end and the 750 is a bigger heavier bike so it doesn't fit the bill, it looks like it might be worth just putting a 650 camshaft (which I believe also needs some alteration) and a big bore kit, does anyone know if the 650 crank is a straight swap ? I understand the ignition pickup is 180 degrees away but easy enough to swap over the ignition coil trigger wires ?

I might be in luck with buying a complete 650 engine, I am favouring keeping the crankcases etc of the 550, I am not bothered about the work as I enjoy tinkering as much as riding my bikes,

Unfortunately the link to fix the photobucket issue (for Chrome) wouldn't work for me (looks like the link has been disabled)

A quick thought, I might do a twin disc conversion, does anyone know an original looking master cylinder that is suitable for the twin disc setup

Thanks

[OZZYSBIKES]

I have found a correct master cylinder, the one from the 76 Gold wing fits the bill, a repro one from David silver is available and cheap

[DaveBarbier]

The 650 cam cover is drastically different than the 550, but I see what you’re saying. Trying to keep the look of the motor as much as you can while upgrading the internals.

The 650 cam swap doesn’t normally need modification. I have read some members need to dremel down where the lobes may contact the head. Other than that, it’s a direct swap...will also need the tach gear and tachometer.

[OZZYSBIKES]

The tachometer ? I have heard about the drive may need swapping but not heard of having to put a new tacho head unit on ??

[calj737]

The tachometer ? I have heard about the drive may need swapping but not heard of having to put a new tacho head unit on ??

Different gear, different gauge ratios.

[flatlander]

i see what you want, preserving the original look of the 550 but giving it more power. however, swapping in a 650 topend will make it look very different there, apart from the heavy work needed which i think is not worth it. you have mainly three options:

550 engine + bigbore + 650 cam
cheapest option, gives you more grunt but less power than the others.
easy: get a low compression bigbore kit from.cruzinimage on ebay, get a second hand 650 cam... engine will look like original 550 only the tach gauge will need to be swapped to a 650 or 750 for accurate reading.

650 full engine swap-in
gives you the most power increase at relatively low cost (if you can keep.your fingers off making additional performance mods). but of course it won't look like a 550 any more.
there are a few threads on here covering this, including dave who posted here.

550 engine + heavier performance mods
most expensive option giving a lot more power over stock but less than the 650 engine. keeps the complete original 550 look. check the link in my signature for details.

[DaveBarbier]

i see what you want, preserving the original look of the 550 but giving it more power. however, swapping in a 650 topend will make it look very different there, apart from the heavy work needed which i think is not worth it. you have mainly three options:

550 engine + bigbore + 650 cam
cheapest option, gives you more grunt but less power than the others.
easy: get a low compression bigbore kit from.cruzinimage on ebay, get a second hand 650 cam... engine will look like original 550 only the tach gauge will need to be swapped to a 650 or 750 for accurate reading.

650 full engine swap-in
gives you the most power increase at relatively low cost (if you can keep.your fingers off making additional performance mods). but of course it won't look like a 550 any more.
there are a few threads on here covering this, including dave who posted here.

550 engine + heavier performance mods
most expensive option giving a lot more power over stock but less than the 650 engine. keeps the complete original 550 look. check the link in my signature for details.

Forgot about the 650 motor swap with a 674 kit, ported head, hotter cam and race carbs . Worst of both worlds, expensive and looks nothing like a 550, haha.

[flatlander]

ha ha worst of both worlds indeed 

[crazypj]

You may have read this post by Paulages: http://forums.sohc4.net/index.php?topic=40414.0

Other than keeping the look of the 550 bottom end or to maintain a kick starter, I don’t see any reason to do a mod like this. The 650 bottom end is an improvement over the 550.

I think you’d need the 650 crank, not sure the stroke is the same as the 550.

I got one, with rods and cam sprocket
Not sure if I'll ever get around to fitting it in my 550

[scunny]

650 stroke 55.8mm
550 stroke 50.6mm

[crazypj]

I think I'll keep the 650 crank I have, sounds like a CB750 piston, longer stroke motor will eventually get built 
(unless I find a 650 block, already have some Suzuki liners for 70mm bore, if that's even possible?)

[Gordo]

Hey dude this is a very good how to http://manuals.sohc4.net/cb550/technical_reference/TR550650_BIG_BORE.pdf

[dave500]

the 10 or 12 horsepower increase from 550 to 650 is because its 100cc bigger,about the power of any old era Honda 100cc.

[flatlander]

does anyone know actual, dyno measured rear wheel power of an original 650?
i think honda advertised it with 63hp at the crank but considering how "optimistic" their numbers were, they may only have around 50hp at the rear wheel?

[DaveBarbier]

does anyone know actual, dyno measured rear wheel power of an original 650?
i think honda advertised it with 63hp at the crank but considering how "optimistic" their numbers were, they may only have around 50hp at the rear wheel?

Don’t know the actual number, but I have heard around 49-53 quoted at the wheel.

[flatlander]

that sounds realistic. then the mods that i did to the 550 actually get you in the same area or potentially slightly better than a stock 650, only at higher cost than the engine swap.

[crazypj]

Hey dude this is a very good how to http://manuals.sohc4.net/cb550/technical_reference/TR550650_BIG_BORE.pdf

Thanks Gordo, the PDF is much easier to save