Reprofiled camshaft

[DomP]

Before I complete my engine rebuild I want to make sure I'm not missing a trick by getting my cam reprofiled, is it worth circa £180 to have it done or will I not notice the difference?  (in reality I won't as I've not ridden this bike yet) 

Will it change the sound of the bike at all?

[Oddjob]

AFAIK it's about £100-£120 plus VAT plus delivery or was in 2022.

If you get the right profile you should notice a difference, you don't want the engine to become cammy, it needs to be just a gentle re-profile.

Shouldn't change the sound no.

Detecting the difference may be hard if you don't know the baseline of the engines performance. Maybe find a cam that needs work rather than getting a good one done. Try the standard and then fit the re-profiled one after you get used to what it is like standard. If you prefer the new profile sell the old standard one.

[DomP]

Sounds good enough reasons to leave it as is to me then Ken.

[Johnwebley]

I had a spare cam reprofiled by Newmans

Asked for fast road work,

There is a difference

But you will need to in 6 to 9k rpm to get the real benefits ,

It does help the motor breathe better

Maybe even give more pull in midrange

Cost about £180

The time was long, as they had a  machine down,

Hopefully everything should be OK  now

Can't tell any changes in noise/sound

Tickover still the same



Sent from my SM-A546E using Tapatalk

[SteveW]

Check this out:

http://www.chinonthetank.com/2016/05/cb650-cam-in-a-cb550/

This is what I’m currently doing.

[DomP]

Looks interesting Steve, possibly a cheaper option too.  Let us know how it goes.


Only one cb650 camshaft on Ebay for the model years that will work and that one is pitted.

[Sesman]

I’m no expert, but I can’t imagine that a cam re profile would be of practical or appreciable benefit without all the other associated work required for improved performance such as bigger bore, porting work, carbs and exhaust. At which point I’d be inclined buy a better bike! I guess it might ‘pep it up’ a bit, but if owners have difficulty in appreciating the performance difference between a 500 and 550, the cam change on its own is pretty futile?

[Oddjob]

No, it's not like that at all Phil..

Honda made compromises in performance etc when making these bikes, it needed to be reliable and to some extent fuel efficient. It also needed to be drivable, so no massive power band surges like the Kwack 2 strokes. So the present cam was a good compromise. Did all of those things. However it left the mid range of the engine a little flat shall we say. The 650 corrected some of that by having a cam that got more duration etc. However just fitting the 650 cam whilst a good fix for the problem causes problems of it's own, you need to fit the tacho drive off the 650 as it's different and needs to mate with the spiral on the 650 cam, this caused the 500/550 tachos to read fast as it was differently geared from those models. So to cure that you need to fit the 650 tacho head, this meant a mismatch of the clocks, different colour faces, different shaped needles. Ok for a custom job but it would upset a lot of owners to have that look I'd imagine.

Getting the existing cam reprofiled avoids all those problems, you get it done to approx the same profile as the 650, so all the pros but none of the cons. It wakes up the 500/550 mid range, gives it more grunt, it also has a benefit top end but not that much. It's more to do with making the engine more tractable, less of revving it nuts off to get anywhere etc.

If you went for a more radical profile then yes, you'd need to do other stuff to make the most of that but there are quite a few things that can be done to the standard engine and the standard frame to improve the bike without it becoming like a race bike. Matching the inlet manifolds to the head ports is one, even reducing the length of the vac screws is another, by themselves just small gains, add enough of them and you can start to feel the difference.

There are mods out there that improve MPG, from say the normal 50-52mpg of the 500/550 to around 60mpg. Just simple stuff that we can all do but that won't make the bike less drivable.

I intend to do all of them on my engine, cam is definitely being done, port matching yes, even stuff like setting the timing back a few degrees and shortening the advance/retard springs. All tried and tested many years ago but seem to have been forgotten for some reason.

[Sesman]

Out of interest do we have any measurable evidence attesting to the  ‘improvement’ in torque and horsepower. Or is this just Honda lore? Genuinely, has anybody conducted a before and after dyno run.  I’m not sure I’m sensitive enough to detect a meaningful change of performance on a 50 hp machine. It might feel different, but is it actually more powerful, torquey…just asking.

I wonder if the American site has the info, I’ve seen a few posts offering opinions, but no actual data? I’ve also seen a post from an authoritative source on the American site who claims a flow job (steady Roo) effects a more appreciable improvement than changing the cam. I wouldn’t know, but elected to port match, clean the castings up and a Newman profile.. just cos I could.

 It Still won’t compete with my GS though.

[Oddjob]

It's been done so many times Phil and it's a historic mod, we ain't breaking new ground here. AFAIK it's a proven method of improving the mid range power of the 500/550. You can refine it further by doing other little things as I said, port matching the inlet tract, if you lay the inlet manifold over the head and look through the valve hole you can see they don't line up. This causes an obstruction in the flow of the air/fuel mixture when you want it to be as smooth as possible, the way to do it is to cut a thin piece of card and cut holes where the inlet studs are, tight holes, you don't want it moving. Then press the card down into the hole so it leaves an imprint, you then cut the imprint out carefully, lay it over the inlet manifold lining up the holes where the studs go and you an see what needs to be removed to get them so there is no shelf etc. Same applies to the vac screws, they are too long and protrude into the airflow, again causing turbulence, trim them down to they are flush.

Gas flowing usually involves the old saying raise the ceiling, don't lower the floor. All that means is you enlarge the area where the valve guide sticks through a little, smooth it out a little, you want the curve to be progressive so the mixture flows through the head instead of getting caught on lots of little protrusions, hence the name gas flowing.

You can go for trimming the length of the valve guide that protrudes into the inlet tract and shaping it so it more of a sharp edge into the flow than a round edge.

Then there's altering the emulsion tubes to make the fuel air mixture emulsify better, this gives an increase in MPG.

Nothing radical, just small steps to make a better and more responsive engine.

[davidcumbria]

What is the change in timing you refer to Ken ? Ignition or valve ? I would have thought the optimum ignition timing may well be different from the mark due to the change in petrol composition over 50 years.

[DomP]

I'm still tempted to get mine done while I'm spending so much doing an engine rebuild.  What are the reprofiling details I'd need to pass on to Newmans Ken?

[Sesman]

See post 43. It’s what I used. http://forums.sohc4.net/index.php?topic=134461.0

Reply #14

Don’t move until Ken comes back.

[DomP]

See post 43. It’s what I used. http://forums.sohc4.net/index.php?topic=134461.0

Reply #14

Don’t move until Ken comes back.

Thanks for that, I'll be honest I don't quire understand the figures .

[Oddjob]

5 degrees of overlap and 10 degrees of duration is the recommended settings to give to Newmans. They have confirmed they can do this.

I'll detail the timing issue later