Topic: cb500 ex 70's racing bike now cafe racer

[ivanhoew]

damn right keep going ! now you have made me regret owning my 400/4 since 78, i have nothing to research !

[mjc477]

Well atleast you will know what is spinning around in that engine of yours.

I just haven't got a clue.....
It's hard to explain just how quick it is ...but It is making sence now....

This is another email dave bexley sent me .....I had forwarded on jeff pearce's email and this is a snippet of his reply:

Well done!  The info was interesting for me too.  If the camshaft fitted was one of the more extreme drag racing cams, it may be that it will have a gutless midrange and exhibit the symptoms you have described.  We never used the dedicated drag cams even on the road race bikes as they were quite extreme.  Maybe a little playing around with the carb jetting, especially trying raising the needles a notch, might help.  The 750s were notorious for getting the oil feed to the camshaft bearings blocked and wrecking the camholders and, usually, the cam (cured by drilling out the restrictors between head and camholder) but I don't remember the 500s suffering the same problems.  Maybe the stress of a very high lift cam has put an unusual load on the cam bearings or someone was careless with oil changes.  The fitting of white metal shell bearings is a new one on me but we used to discover all sorts of ways round the more expensive failures so someone has clearly found a way round this problem.  If it is still the original spec, the engine is quite a collector's piece.  The 570 pistons and the cam will be unobtainable now.  Actually, I reckon that Kenny Harmon, who made the Action Fours cams may still be in business so it may not be irreplaceable but certainly expensive.  I think the engine merits a careful strip-down and examination to be sure that it will remain in good health. 


So am I looking at a real drag racing engine .....it most definately could be!!!

[ivanhoew]

maybe pop a tappet cover off ,turn the engine over and measure the valve lift for a cam clue ?

[Steve_K]

I seem to remember that some pistons from a Honda twin were used with some machining of the piston to get the CR lower.   I believe that it was written about either in "Mantlepiece" or in one of the "Gentleman's Express"  articles in Cycle magazine.  I think later they went to 750 pistons modified.  I am sure other members have done that modification over the years. 
Steve

[mjc477]

So its been a nice day here today the first one for along time and I'm out on the honda.
No real dramas and it's buzzing along nicely ....but I have torn up the speedo...i know it wasn't expensive but I have not been going any quicker than the tracffic
Does Anyone know of a nice 70mm speedo that won't rip itself to bits

It is now as we speak sitting at 140mph stationery

And a brief update on history search I spoke to the guy I originaly brought the bike from and he verified that he got it from John vine who Jeff Pearce rented a flat from so that ties in niecly

Now I'm trying to find the drag racer who Jeff got it from in the late 70's/early 80's

But this is proving a tad trickier

And after speaking to dave Bexley again it seems it most probably is a mix between action four tuning bits and perhaps a extreme Phil joy drag racing cam.....eating my speedo

I also found a write up on action four tuning kits I will post a Link later

[mjc477]

http://davestestsandarticles.weebly.com/uploads/4/8/4/5/4845046/modcycap78cb550bigbore.pdf

Not only is this a great article but it has a pretty nice looking bike photo to boot

I particularly like this last paragraph or so about 750 carbs?

[mjc477]

we had some funshine this weekend so i headed off to redmax speed shop...
they mainly deal with cafe racers..bobbers and flat trackers................they were closed ...but it was a good ride out anyway
i wanted to see if they could help with ideas on the clock situation on the 500

i also have a cb450 flat tracker on the go and i wanted to pick their brains on that too,,,,

and no luck so far on the drag racer who owned the bike but i cannot complain as i kinda feel i have already had plenty of luck so far....

[seanbarney41]

this is a great story about a great bike....thanks for sharing

[mjc477]

Out at brooklands/ace cafe ton up day Sunday?
Great day out but the bike was trying to tell me something

I shall explain.....
In the morning I went to start the honda......when I turned the fuel on the petrol poured out.....so in a rush I popped the of and had to replace the O ring on the fuel intake t piece....not a great start but never the less sorted!

I had a nice run out saw some great cafe racers and a burger to boot.....
Then they had a run up test hill a kind off drag race up a very steep hill.....no one told me you needed to go to a briefing so I got in line only to be turned away on the start line..I was absolutely gutted the bike was running like a dream and would've pissed the hill?? And after all it was built for drag racing....

After a chat with some great old boys time to leave....I took the longer twisty route home..and coming through a local village at 30-40 mph. The bike decided to eat the chain guard and I mean eat...(see pics)

Not a great way to end my trip locking up solid at that speed although it could've been worse luckily I didn't drop it just spectacularly skidded to a stop..

A few calls and I got picked up and took the tools to get it rolling with my van to load it .  As it was jammed solid I thought I could just pop the chain link ......no if you look at the pics you will see it couldn't have been in a worse place so the cover had to be taken off.   
I think you will agree the bike certainly was hungry???
And now I have a little repair on my hands?

I thought you might like to see the carnage...and the aftermath of the guard getting completely wrapped around the front sprocket...

[RAFster122s]

Wow, it did a nice job of wrapping it tight...recycle one chain guard into bits.

CB550K had a plastic chain guard and the guard on the CB550F was chromed steel of heavier build than what you show. Guessing this was an aftermarket/one-off piece.

David

[ivanhoew]

strewth!! lucky is right!

[mjc477]

This guard must have been an after market part
It was chrome but I painted and shortened it back when I sorted the bike

I now need another one I don't think I can straighten or re use the old one....
Anyone got one???

I also had a close look at the damage tonight and I  need a new clutch push rod..and ball bearing ..... has any one got any suggestions as to obtaining a push rod
it also cracked some of the casing but I might be able to run it as is it really only gets out on dry days and I will have to tolerate the oil getting flung around!
 ill use the standard 500/4 in the wet....it's not so hectic

[Statenheimer]

Sorry to hear about the small mishap, but glad that you kept it up and avoided injury.

Thank you very much for posting all of this information, it has been a joy to read through as you discovered more and more about this great machine.

I wholeheartedly agree that there is a magazine out there that would die to be able to print your story.  Being from the US I do not know of many of your magazines, but I have read Classic Motorcycle Mechanics, and am sure that they would be interested in the story...

[SF]

I wholeheartedly agree that there is a magazine out there that would die to be able to print your story.  Being from the US I do not know of many of your magazines, but I have read Classic Motorcycle Mechanics, and am sure that they would be interested in the story...
[/quote]
I totaly agree this would make for a great read

[davis96]

This guard must have been an after market part
It was chrome but I painted and shortened it back when I sorted the bike

I now need another one I don't think I can straighten or re use the old one....
Anyone got one???

I have one you are more than welcome to, but shipping overseas might make it cost-prohibitive

[mjc477]

Hey that's really good of you

I don't mind paying shipping if its the right part
Is it similar to the one I crushed at the weekend???
I do have a  plastic 500/4 one here but it just won't look right....

I think the one I had was abit smaller than the ones fitted to the 550f

Any pics of it

Cheers

[jaguar]

Very cool bike

[davis96]

Hey that's really good of you

I don't mind paying shipping if its the right part
Is it similar to the one I crushed at the weekend???
I do have a  plastic 500/4 one here but it just won't look right....

I think the one I had was abit smaller than the ones fitted to the 550f

Any pics of it

Cheers

I will take a look at it when I get back home. I'm almost certain it is steel, but it is definitely not chrome.

[mjc477]

Hi
Steels good ...much easier to paint?

As for my clutch rod ....so it seems they really are unobtainable
I,went to,the local metal,work,shop to get some silver steel rod and the guy is out until next week

I had some 9.5 rod in the garage so made one up to the specs given on the clutch mysteries  thread?..
9.5 diameter and 25.7 long


My original rod was a tad shorter by 1.5 mm I guess that's from a few years of compression ?

Now this rod was just kicking around I don't even know where it came from...
Is there any way of telling if it is silver steel or just mild steel...

[mjc477]

All back together now
I had some stainless rod that was the correct diameter and it done the job

I also bent the cable cinch arm thingy and it was rubbing the sprocket ....
That's been sorted too

Now just a new drive chain and fingers crossed I'm off again...plus a new chain guard. If Davis96 cant dig his old one out. I might have ago at fabricating one myself as it was pretty simple

Both items I buggerd up were unobtainable...how greats that's ??

If anyone can list all the other unobtainable parts now at least I know what I will bust next?

[davis96]

All back together now
I had some stainless rod that was the correct diameter and it done the job

I also bent the cable cinch arm thingy and it was rubbing the sprocket ....
That's been sorted too

Now just a new drive chain and fingers crossed I'm off again...plus a new chain guard. If Davis96 cant dig his old one out. I might have ago at fabricating one myself as it was pretty simple

Both items I buggerd up were unobtainable...how greats that's ??

If anyone can list all the other unobtainable parts now at least I know what I will bust next?

I found the chain guard in question, it turns out to be from my previous bike, CB350F, so none of the mounting points match up to the 500. Sorry pal, wish I could've helped

[mjc477]

No problem at all Davis thanks for offering
I'm gonna have a go next week some time at making one

[mjc477]

Well back at it

I tried a standard plastic chain guard I had spare?   .it looked daft?

I couldn't find a suitable looking one on the net that was cheap enough to take a chance on?

So today I went from this.



To this?



To finally



I was really happy until I looked at the last picture and it looks low at the front.    But it has a real solid connection with no brackets and seems it appears that's what gave way last time I might just live with it for a bit and see how much it niggles me?  It shouldn't take much to tack another bracket on

But at least it is all done and working again?