Topic: CB500/4 racer resurrection - airbox finished, didnt quite work....

[turboguzzi]

fork looks just fine, piece must have stayed on till last moment, not causing any damage

in the early 500/4 it's the middle fork that suffers badly. i put a new one back in 2008, did two seasons with it and by now it's showing signs of distress but nothing terminal.  the problem was only fixed in the K3 series and subsequent 550.

like that gear, i managed to find a new middle fork by pure chance.
they are not available anymore, luckily most 500/4 owners dont even know how bad it can get and simply ride on.

[turboguzzi]

new gear is home, just as mama honda made it....
dont you just miss the time when spare part labels had a rubber stamp number on them, parts were put in super strong brown paper bags, and quality confirmed by a hand signed V on them? a simple and very reassuring human touch gesture...
In theory i could start closing the bottom end but tuner friend Flavio strongly recommended to do the "clean under you balls" thing, so that's coming next.  should be fun

[bwaller]

Indeed, clean under your balls while it's apart! How did it go at Misano?

[turboguzzi]

went really fine, starting with having a deluxe pit lane garage (the ones used by the motogp teams) for free....
An endurance team broke an engine, didnt have spares, so they went home on friday and left their paid rented garage space to Riccardo and me! It was VERY red, so fitted the gpz well.
Funny how with less power of the 550 i've learned to do the turns 11,12,13 much better than with the 750/810 bike, was quite an eye opener. no trophy this time though.
now then, you need to post YOUR Barber weekend stories in your thread! looking fwd to that

[turboguzzi]

under ball cleaning went fine, glad i did it, quite a bit of muck there...
less exciting news are all sort of issues coming up under deeper inspection.

center crank bearing area has a tiny step form wear, micrometer says it 0.01mm lower, waiting for a new plastigauge kit to make sure.
what's a bit worrying is that two of the four sizes of bearing shells are now "no longer in production", hope i wont need the size thats not available.... any alternative sources?

next, and this is a bit unexpected, quite a bit of fretting on the seats of the two larger bearing of the tranny. unlike the two needle ones, these are not pegged and looks like under racing abuse they did rotate... anyone ever seen this type of wear?
the clutch side one looks worse and its only now that i realize that unlike the drive side, this one doesnt have a bolt in the middle to clamp the bearing better...  your thoughts on the subject are welcome!

[MessnerMoto]

http://www.cb-four.de/cgi-bin/shop/

If I remember correctly I bought from them

[turboguzzi]

tnxs mirko
like al the other online shops, they have only B & C size. A & D not....

[turboguzzi]

work continues... under balls cleaning now done, tried to use 1/4" (6.4mm) set screws but as the hole is already 6mm didnt feel safe. ended up enlarging it a bit and using M8 set screws, tapping into the hard steel was a bit scary...
parts ordered from CMSNL in Holland and already here. They are not exactly the cheapest but as they support Carl Crutchlow, coolest guy in MotoGP, i'm happy to give them my money. they even sent a key holder with the same winking mechanic as on Carl's bike

[turboguzzi]

the CBR600 rod bolts require as brent noted some grinding to fit into the 500 rods, but they certainly look beefier. essentially the underside has a big 45 degs chamfer and you need to grind one side until it more or less disappears. 8 bolts, takes a while...

[turboguzzi]

after discussing with fabio the tuner about the signs of the tranny ball bearings rotating in their seats he confirmed he's seen it more than once. as the signs were more noticeable in the clutch side where there is no clamp bolt between the bearings (see pics a few posts above), ive decided ill sleep better if this is corrected. quick assessment showed that there's enough meat to put there a 6mm stud just like in the drive side. Another scary operation with my basic machinery, but glad that i did it.

[turboguzzi]

and for double insurance, also added indexing pins in the seats, just like the needle bearings have. on the bearings i created a small groove for them with a grinding stone. think i'm pretty ready to button up the bottom end and fix back in the frame.

next update will be when the home made flow bench i'm building is ready to work on the porting a bit more scientifically than i did 10 years ago

[bwaller]

Good fix. Blind hole in the upper case with a heli-coil?

[turboguzzi]

there is good depth, some 12mm of thread, so no helicoil needed IMHO.
yesterday was closing the cases and i found why there were signs of wear also on the chain side ...
just as i touched the long M6 bolt it snapped! looks like it was half cracked already so not putting any pressure. I cant believe i over-tightened it, looks like these pinch bolts take a real force
had to reopen the cases, clean all the fresh loctite 518...
found a longer bolt today, will button it all up together again tonight.

[MRieck]

tapping into the hard steel was a bit scary...

It sure is.

[turboguzzi]

holidays updates, finally had the time to finalize the flow bench, calibrate it and it's totally fascinating...
knowing where i stand in terms of flow, if there is potential for improvement, try out manifolds, stacks, etc. , very interesting.
It's all based on the idea of David Vizard for a simple calibration plate which i had CNC machined, so the numbers should be in the range of +/- 2-3% accuracy. Above all, after a few tests, the repeatibility of the results is within +/- 2 CFM.
 Mike also kindly supplied me with some numbers for the stock head and manifold to compare to and turns out that my DIY job from ten years ago, the infamous "10 degree downdraft project" was not bad at all. compared to a totally stock head i picked up some 25% more flow, so cant complain. My port peaks out at 84CFM @ 28"H2O (or 50CFM @ 10") and it's a good figure for a 27mm valve and stock seat but not stellar.
We all heard the stories as how air doesnt do what you think it should, now i understand. one of the bigger shockers was that my 10 degree downdraft manifold hardly makes a difference! Got almost the same numbers with a simple perpendicular manifold. Odd but true... Amazing what you can discover with a 50$ flow bench.
Big question is where to go from here. opening the seats to 90% is next, will update...

[MessnerMoto]

Show us some pictures of your flow bench and what are u using to remove loc. 518? I had a hard time to remove it last time. Used some special gasket removal but it was hard....

[turboguzzi]

i use nitrocellulose thinner to remove all loctite products.
pictures coming up.

[turboguzzi]

so then, by very popular demand
My plywood box flow bench in all it's splendor
vaccum cleaner 2000W/2.5hp motor from ebay, water column with high tech freebie meter ribbon from local DIY shop.

[turboguzzi]

heart of the system is this CNC'd calibration plate, dimension are from the said Vizard article and supposedly was designed by a certain airflow expert, mister Helgesen.
the holes represent flows of 160, 80, 40, 20, 10, 5 CFM at 28". essentially you mark the water column every 5 CFM by opening and closing holes and that calibrates the water column.
i used an M6 screw to open the valve which has perfect 1mm pitch. Initially used also a dial indicator to check lift, didnt make any difference in accuracy...
here's the article for those who wanna try
https://www.musclecardiy.com/cylinder-heads/build-flow-bench-port-flow-testing-cylinder-heads-part-3/

 

[turboguzzi]

next step in porting will be opening seats to 90% of valve throat, lets see where it gets me in flow

in the meantime, discovered by chance that a spare KZ750 swingarm (on the right) i had around could be a nice improvement on the stock honda part. They weight exactly the same but the kawi tubes are 10% bigger, so if i remember statics right, torsion strength increases by a power of 3 to diameter, hence 33% stiffer. it's not just the diameter, look at the difference in section of the stiffening box behind the pivot tube. the kawi arm also works on needle bearings instead of bushings, so another little bonus. only challenge is that the 750 arm uses a 17mm axle while i really want to use the 20mm hollow axle i used before. milling the slots to +3mm is a bit of a challenge just in terms of positioning the arm on a mill, but where there's a will there's a way.

[crazypj]

there is good depth, some 12mm of thread, so no helicoil needed IMHO.
yesterday was closing the cases and i found why there were signs of wear also on the chain side ...
just as i touched the long M6 bolt it snapped! looks like it was half cracked already so not putting any pressure. I cant believe i over-tightened it, looks like these pinch bolts take a real force
had to reopen the cases, clean all the fresh loctite 518...
found a longer bolt today, will button it all up together again tonight.

Been a long time since I signed in to SOHC4, but found this and had to take a look.
Would it be possible to use CB550 cases? They have the same issue of the 100mm(+?) long bolt breaking (even if not overtightened) but already have extra bolt on clutch side plus a 'better' gearbox with built in oil pump.
Also, do you have any spec on CB500f cylinder head? I'm particularly looking for combustion chamber dimension or even a picture. I'm modifying a set of CB750 pistons  for a CB550 and the only head I have access to at present is a well worn CB550. The piston mods for 'Gentlemans's Express' from 1974 (?) are for a 500f. I'm  pretty sure the 550 has the 12 degree 55mm od chamfer added but can't remember as I haven't looked at a 500 head for years

[gschuld]

in the meantime, discovered by chance that a spare KZ750 swingarm (on the right) i had around could be a nice improvement on the stock honda part. They weight exactly the same but the kawi tubes are 10% bigger, so if i remember statics right, torsion strength increases by a power of 3 to diameter, hence 33% stiffer. it's not just the diameter, look at the difference in section of the stiffening box behind the pivot tube. the kawi arm also works on needle bearings instead of bushings, so another little bonus. only challenge is that the 750 arm uses a 17mm axle while i really want to use the 20mm hollow axle i used before. milling the slots to +3mm is a bit of a challenge just in terms of positioning the arm on a mill, but where there's a will there's a way.

Would you mind letting me know what the OD is on the main tubes on the KZ750 swingarm?  And that is an 80-83 arm correct?  The 76-79 KZ750 arms had a 2 piece stamped fwd brace.

Is the spacing width for the pivot bolt the same as a cc500/550/750?

Thx,

George

[turboguzzi]

good to see you crazy, long time.
yes, i could use 550 cases, just not as easy to find in italy as in USA... for some reason the 500 was way more common here.
500 head is same as 550, it also has the 12 degs chamfer around.

George, arm tubes diameter is 38mm. The four cylinder KZ750E came out only in 1980, so yes, it's a 80-83 arm.
the 76 KZ750B twin might have a different arm, dont know really.
there is a good chance the the kz650 arm is same as the kz750E

the kz750 arm is some 10mm narrower ath the tube. i am going to use a pivot from a kawaski vulcan 800 that i need to shorten to 345mm to fit the CB500 and then turn some teflon spacers to make up fo rthe diference

[crazypj]

Hmm,  thanks for te info, wonder why the piston mods for 750 into 500 are so far away from the actual shape?
Anyway, I welded a short section of CB750 fork tube across width of my 550 swing arm in 1978 then heated it up and beat tyre clearance into it. 
 It was noticeably stiffer (and heavier) but still really needed another 2" length to improve stability at 115~119mph, for some reason it straightened out real well at 120 or more?
Mine is still in Britain, they were popular there because of 600cc insurance bracket.  You got a 250, 400 Yam RD or 400F (depending on how much of a hooligan you were) Suzuki GS550 or CB550, Kawasaki meant going to Z650 and big jump in insurance, had 4 or 5 at one time, plus a few wrecked/written off and 500f bits. I remember selling one to my brother (78 FourK) touring style just wasn't me, to soft and too little ground clearance 
The Lesters would be worth a bunch now though  (he traded it for a GS1000)

[gschuld]

George, arm tubes diameter is 38mm. The four cylinder KZ750E came out only in 1980, so yes, it's a 80-83 arm.
the 76 KZ750B twin might have a different arm, dont know really.
there is a good chance the the kz650 arm is same as the kz750E

the kz750 arm is some 10mm narrower ath the tube. i am going to use a pivot from a kawaski vulcan 800 that i need to shorten to 345mm to fit the CB500 and then turn some teflon spacers to make up fo rthe diference

Thanks for the info

George