Topic: CB750 (810) Racer

[Doc.]

Originally posted this in the 'new members' section, thought I should give it it's own topic.

Long story short, a friend of a new friend of mine has a couple of 'Post Classic' Race Bikes.
One is a 'Kerby' Honda 500 (Dave Kerby built frame kit, with modified '82 Honda 500 single).
The other is an 810(?) SOHC Honda. We (my new friend and I) went to see him at Brands a few weeks ago, he was there with the Kerby at a Classic Race (CRMC) meeting.
Someone else was riding it, for health reasons he can't get a race licence himself.

Anyway, after chatting for a while, and me spotting and fixing a few issues with the Bike, he invited me to ride the Kerby at the Belgian Classic TT at Gedinne, end of Aug   
He'll be riding his 750.

We were to take it to a trackday on Sunday (9th), but it had a problem with the Clutch slipping on the Dyno beforehand, so we took his 750 instead.




Perfect day for it, pity it had an oil leak that stopped play   

Went out in the first session, and was impressed with how well it went.
I've never ridden it before, and hadn't been on track for a few years, so took it fairly gently (luckily).
First three laps were 'sighting' laps, following a staff member.
Just after he pulled off, I felt my left Boot slipping on the peg, looked down to see Oil all over it.
Pulled in to check it over.
Looked to be coming from the bottom of the gear-change cover, so we whipped it off and found the gasket was broken at the rear lower corner.
As we didn't have a spare, we refitted it with some blue Hylomar, wiped the oil off the rear tyre, and I went out again.

Kept an eye on it, and after four laps or so it was doing it again.
Pulled in and whipped the Crank cover off.
Gasket was fine, as was the surface of the Crankcase.
Then I looked at the inside of the Cover itself, and there was the cause.
It's not got an Alternator fitted, and the gap in the casing where there should be a rubber bung (where the loom passes through), was just empty, no wonder it leaked!



It's sitting in the workshop now, as in the pictures.
What a palaver getting the front wheel out, horrible design, having to remove the Caliper mounts is a real b**l-ache, the Tyre is too wide to pass between the Pivot mounts, any 'tips/tricks' for that?
Can you, for example, slot the top pivot mounts so the two bolts don't have to be fully removed, just loosened?

I've stripped the front Brake assemblies down now, to check over and clean.
Made a couple of small mods, new adjuster screws, and spring seats . . .



Rear drum is worn beyond limits, anyone had one relined?

[MCRider]

Noticed your "810(?)". The stock bore was 61mm = 736cc. 64mm = 811cc which Yoshimura used on his roadracers and rounded the number down to an appealing 810cc. 65mm = 836cc, the most popular hotrod oversize.

Not sure why Yosh thought 810cc was more effective than the 836, but he stuck to it. I suspect it may have to do with head/valve theory saying that an 810cc was the size to use.

Back when, a group of Yosh enthusiasts challenged the hotrodders to drag race at the shop and strip where I worked in Tucson. The 810s got soundly beaten by the 836s. But I would guess it had to do a lot more with the full set up than just the displacement. The 836s ran bigger bumpsticks RC Exhausts etc. The Yosh engines were for high rev finesse, should never have gone to the drags. Drag motors wouldn't last in a 50+ mile roadrace either.

[scottly]

One is a 'Kerby' Honda 500 (Dave Kerby built frame kit, with modified '82 Honda 500 single).

Rear drum is worn beyond limits, anyone had one relined?

Please post more about the Kerby, either on the high performance and racing board, or the other bikes board. I'm a fan of the thumpers!
I believe the rear drum is cast into the hub, and can't be relined.

[brandEn]

What kind of front fender is that?

[Tews19]

Oh this is exciting!

[Doc.]

Thanks for the info MC Rider, this is a learning curve for me.
The Bike has some history, apparently it won a Club Championship at some point.

brandEn No idea what it's from, but it's very 'period'. Probably cut down from a larger item.
I don't actually like the look of it to be honest . . . 

Please post more about the Kerby, either on the high performance and racing board, or the other bikes board. I'm a fan of the thumpers!
I believe the rear drum is cast into the hub, and can't be relined.

Will do Scottly.
Nearly finished prepping that one now, just needs the Clutch doing (new plates and up-rated springs), and the rear Brake sorting out.
The original layout had the torque-arm attached to the frame below the swing-arm pivot, yet there's no bearing or bushing in the back-plate.
With the wheel spindle torqued up, the torque-arm was forcing the back-plate to move (due to suspension movement), which was causing wear on the spindle spacer and back-plate.
Explains why the original torque-arm was such a heavy-duty item.

I've machined up a mounting bracket, which clamps round the R/H end of the swing-arm pivot tube, and made a lighter weight torque arm to suit.

I've also made new foot-peg plates for it, the originals were a bit 'untidy', and I've also raised them a little.

As for the drum, it should be possible to have the old lining machined away, and a new one shrunk and riveted in place.
My Lathe's not big enough, otherwise I'd do it myself . . .

[MCRider]

What kind of front fender is that?

That's a period "needle" fender, common in the day. But I've done a Google on it and can't find any current references. ITs held on simply by hose clamps at the fork legs. They were bound to loosen from jostling then the fender woould fall onto the tire and get destroyed (personal experience).

Doc must be having better luck with the mounting. Very sensitive to the shape of the top of the fork leg. If it had any taper to it at all, the clamps would come loose.

http://www.ebay.com/itm/Cafe-Racer-Fiberglass-Front-Fender-Chopper-Bobber-Flat-Tracker-/181481637912?pt=Motorcycles_Parts_Accessories&hash=item2a41260818&vxp=mtr

That front wheel looks like an 18". Hard to get an 18" needle, and make the curve look right. But it could be an 19" also, which is/was more common.

http://www.oldbikebarn.com/Cafe-Front-Fender?sc=132&category=1503372

http://www.airtech-streamlining.com/vintage/vintagefendersstreet.htm

[754]

When i ran dual disc, had to let air out to get wheel in or out.
 You may set up the pins , with eashers instead of o ring, so you could tap pin out ans swing away caliper.
 But I think using a long balldriver allen wrench, you can split one caliper, and smply remove back portion to get wheel in.
 You will love having a Morris or Lester  wheel when you try this.

[Doc.]

. . . Very sensitive to the shape of the top of the fork leg. If it had any taper to it at all, the clamps would come loose . . .

Thanks, I'll keep an eye on that then, might be an idea to slip a couple of pieces of rubber sheet between it and the Slider.

. . . you could tap pin out and swing away caliper . . . But I think using a long ball-driver Allen wrench, you can split one caliper, and simply remove back portion to get wheel in . . .

Problem is, the Tyre fouls on the top pin mounting, so leaving those in place doesn't help, and on top of that, the Caliper won't clear the Rim.

[Doc.]

As requested Scottly, Kerby has it's own Topic now . . .
http://forums.sohc4.net/index.php?topic=140256.msg1588321#new

[brandEn]

Thanks for the reply Ron

[scottly]

Actually, the "needle" fenders were much narrower than that, although they attached the same way, with hose clamps. That may be a Dunstall style fiberglass fender.

[Doc.]

Got the Calipers and mountings cleaned up and reassembled.
Used Dry Film Lube on the pivot pins, and the bearer surfaces on the pads and calipers.
New O-rings too, the old ones were shot.
New bolts for the pivot pin and top mount as well.

On the subject of pads, why would someone do this to one of the static ones . . .

Is it a known 'trick'?

Opening in the Crank cover plugged now.
Made a 'well' around it with Plasticine, then poured in a two-part polysulphide compound, sets like rubber.
Trimmed it when cured, but left it a little proud of the casing edge, so it gets compressed slightly when the casing's fitted.

[Doc.]

Reassembled the Calipers and mountings now, had a small problem with one of the upper mount bolts though.
I put a new bolt in the left-rear, same length as the other three, but it went tight well before it was fully home.
I took it out, and the end few threads were damaged.
No problem, I thought, I’ll just run a 6mm tap through to clean up the threads in the leg.
Did that today, but that went tight too after half a dozen turns, when I wound it out, a 6mm Helicoil came out with it!
Luckily there are enough good threads left in the leg to take a longer bolt, so that’s all back together and secure now.
I can always put another Helicoil in at a later date as a more permanent repair.



Took the Mudguard off, easier to work on the Calipers and mounts, plus I want to see if it makes wheel fitment any easier, being able to spin the legs, will still be a pain I reckon, but maybe will help.
It's a very 'snug' fit on the legs MCRider, don't think we'll have any problems with it coming loose, but I'll try the rubber strip trick as well, will stop the legs getting scuffed.

[MCRider]

Yes the U shaped moldings that grip the legs are much more pronounced than any I've seen. Should grip well.

[MRieck]

Actually, the "needle" fenders were much narrower than that, although they attached the same way, with hose clamps. That may be a Dunstall style fiberglass fender.

That's what I think it is

[Dream750]

Doc, nice bike!
 
Looks more like a Tracy fender than anything else, but definitely not the needle style. Here’s a couple of 750 fenders from my 1974 Tracy catalog to compare with:

[brandEn]

Maybe one of these....

[754]

I think the Rickman Metisse used the wider one..

[Doc.]

I think that may be it brandEn, if not, it's damn close.





Can't believe the mudguard's provoking the most discussion . . .   

[Doc.]

Got it all back in one piece and loaded in the Van with the Kerby, ready for the Track-day tomorrow.
What a complete ba**ache it is getting the front Wheel in (or out).
You have to disassemble the Calipers, and completely remove the mount on one side, then slot the Wheel in place loosely, re-fit the mount, then reassemble the Calipers.
There's just enough room to get the upper mounting bolts in, between the mount and the tyre.
I reckon it took us around half an hour to get it in and all locked up 

I've made up a stand to sit the lower Yoke on, we had it on a front Paddock stand, which prevents the Fork Sliders being turned.
If it's supported on the Yoke, then with the mudguard off, you could spin the Sliders round, so the Caliper mounts will clear the Tyre.
Will still need to disassemble the Calipers though, but that's only four bolts to remove and refit, as opposed to seven.
Wish me luck . . .

[Doc.]

So, another perfect day for a Track-day, but another cut short by mechanical gremlins.

Took the 810 out first, just to check the oil leak was cured really, and to put a few more miles on it to make sure nothing else cropped up . . . well it did!
I'd cleaned the K&N filters since the last run, as they were filthy, and I suspected they were making it run rich.
It would start on the button with no choke and settle down to idle with minimal warm-up time.
I didn't re-oil them though, as the owner is thinking of running open bell-mouths next.

Anyway, it started only with choke, and wouldn't pull cleanly even when fully warmed up, in the end I had to run with the Choke slightly on, but it still wasn't right, obviously.
I decided to pull in early as it felt like it was overheating, I looked round to check it was clear to pull-in, and that's when I saw the plume of smoke behind me 
Fearing the worst, I coasted into the pits.
Only when I got off did I notice the big ball of fibre-glass fluff and melted rubber on the front of the mudguard 

 Phew! That's where the smoke was coming from.

I took it off to get more access when I fitted the Calipers and mounts, must have put it back a shade lower than it was originally, although it could be I was going a bit quicker (briefly) this time out, and there was quite a head-wind on one of the straights.
I reckon the long rear section was catching the wind, and forcing the front down onto the tyre.

I whipped the #1 Carb jet out to see what was fitted . . .

Is that an 'H' 12.5, or a 112.5, is it even a main jet?

[MCRider]

So, another perfect day for a Track-day, but another cut short by mechanical gremlins.

Took the 810 out first, just to check the oil leak was cured really, and to put a few more miles on it to make sure nothing else cropped up . . . well it did!
I'd cleaned the K&N filters since the last run, as they were filthy, and I suspected they were making it run rich.
It would start on the button with no choke and settle down to idle with minimal warm-up time.
I didn't re-oil them though, as the owner is thinking of running open bell-mouths next.

Anyway, it started only with choke, and wouldn't pull cleanly even when fully warmed up, in the end I had to run with the Choke slightly on, but it still wasn't right, obviously.
I decided to pull in early as it felt like it was overheating, I looked round to check it was clear to pull-in, and that's when I saw the plume of smoke behind me 
Fearing the worst, I coasted into the pits.
Only when I got off did I notice the big ball of fibre-glass fluff and melted rubber on the front of the mudguard 

 Phew! That's where the smoke was coming from.

I took it off to get more access when I fitted the Calipers and mounts, must have put it back a shade lower than it was originally, although it could be I was going a bit quicker (briefly) this time out, and there was quite a head-wind on one of the straights.
I reckon the long rear section was catching the wind, and forcing the front down onto the tyre.
I whipped the #1 Carb jet out to see what was fitted . . .

Is that an 'H' 12.5, or a 112.5, is it even a main jet?

That's been my experience with the clamp on fenders. They look good but you can't trust them at speed or bumps.

AS to the last question, yes it is a main jet and I vote 112.5.

[Doc.]

Yes, definitely 112.5.
We now have a set of 115, 117 and 120.


Any suggestion on the setting for the pilot screws?
When I checked them they were only one half turn out from fully seated, seems off to me, aren't most set at around two turns or thereabouts, as a starting point?

Might trim the mudguard down front and back, or just run without it.

[bjbuchanan]

Stock setup is 1 turn for your bike. Try it at 1 turn and see if you need any choke at all. What's the weather like around you? During warmer summer months I can usually get away with almost no choke to start.