019 1975 CB750 progression...

LOTS OF HOW TO CHOPPER PROJECT REPORTS... We build choppers the old school way... craftsmanship and artistry. Photos of our work to give you ideas... Aftermarket parts, parts for Shovels, CB's and XS's, our own unique parts for sale...
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Prof
Founder, Choppers Australia
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Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
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019 1975 CB750 progression...

Post by Prof » Sat Nov 20, 2010 12:32 am

I bought this earlier this year as a project bike to chop. Motor was quiet, though gutless and rest of bike was really ratty. Some benefits were 6" extended forks, mini speedo, bates style headlight and lowering blocks. Forks were rock solid, clutch and rear brale so maladjusted to be almost unrideable.

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I spent a day adjusting and tidying things up, added some W bars and small screen.Sissy bar is off my first chopper while I commuted at teachers college. The pad is actually from an earlier custom I built and then totalled a week later! Rejetting for the pod filters solved the gutless problem. This was thanks to advice from Shakey. I pulled the forks apart and drained out the water!!!!! They still clash on bigger bumps so need more work yet. Clutch cable broke one day and on inspection someone had migwelded a 1/4" nut onto the bottom end of the inner cable... never believed anyone could be so stupid ! I also dropped the rear end another inch by shortening the shockers.

While I had another Honda in for some mods, I used this bike as a test bed to try out a different style rear guard/taillight assembly and roughly added a sissy bar I built in 70's. A flat narrow seat got added into the equation...(The other owner liked the rear guard, so I did an improved version for him).

The bike still looks pretty ugly, but is reasonable to ride and has a bit more chopper feel to it
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Last week I loaned the bike to Steven, our member coordinator so he can come on our Murraylands trip. He did a full service on it including new chain and sprockets. We bent up a set of apehangers he and took it home for the two weeks to get used to riding again.

He came up today and as he rode in the #3 plug blew out... stripped thread. I rang around everywhere local but no one had a thread insert kit for 12 mm plugs... however I do have another motor in the workshop I bought from Bacca, waiting to go into a chopped frame when I have time... so looks like another motor if Steven is to come next weekend!
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Its now 6pm as I have been working on Daves 750 Trumpy all day and we need to do something moving...

Now I have been wanting to do a temporary rake on this bike since i got it, so with the motor coming out why not now. Steven said he could stay the night, so we could make some progress, as he has to have the bike again by tommorrow night.
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An hour later and we are ready to pull out the motor... bit of a tight fit, so might as well start cutting now...
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Lots more room and the motor pops out easy as!
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Now measure where to cut the down tubes. Get the distance exact each side leaving 30mm space above engine mounts for slugs. I use a pipe cutter to mark the cut and it gives a perfectly perpendicular cutting guide. I then cut very carefully with angle grinder.
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Some heat applied to the underside of the top tube, a bit of a push on the down tubes and the bike sinks to its required position... basically the bottom rails are level. Slugs length required will be 75mm.
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We check front axle to steering head measurement... 495mm, so 55mm within max legal distance. Rake works out at approx 38-40 degrees.
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This old tank looks good and requires minimal mods to fit for the time being. Bike now has a whole different stance. Juts time to knck up a pair of slugs, come in and do up this story and get to bed ready for a big day tomorrow...
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Last edited by Prof on Wed Nov 24, 2010 9:21 am, edited 1 time in total.
Chopit'nrideit... Prof

Bearcx
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Post by Bearcx » Sat Nov 20, 2010 11:47 am

Awesome work Guys, looks like a different bike. Way cooler !!
The brave may not live long, but, the cautious do not live at all.

Prof
Founder, Choppers Australia
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Joined: Sat Oct 22, 2005 3:54 pm
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Post by Prof » Sat Nov 20, 2010 10:06 pm

Well we stopped at 7pm with everything welded. tank mounted some extra gusseting etc... but not quite ready to paint. At one stage, late morning The Chopper Shed had 9 people working or visiting... including Steve taking our car and trailer to rescue a broken down member... quite a shindig. More about it tomorrow night.
Tomorrow will give it a quick paint on affected parts, adjust tappets on new motor and get it all in. Hopefully the motor will be a runner, or it will be off to Adealaide on Monday to find a 12mm insert set and do another motor swap.
Chopit'nrideit... Prof

KeithinSB
Posts: 866
Joined: Sun Jan 14, 2007 4:21 am
Location: Creston California USA

Post by KeithinSB » Sun Nov 21, 2010 4:23 am

Great Job!!!
Ride it like you can fix it.

Bacca

Post by Bacca » Sun Nov 21, 2010 11:20 am

Coming on well Image

RickB56
Posts: 370
Joined: Sun Jan 25, 2009 1:13 am
Location: Melbourne

Post by RickB56 » Mon Nov 22, 2010 7:14 am

Your makin it look way too easy Prof!

Prof
Founder, Choppers Australia
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Joined: Sat Oct 22, 2005 3:54 pm
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Post by Prof » Mon Nov 22, 2010 10:13 am

It is easy when you have done it a few times. Raking this way means alighnment is not a problem. If you keep the slugs the same length and double check when welding (I get it exact using a verniers) and line up the cut at the back of the top tube you can't go wrong.

Then make sure welds are good and you intelligently make up for lost side tubes and extra stress on headstem, you'll be fine. First time I did a frame, I tacked it all up and got a professional shop to do the welds around the down tubes.

Things took a bit longer than expected. I turned up and welded on lugs for forward pegs while I was at it. We ended up with a fault in the wiring that took an hour or so to find and correct (30 year old loom that has been hacked a few times!) and did a service on motor as well as relocating the ignition switch.

However, we got the bike started up by 9pm, took it for a test run and then I accompanied Steven home just in case. Motor is smokey, but otherwise idles nicely and has good pick up so probably has a kit. Bike is now a real treat to ride, runs straight and not over heavy at low speed.

Steven is coming up Tues so we'll check everything over and through in some Morey's and try to reduce smoking a bit.

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More pics shortly.
Chopit'nrideit... Prof

Cromag
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Joined: Tue Nov 15, 2005 10:58 am
Location: NSW

Post by Cromag » Mon Nov 22, 2010 7:36 pm

Looks great Prof? Is your smoke problem, fuel or oil?
Does not work or play well with others
Loud pipes save lives
"These are not the Droids you're looking for"

Chainblock Dave
Posts: 211
Joined: Mon Jan 21, 2008 7:44 am
Location: Palmer, Sth Aust

Post by Chainblock Dave » Mon Nov 22, 2010 7:44 pm

As is makes a damned sexy rat!!! :twisted:
Dave

Youngblood
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Joined: Wed Oct 24, 2007 1:48 pm
Location: North-Eastern suburbs- Adelaide

Post by Youngblood » Tue Nov 23, 2010 12:23 am

The Bike looks heaps better than before. Great Job Prof., Steve must be happy.
Youngblood

Prof
Founder, Choppers Australia
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Post by Prof » Tue Nov 23, 2010 11:29 am

Took the bike for a run this morning and no smoking, nice quiet motor, o pretty pleased.

A number of the threads on the engine casting are broken off so can't be recoiled etc... Have to find an alternative fixing for the countershaft sprocket cover. The points cover is secure but only just on the one of the threads.
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
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Post by Prof » Wed Nov 24, 2010 12:26 am

Here's the rest of the exercise... Sunday morning appeared way too soon, but a bright and beautiful day... just the ticket for getting some serious bike building completed!

75mm slugs were machined up the night before and here are being put into the down tubes. You'll notice they are hollow... allows a better weld between the thin tube and thick slugs... preheating the slugs would also work. You can also see one of the two holes drilled at each join for plug welding to reduce any movement of the slug within the down tube.
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Because the slugs lift the whole front section of the frame, it will need to be bent back down so the two ends of the top frame tube meet. Arrow shows one of the two cuts being made into cross members under steering head... makes for a stronger job with the bend being kept within the cross members. Because we are in a hurry, as much as possible has been left attached which makes things a bit less convenient but saves a lot of time...
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Steve and Brian rolled up and got roped into the production crew! Steering head section is slid over the slugs and tack welded in place, so we can now bend the top tube sections to match...
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Arrows show where heating has been done to line up the top tube sections. Note the bolt through the bottom front engine mounts to keep correct width of down tubes... we do want the motor to fit back in!
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Some 4mm wall thickness pipe whose inner diameter matches the outer diameter of the top tube is split down the centre and here is seen clamped very firmly ready for welding. The weakest spot will be where the top tube meets the back of the original pressed steering head gusseting. This will be strengthened with a gusset cum coil mount. Rear join is also strengthened with gusseting...
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... which here is been welded up.
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New petrol tank mounts have been machined up. They are threaded internally for 8x1.25mm metric (only thread pitch I can getmetric stainless bolts in). They fit over the front coil mount and are about to be welded in.
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A pair of brackets are bent up to weld to the tank. This shows how to use a chisel to get the second close bend. In my haste I put petrol in the tank to check everything for leaks including novel tap set up, forgetting I had only tack welded the brackets onto the tank... instant headache... overcome by COMPLETELY filling the tank with water and then welding brackets. After judicious draining of the water, blowing a lot of compessed air in we readded the fuel 15minutes later plus half a cup of metho to break up the water. we than ran out a litre and hoped for the best. All worked fine and no blocked jets.
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Tank is an old DKW tank I picked up for $40 from the Balhannah swap meet recently. It has an unusual outlet that I have no fitting or thread tap for, so we thread it internally to match a bolt we do have...
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...and drill out the bolt for the passage of the go juice. Slsightly larger hole is drilled into the head end to take a piece of heavy walled tube I have added some grooves to to keep the fuel hose in place.

We'll use a Triumph style fuel tap on a length of hose. Threads on each end of the tap are the same so we can use a nut/tail on both ends for the hose... tricky!!!
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Gusset cum col mount ready for welding. Closer the fit the stronger the weld.
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Sad day here. I cut off the original foot of this CB500/4 side stand in 1974 and arc welded on a matching diameter piece of round bar. Over the years it has been bent into at least5 different configurations. Today most of it is being cut off to serve its purpose once more.
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Although we are running short of time and Steven wants to get home, I take the opportunity to machine up forward control mounts. The have a 17mm hole in them to match a great number of lengths of 17mm bright bar I have. The bolts poking out of them are 8mm metric lock bolts. This set up allows easy removal if controls get damaged in an accident. I use stainless fasteners everywhere possible and always use metric on metric bikes and imperial on imperial bikes.
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Down tubes are heated and flattened. Dimple marks centre and was done with a centre punch so it could still be seen while heating tube with oxy...
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Finished mounts...
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Finished and painted frame...
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Steven on the road this afternoon... loves it and feels far safer. Bike is really sweet to ride... and we'll trust it handles itself well this weekend.
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Chopit'nrideit... Prof

Rayman
Posts: 62
Joined: Sat Jul 10, 2010 12:26 pm
Location: Aberfoyle Park

Post by Rayman » Wed Nov 24, 2010 3:54 pm

nice work there guys -
you were all really busy in the shed - just as well I didn't get to stick around - I would've been in even MORE trouble then !

thanks fort he assistance too -
sorry i couldnt hang around - but as it was barely got the kids to swimming lessons in time -

Had some trouble with the kill switch on the way back until I unplugged the sucker -

all sorted now - just one of those days !

Rayman

($%^$% CDI ignitions )
currently working on
modded cx500 - untertail exhaust + lots of changes
VF750f - restoring a basket case very nearly there
vf750S - just needs the paintwork done and some tyres

gathering parts for - moto guzzi bellagio lookalike
version based on cx500

others
cm250

Bearcx
Posts: 1894
Joined: Thu Oct 18, 2007 12:31 am
Location: Gawler, Sth Aust
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Post by Bearcx » Wed Nov 24, 2010 6:19 pm

Well sorted, Fella's.

Steve, ya look a little squashed in that riding position, definitely needs highway bars or Prof's home made forwards.

Great stuff. lots of informative photos for the newbie's. Great job.
The brave may not live long, but, the cautious do not live at all.

Prof
Founder, Choppers Australia
Posts: 5884
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Post by Prof » Thu Nov 25, 2010 10:08 am

Was very tempting to spend a nother day on forwards... but bit too busy atm. Will do them when I have a few othe guys jobs out of the way.
Chopit'nrideit... Prof

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