Author Topic: CB750F2 .... silk purse from a sows ear.  (Read 4663 times)

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #165 on: October 27, 2018, 02:13:59 PM »
Today we got something useful done. Aside from cleaning and trying to get paint and rust off..... we sorted the broken No2 carb.

The problem was the bracket that holds the throttle cable. The bracket locates to No2 carb with a screw and a peg cast in the carb body. The peg had sheared, using a little cast nub on the carb as a stop...and that had cracked the top of the carb body.

The mission....re-instate the peg and patch the body to keep things airtight.



The flat square area just above and right of centre is where the peg used to be. I checked the depth of metal, and drilled a 1.5mm pilot hole as near centre as I could. I checked the depth and made sure I did not drill too far in so as to break through into the carb body and cause more issues than I solved! The bit I had that split was above the machined part the carb slides move on...but this is not. So blind hole it must be!

After the 1.5...we went again with a 2.5mm and tapped it with a 3mm thread. Fortunately...I have all this stuff in small size for my other hobby...Rc cars...and I also had a good seelction of cap-head M3 bolts. The heads on these were a close match to the original peg. The plan being to screw one in to form a new peg.

The bolt head was a bit too big...but shoving it in the drill and running it over a fine file soon had the thing down to teh size I wanted. A quick dip in solme silver paint made sure it was rust proof again! I hate tapping threads with small taps and blind holes....you have to be SO careful not to bottom the thread as it will strip it or break the tap. Neither would make me happy.....


The bolt was trimmed to size with the Dremel, using the old 'put a nut on first so taking the nut off cleans the thread' trick. Screwed the bolt in with a dab of threadlock to make sure it stayed where I put it. It all went together like a little sweetly :)


The final step was to stop-drill the crack to relieve pressure and to channel the crack a little with the Dremel to make a nive valley for the epoxy to sit in. Tried to build a little fillet of epoxy on the outside to support the crack, but not so much it wasn't neat anymore. A little brush over with aluminium coloured paint on the outside should help to hide the repair if the epoxy yellows.


The bracket sits nicely and the peg should be stronger than the previous casting ever was.

The only slight issue with the job was the half hour I spent looking for the screw that holds the bracket in. I checked in carb bag 3 ..... and there was no trace. Checked the bench, the shelf...everywhere.

The mystery would have been solved quicker if I had remembered the bracket was on carb 2 ...... no harm done.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #166 on: November 08, 2018, 02:38:24 PM »
Not had much time to work on the bike over the last couple of weeks, but small progress has been made. Work has been interfering but the worthless bunch of petty ingrates who employ me have allowed me the grace to spend some time otherwise engaged while they work out whose lifeless corpse they could best employ to climb higher up the greasy pole.....

That aside....

I thought I would have a go at breaking down the forks so I could get them sent off for rechroming while I figure out how one goes about measuring crankshafr bearing clearances.....

wish I had chosen something else...but oh well.

I have had many a fine tussle trying to undo the damper bolts at the bottom of the forks, and expected the same again here. Nope. Both undid really sweetly with just the pressure opf the spring stopping the damper from turning. This was clearly just the old beast trying to lull me into a false sense of security....

Next I went to undo the fork caps and get the springs out. Had to bolt the tubes back into the yokes to grip them, but hte first one undid. The second one did not buidge. Will not budge and broke free from the vice damaging the steering stem bearing cover that was still on it. The top nut has started to chew and still the damn thing won't budge. Breaker bar and the thing will twist in the yokes before it undoes. Tried shocking it and no joy. Next...I suppose I will have to try heat. I suppose the o-ring in there will want replacing anyway...

Anyway...Out with the damper bolt so I could get the tube out and remove the old seal. A lot of rust under the dust cap when I finally got that off. It was cracked and rock hard. I soaked it in ht water and pulled it out with moile grips like a rotten tooth. Then I pop out hte retaining clip...or I thought I had. What I had was half a clip. The other half remains in the groove. Corroded firmly in place. It's currently soaking in penetrating fluid before I try and pick it out. Had broken clips before...had rusty clips before. Never had one corroded in place or actually rusted clean through. The alloy, however, was not corroded at all. No fur...just red rust.

When that finally shifts I can have a go at getting the damn fork seal out. I expect another battle...........
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Bryanj

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #167 on: November 08, 2018, 04:37:14 PM »
Fork top nut impact hammer with 6 sided socket, seal make sure you do not damage the surface oinside the slider, seen lots of leaks from that. Broken circlip may respond to heat from one of the canister plumbers torches---i use those on the master cylinders to clear out all the crap and make the clip moveable.

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #168 on: November 08, 2018, 06:27:04 PM »
I hear you on the seal ....made that mistake before. Will be popping it in hot water and try to pull the seal....no metal tools trying to pry it out. Will try heat on the clip too....but can't start on the seal until the clip is sorted. I really don't want to damage the groove either.

My impact screwdriver has a socket 1/2" drive thing on it. Will try that.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Bryanj

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #169 on: November 08, 2018, 06:57:11 PM »
I was think more of a widy hammer like tyre fitters use on wheels, maybe you can take it to your nearest tyre shop and ask a favour? As to the clip and seal the small torch will not damage the groove just loosen all the crap on the metal and the seal is shot anyway.

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #170 on: November 10, 2018, 11:51:10 AM »
Ha Ha! One step forward. Not all the steps...but I will take 1 step forward and no steps back any day.

The fork cap is off and the other leg is apart. Now, I read somewhere that oil and water don't mix....but it appears the previous owner of this bike had a very good go. What fell out of hte fork legs was an interesting mix of sludge, oil and a bit of water. It didn't mix on my shed floor either.....

Note to self...use a bigger bowl to catch the mess so you don't pour it all next to the bowl....not in it. Still...the shed floor needed a good clean anyway.

Mess cleaned up, the opther clip came out easy and in one piece. I could almost consider putting it back in ...but I won't. Both dust caps were cracked and hard as nails so both will want replacing. They won't keep the dust, grit water or field mice out.

After a gfood soak in WD40, the broken bit of clip popped out nicely. I was able to get a pointy thing under the end and it came out. Wooden cocktail stick for the win! The same stick has got the crud out of the groove aided by the Mk I Fingernail. No pointy screwdrivers here.



So...that's progress!

Neither fork seal will budge a bit, so the next thing to try after an overnight soak will be some heat. Hot air gun should help to expand the alloy a bit and hopefully break the seal and let the seals come out. So far..I have been using a reverse puller just hooked under the seal held in a vice while I try and tap the leg off the seal with a rubber mallet. Not having it....and I don;t want to try force...so will try chemicals...followed by fire. I can think of more drastic things to try...but I REALLY don't want to be doing things like them.

CB750F2 - in pieces
CB900F Hornet - the daily transport

Online Trigger

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #171 on: November 10, 2018, 11:40:07 PM »
I always put them in the oven and the heat will soften the seal to make it so easy to pull out  ;)

Offline Yoshi823

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #172 on: November 12, 2018, 05:13:08 PM »
Only just had a chance to begin to read about this project. Got as far as the part where the basic part of the bike was carried through the house & it reminds me of the 3rd rebuild of my 750F2 back in the early '80s. At the time I had an upstairs maisonette so there were several flights of stairs to navigate so as to get the frame & engine assembly down to the garage.

This was in my bedroom...

Bikes...they're in the blood.
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Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #173 on: November 12, 2018, 06:05:49 PM »
Glad I didn;t have to negotiate any stairs!

Have to ask though...that frame...doesn't look standard. Looks like you can actually work on the engine with it in the frame.....
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline Yoshi823

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #174 on: November 12, 2018, 09:57:17 PM »
The standard frame was modified so that the top end was able to be worked on, mainly because I had a tacho drive oil seal go & I ended up having to remove the engine just for that 20p (at the time) seal. As I didn't have any of my own facilities at the time, I had to use a friend's garage, much to his mum's annoyance.



The modified frame needed a new tank to be made, which wasn't a problem as I wanted a Phil Read Replica style tank


« Last Edit: November 12, 2018, 09:58:55 PM by Yoshi823 »
Bikes...they're in the blood.
Yamaha 2001 R1
Yamaha 1990 FZR1000R EXUP
KTM 2004 450 EXC RFS
Honda 1997 XR400R
Honda 1980 CB125T2
Yamaha FJ1200 3XW

Offline SumpMagnet

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #175 on: November 18, 2018, 12:36:23 PM »
OMFG ..... I feel exhausted...but I AM VICTORIOUS!!!!!!

One by one the last bastions of cruddy fork seals have fallen to the onslaught of my mighty hammer, consigned to whatever foul hell spawned them. The battle was tough, and many were slain, but at last, I stand victorious atop a heap of severed seals.....

well.....I blame that on reading too much Tolkien as a child.

Anyway. The fork seals finally shifted. Much heat from the heatgun was required along with careful application of ultra-violence. A piece of 10mm OD steel tube was found in the spider haunted recesses of the shed, which fitted up the damper bolt hole and located in my smallest 3 leg puller. The pushed against the centre threaded bar and also kept all 3 legs spaced evenly at the right diameter to bear on the seal. This was after I had ripped off the rubber section on the inside to reveal the steel 'ring' and it's flange. ( a much under-used word...flange.... )

I could then beat seven bells out of the end of the steel tube and apply direct pressure on the puller without hte legs trying to close up and slip out of place.

Next...much heat was directed at the area from my hot air gun. Heated to the point the remaining rubber started to stink a bit and things got too hot to touch.

With much hammering, the odd bruised finger and much yelling of 'shift you bugger' ... first one and then the other came out.

What surprised me was the fact that there appeared to be virtually no corrosion of the alloy under the seal, and nothing but age and friction was keeping them in place. Still....that was enough to hold out for slightly longer than the allies held Tobruk in 1941.

With the seals out, I could properly clean up the last remnants of corroded steel stuck from the rusted springs and clean the muck from inside the legs where the sludge collected at the base. They a\re now ready for a quick rub down ( as am I ) followed by a coat of paint.

Not sure if the finish here is supposed to be gloss black...or satin. I am leaning towards satin as i plan on the same finish for the brake calipers and will fit rubber fork gaiters as it fits the look I am going for...and stops stone chips. I had some smart Neoprene ones on a supermoto a few years back. Might see if they are still being made.

Some days...restoration work s a bitch when it won;t work. Other days...simple things just give so much pleasure when you make progress.
CB750F2 - in pieces
CB900F Hornet - the daily transport

Offline paul G

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Re: CB750F2 .... silk purse from a sows ear.
« Reply #176 on: Today at 08:09:34 AM »
 yelling of 'shift you bugger'

Never in a million years did you say BUGGER ;D ;D ;D ;)
Keep up the good work.
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Honda CB750 UK K1 restoration
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