1974 GT750 Rebuild

Here you can write about your restoration highs and lows and hopefully final success
Peterg
Posts: 32
Joined: Sat Mar 30, 2019 1:46 pm

Re: 1974 GT750 Rebuild

Post by Peterg »

It’s standard, unrestored believe it or not, look forward to seeing yours my friend, keep at it
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Harrymail
Posts: 638
Joined: Thu Jul 07, 2016 8:35 pm
Location: East Yorkshire

Re: 1974 GT750 Rebuild

Post by Harrymail »

teazer wrote: Tue Feb 23, 2021 8:55 pm When you get the plated, ask the plating shop to bake them. During plating, hydrogen permeates the steel and makes it brittle. Heat treat (baking) at somewhere around 450F for a couple of hours bakes out the hydrogen.
Never knew this. I hope my S bolts were heat treated when I had them plated. It was never mentioned. Is it only High Tensile ? Do normal bolts not need this ? I'm thinking about my engine mount bolts, axle shafts etc. All have been plated.

Paul
Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
burgs
Posts: 70
Joined: Mon Feb 06, 2012 9:07 pm
Location: Hunter Valley NSW Australia

Re: 1974 GT750 Rebuild

Post by burgs »

Hi
Well progressing slowly, cases are prepped ready for gears ectara, now waiting on seals and bearings.
Received full profile thread inserts for machining the new cylinder/head studs, so gives me something to do, might make a spare set as well CNC lathe could do with a bit of a work out, as it hasn't been used for about 18 months.
Welded the thermostat housing on the head, broken bolt, have it set up on the machining centre at work but boss decided to come to work today, so will machine after work tomorrow.
Still waiting for the cylinder block to be bored and honed :roll:.

Found two cracks in the engine chain guard, from what looks like a chain failure somewhere along the way, welded them and dressed back.

Noticed tonight that the footrests are both bent a bit so will straighten at work tomorrow, footrest rubbers are in very good condition but I haven't been able to get them off yet, might have to relieve the stiction between the steel and rubber with a thin screw driver.

Checking the new second hand clutch and noticed that every second set of shock absorption springs is loose, so checked the old clutch housing and it is the same Is this correct? :?
Burgs
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canaletto5
Posts: 5228
Joined: Tue Jul 23, 2013 8:43 pm
Location: Derbyshire

Re: 1974 GT750 Rebuild

Post by canaletto5 »

Spray WD40 into the joint between the footrest bar and the rubber. Warm the rubber with an air blower. Gently twist the rubber until it breaks free. Kev
burgs
Posts: 70
Joined: Mon Feb 06, 2012 9:07 pm
Location: Hunter Valley NSW Australia

Re: 1974 GT750 Rebuild

Post by burgs »

canaletto5 wrote: Tue Mar 02, 2021 8:44 am Spray WD40 into the joint between the footrest bar and the rubber. Warm the rubber with an air blower. Gently twist the rubber until it breaks free. Kev
Hi will give this a try, thanks.

This weekend has been one step forward two back.
I cleaned out all the crankcase threads of gasket cement, and all felt ok, put the gears and crankshaft in, put the top case on and fitted all the bolts, went and bought two new tension wrenches because my old ones are some 50 odd years old and most likely not that accurate anymore.

Tensioned all the bolts to about 10% below specification and found number 16 stripped, and one of the front M6 threads stripped/failing as well!
So need to fit thread inserts tomorrow afternoon.

New second hand clutch fitted twice, due to me thinking I had forgot the shim between the bearing and clutch, spent an hour looking for the shim only to find it stuck to the bearing, need to wear my glasses more often :D

Will start machining the head/cylinder bolts tomorrow, will do in the manual lathe, couldn't be bothered to do the program and setup the chuck in CNC Lathe.

Count down is on only a couple of weeks before Bathurst Rally, so might need to burn the midnight oil a bit.

Regards
Burgs
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PaulD738
Posts: 3962
Joined: Thu Sep 25, 2014 6:57 pm
Location: Warrington Cheshire

Re: 1974 GT750 Rebuild

Post by PaulD738 »

I've got an airline gun with a thin nozzle I use mainly for carb cleaning. It's also useful for removing stubborn handlebar and footrest rubbers, warm them up with a heat gun the poke the thin nozzle inbetween the rubber and metal. Hey ho one rubber removed undamaged 8-)
They're rubbish them Jap bikes lad they won't last five minutes! you want to get yourself a nice Royal Enfield!
A quote from my old dad 8-)

I started out with nothing and I’ve got most of it left!
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: 1974 GT750 Rebuild

Post by teazer »

Harrymail wrote: Sat Feb 27, 2021 8:42 am
teazer wrote: Tue Feb 23, 2021 8:55 pm When you get the plated, ask the plating shop to bake them. During plating, hydrogen permeates the steel and makes it brittle. Heat treat (baking) at somewhere around 450F for a couple of hours bakes out the hydrogen.
Never knew this. I hope my S bolts were heat treated when I had them plated. It was never mentioned. Is it only High Tensile ? Do normal bolts not need this ? I'm thinking about my engine mount bolts, axle shafts etc. All have been plated.

Paul
I always ask the plating shop to bake them. I figure better safe than sorry. We have had a few spokes snap after plating, so we bake them a second time just to be sure.
burgs
Posts: 70
Joined: Mon Feb 06, 2012 9:07 pm
Location: Hunter Valley NSW Australia

Re: 1974 GT750 Rebuild

Post by burgs »

Hi
Machined most of the ew head studs, dropped wheels off for new tyres to be fitted.
The number 16 stripped thread in the rear of the crankcases is a bit of a pain, the thread has been completely stripped out of the upper case, I have worked out a repair over a couple of beers, :D I will drill and tap M12 through both cases, machine an insert M12 to M8 to fit in the upper case, set it in place with Loctite 680, then machine and fit a M12x Dia 8.2 sleeve into the lower case and lock it there with clearance to the upper insert, screw in the new bolt and torque it to spec, job done :lol: .

Still waiting on cylinders to be finished :evil: roughly two weeks to go before we set off :lol: .

Burgs
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: 1974 GT750 Rebuild

Post by teazer »

Can't you just dill and tap for a helicoil or is it way too damaged?
burgs
Posts: 70
Joined: Mon Feb 06, 2012 9:07 pm
Location: Hunter Valley NSW Australia

Re: 1974 GT750 Rebuild

Post by burgs »

teazer wrote: Wed Mar 10, 2021 5:55 pm Can't you just dill and tap for a helicoil or is it way too damaged?
HI Teaser
Helicoil was the original plan, but when I went to drill the hole for the inert, it was already too big for the thread tap, the hole through the bottom case was smaller than the upper case with the thread in it?
I could have used a solid insert such as the Caterpillar (Full Torque) style but they are bigger OD still, and the wall thickness wouldn't allow it.
The cases are already together which is making it a bit more difficult, but not impossible to fix.
Burgs
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