GPX750R resurrection

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Re: GPX750R resurrection

Postby The_Fixer » Fri Dec 29, 2017 6:09 am

Mister_T wrote:
The_Fixer wrote:Tyres may also be prone to catastrophic failure past this time frame,

Suits my riding style then.

Not much tread left in the middle of this Bridgie BT17F but still plenty left to exploit on the sides.
gpx750r_a_bit_more_to_go.jpg


You could always employ the Burt Munro principle and use the neighbour's carving knife to resurrect some more centre tread. :P :kuda:
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Re: GPX750R resurrection

Postby Mister_T » Fri Dec 29, 2017 5:57 pm

The_Fixer wrote:You could always employ the Burt Munro principle and use the neighbour's carving knife to resurrect some more centre tread. :P :kuda:


Nothing quite so dramatic required yet. The profile pic of the Bridgy shows that the previous owner did not spend much time searching the outer limits, there are 2 definite arcs there:
gpx750r_bridgy_bt17F_profile.jpg
gpx750r_bridgy_bt17F_profile.jpg (49.84 KiB) Viewed 781 times


On ther other hand I could commandeer the Metzeler ME33 Laser from the front of my RC17. The Metzys have alway been good to me:
rc17_metzeler_me33_laser_profile1.jpg
Happily tips in so a good match for the quick-steering 16 inch front on the RC17
rc17_metzeler_me33_laser_profile1.jpg (49.08 KiB) Viewed 781 times


The ME33 didn't mind life on the edge although the footpeg, sidestand and centrestand complained loudly:
rc17_metzeler_me33_laser2.jpg
I want to get my money's worth so I try to use all the tread
rc17_metzeler_me33_laser2.jpg (86.36 KiB) Viewed 781 times


I won't rule out a Bridgestone BT45 but I'd want to see how much tread those have up the side when fitted and inflated. The GPX has more clearance than the RC17, at least on the left hand side.
Heck, I wouldn't rule out Dunlop K205's (OEM fitment) if they were still available. Pics from the era showed good tilt possible:
gpx750r_jap_brochure.jpg
gpx750r_jap_brochure.jpg (49.02 KiB) Viewed 781 times
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Something not to like about a GPX750

Postby Mister_T » Fri Dec 29, 2017 6:33 pm

Sadly the GPX750 is not perfect. The obtrusive sidestand spring is one example. Here is another.

It is not unusual to see pics of a GPX with the bottom corners of the taillight broken. Here is one possible explanation.
The tailpiece is not held very securely:
gpx750r_tailpiece.GIF
gpx750r_tailpiece.GIF (19.4 KiB) Viewed 780 times


A couple of screws on each side at the front hold the tailpiece rigidly to the subframe. At the rear, the tailpiece hangs from a bar under the grab handle and is isolated through rubber grommets (aka "damper" in Kawi speak):
gpx750r_tailpiece_rear_retainers1.jpg
Wobble, wobble, plastic and trouble. Too much movement here.
gpx750r_tailpiece_rear_retainers1.jpg (58.45 KiB) Viewed 780 times


This leaves the rear of the tailpiece to flex around. The wide indicators attached directly to the tailpiece and nothing else make things worse by flapping in the breeze and their weight is exaggerated by sticking out so far, leverage and all.
The close fitting tailight gives up trying to keep the tailpiece straight and flips its bottom corners out.
It's not just twisting movements, there is up and down as well. The dampers don't do much damping after a while:
gpx750r_tailpiece_rear_retainers2.jpg
I don't think there is supposed to be a gap here
gpx750r_tailpiece_rear_retainers2.jpg (65.02 KiB) Viewed 780 times


All that movement does not do the rigid mounts at the front any favours, either.

Here I have inserted a couple of thin washers to stop excess movement. Each washer is about 1.2mm thick. With thin washers you can put them above or below the damper to adjust the rear height of the tailpiece.
gpx750r_tailpiece_rear_retainers3.jpg
Maybe a single 2mm washer would be better and preload the damper a bit less.
gpx750r_tailpiece_rear_retainers3.jpg (62.51 KiB) Viewed 780 times
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Product impression - RhinoMX Seal Doctor

Postby Mister_T » Sat Dec 30, 2017 8:43 pm

The right fork seal on the Resurrection GPX has been leaking of late. It leaked not just when riding but when parked up on the centrestand. Some leaks just leave a stain you wipe off occasionally, this leak was enough to run down the fork leg onto the caliper. :(
I'd seen the Seal Doctor around on websites and decided to give it a try. It is designed in Australia and endorsed by Geoff Ballard so it can't be too bad. It was designed for upside-downy dirt bike forks but fork seals are fork seals and the tool will work on right-way-uppers as on the GPX 38mm KYB units.
There is a link on the RhinoMX website ( http://rhinomx.com/ ) to a vid that shows Geoff Ballard demonstrating the operation of the tool.

Here is what came out the the right fork seal after one rotation:
gpx750r_fork_rh_seal_cleaning.jpg
Barf me out, gag me with a spoon, like totalleee
gpx750r_fork_rh_seal_cleaning.jpg (70.57 KiB) Viewed 768 times

Yeah the oil is due for replacement as well, but that is a lot of nasty looking gunge to be near a sliding chunk of precision metal. I cleaned off the tool and gave it a couple of more laps and ended up only getting dirty oil.

The left fork was not leaking but I gave it a shot anyway:
gpx750r_fork_lh_seal_cleaning.jpg
A bit of snot there
gpx750r_fork_lh_seal_cleaning.jpg (52.56 KiB) Viewed 768 times

The left wasn't too bad but apparently worth doing.

The result so far is the right fork seal no longer leaks when parked. Crikey
I haven't ridden it yet so we'll have to see what happens there but so far it's a win. :D
Tomorrow looks like it will be nice weather to burn a log book day and see how the fork seal holds out.
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Re: Product impression - RhinoMX Seal Doctor

Postby Mister_T » Mon Jan 01, 2018 9:06 pm

I've been for ride, taken the GPX over speed bumps, corrugations and level crossings, let it sit in the sun and parked it overnight. No pool of fork oil detected! Bonus win! :D
I avoided pulling a monster wheelie then hitting the rev limiter and slamming it on its nose. That would be just asking for trouble.
gpx750r_fork_rh_seal_cleaning2.jpg
No more zip-tieing a discreet black rag around the top of the slider, for a while at least.
gpx750r_fork_rh_seal_cleaning2.jpg (60.83 KiB) Viewed 752 times
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Re: GPX750R resurrection

Postby Smitty » Tue Jan 02, 2018 11:14 am

Mister_T wrote:
The_Fixer wrote:.....................

I won't rule out a Bridgestone BT45 but I'd want to see how much tread those have up the side when fitted and inflated. The GPX has more clearance than the RC17, at least on the left hand side.
Heck, I wouldn't rule out Dunlop K205's (OEM fitment) if they were still available. Pics from the era showed good tilt possible:
gpx750r_jap_brochure.jpg


you do run out of clearance on a GeePeeX7Fiddy... before the Bridgy does
I can vouch for that ;)

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Re: GPX750R resurrection

Postby Mister_T » Tue Jan 02, 2018 2:17 pm

Smitty wrote:you do run out of clearance on a GeePeeX7Fiddy... before the Bridgy does
I can vouch for that ;)

Nice to know the hardware will give some warning before you go over the edge and find out the hard way.
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Underbelly: Uni-track

Postby Mister_T » Tue Jan 02, 2018 3:04 pm

Beneath the glitz and glamour of shiny metallic painted fairirngs and chrome there is a dark, dirty and seamy underworld that few people will venture into, the world of the monoshock rear suspension.

One of the things I noticed when I first peered into the dirty underworld of this GPX were the tantalising grease nipples on the Uni-track rocker arm. The middle one has copped some rust and damage.
gpx750r_unitrak_lube1.jpg
From the factory these greasing points are a very welcome addition to important parts of the rear suspension.
gpx750r_unitrak_lube1.jpg (47 KiB) Viewed 736 times

The caps on the nipples are not factory items so it seems that sometime in the past somebody has shown some consideration.
The middle nipple won't take grease so it will have to be swapped around with another one for now.

gpx750r_unitrak_lube2.jpg
Ready for some gentle pumping with Penrite moly grease.
gpx750r_unitrak_lube2.jpg (97.02 KiB) Viewed 736 times

Not shown are the the nipples at the top of each dogbone which are fairly easy to get to as well.

The swingarm has its own greasing point. The problem is that it is a bit tricky to get to.
gpx750r_unitrak_lube3.jpg
In this dark and dirty recess lies the hidden grease nipple for the swingarm.
gpx750r_unitrak_lube3.jpg (69.34 KiB) Viewed 736 times

Attaching a grease gun to this swingarm may require skill, daring, cunning and dedication. And then I will have to get the gun off again which may be a whole 'nother story.

This pisses me off because chances are that since the swingarm is difficult to lube, it may never have been done. The Uni-track links are easy to get to and at the moment may require lubing less than does the swingarm. Out of sight, out of mind.
All the 106-odd neddies the GPX can produce work their way into the frame through two small needle bearings in the swingarm pivot. When the rear brake does its job it tries to pull the swingarm out of the frame. All this happens while the rear wheel is bouncing around. It's a tough life being a swingarm bearing. Show them you care.
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Re: Underbelly: Uni-track

Postby Smitty » Tue Jan 02, 2018 5:06 pm

Mister_T wrote:.....................

The swingarm has its own greasing point. The problem is that it is a bit tricky to get to.
gpx750r_unitrak_lube3.jpg

Attaching a grease gun to this swingarm may require skill, daring, cunning and dedication. And then I will have to get the gun off again which may be a whole 'nother story.

.............


never had a problem on mine....
but
my McNaught grease gun had a flexible rubber hose and snap on/snap off coupling (you can hear it click on and a quick twist and its off)
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Re: GPX750R resurrection

Postby Mister_T » Tue Jan 02, 2018 10:35 pm

Mister_T wrote:
Smitty wrote:you do run out of clearance on a GeePeeX7Fiddy... before the Bridgy does
I can vouch for that ;)

Nice to know the hardware will give some warning before you go over the edge and find out the hard way.

If I could get this sort of angle-of-dangle out of it then I'd be happy:
Dec_1986_Motorcyclist_Magazine_cover.jpg
Dec_1986_Motorcyclist_Magazine_cover.jpg (37.12 KiB) Viewed 726 times

I've seen the Pirelli tyres infesting ebay lately and but, I dunno, I don't like the look of them. Anybody used their 110/90 V16 Sport Demon front?
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Re: GPX750R resurrection

Postby pkay » Tue Jan 09, 2018 2:26 pm

I was having a chuckle about your posts as I am mid GPX750 resurection as well (check Brisbane Classic Motorcycle Collection on Facefart). Just done the mono shock - the middle shock pin (the one that runs through the needle bearing) is NLA.

I was interested whether in your experience you know of anyone who does a decal set for the Euro/Australian paint set? The guy I normally use has shut up shop.
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Re: GPX750R resurrection

Postby Mister_T » Tue Jan 09, 2018 4:55 pm

pkay wrote:Just done the mono shock - the middle shock pin (the one that runs through the needle bearing) is NLA.

Bummer. I suppose you would have to get one fabricated in a case-hardenable steel then tuftrided or nitrided. Or maybe just sleeved and treated.
I'll resist the temptation to properly pull mine apart for now. What I don't know won't cost me.

pkay wrote:I was interested whether in your experience you know of anyone who does a decal set for the Euro/Australian paint set? The guy I normally use has shut up shop.

I haven't looked closely at the bodywork side. I did look for ESCS stickers a while back. Or course the red one is NLA but the gold-lettered sticker for the black/gold scheme is/was available.
The red ESCS sticker loves to fade to pink and really stands out. If you have a close look at the jap brochure pic above you can see that sticker is already on the way out and that was way back then.
Eventually I may have to pull the forks off and carefully hand paint in the red, just like a squinting kid with an Airfix model with my tongue sticking out and getting high on Humbrol fumes.
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Another one bites the dust

Postby Mister_T » Sun Jan 28, 2018 10:38 pm

What is it with these stupid plug caps?
gpx750r_another_bad_plug_cap.jpg
Is there somthing I'm doing wrong? This is getting old, fast.
gpx750r_another_bad_plug_cap.jpg (109.19 KiB) Viewed 568 times

It's not like the coils put out a massive amount of power, the spec plug gap of 0.65mm (or 26 thou) confirms that.
It's not the same cylinder affected as last time but it's on the same coil. Coincidence? Hmmmm. dontknow.gif
The meter is probably only reading a carbon track from the burned out resistor.
On the plus side, it does cause a lumpy random idle like a race cam. 8)
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Re: GPX750R resurrection

Postby pkay » Mon Jan 29, 2018 12:23 pm

I was fascinated yesterday by the amount of junk the early GPX's carry on the swingarm. I have a lter model wreck that I am puylling assorted bits off as needed and they certainly tidied things up when they moved to the brakes above not below the swingarm.

The other challenge will be getting the torque arm in. Japanese factory workers must have vely vely small fingers!
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Re: GPX750R resurrection

Postby Mister_T » Mon Jan 29, 2018 9:44 pm

pkay wrote:I was fascinated yesterday by the amount of junk the early GPX's carry on the swingarm. I have a lter model wreck that I am puylling assorted bits off as needed and they certainly tidied things up when they moved to the brakes above not below the swingarm.

Yes, the reduced semi-sprung and unsprung mass would probably help more than some simple articulation of the caliper carrier.
Having the caliper above also may reduce the amount of crap hurled at the exposed caliper pistons.

These days the pistons tend to be more exposed than they used to be. The genuine GPX rear pads are a different part number to the fronts even though they look the same. I suspect the original rear pads had thicker friction material than the fronts even though the FSM makes no specific mention. My RC17 FSM specs thicker pads on the rear. Unfortunately the aftermarket cannot be bothered to make specific rear pads and just list the thinner front pads on the rear. This leaves the rear pistons sticking out further than they would otherwise.

pkay wrote:The other challenge will be getting the torque arm in. Japanese factory workers must have vely vely small fingers!

I have looked at the torque arm with the intent to lube the needle bearings. Without taking off the swingarm, exhaust and RH footpeg hanger it looks near enough to not possible. As I have more pressing matters to attend to for now that job can wait.
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