'73 Suzuki GT250 - Part 14 - GT550 front fork swap - 2/2 - Refurbishing top and bottom yokes

I decided to get bottom yoke painted with same color than front and rear wheel so I started by prepping it properly. First thing was to pull out lower steering head bearing and remove fasteners and old steering lock. I only covered axle with masking tape and then got lower part of yoke sand blasted. While it was getting painted I sourced new bearings, steering lock and fasteners for both yokes. M10 bolts used to tighten stanchions had to have fine threads. Those I managed to find through eBay.

Sand blasted bottom yoke

New fasteners for top and bottom yokes

Nut for steering stem (#51631-28000)

Neiman GKS steering lock for Suzuki GT550

Pyramid Parts steering head bearings kit (#BR21)...

...which included new bearings, dust seals and tube of lubricant

Upper (25x48x15) and lower (27x48x14) steering head bearings

Refurbished bottom yoke/steering stem

Now that I got bottom yoke back together with new bearings I tested how it fit to the head of the frame which still had old bearing races on. It turned out that in GT550 bottom yoke bearings are tiny bit more further apart from each other than in GT250. Due to that I couldn't get the steering stem nut (#51631-28000) tightened all the way. 

To fix issue with bearings I designed a 1 mm thick shim plate which I put underneath lower steering head bearing race while I replaced both races. Shim plate was laser cut out of stainless steel sheet. 

Since I don't own special tools to replace steering head bearing races I just used Dremel with a grinding stone and a punch to remove them. By taking my time I managed get them out without damaging bearing houses on the head. 36 mm socket turned out to be just the right size to gently hammer new races in. Counter part of steering lock in frame will still require bit of modification since lock is positioned differently in GT550 bottom yoke. That I will handle later.

Lower race had more space to fit a 1 mm shim plate underneath it

Dimensions of shim plate

Shim plates were laser cut out of stainless steel sheet

Dremel with a grinding stone together with a punch
were used to remove old steering head bearing races...

...and 36 mm socket to hammer new ones in place

New lower race with shim plate

New upper race

Unluckily GT550 front fork I bought had a broken top yoke which I didn't notice until later when I took it apart. I had to replace it with another one since it was unrepairable. I decided to use one out of GT250 which I already had and modify it to fit. 

Only difference between GT250 and GT550 top yokes is bigger bore for stanchions in GT550. GT550 comes with 35 mm and GT250 with 32 mm thick stanchions. I used a milling machine with adjustable boring tool to oversize holes on my GT250 top yoke. 

GT550 fork fork had a broken top yoke

GT550 and GT250 top yokes

Spacer and chock used for fixing top yoke to table of milling machine 

Finding center point of hole with centering device

Adjustable boring tool

Measuring hole diameter with a micrometer

Other side machined as well

I wanted to use a fatbar handlebar I lying around so I got a clamp kit made by Magura which fit perfectly to GT250 top yoke. I ended up polishing top yoke, clamps and handlebar. I assembled front fork and mocked it up with engine, swingarm and wheels. 

Next I will focus on fabricating kickstand and parts for rear brake. After those are done frame mods are almost complete and it might be time to start cleaning in it up for paint 😎

Magura X-line Offroad Clamp kit 28,6 mm (#0720474)

Polished top yoke, clamps and handlebar

Refurbished Suzuki GT550 front fork

Mock up

'73 Suzuki GT250 - Part 11 - GT550 front fork swap - 1/2 - Rebuilding front shock absorbers

Some of you might remember me purchasing a set of Suzuki GT550 front forks quite a long time ago. At the time I wasn't sure what to do with them until I got my GT250K project going. First I was thinking of rebuilding GT250 forks for this project but the set I have was in worse condition than these ones. Good thing about these are that they are more rigid than GT250 front forks. Main difference is that stanchions have 35 mm diameter compared to 32 mm ones in GT250. Otherwise main dimensions like spindle diameter and steering bearings are the same so it's easy to swap them. I will feature triple trees and mock up more detailed on next part. This part will cover rebuild process of front shocks.

Suzuki GT550
front forks

Below is a picture of steps how to assembly Suzuki GT250 & GT550 front shocks (left to right). Same process applies also for disassembly but from right to left. I disassembled my forks long time ago I didn't unfortunately take pictures of that process.

Steps of assembling GT550 front shock absorbers

Upper parts of old stanchions were very pitted and rusty most likely due to moisture accumulating inside headlight brackets. Since I wasn't going to use original headlight brackets and wanted to leave them exposed I went ahead and bought myself a new pair of stanchions from eBay instead trying to do anything with the old ones. I cleaned sliders and circlips, which attach to bottom of the stanchions, and installed them to the new ones.

New stanchions for Suzuki GT550 front forks

Unboxed

Comparison of new and old stanchion

Sliders and circlips in order

I decided to shave off ears from outer tubes which the stock front fender attaches to since I didn't have any use off them anymore. I started by cleaning outer surfaces of them with soda blasting gun. After that I removed most of material with a saw and an angle grinder. Since there were still a lot of excess material to be removed I used a file next. I tried to be careful and not remove too much or making too deep scratches while filing so I marked a spot with a red marker pen to indicate when to stop and move on to sanding. I used normal sand paper for rough and wet sand paper for finer sanding. Last step was to polish them with buffing wheel and polishing paste. I purchased new hardware for inner tubes and axle holders and screwed them back on.

Outer surface of outer tubes cleaned with soda blasting

Ear sawed off

I marked an area which I wanted to file flat
with a red marker pen

After rough sanding...

...and finer wet sanding

Buffing wheels and Autosol polishing paste

Outer tubes and axle holders after polishing

New M8x27 hexagon socket head screws
with low head (#51147-48130) and copper washers

Rebuilding outer tubes

Non-serrated M8 flanged nyloc nuts DIN 6926 for axle holders

After getting stanchions and outer tubes back together it was time to mate them together. I started by sliding the rebuild stanchion inside the outer tube. Before installing a new oil seal I made sure that the upper slider was inside the outer tube. Otherwise it would have been a nightmare to get the oil seal out to get it back inside. For this project I chose fork seals made by Pyramid Parts (#FOS 013) just like I did with my CBR600F. After knocking oil seal in place I put on a washer on top of it and installed circlip with circlip pliers.

Pyramid Parts fork oil seals #FOS 013

Box comes with a pair of 35x48x11 mm oil seals,
seal buddy tool, lubricate and a sticker

Slider, oil seal, washer and circlip

...and order how to put them back together

Circlip installed with circlip pliers 

Last step was to install new fork dust seals, slide in springs, add fork oil and screw on caps to top of stanchions. Since these forks originally had boots instead of dust seals I wasn't sure if I was able to find a suitable pair for them. I ended up ordering a set of Pyramid Parts fork dust seals (#DB10) which seemed to work decently well with them. I got myself a one liter bottle of 15W Motul fork oil and measured 2.35 deciliters for each shock. Caps were little bit pitted as well so I took a small piece of aluminum foil and brushed rusty spots with it under a running water. That's an easy trick to get rid off small rusty spots from old steel parts which are chrome plated. Off course it's not a permanent fix but a lot cheaper than new parts or chrome plating. I replaced old O-rings with new ones (#51181-31030) before screwing them back on.

Outer tube dimensions

Pyramid Parts fork dust seals #DB10

Springs, caps and set of dust seals

Fork inner tube caps and O-rings (#51181-31030)

Motul SAE 15W Expert Medium Heavy fork oil (#101138)

Measured roughly 2.35 decilitres of fork oil
for each shock

Rebuild Suzuki GT550 front shocks

Check out also part 2 where I complete this swap after refurbishing top and bottom yokes and fitting it to my GT250K 😎