'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