Last weekend it was time to brush of dust from my GT250 project bike 😀, which it had unfortunately gathered for a while 😬
Couple of weeks ago a blue box arrived from England to my local post office with a pair of
Betor Expert rear shocks inside. At first I planned to order them straight from Betor (located in Spain) but unfortunately they didn't have shipping option to Finland so I had to find another supplier.
Luckily Google found me
Villiers Services from England. I went and asked them by email how much the shipping would cost and after getting their answer I made my order through their website with these specifications:
Mounting bolt size:
10 mm / 3/8"
Spring weight:
50 lb
Shock length:
340 mm
Shocks have 12 mm diameter holes for mounting bolts and came with
four 10x12x24 mm bushings.
I made a simple sketch in CAD to check the fitment with T250 frame, which I had modeled earlier. At first I thought about ordering longer ones than 340 mm, but after coming to conclusion that the chain would eat up my swingarm quite badly I decided otherwise. The sketch has dimensions of 21"/18" tires and GT front forks and they are just close estimations.
It's good to notice that there are differences in T250 and GT250 frames. For example head tube of GT250 is different than T250 due to different forks. Basic geometry of both frames are however pretty similar 👍
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| Sketch of rear suspension dimensions |
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| Bushings (10x12x24mm) |
I decided to use and modify the old GT250 rear shock mounting points to fit the new shocks. Mounting points in the 80's RM250 swingarm are not symmetrical in my setup and they are just a bit wider than the ones in the GT250 frame.
Shocks mounted very well to the swingarm and they didn't require other modifications than drilling the mounting holes from 8 mm diameter to 10 mm. After mocking up both shocks to the swingarm it was obvious that left side needed a longer spacer (14 mm).
I decided to drill through the frame mounting points to fit long bolts. I lathed two support sleeves which helped to keep the drill bits straight while drilling. I used 8 and 10 mm drills. After both sides were drilled I cut off the 10 x 12 mm sleeves which were left to the both ends and fitted the spacers in place together with shocks. I finished the job by welding the 14 mm spacer to the frame.
I used zinc plated bolts and nut for mockup and will use acid resistant DIN 931 bolts with DIN 6926 flanged Nyloc nuts for final assembly. Hopefully they will withstand the load and shear from the swingarm. Time will tell 😅
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| 12 mm GT250 rear shock mount with 10 mm thread |
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| Bushing helped in figuring out side offset |
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Swingarm didn't require other modifications than
drilling the mounting holes from 8 mm to 10 mm |
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| Left side mockup |
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| Dimensions for spacers |
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| Left side spacer |
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| Support sleeves, centre drill , 8 mm and 10 mm drill bits |
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| Lathed sleeves helped keeping the drill bits straight while drilling |
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| Drilled through |
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| Cut off the 10 x 12 mm sleeve and mocked spacer in place |
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| I used just a long bolt to keep the spacer in place while welding |
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| Job done! |
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Acid resistant M10 hexagon bolts (DIN 931) and
flanged Nyloc nuts (DIN 6926) for final assembly 😀 |
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