Suzuki T20 selector drum

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gammakeith
On the street
Posts: 41
Joined: Mon Dec 14, 2020 4:50 am
Country: United Kingdom
Suzuki 2-Strokes: 1966 T20

Suzuki T20 selector drum

Post by gammakeith »

Dear all,

While I wait for my crank to come back from SEP, I've been checking the gearbox over. Due to the state of the engine I couldn't test drive so I want to make sure all is well. I assembled and found that the selector mechanism is too stiff to turn. I thought I had done something wrong but careful inspection reveals two problems;

1: With the selector drum sitting on the spring detent it protrudes slightly on the neutral switch side. Thus, bolting up the neutral indicator case pushes the drum slightly inwards. I carefully flatted down the neutral side plate on a surface plate and it is clear that two of the screw heads were rubbing slightly against the end of the selector drum (see pic). It helped a little now I have a fresh smooth surface but bolting it up pushes the selector drum towards the change mechanism side.
2: The two selector drum plates have been modified to reduce selector drum float (see pic) which makes things even worse. The end of the right hand plate has been bent over slightly whilst the stopper plate has been ground so it fits in closer to the cases (its worse than it looks on the pic). The upshot is that there is no side float whatsoever and the whole thing nearly locks when the neutral plate is bolted up tight.

If I have the screws on the neutral switch plate loose then the selector mechanism works great so proving I have insufficient end float. I will attend to the selector drum plates which should restore some clearance but that still leaves the selector drum sitting hard against the neutral indicator plate and slightly pushing the detent plunger out of its groove. I'm tempted to chuck the selector drum in my lathe and take off just enough material so it sits flush with the end cover. I guess the alternative is to try and shim the cover out a little.

This is all a little baffling as I cannot see how the gearbox could have worked in the state it is now! Can anyone supply any advice please before I resort to modification? Is there a specification for selector drum end float that I can work to achieve?

Thanks!

Keith
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1927 Scott 3 Speed Super Squirrel
1948 Scott Flying Squirrel
1951 Cyclemaster
1966 Suzuki T20
1981 Montesa 349
1985 Suzuki RG500
1999 Honda CRM250AR
Definately NO 4 strokes :-)
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jabcb
Moto GP
Posts: 4240
Joined: Mon Dec 13, 2010 4:32 pm
Country: USA
Suzuki 2-Strokes: 69 T350 thru 75 GT750
Location: southwestern Pennsylvania

Re: Suzuki T20 selector drum

Post by jabcb »

Not familiar with the T20, but that plate has the wrong type of screws.
See pics of same part listed on eBay:
https://www.ebay.com/itm/66-67-68-SUZUK ... 2054195279

Looking at the parts diagram, its either part #20 or 21. (I didn’t find part #20 so its probably incorrectly identified as #21.)
https://www.partzilla.com/catalog/suzuk ... tor-switch

So the correct part # is 02121-04121, -04128 or -06128.
Its a screw of type 02121 that is either 4mm x 12mm long, or 6mm x 12mm long. Last digit typically is for the finish.

Screws 02122-0412A or 02122-0612A are currently available — one of them likely will work.

Shop manual: T20 shop manual: https://www.oldjapanesebikes.com/mraxl_ ... /index.php

You might find that a printed parts manual is useful: https://www.ebay.com/itm/Suzuki-T20-TC2 ... 3442043360
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
gammakeith
On the street
Posts: 41
Joined: Mon Dec 14, 2020 4:50 am
Country: United Kingdom
Suzuki 2-Strokes: 1966 T20

Re: Suzuki T20 selector drum

Post by gammakeith »

Thanks for that. I was pretty certain that the screws were wrong as all the other countersunk crossheads on the bike have flat tops. Just goes to show that small errors like that can have an impact. They no longer foul now though after dressing on my surface plate.

I decided added a gasket to the neutral indicator housing to space it out a little rather than take any metal off the drum. Now there is a tiny bit of detectable play in the selector drum in that direction when its all bolted up. I sorted the plates at the other end to what I assume is stock condition. The selector mechanism now appears to work fine through all the gears. Its all very baffling but I can only assume that the addition of the wrong screws caused some selector problems that meant the owner tried modifying the stopper plates but, if so, he made it worse!

Keith
1927 Scott 3 Speed Super Squirrel
1948 Scott Flying Squirrel
1951 Cyclemaster
1966 Suzuki T20
1981 Montesa 349
1985 Suzuki RG500
1999 Honda CRM250AR
Definately NO 4 strokes :-)
dollydog
Yeah Man, the Interstate
Posts: 630
Joined: Fri Aug 11, 2017 7:09 am
Country: england
Suzuki 2-Strokes: several gt250 ramairs

Re: Suzuki T20 selector drum

Post by dollydog »

you probably know why i'm asking this, but did you impact drive the countersunk bolts/screws tight? if not, you need to :D
cheers, dd.
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.
gammakeith
On the street
Posts: 41
Joined: Mon Dec 14, 2020 4:50 am
Country: United Kingdom
Suzuki 2-Strokes: 1966 T20

Re: Suzuki T20 selector drum

Post by gammakeith »

Ha ha, yes those little screws are not coming out again! I'm now itching to get my crankshaft back so I can start to get the engine back together :P

Keith
1927 Scott 3 Speed Super Squirrel
1948 Scott Flying Squirrel
1951 Cyclemaster
1966 Suzuki T20
1981 Montesa 349
1985 Suzuki RG500
1999 Honda CRM250AR
Definately NO 4 strokes :-)
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