First Series GT swingarm

A

Andy750

New member
Location
Boston, MA USA
Hello All. I have a question regarding the swingarm for the early GT. I noticed existing swing-arm the axle slots are not parallel to each other. The flats are
kind of bent a bit as well and frame and wheel axle axis are not parallel. Also, the rear mudguard has been trimmed back. Thinking it might have been in an accident and been damaged, I sourced another swingarm from Wolfgang. Upon arrival I notice it has the same conditions. Is there an explanation for this or just Breganze charm?
 

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Andy750 said:
Hello All. I have a question regarding the swingarm for the early GT. I noticed existing swing-arm the axle slots are not parallel to each other. The flats are
kind of bent a bit as well and frame and wheel axle axis are not parallel. Also, the rear mudguard has been trimmed back. Thinking it might have been in an accident and been damaged, I sourced another swingarm from Wolfgang. Upon arrival I notice it has the same conditions. Is there an explanation for this or just Breganze charm?
Click to expand...
You’ve bought an ex Evel Knieval bike! Joking apart, I would pop the spindle in and see how horizontal it is in use, might look worse than it is, may have even been made like that.
 
I,ve always heard that the stamped marks aren’t accurate to each other, but this is another level. Hopefully the end plates are at least parallel to each other, and that discrepancy won,t cause the wheel to be crooked.
 
I made a Tramel, or maybe better called a set of dividers, to check wheel alignment. I bolted one end of a couple of 50mm x 25mm or 2 x 1, both 600mm long, together and inserted a couple of nails into the other end. It's hard to run a tape from the centre of the swingarm to the wheel centre, check that both sides of the bike have this dimension equal. Try using a 200mm long plumbers spirit level across the front of the swingarm and then the wheel axle without the wheel fitted to check their level and parallel to one another. Another test is inserting a long, snug-fitting steel rod through the swingarm pivot end and another through the wheel slot and sighting them, it's a joinery term called checking for windage or winde. Or in layman's terms, twist.
 
I have used a massive vernier caliper to measure swing arm centre to wheel spindle centre (on both sides) to ensure correct wheel alignment, but truthfully even if the frame is twisted or bent, the very best way will always be to compare the front wheel to the back wheel, or get a sidecar and dont give a stuff.
CLEM
 
CLEMTOG said:
I have used a massive vernier caliper to measure swing arm centre to wheel spindle centre (on both sides) to ensure correct wheel alignment, but truthfully even if the frame is twisted or bent, the very best way will always be to compare the front wheel to the back wheel, or get a sidecar and dont give a stuff.
CLEM
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I agree. The issue here as I see it is that the rear wheel can be tilted, not ideal. It is a strange issue.
 
I think that those early swingarms without a brace between the two arms behind the spindle are prone to doing that. It induces a wallow in the roadholding.
Paul
 
Obviously a manufacturing fuck-up if 2 swingarms show exactly the same condition. Luigi disturbed the welding jig and nobody noticed for months...

piet
 
"Since I'm not a welder or machinist, is possible to "fill in" the crooked slot and then bore a correct slot to match the other side? Just curious-"

yes it is but its still a skilled job to get it dimensionally correct, so not worth it, go and buy a used swingarm, later (more normal) ones with the brace will fir,

as will SF3/3C/Jota type ones with disc brake (those two have the same part number.) not that this is relevant just interesting.
CLEM
 
CLEMTOG said:
"Since I'm not a welder or machinist, is possible to "fill in" the crooked slot and then bore a correct slot to match the other side? Just curious-"

yes it is but its still a skilled job to get it dimensionally correct, so not worth it, go and buy a used swingarm, later (more normal) ones with the brace will fir,

as will SF3/3C/Jota type ones with disc brake (those two have the same part number.) not that this is relevant just interesting.
CLEM
Click to expand...
They might fit the frame, but these are considerably longer, Clem. 40-50mm?

And... the early swingarms for the Grimeca hubs (what we're looking at here) had equal-sized slots left and right, those for the Laverda hubs had the enlargened RH slot to accomodate the sprocket carrier for the "quick release" rear wheel. A sleeve would then be required on the RH end of the axle... one bodge leading to the next.

Equal-sized slots only returned with the switch to rear discs.

Quite possible to weld up the slot and re-machine, one bastard of a job though.

piet
 
Andy750 said:
Hello All. I have a question regarding the swingarm for the early GT. I noticed existing swing-arm the axle slots are not parallel to each other. The flats are
kind of bent a bit as well and frame and wheel axle axis are not parallel. Also, the rear mudguard has been trimmed back. Thinking it might have been in an accident and been damaged, I sourced another swingarm from Wolfgang. Upon arrival I notice it has the same conditions. Is there an explanation for this or just Breganze charm?
Click to expand...

Great pictures to show the fuck ups. Sends the right side shock mount forward too.
 
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