The GT550S: then and now

The GT550 featured in Suzuki’s portfolio from 1972 through to 1977 with some final B models being discounted and available as late as 1979. Aesthetics switched year-on-year, but the bike only ever changed in a few areas. 1973-on K models all came with disc front brake along with polished alloy outer cases and Ram-air cowling instead of gunmetal paint. The biggest change came on the M-model. Suzuki moved from alloy cylinders with iron liners and opted for chrome-plated bores. So it’s not possible to over-bore the post-1974 barrels. If the chroming is worn it’s possible to get the plating renewed which is not cheap. Pistons for the M onwards model come in one size only; the earlier models can be rebored but Crooks Suzuki warns it’s expensive! Con rods are no longer listed for the 550, making refurbishment of a dead engine difficult. Suzuki said the linked exhaust downpipes fitted to the early GT750 and GT550 delivered greater torque: it also offered more places for exhaust residue to escape from! In the UK at least, the link pipes were deleted from the 1974 M models but were still used in other markets. Trim parts are no longer listed so it’s online and jumbles to find some. There is limited component commonality with the GT380 and GT750 but before buying it is worth checking parts books. Failure of the vacuum tap can kill a GT. If the tap doesn’t close fully due to age or debris, petrol can leak past the carburettor float valves into the crankcases. Similarly long term immersion in petrol will take out the crank seals and may even wreck the crank journals. Buying a GT550 now? Look for a good, quiet, running engine but avoid J models missing the original front drum (classic racers nab ’em) as they are pricey to replace!