polaris sells a aftermarket head gasket its thinner than stock about $85.00 avarage but you might have to change the jettting alittle did you do a compresion test on yours if so what was it? i have a friend thats as 87 400 also he has 30,000 miles on it he as 85 commpresion on both cyclinders time for a ring job
newer indy 500s come stock with a Aprox .0025 metal head gasket like my 2002. Comatec Hi Comp gaskets found in a High Perf magazine are .0045 i think. Old stock gaskets are prolly at least .005 but i never measured. I know of nobody that makes thin gaskest for the 400s. Perhaps a 500gasket could work but most likely not.
go down to the dealer and have them measure some for you and see what you get. mabye a 440 gasket would work. Or just mill it.
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