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I understand that you are only doing 'O' rings for 500/550 but someone needs to come up with a suitable replacement for 12115-300-305(See Service Bulletin no. 42) attached. These allow the later head gasket intended for later cylinder heads with the knock pins to be used on early heads.As I understand it, a nitrile 12.5mm ID x 2.0 O ring is a decent alternative. A quad ring 'x' section, might be even better but might take a bit of sourcing. (Attachment Link)
Quote from: Toko_Jo on July 15, 2023, 10:27:38 PMI understand that you are only doing 'O' rings for 500/550 but someone needs to come up with a suitable replacement for 12115-300-305(See Service Bulletin no. 42) attached. These allow the later head gasket intended for later cylinder heads with the knock pins to be used on early heads.As I understand it, a nitrile 12.5mm ID x 2.0 O ring is a decent alternative. A quad ring 'x' section, might be even better but might take a bit of sourcing. (Attachment Link) I have many suitable replacements but, it all depends on what head gasket you will use as different manufactures used different thickness
Closest I can find in Xring is 12.42 x 1.78
I always upgrade to Viton on the hundreds of SOHC engines i have built over the years