I have a 1978 FLH, a friend of mine talked me into isolating the primary from the motor oil so the primary oil is not circulating through the engine. But now there is pressure in the primary coming from somewhere and I can't keep the primary cover sealed well enough to keep it from leaking. Any ideas on how to fix.

Might be coming through the main bearing behind the motor sprocket. When I closed off my '78 FLH I vented it through the top hose connection.

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As pococj said no matter what you have to vent it and did you disconnect the feed and return lines? I did mine several years ago and used the chain oiler line as a vent . I ran it up under the seat. the only issue i had is I had to change the clutch to a kevlar wet or dry and because of the synthetic gearcase oil I get some seepage through the primary gasket,not bad just annoying

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