small oil leak
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2nd Gear
Joined: Jul 2007
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small oil leak
i've got a 1945 74" flathead and after i came from the local gathering last night i noticed thats it's seeping on the backside of the front cylingder right around the head. could it possibly be a slight oil leak or a bad gasket or what could it be? if it is a bad gasket, what do i need to replace, just the gasket or do i need to tear it down and have the head and jug milled? any input would be greatly appreciated.
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2nd Gear
Joined: Jul 2007
Posts: 6
Likes: 0
RE: small oil leak
i know older bikes have a tendency to leak and im welll aware of it happening on mine. but i've been riding the bike for a few weeks now and this is the first leak that has surfaced. and just for reference, im still figuring stuff out about the bike seeing as though it's 39 years older than me and it's kinda uncharted territory for me. and with it being at the head gasket is the only reason why it concerns me as much as it does. and it started to sputter pon me last night also. it hesitated like it was low on gas and when i pulled the reserve up, it gained steam and came back to life and ran fine. but when i checked my fuel level, i was over 1/2 tank on each side. any ideas on this preoblem?
Road Master
Joined: Jan 2007
Posts: 770
Likes: 2
From: East NM
RE: small oil leak
You might want to start by running a compression test. If it's very high on that cylinder, something is leaking oil into the cylinder. Could be a bad ring, cracked ring land on the piston or a loose valve guide. The oil has to be coming from someplace and there is none pumping into the head on a flathead.
If your compression comes out a little low, you may be seeing fuel resedue instead of oil. Try loosening the head bolts and then retorquing them. Flatheads, especially the aluminum ones tend to get out of shape if the engine ever gets really hot or suddenly cools down like when you are caught in a rainstorm. This is sometimes correctable by releasing the pressure then retorquing.
If the compression is normal, you might not have a problem. If the engine has been rebuilt using OEM cork head gaskets, it was common practice in the old days and some old school school mechanics still coat the gaskets with grease before installing them. This made the gasket stick in place and softened the surfaces for a better seal. Whne the head is tightened down and the engine is run, the exess grease squeezes out ant then melts.
If it turns out the gasket is leaking and can't be corrected, clean off the head and barrel and check for flatness with a good straightedge. If any milling needs to be done, chances are it will be only the head. If they have to take off more than .010, it would be a good idea to get both heads done to keep the compression in balance.
If your compression comes out a little low, you may be seeing fuel resedue instead of oil. Try loosening the head bolts and then retorquing them. Flatheads, especially the aluminum ones tend to get out of shape if the engine ever gets really hot or suddenly cools down like when you are caught in a rainstorm. This is sometimes correctable by releasing the pressure then retorquing.
If the compression is normal, you might not have a problem. If the engine has been rebuilt using OEM cork head gaskets, it was common practice in the old days and some old school school mechanics still coat the gaskets with grease before installing them. This made the gasket stick in place and softened the surfaces for a better seal. Whne the head is tightened down and the engine is run, the exess grease squeezes out ant then melts.
If it turns out the gasket is leaking and can't be corrected, clean off the head and barrel and check for flatness with a good straightedge. If any milling needs to be done, chances are it will be only the head. If they have to take off more than .010, it would be a good idea to get both heads done to keep the compression in balance.
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