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6th Gear
Joined: Apr 2012
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From: Tennesee
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Got a 78 shovelhead keeps fouling out front plug i have completely rebuilt top end s&s pistons .20 over hade heads completely rebuilt valves,seats etc..seems like oil is getting by cause it is caked on spark plug once its fouled i babied it and keep plugs n it for over 1200 miles no problems with back cylinder i have torn down front cylinder and had machine shop check the valves all is ok with the valves took piston cylinder to machinist found to have a oil ring worn out he honed out cylinde and went with .30 rings got it all back together and same **** about 150 mile down the road and gotta change a plug i am fairly mechanically inclined but i am stumped i have changed to different oiling setup where it has seperate lines for each cylinder to prevent front head starvation upon startup and no luck i need someone that has messed with these engines b4 compression is same on both cylinders please help need fresh outlook also have s&s carb
Club Member
Joined: Mar 2009
Posts: 66,106
Likes: 51,387
From: Niles Canyon Ca.
Couple things here , first shovels are over oiled on the upper ends from the factory so your way over doing with your setup they don't starve believe me that bullshit is a fairy tale with a shovelhead . That was left over from the old pan guys who would trash rockers on those , shovels got a much better oil pump and rocker arrangement . I'd suspect right off your flooding the guide area and it's gotta go somewhere .
You can pull the fitting for the 1/8" oil like on the cases and solder the small port closed the drill a .060" hole to choke the oil supply down so the rocker boxes don't flood like they are prone to . ( one of the reasons shovels seen to leak a lot on the uppers ) . I'd do this anyway .
Did you have or did the shop put seals in ? and did they do it correctly for your cam lift ? 30 seconds running not done right and the seals are gone . Also did they size the guides correctly ? Some places will ream a little loose so they won't have come back problems from guys who won't do a proper break in which is most of them .
You may have had the valve's done but a lot of the old heads can be damaged during valve jobs by not very knowledgeable shops , the clearance fit around the guide in the head can be enlarged or egg shaped a bit and oil will seep around the guide after it heats up , happens more often than you think . One out every 4 shovels I see have this going on to some degree .
Way to ckeck is clean plugs and ride the bike a few miles to get her up to temp , park her wait a few minutes and pull a plug and look at the tops of the pistons . Dull carbon blacked or shiny with oil ? If you see oil drop the pipes & carb and look at the guides and see if they look wet on the outsides , if so it's loose guides in the heads .
You can pull the fitting for the 1/8" oil like on the cases and solder the small port closed the drill a .060" hole to choke the oil supply down so the rocker boxes don't flood like they are prone to . ( one of the reasons shovels seen to leak a lot on the uppers ) . I'd do this anyway .
Did you have or did the shop put seals in ? and did they do it correctly for your cam lift ? 30 seconds running not done right and the seals are gone . Also did they size the guides correctly ? Some places will ream a little loose so they won't have come back problems from guys who won't do a proper break in which is most of them .
You may have had the valve's done but a lot of the old heads can be damaged during valve jobs by not very knowledgeable shops , the clearance fit around the guide in the head can be enlarged or egg shaped a bit and oil will seep around the guide after it heats up , happens more often than you think . One out every 4 shovels I see have this going on to some degree .
Way to ckeck is clean plugs and ride the bike a few miles to get her up to temp , park her wait a few minutes and pull a plug and look at the tops of the pistons . Dull carbon blacked or shiny with oil ? If you see oil drop the pipes & carb and look at the guides and see if they look wet on the outsides , if so it's loose guides in the heads .
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6th Gear
Joined: Apr 2012
Posts: 11
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From: Tennesee
I will add that if u ride to hard tends to loose front head gasket And then again rear cylinder still holdn good pipes r 40" drag specialty no baffles i even tried conversion cones but after u warm up give throttle and let off as rpm comes down starts smoking on that front cylinder i will look n2 that fitting i seen to add n line with oil line to choke doWn
Club Member
Joined: Mar 2009
Posts: 66,106
Likes: 51,387
From: Niles Canyon Ca.
The cones don't really help the shovel they like 1-3/4' straight drags , the way the heads are ported is why . 78's had issues with the cylinder head gasket surfaces being cut wrong at the factory , some of them had almost a .007" plus taper instead being flat and they ate head gaskets , been a lot of years since I ran across one but ???? . I'd also look at the heads & gasket surfaces with a straight edge looking for warps or dips and make sure the threaded inserts aren't pulled up above the mating surface . A few thou and they'll let go run hard .
Keep me posted and repost this over in the shovel thread , there's a couple of us who haunt in there that are real sharp on these old beasts .
Keep me posted and repost this over in the shovel thread , there's a couple of us who haunt in there that are real sharp on these old beasts .
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6th Gear
Joined: Apr 2012
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From: Tennesee
Thanks for all help i am gonna check all above suggestion i was told from guy who built lower end that it has mild cam in it but i have never had a single problem with rear cylinder and head since the rebuild and again thanks
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