engine runs zero comp. rear clyinder
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Stage III
Joined: May 2012
Posts: 3
Likes: 0
From: lathrop,ca.
engine runs zero comp. rear clyinder
looking for some suggestions. 1980 fxwg rear cylinder no compression. See push rods moving up and down has solid lifters air is coming out around lifters, was rebuilt a few years back. looked in spark plug hole see piston going up and down don't see any holes. poured oil in no change. when bike is running feel air coming out exhaust not as loud or hot as front, when riding it only notice a little vibration. to me sounds like hole in piston. does not smoke with hand over back pipe it will suck every other fourth stroke. any ideas?
Road Master
Joined: Apr 2012
Posts: 979
Likes: 38
From: new orleans,la
bent valve-- burnt valve - trash between valve and seat - oh its a vavle issue -- just pull the head - your gonna have to anyways -- you could take out the push rods and put air pressue via the spark plug hole from a compressor and it will tell you if the valve is leaking --- from what you say -- pull the head off -- 1 last item -- IF it holds pressure take the rear lifter block off and see if the tappet roller went south... i saw a dude install a andrews "B" in a 69 shovel and my last words were -- replace the rollers -- nahhh there ok -- after he drove it home from the blue ridge mountains it sounded like yours -- yep intake roller gone and that brand new cam -- history .... IF it did destroy the cam get a SIFTON #116 .400 lift more power than a andrews J,A,B and the lower lift makes the valves and guides live longer.. the only thing with the new siftons ya have to make sure the cam gear is in alignment with the key groove.. out of 10 new siftons 4 will have to be re aligned. i just bought a brand new in the box #101 (55Q) yep had to align it-- its now in a friends 1976 shovel and runs perfect --
Club Member
Joined: Mar 2009
Posts: 66,115
Likes: 51,405
From: Niles Canyon Ca.
Blowing around the lifters ? Getting any smoke or excessive blow by coming for the crank case breather ? Busted rings will do what your describing if the valves aren't too tight on the rear . Need to do a cylinder leak down test on it , tell you exactly where the problem is .
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Stage III
Joined: May 2012
Posts: 3
Likes: 0
From: lathrop,ca.
It has sifton cam do not know what lift. If it was rings I think putting oil in cylinder would of build up compression at least a little. The fact that it sucks at end of pipe maybe exhaust valve? would a intake leak cause a hole in piston? what I don't understand is no smoke plug looks like it's firing fine.crank case breather no excessive oil. With throttle wide open and gauge in hole the only place I here air coming out is around back lifters with push rod tube clips out and bottoms pushed up.
Road Master
Joined: Apr 2012
Posts: 979
Likes: 38
From: new orleans,la
remove the push rods --- put compressed air to the cylinder -- listen for a hissssss either out the intake or the exhaust ,or if it blows into the bottom end -- what was the letter/number on the cam?
like 412 or 116 ?? i'll bet its a 112 most common cam ---
like 412 or 116 ?? i'll bet its a 112 most common cam ---
Club Member
Joined: Mar 2009
Posts: 66,115
Likes: 51,405
From: Niles Canyon Ca.
You can have a pencil line grove on the piston wall and not see it and the oil trick won't help . Do the leak test with air in the cyl. you'll know quick exactly where the problem is .
Road Master
Joined: Apr 2012
Posts: 979
Likes: 38
From: new orleans,la
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Club Member
Joined: Mar 2009
Posts: 66,115
Likes: 51,405
From: Niles Canyon Ca.
I use photobucket , much easier than dicking around with the software in here and the picture is bigger . If your talking about a signature picture like my shovel open your user CP and follow the instructions there , those you have to do it their way
Last edited by TwiZted Biker; May 27, 2012 at 10:41 PM.
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Thread Starter
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Stage III
Joined: May 2012
Posts: 3
Likes: 0
From: lathrop,ca.
you were right it was the valves. the rods were to tight backed them off a little to much rattle but it is firing out of rear cylinder.Took it for a ride no vibration. I must not have tubes in right leaking a lot of oil from top. have to wait tell morning to adjust rods.
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