Sudden loss of compression
#1
Sudden loss of compression
Hey, just picked up a 1976 FXE as a second / project bike. Previous owner refreshed the top end then never installed the gas tank or ran it, it sat for 5 years under a carport afterwards.
Got it home, mounted tank fuel lines etc. new battery & she fires right up and runs awesome. I was taking it real easy warming her up and breaking in easy,changing fluids etc, etc.
Today I took for a ride and everything was great. The after 3 miles rear cylinder started popping & then suddenly it sounded like an exhaust leak at the rear cylinder. Now she's pretty much running on the front cylinder. Compression is 110psi front & 50 psi rear. Checked the push-rods and they seem normal.
Maybe someone has seen rebuild failures similar? I realize I need to tear it apart but wanted some past experiences with Shovels as most of my tear-down experience is on Evos. I have a manual, tools and decent wrenching experience. Just seems to me with the leaky hissing sound that it may be a bad seal in the head, otherwise would it be a valve, rings, or worse a HOLE in the piston? Something else?
Thanks in advance.
Got it home, mounted tank fuel lines etc. new battery & she fires right up and runs awesome. I was taking it real easy warming her up and breaking in easy,changing fluids etc, etc.
Today I took for a ride and everything was great. The after 3 miles rear cylinder started popping & then suddenly it sounded like an exhaust leak at the rear cylinder. Now she's pretty much running on the front cylinder. Compression is 110psi front & 50 psi rear. Checked the push-rods and they seem normal.
Maybe someone has seen rebuild failures similar? I realize I need to tear it apart but wanted some past experiences with Shovels as most of my tear-down experience is on Evos. I have a manual, tools and decent wrenching experience. Just seems to me with the leaky hissing sound that it may be a bad seal in the head, otherwise would it be a valve, rings, or worse a HOLE in the piston? Something else?
Thanks in advance.
#3
#5
sure it bottomed out and had no place to go so it went to the side ( bent pushrod )
you will be in a box if you dont remove both heads just to check, also i would replace the lifer roller and even the hydraulic unit as they both were maxed out and just might not work correctly again -- jz
you will be in a box if you dont remove both heads just to check, also i would replace the lifer roller and even the hydraulic unit as they both were maxed out and just might not work correctly again -- jz
#6
sure it bottomed out and had no place to go so it went to the side ( bent pushrod )
you will be in a box if you dont remove both heads just to check, also i would replace the lifer roller and even the hydraulic unit as they both were maxed out and just might not work correctly again -- jz
you will be in a box if you dont remove both heads just to check, also i would replace the lifer roller and even the hydraulic unit as they both were maxed out and just might not work correctly again -- jz
OP , the bike have hyd. or solid lifters in it ?
#7
Has hyd lifters.
I just removed the rear head to have a look. My head gasket is burned up near the intake. When I removed the intake manifold, I found the rear seal (big o-ring) was pinched off with 1/2 of it flopping around inside. I believe that the heavy detonation due to the intake leak was the culprit to the fried gasket.
Now next the pushrod & valves. The valves look fine, matter of fact they look as new as the previous owner claims, they look like they have the 5 miles I put on them. The pushrods are original according to the last owner and I believe they are and were bent before the refresh.
Rewind - The reason the last guy rebuilt the top end was due to an air breather mounting bolt that got sucked into the rear intake and jammed into the intake valve. The pushrod in question was bent by this incident and was installed back where it was originally.
So, I plan to replace the pushrods, head gasket and give her a whirl.
I just removed the rear head to have a look. My head gasket is burned up near the intake. When I removed the intake manifold, I found the rear seal (big o-ring) was pinched off with 1/2 of it flopping around inside. I believe that the heavy detonation due to the intake leak was the culprit to the fried gasket.
Now next the pushrod & valves. The valves look fine, matter of fact they look as new as the previous owner claims, they look like they have the 5 miles I put on them. The pushrods are original according to the last owner and I believe they are and were bent before the refresh.
Rewind - The reason the last guy rebuilt the top end was due to an air breather mounting bolt that got sucked into the rear intake and jammed into the intake valve. The pushrod in question was bent by this incident and was installed back where it was originally.
So, I plan to replace the pushrods, head gasket and give her a whirl.
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#8
you should take the two heads out side and turn them upside down - put something ( thinner - parts washer fluid - gas - ) out side and in the shade and leave it an hour - if the fluid has gone into the port than you need to have that taken care of - the valve or the valve job is not good -- jz
#9
you should take the two heads out side and turn them upside down - put something ( thinner - parts washer fluid - gas - ) out side and in the shade and leave it an hour - if the fluid has gone into the port than you need to have that taken care of - the valve or the valve job is not good -- jz
#10
OK, did the leak by test on the valves by using gasoline mixes with Marvel oil for coloring. After waiting 1 hour - both heads are good to go with no leak-by whatsoever. Valve job is good, but assembly was very bad.
The head, valve, & cylinder work was all performed by a good reputable local shop.....assembly was by the previous owner.
Thanks again jz for the pointers.
The head, valve, & cylinder work was all performed by a good reputable local shop.....assembly was by the previous owner.
Thanks again jz for the pointers.