TimmyT
XS400 Addict
Compression test showed 100 psi on the left and 75 on the right. So I took it in my hands to tear the top end down. Set gas tank to PRI and remove (good to have a working petcock). Drained the float bowls and pulled the carbs. Removed ignition coils. Removed top end engine mounts. Then got into the top end. Followed the cross pattern for removal doing only fragments of a turn at a time until bolts were free, and finger loose. Each bolt was set in a cardboard jig with a co-responding number for reference. Removed the head, removed the cam chain tensioner/guides, removed the cam from the sprocket with a wire tied through the sprocket and chain to the frame. Everything came apart alright, the pistons may have came out too easy for my liking. The only thing is I need a "C" clamp to compress the valve springs for disassemble.
So all in all I have a good day of cleaning ahead of myself and another good day of rebuilding this sucker. In the interm I decided to start this forum to share photos and get pointers. There is alot of carbon deposits on the pistons and valves as expected after 20k miles. Nothing seems gouged or even scratched enough to cause a problem the only blue I see is on the piston wrist collars. what could cause my huge drop in compression. Piston rings? valve seals? I have a new engine gaskets waiting for the install. Pointers are appreciated, these measurements will take some time I guess Im hoping to find a shortcut. I was going into this with the assumption everything is still good on the inside but too much carbon is not allowing valves to seat properly. Sorry photos are too large for now I will upload after resize so they fit.
So all in all I have a good day of cleaning ahead of myself and another good day of rebuilding this sucker. In the interm I decided to start this forum to share photos and get pointers. There is alot of carbon deposits on the pistons and valves as expected after 20k miles. Nothing seems gouged or even scratched enough to cause a problem the only blue I see is on the piston wrist collars. what could cause my huge drop in compression. Piston rings? valve seals? I have a new engine gaskets waiting for the install. Pointers are appreciated, these measurements will take some time I guess Im hoping to find a shortcut. I was going into this with the assumption everything is still good on the inside but too much carbon is not allowing valves to seat properly. Sorry photos are too large for now I will upload after resize so they fit.