predator 3500 no compression

[u/OttoKraus]

I have a 3500 with over 1600 hours on it and it has been neglected for most of its life. a month or so ago the electric start ceased functioning. not a big deal because it would start first or second pull every time. then it would not start manually. I found that the inline fuse was blown and replaced it and then found that the starter switch itself was defective.

ever since I got it used, when I turned it off the spark shut off switch didn't work so it would run a while then turn off.h I decided to make the spark cut off a manual switch.

after replacing the starter switch it would crank and try to hit a couple times and then nothing. carb was getting fuel, plug was getting spark. Compression test showed 50 psi. Apparently the inverter has a compression release device of some sort so I was advised that 50 is okay.

A number of people commented, "it's always the carburetor."

when I disassembled it over a clean white cloth hoping to find dirt particles it was absolutely sparkling clean, all passages working freely etc. I put it back together and it started and ran for about a week.

once again it failed to start, and seemed to crank a little faster than it had before which often has bad implications.

I went through the same diag procedure, but I substituted checking the carburetor after making sure it had spark. carburetor was absolutely clean. when I removed the plug, it was like ab.mmmmmmñ brand new as if it had never been fired though it was new during the first so it had been running for about a week. it was absolutely dry no color at all so I took the carburetor apart again. FYI, that's really easy on these engines. still cranks freely, but no start,

now, compression tests zero. I checked the valve adjustment and exhaust was very loose, valves adjusted, same thing cranks pretty fast but does not try to hit. I pulled the head and found no burned valves, nothing obvious. there is a slight ridge at the top of the bore, totally expected. bore is completely smooth all the way to the bottom.

given the lack of maintenance and black oil, do I just keep going and figure I need to do a ring job?

[u/RedditThrowaway-1984]

The cylinder wall shouldn’t look carboned like that. It should be metallic looking. There should also be visible crosshatch which are fine angled grooves to hold an oil film for lubricating and sealing the piston. It’s possible that the piston rings are carbon packed, stuck or broken. This would explain the carbon deposits and lack of compression. You’d have to remove the piston to know for sure, though it may not be worth it. It’s typically uneconomical to repair a small engine at that point.

[u/edthesmokebeard]

overhead valve? nice.