Hi, everyone, longtime lurker here.
I came into possession (cheap!) of a Yanmar 3YM30x1 engine in externally nearly perfect condition. The first mystery I faced was why I was able to get it so cheap (from a 3rd party so no story came with it). I think I solved that mystery when I found that I could turn the engine over by spinning the crankshaft pulley -- by hand. Hmmm, not good, it's supposed to have compression! And, mysteriously, all the cylinders (apparently) lack compression.
I know I'm going to have to start taking things apart to diagnose the problem, but before I start going down low-probability channels I thought I'd ask for ideas about what might be the problem, and whether I'm on the right track.
Here are my ideas about the lack of compression, more or less in order of simple>>complicated:
1. The compression relief switch is stuck open (but I don't see such a switch on it and the downloadable manual on this site doesn't mention one)
2. The key locking the crankshaft to the pulley is sheared and the two are turning freely and independently
3. At least one valve per cylinder stuck in an open position
4. The crankshaft is cleanly and smoothly (unlikely!) broken between the pulley and the first con rod
That's all I can think of. I can't imagine all three pistons having holes in them. What else could it be?
Thanks!
Dan
I came into possession (cheap!) of a Yanmar 3YM30x1 engine in externally nearly perfect condition. The first mystery I faced was why I was able to get it so cheap (from a 3rd party so no story came with it). I think I solved that mystery when I found that I could turn the engine over by spinning the crankshaft pulley -- by hand. Hmmm, not good, it's supposed to have compression! And, mysteriously, all the cylinders (apparently) lack compression.
I know I'm going to have to start taking things apart to diagnose the problem, but before I start going down low-probability channels I thought I'd ask for ideas about what might be the problem, and whether I'm on the right track.
Here are my ideas about the lack of compression, more or less in order of simple>>complicated:
1. The compression relief switch is stuck open (but I don't see such a switch on it and the downloadable manual on this site doesn't mention one)
2. The key locking the crankshaft to the pulley is sheared and the two are turning freely and independently
3. At least one valve per cylinder stuck in an open position
4. The crankshaft is cleanly and smoothly (unlikely!) broken between the pulley and the first con rod
That's all I can think of. I can't imagine all three pistons having holes in them. What else could it be?
Thanks!
Dan