79 Johnson 100HP problems

[mrodey]

All right gentleman, I have some problems and need some help. Bear with me, it might take a while. So my engine is very hard to start, sometimes it does and sometimes it dosn't fire up. I took it out to the bay and got it started and I couldn't get it above about 5mph. I noticed that the spark wire wiggled out of the ignition coil. So thinking that was the problem, I screwed it back in and it seemed to run a little better. I could get going about 20mph. So today I was trying to start it in my driveway. After many unsuccessful tries, I ran a compression test, the top right cylinder had no compression. I took the cylinder head off and noticed that the left side of the piston was missing bits, you could see the ring. Also the inside of the head was tore up as well. Like a bolt got lose inside there and wrecked havok. Here comes the stupid question, could that be the reason that it dosn't want to start? Any ideas how to get her running again?

 

[fishinhole]

Re: 79 Johnson 100HP problems

YES! ENGINE IS TOAST, DO NOT PUT MORE MONEY IN, ITS NOT WORTH IT UNLESS YOU WANT A REBUILD, SORRY TO LET YOU KNOW THIS, BUT IT WILL JUST KEEP GETTING WORSE UNTIL IT DOES NOT RUN AT ALL

 

[Joe Reeves]

Re: 79 Johnson 100HP problems

Mrodney.... Those engines around that year of manufacture had what was called "High Ring Pistons". There was only a few thousands of material between the rings and the top edge of the piston.<br /><br />This design was okay until the quality of gasoline went down, then the top edge of the piston would curl upwards which allowed the rings to grab the ports, obviously resulting in piston damage, cylinder wall scoring etc.<br /><br />Your engine now requires a major overhaul, piston replacements, carburetor rebuilding etc etc. This usually runs in the amount of $1500, $2000.<br /><br />Don't waste your time attempting to get the engine to run properly..... with that blown piston, it's just not possible.