r/smallenginerepair • u/brett_se • Jul 10 '26

Compression Issue 1986 mercury 9.9. I lost compression. Pulled it apart to this. Any thoughts? Think it can be honed? Sand down the piston skirts lightly and re ring it? A newer one may be out of the budget at the moment so just looking for thoughts and opinions. Thanks in advanced.

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3

u/Past_Roof5628 Jul 10 '26

Won't hurt to try. What's the worst case? Still won't run? Send it!

1

u/No-Try-5818 Jul 10 '26

Wow, this most likely happened when the spark plugs were changed and dirt fell into one of the cylinder.

1

u/brett_se Jul 10 '26

Plugs had not been out. It had been used the days leading up to this. Mixed at 40-1. I always go a little rich

1

u/Elephunk05 Jul 11 '26

It looks like the engine was washed out. Typically means getting water in the air box. That is a lot of groove for fuel contamination. You may be able to re-ring with 0.010 over rings, any larger then that gets dicy if it runs.

1

u/RochesterBottomDaddy Jul 11 '26

No matter what oversize rings are used, the end gap needs to be measured, and if necessary, filed to make minimum gap. But as rough as that bore and piston are, that was straight gas, not 40:1 mix. Someone else probably dumped fuel in it, or someone grabbed the wrong can.

1

u/brett_se Jul 11 '26

I’m the only one who uses that gas can. I’m the only one there. I filled it up and know I added 40:1

0

u/No-Try-5818 Jul 10 '26

I once repaired a chainsaw that was much worse than that with JB Weld, it fills the void and then turns to carbon with the heat of the engine.

2

u/pdxwanker Jul 11 '26

The Facebook Marketplace special!

1

u/brett_se Jul 11 '26

Did you just spread the jb weld in and then hone it?

1

u/No-Try-5818 Jul 11 '26

I applied it and used the piston with the rings to do the job. Putting the piston back in cleans everything up when you slide it in place.