OK to Re-Use Piston?

[45Auto]

Would it be OK to re-use this piston if I used some JB Weld to re-build the ring groove? It's the #4 piston in a 1986 5.7 with 630 hours.

The motor idled and ran smooth, but couldn't reach max RPM. It's the starboard engine on a 30' Sea Ray with twin 5.7's. Port motor can turn over 5000 RPM on 19" High Five prop, this one couldn't quite reach 4000 and was obviously down on power.

Compression was 150-160 PSI in all cylinders except 110 in #4 & #6 (center cylinders on right bank). A squirt of oil didn't change it in either cylinder, I figured a blown head gasket between the cylinders.

Pulled the head and saw the beat-up top of this thing. Cylinder and cylinderhead look good. All other pistons and cylinders look good. No wear ridges at all in any cylinder.

Looks like it's obvious why this cylinder (#4) was low. Looks like losing one compression ring costs about 40 PSI. A little more than half the top ring is missing. I'm surprised that there were no signs of blow-by on the piston walls or skirt. I'm guessing something was dropped down the carb or a spark plug broke? The ate-up part is directly in front of the plug, could have been detonation that originally ate it up but all other pistons look like new.

Looks like cylinder #6 was low because of a leaking intake valve.

#4 Piston:

#4 Piston Again:

#4 Combustion Chamber:

#6 Combustion Chamber:

Official Engine Removal Apparatus:

 

[stonyloam]

Re: OK to Re-Use Piston?

If I were doing the rebuild, no way!!

 

[WizeOne]

Re: OK to Re-Use Piston?

If I were doing the rebuild, no way!!

Regardless of who is doing the rebuild, NO WAY, JOSE!

 

[cr2k]

Re: OK to Re-Use Piston?

How does the cyl. look? Is it scratched? You may have to bore it.

You could re use that piston, if you like doing the job so much you would want to do it again, real soon.

 

[mkast]

Re: OK to Re-Use Piston?

My sister's husband's uncle's nephew"s brother, who washes boats at the marina said, "No Problem." Just make sure to allow for expansion around the JB Weld.

 

[TilliamWe]

Re: OK to Re-Use Piston?

45Auto, I get the joke! Sure, you can reuse Broken Pistons any time you want!

 

[WizeOne]

Re: OK to Re-Use Piston?

45Auto, I get the joke! Sure, you can reuse Broken Pistons any time you want!

You think we've been had Tilliam?

 

[45Auto]

Re: OK to Re-Use Piston?

 

[picklenjim]

Re: OK to Re-Use Piston?

Are you serious? If the cylinder isn't damaged you could get by with a hone job and new piston but there's no way that piston is good for anything but an ashtray.Your intake valve is probably ok.If it was leaking it would have been backfiring through the carb when that cylinder fired.Lay the head with the combustion chambers facing up. Fill the chambers with gasoline and then look into the ports to see if the valves are leaking.If so just have a valve job done on them beings their off already.You should have the heads resurfaced also.That's a very common piston which should be pretty cheap.You don't need to get it from mercury or it will be expensive.Should be able to get it from an auto parts store or machine shop.Have them mic it so you get the correct size in case it's been bored before.Also they will have to install the connecting rod on it.

 

[TilliamWe]

Re: OK to Re-Use Piston?

You think we've been had Tilliam?

I know you have been had Way to go 45!

(For those of you clueless, please find the thread from earlier today, where the guy wants to reuse a piston with one of the skirts broken off!)

 

[Don S]

Re: OK to Re-Use Piston?

 

[airdvr1227]

Re: OK to Re-Use Piston?

That hook in your lip looks painful.

 

[rs2k]

Re: OK to Re-Use Piston?

I'll let you use that piston if you let me use that "Official Engine Removal Apparatus"