90hp 1986 J VRO, piston/head chewed, cylinder ok?

[jpbohney]

I have a singe chewed piston, margins moth-eaten, head looks like ice pick used to dig out metal. (Search "hosed") The cylinder incredibly looks ok with the exception of a tiny dink at the margin of one of the exhaust ports. I will tear the engine down, replace piston and head, but will I need to redrill the cylinder if only a tiny dink at the exhaust port. There was no loose metal in the cylinder. What would cause such a failure? Any source for a used head? (starboard side)

 

[JUSTINTIME]

Re: 90hp 1986 J VRO, piston/head chewed, cylinder ok?

i would honed the cylinder

 

[DJ]

Re: 90hp 1986 J VRO, piston/head chewed, cylinder ok?

Most likely water intrusion caused it. But make sure the carbs are rebuilt before you run it again .

Used parts here:

www.twincityoutboard.com

 

[funpilot]

Re: 90hp 1986 J VRO, piston/head chewed, cylinder ok?

Anytime you put in new rings honing is a good idea to get the cross hatch pattern needed to bed the new rings. The cross hatch files the rings to fit the bore, and most of that happens in the first hour of running.

warmly,
fp

 

[iwombat]

Re: 90hp 1986 J VRO, piston/head chewed, cylinder ok?

Have to agree there. New piston, rings (all around) and a nice hone job of all the cylinders. If all is as you say you're good to go.

In the course of honing you might find some scoring that you didn't think was there after visualy inspecting a cylinder that I'm sure is a total mess.

 

[emdsapmgr]

Re: 90hp 1986 J VRO, piston/head chewed, cylinder ok?

Sounds like part of the ring let go and wound up in the combustion chamber. I would not run the pitted head. Can cause hot spots and predetonation. When we rebuild for customers we always replace a damaged head. You might think of locating an older set of 140 heads. 1978-79 vintage. 322864, 865. There are still a lot around and the increase in compression is worth it.

 

[iwombat]

Re: 90hp 1986 J VRO, piston/head chewed, cylinder ok?

That's a pretty good call.

It sort of depends on how badly it's pitted though. Carbon deposits will fill those pits pretty quickly if they're not all that big. A few minutes with a grinding stone and a drill in the combustion chamber can restore most of the flow properties as well. Just get rid of any protrusions and smooth out the scores as best you can.

If it's badly damaged, as in gauges, then it's best to replace the head.