Picture of blown piston circlip

[h_lankford]

Thanks to this boards help, I replaced my blown engine with a rebuit powerhead last fall. I finally got around to a full autopsy. Here are the pictures. 1986 3 cyl Johnson 60 hp. Middle piston circlip problem. My "advisor" tells me that this engine's middle cylinder runs hot and the piston pin hammers the softer piston until something finally gives. No signs of blue/lack of oiling. Only 500 or so hours on it. Max rpm 5400. Whadd'ya think? Harvey

 

[h_lankford]

Re: Picture of blown piston circlip

Second picture with slipped circlip. Both ends of the piston pin had opened up the side of the piston. I may need to send this pictures enlarged. Double click on it and it should be larger.

 

[Walker]

Re: Picture of blown piston circlip

Never seen that before. First though in my mind is a manufacturing defect to allow slop on the wrist pin.

 

[R.Johnson]

Re: Picture of blown piston circlip

I always seat one circlip first, push the pin up to the clip just lightly, then seat the second clip. It look's like those clip's were never properly seated, if I am looking at those photo's correctly.

 

[Dhadley]

Re: Picture of blown piston circlip

What you're seeing is not that unusual in a motor like that (49 cid), that was being lugged. The middle cylinder tends to run the hottest and the lugging creates even more combustion heat. With that much heat and strain it's not unusual that the pin will pound out the boss. Once the boss has pounded out or becomes elongated the clip(s) can / do move.

To prevent this from a repeat performance, get rid of any heat sources that are unusual. Get the top rpm up, use the correct Champion plug, use fresh 87 octane, good oil and make sure the cooling system is at it's best.

 

[ezeke]

Re: Picture of blown piston circlip

While it is not in the actual list, the engine is of the type covered by OMC Service Bulletin 2276. If the tell-tale outlet is located at the bottom of the engine, it should be moved to the top.

This was to eleminate air trapped in the cooling system that caused overheating and damaged the engine and electrical system.

The same information is published on page 77 of the Rapair Trouble Shooting Guide found at "Rapair.com". Navigate to "Product Information", then to "Downloads". Be patient with the download - it is a large pdf file.

 

[h_lankford]

Re: Picture of blown piston circlip

the telltale was located in the middle of the exhaust chest.

On the replacement /rebuilt powerhead i received, there was none at all ( must have been earlier model) so I installed one at the top of the chest.

I think the problem with my original set-up was lugging as Dhadley said. And the heat issue made the center cylinder more problematic.

With 4 people in the boat, it took a while at 3000 rpm before it would get up to 3500 and be on plane climbing eventually to 5000 and over. On really hot days 5000, cool days 5400. I did drill holes in the prop to help the hole shot but it needed a different prop altogether. The one now is 4 blade composite and really makes a big improvement in acceleration, therefore no lugging, really pops outta there.

Thanks for everyone's comments. Harvey