Finally started my 250/AOD project. When I pulled the valve cover noticed a brocken rocker and two bent pushrods. Great! Once I removed the head #2 piston has a hard gloss black ceramic like glaze on it. Anybody seen this before? Other pistons had a hard crust that appears burnt on.
Pistons with black hard glaze
- Thread starter jahearne
- Start date
Which cylinders had the rocker and push rod problems? Was one of them the glazed one?
The normal reason I see for rocker and push rod damage is when and engine sits a long time the valves rust into the guides and sometimes when you turn it over or worse yet start it quickly with starting fluid the rod or rocker gets slightly bent breaking it loose. Once a rod starts to bend even if the valve no longer drags it will keep bending with every stroke till it finally falls out. Same thing could happen with some of the rocker designs.
The normal reason I see for rocker and push rod damage is when and engine sits a long time the valves rust into the guides and sometimes when you turn it over or worse yet start it quickly with starting fluid the rod or rocker gets slightly bent breaking it loose. Once a rod starts to bend even if the valve no longer drags it will keep bending with every stroke till it finally falls out. Same thing could happen with some of the rocker designs.
Typically if its a high mileage engine the black stuff is carbon baked on from years of heat and pressure.
Soak in something that breaks up carbon and then hit with a toothbrush and green scothbrite. Try to clean tops only, be very careful not to cause scratches on pistons skirts or damage ring land area. You can get a ring groove cleaner designed to remove carbon from ring groove areas.
carb cleaner, kerosene, Coca-Cola, Hydroseal, and some stuff by Gunk have all been mentioned at one time.
Soak in something that breaks up carbon and then hit with a toothbrush and green scothbrite. Try to clean tops only, be very careful not to cause scratches on pistons skirts or damage ring land area. You can get a ring groove cleaner designed to remove carbon from ring groove areas.
carb cleaner, kerosene, Coca-Cola, Hydroseal, and some stuff by Gunk have all been mentioned at one time.
Thanks for the suggestions. The broken rocker was on an adjacent cylinder to the black hard glazed piston. The rod and main bearings look okay with not much wear. The engine is clean, valve cover, inside the timing cover nearly spotless, no corrosion anywhere. However, the cylinder walls are all scored; I can feel them with a finger nail. Burnt oil smell. Think it's a good excuse to put in a set of 255 pistons.
Good news is that the AOD & 250 block fit perfectly in my '67.
Good news is that the AOD & 250 block fit perfectly in my '67.
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