Do rings lose their compression

[KustomKulture62]

Bought an engine that been sitting unused for a long time its also been fully rebuilt with the head and sump off and am wondering would I need to replace the piston rings or would they be as good as the day they were installed.
Is there anything else I should replace on an engine that's been sitting unused, I have it fully dismantled for reassembly.

[zuffen]

I would be checking the bores for corrosion and valves for operation. If the bores are clean and valves moving when turned with the plugs out I'd give it fresh oil and turn it over to get oil pressure.

Throw the plugs back in and fire it up.

Rings don't loose tension from sitting.

[steve the ford guy]

If the engine history is unknown and you don't have access to the guy who assembled it, plus just the fact it's not together would ring alarm bells for me. In fact, there's a high possibility the bores werent honed and the rings weren't gapped and bearing clearances werent checked etc, and there's many other mistakes that could have been made at the same time as well, if your not sure about all these things, it would be wise to strip it back down and start over.

[FRANK BASILE]

If the engine history is unknown and you don't have access to the guy who assembled it, plus just the fact it's not together would ring alarm bells for me. In fact, there's a high possibility the bores werent honed and the rings weren't gapped and bearing clearances werent checked etc, and there's many other mistakes that could have been made at the same time as well, if your not sure about all these things, it would be wise to strip it back down and start over.

Pretty much good advice with the "unknown" especially if an amateur rebuild and you do not know the expertise of the builder . Some clues though . Head is off , look for a ridge on the top of the bores , also the bores should have a visible crosshatch pattern . This would tell me that someone has not just slapped rings on without complete thought. No ridge can have you safely remove pistons . Are they new pistons ? . If not, check the piston ring side clearance also . Ring gap is the other issue , unless the rings are removed and checked in each bore it is a bit difficult as far as I know to properly check . Piston /rod out lets you check the crank and bearings . clearances can be re checked .

From past experience I can vouch for what happens with insufficient ring gap . The rings Bust . And one ring actually took a chunk out of the bore .

[Big G]

It sounds to me you need someone experienced in engine rebuilding to have a look before you put it back together.

[steve the ford guy]

the reason I made a comment is I once bought a poorly assembled 302W on ebay, it had new 40 thou pistons and was a rebored short engine for only $200 and was a "mexican" block, even with the problem it was a good price I thought, the problem with it was one of the conrods had been installed with the crank journal radius side facing the wrong way, it might have caused damage to the crank journal if it had stayed assembled and been fired up

[FRANK BASILE]

It is a good comment Steve. Risky buying an engine that has been rebuilt from someone unknown to you without reputation , that has not been fired up and shown running . My example was a Y block that was "rebuilt" [not by me] . In a purchased Customline . The vehicle had a twin exhaust system . One tail pipe would run light grey after a highway trip [back in the days of good leaded petrol] . The other dark This side would puff blue smoke after flooring from idle . I simply thought valve stem seals /worn guides and isolated one cylinder on the particular bank due to plug colour. The head looked ok ,but I swapped it anyway and was dismayed . . I took it to someone who shoved a bore o scope down the plug hole and was shown the chunk missing from the bore . I rebuilt a spare Y block myself and when the old was pulled down , every piston had a busted compression ring , the one that did the damage was intact but warped and had stuffed the piston ring land . . My rebuild ran ok .