Pond Boss Forums AERATION Systems questions Gast 74R rocking piston pump rebuild question

I have a used Gast 74R rocking piston pump on my bench to install a new cup seal before putting it into service.

The cylinder walls show little wear but there’s a band of hard black residue buildup which appears to be the result of material transfer from the cup seal to the cylinder walls. I tried to rub it off with a cotton cloth dipped in either acetone or isopropanol without success.

I’ve searched both forums and YouTube but none of the rebuild guides mention cleaning the cylinder walls. They just slap a new seal on and call it good. Having rebuilt a few engines this would leave me feeling like I’d left some pumping efficiency on the table.

Has anyone tried something more aggressive to clean the cylinder walls? I’d appreciate any info or suggestions folks may have before I reassemble the pump.

Try cleaning the cylinder walls with naptha. Lighter fluid? or some other rubber solvent. Last result fine emery paper.

Do what Bill suggests, then I'd hit the cylinder with a cylinder hone to take out the vertical scratches. Same as in a gas motor, you don't want scratches in the cylinder when you are putting new rings in it.

Some rebuild kits come with new cylinder sleeves too. I don't think you can buy just the sleeve.

Thanks for the ideas everyone, I finally got back to the pump this morning after a few family matters I had to deal with.

I tried a few more solvents with no luck so moved on to a fine Scotch Brite pad. Cleaned it right up without leaving any scratches on the cylinder walls. With the cylinder cleaned the hardest part of the rebuild was installing both flappers straight.

Okay - good idea for using the Scotch Bright pad. It is something to keep handy. Thanks for the update.