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4MV Power Piston Pin Repair

PostPosted: Sun Apr 11, 2021 4:32 pm
by Papastoy72
Decided to resurrect my first Qjet, a 7042210 Holley Reman. Yeah, I didn't know better 25 years ago. Of course, they cut the power piston pin. So I wanted to see if I could fix the pin issue.
After trying to pull it out, I came up with the following way to fix it. Sorry, didn't think to take pictures, but its fairly straightforward:

Pull off the metering rod holder with a pair of needle nose pliers. It pulls right off.
Remove the power piston retaining ring.
Using a 5/64" drill bit, drill down till you hit the steel pin or the cavity it sits in.
Using a 4 penny finish nail drive the old pin out.
The pin is 0.090" diameter, same size as a 6 penny finish nail.
Cut off the pointed end of the nail and file it flat a put a little chamfer on it.
Insert the nail with new end into the hole on the bottom of the power piston where the old pin stuck out.
Drive the nail in about 3/16". It should be plenty tight.
Now measure 0.300" from the bottom of the power piston and make a mark on the nail sticking out.
Cut on the mark, file flat and put a slight chamfer.
Put a new retainer on the power piston, insert the hanger arm assembly back on.
Done. Takes about 20-30 min. Good rainy day project.

Re: 4MV Power Piston Pin Repair

PostPosted: Mon Apr 12, 2021 9:30 pm
by 10132
LOL...talk about perfect timing! I picked up a decent core on EBay, it's a old used remanufactured 7043208 and sure enough the power piston has the snipped pin! At least the APT clip wasn't leveled off...anyway, thanks for the tip as I have to give it a try. I have thrown so many away in the past it's a damn shame.

Re: 4MV Power Piston Pin Repair

PostPosted: Mon Jun 07, 2021 6:02 pm
by rgalajda
Ya there are at least 2 different lengths power pistons with the pin in them, but they both have an overall length of 2.24 inches. ( with rod hanger ) One has a longer body that measures 1.945" and the other is shorter , 1.855" using a longer pin about .390". N ow you can pull the plug out of the baseplate to access the adjusting screw for the power piston. You guys probably already know this stuff though.