alum. piston pin tolerance

[alaska jd]

Hey there again guys. My question is this. Should the piston pin on aftermarket alum pistons (for a 41' B)still be a "thumb push" fit? They a very very tight and plan on honing the piston just a little to make them fit. Any ideas. They are thumb push fit on the original cast pistons just like the book says. Thank for all the help.

 

[Mike M]

Did your pistons come with the pins you are using ? If so they are likely the fit they need to be.

 

[teddy52food]

If they are new, they should be the right fit. Just warm them up a little & they will fall out.

 

[alaska jd]

The pins are new and the alum. pistons are new also. came in a set. pins are way to tight. if i warm them up wont the tolerance be to tight for oil lubrication? planned on honing the pist a litte. don"t have to worry about getting them apart if i cant get them together in the first place. anyone against honing the piston???

 

[F-I-T]

The aluminum piston and pin sets that I have installed had the pins pretty tight when dry. Some of my old Motors manuals and a good, very old automotive machinist friend of mine said that the pins should just drift through slowly by gravity if they are first dipped in clean motor oil. Same for the wrist pin bushings in the rods, an item a lot of people skip during an overhaul then wonder why they have wrist pin slap down the road. Those bushings should be fitted and honed to a point just as the piston pin bores.

 

[Glen D Anderson]

Typically piston pin to bore clearance is .0002" to .0007" depending on application..........which is less than the average caliper can measure accurately.......so, unless you have proper measuring tools, getting the exact measurement will be impossible..........


With the clearance being on the low end of the scale on a new piston, it can be difficult to get the pin started.........make sure there are no burs in the bore of the piston.....then, using red "Scotchbrite" chamfer the edge of the bore to allow for easier "starting" of the pin........

Sometimes it helps to cool the pin(dry ice or freezer will work) and pre-heat the piston with hot water before assy........lubricating the bore and pin also helps.........the key is not to fiddle with the pin too long trying to install it otherwise the heat from your hand alone can cause the pin to expand making it even more difficult to install..........

 

[alaska jd]

Thanks for the feed back you guys. I think I'll give the pistons a slight hone and then try again. Thanks for the info, always helpful.