Pressing OMC pistons.

[duurmeehr]

I need to press new pistons on my 1980 35HP Evinrude. The manual says I have to have a special jig to keep from distorting the pistons. Can someone shed some common sense truth to this statement and tell me how a poor country boy can do it without one? I have a press and about every imaginable tool known to man.

 

[boobie]

Re: Pressing OMC pistons.

If you can find a pic of the jig, you can make one out of a wooden block. I did that yrs ago.

 

[orbanp]

Re: Pressing OMC pistons.

I saved that picture sometime ago, not sure which motor it refers to, but if you need to press in/out the piston pin, this is the way to do.

Good luck, Peter

 

[bob johnson]

Re: Pressing OMC pistons.

I think that to cool the pin in the freezer, and warm the piston is hot water, would make life even easier


bob

 

[F_R]

Re: Pressing OMC pistons.

Does that year pistons have one side marked "L" or something similar to indicate one pin bore is tighter than the other one? If it does, you don't need no durn jig. Insert the pin through the loose side, pressing it into the tight side. If using a press, support the tight side on the press plate and press the pin into it. Yes, it will go together easy if you heat the piston a bit.

Removing the pin is a similar operation if you intend on saving the piston. Supported tight side down, press the pin all the way through it.

 

[duurmeehr]

Re: Pressing OMC pistons.

That picture looks exactly like the jig the manual has in it. Originally I was thinking about taking a block of UHMW and boring a 3" hole in it, (the bore size) cutting it in half and drilling a hole for the wrist pin.

The old pistons don't have any loose or tight markings. I don't have the new ones yet. The only ones left available for that old motor are .020 and .040. I am waiting to see if it cleans up at .020 before I order them.

I was thinking now about putting the pistons in the oven set at about 250 degrees F and freezing the wrist pin and trying that. Sounds safer. I wonder if 250 F would hurt that piston? I think I will press the old one apart and practice one time on it.

 

[bob johnson]

Re: Pressing OMC pistons.

That picture looks exactly like the jig the manual has in it. Originally I was thinking about taking a block of UHMW and boring a 3" hole in it, (the bore size) cutting it in half and drilling a hole for the wrist pin.

The old pistons don't have any loose or tight markings. I don't have the new ones yet. The only ones left available for that old motor are .020 and .040. I am waiting to see if it cleans up at .020 before I order them.

I was thinking now about putting the pistons in the oven set at about 250 degrees F and freezing the wrist pin and trying that. Sounds safer. I wonder if 250 F would hurt that piston? I think I will press the old one apart and practice one time on it.

try boiling water first.....youll need to be efficient, and make sure you dont slip up while hurrying and do some damage to either part

boiling water and a pin from the freezer should be slip fit....but youll have to work dillengtly as the piston will start to make that pin grow right off the bat!!!

bob

bob

 

[Joe Reeves]

Re: Pressing OMC pistons.

The Heat/Cool procedure above appeals to me.

If your pistons do not have the "floating" wrist pin setup (slides easily thru both sides) but rather incorporates the "L" loose on one side, tight on the other side..... I have, many times, slid the wrist pin thru the loose side, thru the wrist pin bearing, and just entering the tight side... then clamping the c/rod in a vice, heated the tight side of the aluminum piston with a hand held blow torch to have that tight side expand, after which I simply tapped the wrist pin in.

Possibly not your cup of tea, but it always worked for me.