Tight Wrist Pins

[Samurai7one]

  I bought some ITM flat top pistons to install in my L28 build.  I intend to use the stock existing connecting rods.  I installed the wrist pins that came with the pistons and about half of them are not free moving.  the ones that are free just flop side to side, good to go.  the other ones I have to move them by hand. it doesn't take a lot to move them but the difference between the free and not-free are  significant enough for me to be writing this right now.   

  If I take my map gas touch and put on the piston on the material adjacent to the wrist pins for about 2 seconds the whole thing loosens up nicely and flops right over.  This makes me think that maybe its ok once the engine was warm, but... what about the warm up period? hmmm.
 Additionally I had a very difficult time getting the wrist pins centered in the piston.  Its close but IDK if its good or not.  It seemed like the pin would move all at once in 1/8" increments, maybe its the press I was using, it was sort of used and abused. I did use the torch to heat the rod to help things along.  After pressing too far , back in forth, back and forth, I got them within 1/6"ish of center.  The pins cannot stick out far enough to hit the cylinder wall.

  So, in your opinions:

          -are the wrist pins a problem? 

          -how centered do the wrist pins need to be, accepting that they will never be exactly centered anyway?

 

 

Or should I take my box of parts to the machine shop..... again?

 

Thanks guys

[1969honda]

I know a lot of the aftermarket SBC pistons and rods are usually bored to correct tolerance by a machine shop before final assembly, this ensures a couple of things;

 

- eliminates possibility of the bores being of center from forging/casting

- gives proper oil clearance

- ensures rod and piston bores are properly aligned.

 

A lot of aftermarket suppliers from what I have read actually plan on press fit pins being sized to the piston this way for the best performance and fit. Your machine shop should have an accurate way to proper center the pins in the rods and piston bore. I don't think it would cost very much ($15 a piston maybe) to have a competent machine shop give them a quick once over and ensure everything is up to spec.  If it were mine I would have the shop take a look at them for the piece of mind.

[NewZed]

Monroe says standard piston bore clearance is 0.0003".  Not much but enough to allow oil penetration.  He also says if they're not lubricated you can gall the surfaces at break-in and ruin the piston.  He also describes letting oil soak in to the bores to make sure they're wet at start-up.  Did you oil yours?

 

Seems weird that ITM would sell pins with pistons but not size them, or at least add a note that they need sizing.  Did you mix up the pins?  They might have been matched sets.  Just a guess.

[Samurai7one]

The wrist pins fit perfect prior to installing them through the connecting rods.  I also installed one at a time so the pins where kept with the pistons as they were delivered.  I put motor oil into the piston holes prior to installation.

Maybe the piston material mushroomed out a bit around the hole. 

[NewZed]

There's a note in Honsowetz's "How to Modify" book about potential damage when installing that type of pin.  You have a dilemma.  Install and hope or take apart and be sure.

 

Note - I'm only relaying what I've read in the two books I referenced.  Never built an engine but understand the concepts.

 

Were it mine, I might throw some heat on the pistons to get some expansion, and dowse the pins in oil to see if I could get some oil in there.  To be sure.  If they loosen up the odds are better that expansion when running will allow lubrication.

 

Hopefully one of the engine builders will have some more experienced comments.

[Samurai7one]

Just an update FWIW,

  I brought my pistons/rods to a automotive machine shop and the guy looked them over.  He felt two that he thought were a problem the rest were in his opinion "just fine".  He had an electric induction heater for the rods which brought them to the perfect temperature and held it there.  he pressed the pins out, ran a hone in the hole, cleaned it, reheated and pressed the pins back in.  took him just a few minutes for each one.  I was impressed....  So now I'm back on track with putting my engine together.    

It cost me $40 dollars and was well worth the peace of mind.  I talked to the guy (Frank) for some time, he seems like he really knows what he is doing and his shop was A-1.  I will bring him more work in the future.

 

shop:

C&F Automotive Machine Shop

1105 Avenue H

Westwego, LA

504-341-3334