Pressing in wrist pins

apbright

apbright

Senior Member
New wrist pins have a 1.000" outer-diameter; the bushings on new connecting rods have a 0.990" inner-diameter. Are such pins intended to be pressed directly into a bushing of such a diameter, or, would reaming be required first?

Also, I assume that when pressing is done, some kind of jig is required, so as not to deform the piston by the force of pressing, correct?

Safe driving, Andrew
 
Purdy, how do you hone them? Do you have a pin honing machine or lathe fixture of some kind? .
Or do you maybe ream them close to size and finish with a brake hone?
I have lots of machine tools but not a pin hone machine. I would like to hone gudgeon bushes in my workshop, since 5 tenths of a thou clearance is getting pretty accurate, if not impossible for an adjustable reamer.
I collect machine tools and use tgem all, but I am not a trained machinist.
SAJ in NZ
 
SAJ said:
Purdy, how do you hone them? Do you have a pin honing machine or lathe fixture of some kind? .
Or do you maybe ream them close to size and finish with a brake hone?
I have lots of machine tools but not a pin hone machine. I would like to hone gudgeon bushes in my workshop, since 5 tenths of a thou clearance is getting pretty accurate, if not impossible for an adjustable reamer.
I collect machine tools and use tgem all, but I am not a trained machinist.
SAJ in NZ
Click to expand...

Most machine shops should have a Sunnen Honing Machine, they work the best !

And yes, Mr. SAJ is right, .000-50 is the best.

With that clearance, oil them and they should be a perfect fit, and should NOT take any pressing.

Herm.
 
SAJ , I don't have a honing machine . I've got a small adjustable hone set that can hone both pin bosses in the piston at once . This is probably an ancient set that was given to me by the GMC dealer after he retired . I don't need to press the pins . I hone for a slip fit by hand . I've got by with this for years . My model A engines are very forgiving .
 
Hello Herm, hello Purdy,
I would love to have a Sunnen but they are expensive second hand especially in NZ. And I only do an engine every year or two, though it might have other uses in my factory workshop.
Purdy's hone sounds interesting. Is it hand powered, how many stones are there, are they spring loaded or rigid adjustable?
Would you have a name or brand so I could try and find one for myself.
A photo would be great.
SAJ in NZ
 
Hi folks,

Your advice was quite apt. Indeed, I spoke with my local machinist, who advised that my connecting rods would need to be honed. He noted that, were I to press these wrist pins in by brute force, they would be too tightly affixed to the connecting rods, potentially resulting in them being forced out of the piston and eventually scraping against the inside of the cylinders. He offered to hone them on, indeed, a Sonnen honing machine (made in St. Louis, probably in about 1950). He did it at no charge, bless the chap.

@SAJ: The machine he used looked just like this one on eBay:
https://www.ebay.com/p/Sunnen-Model...300-Gauge/14004846400?iid=273633845635&chn=ps

I spoke briefly with my machinist (Tom Holthaus, Quality Machine, San Jose) about this tool (while looking over his shoulder, as he was doing the job). He said it really, simply is just for honing connecting rod bushings. He used several different bits, parts, chucks (? I don't know what I'm talking about), which led me to believe that there is more than a little to know w.r.t. how to use one properly.
 
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Apbright, that is a nice machine on EBay and quite a good price. But the hones to go with it and the gauge would add a lot more cost and the freight to NZ would double the price. If I saw a local one like that I would grab it, just for the joy of owning it!!
Hopefully Purdy will come back with more details of his hone too
SAJ in NZ
 
SAJ said:
Hello Herm, hello Purdy,
I would love to have a Sunnen but they are expensive second hand especially in NZ. And I only do an engine every year or two, though it might have other uses in my factory workshop.
Purdy's hone sounds interesting. Is it hand powered, how many stones are there, are they spring loaded or rigid adjustable?
Would you have a name or brand so I could try and find one for myself.
A photo would be great.
SAJ in NZ
Click to expand...



SAJ ,

The name brand of my hone is Ammco Tools Inc. and it is either hand powered or can be powered by a hand drill . My hone has three stones and isn't spring loaded . it appears to be rigid adjustable . I can no longer post pictures here because of the sizing problem . Nearly all of the print on the box that it came in has long since faded off . It may not even be a hone for wrist pins but it serves the purpose , it is after all an adjustable hone . Before I got this tool I got by with a three stone spring loaded brake cylinder hone that was sort of a miniature cylinder hone . I figure that a rigid adjustable hone is more accurate and better suited for my purpose . I seldom use this tool because I only use it when I overhaul my model A engines . This is an old tool that was given to me years ago and I don't have much info about it , Sorry and I hope this may help .
 
Purdy that is very helpuld indeed. I shall now research Ammco and see if I can come up with something.
I have wondered if reaming to within 0.001 and taking the last few tenths outout with a spring loaded brake cylinder hone might work. It sounds as if you have done that.
Thanks again
SAJ in NZ
 
I have reamed and then finished with a spring loaded hone before I got my hone set . It is easier for me to ease up to the measurement that I want with a hone . It can be easier to mess up with a reamer than a hone . Wrist pin bushings and pistons are more critical than king pin bushings and other bushings on the running gear . Just my thought .
 
We never could afford them fancy tools, or a machine shop. Used a brake cylinder hone and hand fitted the wrist pins. May not be "right" but our only option at the time.
Last set of flathead pistons I bought came with the wrist pins and they slipped in and out easily. Never "snug" them in. Chap
 
The AAmco hone mentioned was marketed as a wheel cylinder hone, it is a miniature of a rigid cylinder hone ----not made or parts serviced anymore, I have one and have trouble finding stones for it ---I keep it in my toolbox at work and have used it to fit bushings
in transmissions
 
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