Compatiable wrist pins sources?

No big deal. Use dowel pins, which can be machined with carbide if you exercise some care. They are available in common fractional sizes in a multitude of lengths and are heat treated and ground to very tight tolerances, generally with a decent finish that would lend itself to functioning as a bearing. Being surface hardened, they should withstand pretty much any punishment they'd receive as a wrist pin in a compressor. They're not expensive. The slots you speak of for nails isn't exactly clear to me, but you may be able to grind away enough of the surface hardness to permit drilling or milling them. Dunno. Otherwise, make them as needed and have them heat treated and ground.

Harold

The only size they're *not* available in is, 7mm.

Guess what size my honda snowblower uses to retain the drive gear on the axle?

Yep.

What were they thinking. However HSS drill blanks *are* available in 7 mm size though!

Jim

Is that a good idea, Jim? If it's intended to shear under load, I think you're in trouble!

Harold

A likely similar part might be the small wrist pins in 2-cycle engines. New pins from a dealer probably wouldn't be the route you'd wanna go for this project, but you might get lucky finding something on eBay that could be of use with minor modifications.

WB ..............

You can retain wrist pins with aluminium buttons at each end. If you intend to try and find pins from a more modern piston and shorten them I'd advise caution. The surface finish is so hard you can easily create stress cracks by grinding the ends and god knows what trying to grind notches in them would do.

I agonized over this choice long and hard Harold. Fact was, the part that the honda engineers put in there was hard, through and through. It sheared neatly at the interface between shaft and gear, and I needed a press to remove the remains in the shaft. I could have simply turned up a pin from CRS and stuffed it in there (the tempation was large, the snowblower was in pieces and there was a big storm predicted for the next week) but decided that the honda engineers probably knew what they were doing, so I though I should install the closest thing to what they had in the first place.

MSC shipped me the drill blank in a day so it was ready for action when needed.

Jim

Very unusual, to say the least. I have to agree though, if the engineers felt a heat treated pin was in order, I may have made the same choice. Seems strange that it would shear the way you suggested, though. I can't imagine a drill blank doing that. While I have no stats at my disposal, I know it's not uncommon for many of the HSS's to have a tensile up around

Cool fix, Jim. Like you, I've used drill blanks for a grundle of things. I have a small box of rems from which I can make selections for short pieces, and several indexes of them for a myriad of uses. They're a fine addition to any shop. I've purchased the vast majority of them off ebay at prices that were a small fraction of new.

Harold

Just a thought- Is it possible that the good folks at Honda scored a line around the pin to provide a stress point to shear at & inserted the pin to exactly the right depth to get the score line at the gear/shaft interface???

Howard.

If they did, it was a very shallow score. I kept the two ends that were inside the gear, and matched them up with the piece I pressed out of the axle. Although the exterior was somewhat oxidized at the exposed ends, I could not detect any obvious features like that.

Because it was such a arduous fix (the entire bolted-up subframe of the machine has to be disassembled to get inside the gearbox which uses the steel frame as a cover) I kept all three bits in my 'memories' drawer in my shop.

I like to keep the remains of fixes like that as a reminder of how not to build things.

I'll double check them to see if there is *any* sign of deliberate engineering like that.

Jim

Interesting idea using alum but I find alum doesn't wear right, they gall and too soft in cast iron cylinders. I like to use bronze for buttons.

Good notes on the grinding issues.

Here's this image I took of this worn wrist pin. I had talked to the mechanic who did my caravan's safety check & I had asked him to send out the compressor repair job for estimate and we talked about finding new wrist pins instead of making them and modifying them. Compressor is low rpm (500rpm estimated), will only pump up to 120PSI cut off.

Pistons are 1.5" dia, stroke is appox 1 23/32", bigend for rods (aka eccentric-shaft) is huge 2" to 2.5" dia appox.

Wrist pins specs:

Hollow, with small oil hole drilled completely through, new pins will not have it since the rods already have the hole drilled at top for splash lubing. Made of steel, hardened and plated with hard chrome.

.421" dia (not sure due to wear, see notes).

Note the notches in the wrist pin, it is for the nail's heads as wrist pin retainers. The nails goes through piston at an angle, the shank that is exposed inside the skirt is bent over to keep them from coming out. These notches in the wrist pins are ground or milled with round narrow cutter off center that inner edge at bottom of each notch is higher than outside edge. Wrist pins are slip fit not pressed in.

We can oversize slightly on diameter of wrist pins. Like .422, .425, .430 or whatever and ream both pistons and rods to size for precision slip fit.

You can see the notes written on that scrap of paper wrist pin is resting on is my ways of communication since I'm deaf. :-)

Cheers,

Wizard