HY DUTY pistons 105 S

[GB SISSON]

I have 6 pistons that should be from a 4" stroke merc. I was given the engine about 25 years ago and it was a very fresh rebuild that was badly overheated on the maiden run in a friend's cab-over truck. Upon dissassembly it was determined to be junk by the machine shop. We used the crank in a 59ab block I had and it later got sold in my 38 tonner. The machine shop returned to me 7 very nice pistons which remained in a box in my shop's attic. They are .040 over and marked HY Duty 105 S inside the skirt and .040 on the crown. These days I have a very nice 59 ab block with zero ridge and .040. I also have a std size 4" crank I bought from a guy on a neighboring island. I will get the crank ground over the winter. Where would I look to find 2 more pistons to match? I seem to have miss placed the seventh one over the years? Also what is dimension height of pin in a merc, just in case these aren't the same ones. I was a 40 year old 'kid' back then. Thanks in advance, GB

[tubman]

I ran into this same problem about 60 years ago; I had an 8BA I wanted to do and the local engine rebuilders had a set of seven new pistons removed from a "problem" rebuild. The bores matched, they were free, and the only thing I was missing was one piston. I went to the local junkyard and spent most of a day checking items from their "piston pile" until I found a good one. I put the engine together and ran it in two cars, a '51 fordor (until it succumbed to rust) and then a '52 tudor, which I sold to a friend.

I have to believe that with all of the folks on here, someone may have a suitable piston; I know I'll check my "scrap" pile, but all I have is 8BA stuff, so the piston crown height will probably be wrong.

As my old Irish boss used to say, "It's better to be lucky than smart". Someone may have what you need; that's what this place is all about.

[51 MERC-CT]

Merc. pistons measure 1.437" from c/l of pin to outside edge of dome.
Ford measures 1.562".

[GB SISSON]

Great news! Pretty clear we're in merc territory.

[51 MERC-CT]

Originally Posted by GB SISSON

Great news! Pretty clear we're in merc territory.

If they measure 1.562 they are NOT Mercury but Ford pistons.

Another measurement of Mercury pistons.

[GB SISSON]

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Since I don't have a precise way to place the calipers on the center of the wrist pin, I purposely set them at the ford setting and took a photo. If you study the photo closely it indicates that the caliper is about 1/8" off of center. I had a feeling my method might be confusing.

[GB SISSON]

Thanks! I'll double check it using that method.

[bobH]

Comment and opinion here.... If it's the Hy Duty that I have experience with, I'd say toss them. Back in the 60's, there was a company in LA that went by that name. Pistons were two bucks apiece. And, worth it, too. I used those pistons in two engines. And, regretted it. I have a relative who owned and operated an automotive machine shop back then. He put me on to those pistons. He said he used them for cheap rebuilds when the customer wanted cheap. His experience he said was ok. Usually the customer would get rid of the car before any problem surfaced.
The pistons I used were weak in the skirt area.


edit... some useless info....
From my most recent Hy-Duty invoice:
dated July 1972
Hy-Duty Products Corp.
4927 Pacific Blvd
Vernon, CA 90058
213-587-6111
1972 price was 3.10, 24.80 for 8

[GB SISSON]

Originally Posted by bobH

Comment and opinion here.... If it's the Hy Duty that I have experience with, I'd say toss them. Back in the 60's, there was a company in LA that went by that name. Pistons were two bucks apiece. And, worth it, too. I used those pistons in two engines. And, regretted it. I have a relative who owned and operated an automotive machine shop back then. He put me on to those pistons. He said he used them for cheap rebuilds when the customer wanted cheap. His experience he said was ok. Usually the customer would get rid of the car before any problem surfaced.
The pistons I used were weak in the skirt area.

That's pretty much all I need to hear. I will source a set of 8 matching merc pistons at .040.... Seems like a set of 8 shouldn't be too hard to find. This is my project for the Fall. This block was one of eight I bought a year ago. It passes the pencil test and has a raised intake, drilled lifter bosses, clean as a whistle. I'll get some close up photos.