Reducing the pin hole size of a press fit rod

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Dave Koehler
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Re: Reducing the pin hole size of a press fit rod

Post by Dave Koehler »

There ya go.
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Re: Reducing the pin hole size of a press fit rod

Post by BCjohnny »

As said, before you put the bush in the rod chamfer both sides of the pin hole, 30-40 thou width is enough, with a large enough 45deg countersink, in a drill press or mill etc

Make the bush slightly over length as regards the pin hole width, say 100 thou

When the bush is in and centred, get a couple of spherical steel balls larger than the pin hole, put the whole caboodle in a vice and swage the bush into the chamfer, dress the excess by whatever method you have ...... it subsequently can't move

You'll also have a slight lead to get the pin in

It'll add maybe a couple of minutes or so to processing each rod, but the extra insurance is worth it

For balls, suitable ironmongers railheads might do, but I've a habit of cadging & breaking up any larger old bearings the scrap man has on when he collects, so there's always a selection on hand
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Re: Reducing the pin hole size of a press fit rod

Post by Super_Stock »

Thanks BCjohnny,that's good advice, thanks for posting it earlier.
I used to buy single large balls from a bearing supplier when I had to repair motorcycle exhausts that had been pushed in. I'd heat the ball and then let it cool in sand. The ball could the be drilled, have a cable put through it and then pulled through the pipe as the pipe was heated. Worked quite well.
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Re: Reducing the pin hole size of a press fit rod

Post by Momus »

Dave Koehler wrote: Wed May 12, 2021 1:17 pm
Momus wrote: Wed May 12, 2021 12:28 pm
Dave Koehler wrote: Wed May 12, 2021 8:47 am Sadly, I have been pondering this thin wall bushing deal off and on and came to this conclusion.
To pull this off a lot more press fit is required than seems logical.

Procedure goes like this.
1: Hone rod ends a couple of thou over and to the same size.
Chamfer the hole if needed.
2: To avoid the problem of installing the bushing to the proper depth the first time a special bushing is to be made.
This bushing will be T shaped with just enough thickness to act as a stop. .060?
Bushing ID should be .002 under size
Bushing OD should be .005 -.006 larger than the rod hole
Bushing should be slightly chamfered on the OD.
3: Induction heat the rod and drop the bushing in.
Machine off the excess T portion
Chamfer the bushing ID.
4: Finish hone or bore for .001-.0012 pin press fit
Make sure there are no nicks or burrs however small, on the pins.
My thinking is that is will take less heat than the bush to install the piston pin and this can be pulled off.

Optional procedure
(and probably a good idea.)
.080 wall isn't all that much and would be no problem if it was a free float bronze setup.
A bit more thickness for press fit with steel could prove to be a good thing.

Honing is no fun so I would bore the rod .040 - .060 oversize and make the bushing to match.
This is probably overthinking it but my minds eye says the dodge rods are pretty thick on the top.
This much has to be bored out anyway if you were to bush the rod for a bronze bush at the oem pin diameter.
Boring also gives you the option to blueprint the C to C length.
IF the hole is a bit offset (happens a lot) in the forging you can also move it sideways a bit to center the hole better.

Closing thoughts:

Consider dry ice to freeze the steel bushing for installation. Need all the help you can get.
Resize the Big ends before doing any boring of the small end.
Rods should be spiffy clean and dry before induction heating.
Bronze bushed free float is a lot less work.
That 005 to 006" on the interference might be a bit tight on an 1.090" bore Dave?
Not with induction heating. Cold press would be iffy.
The idea is to have more press on the bushing when heated up just enough to allow the piston pin to be installed.
006" interference on a nominal 1.1" bore is a massive interference- especially if the bush material happens to be stronger than the rod.
Then add the force the pressed in pin will exert. :shock:

Stand back.

I'd be seriously concerned about cracking the small end.

The whole idea of doing this is a shit fight when floating the pin is better in every way.
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Re: Reducing the pin hole size of a press fit rod

Post by naukkis79 »

Super_Stock wrote: Sun May 09, 2021 6:49 pm Thanks Dave,
Using the steel bush allows me the option to use a budget piston that does not have retainer clip grooves. What size interference fit do you think I should use between the bush and the rod? The same as you would normally use between the pin and a rod, 0.0015 inch ?
You could just use floater pins and teflon buttons on pin ends with pistons that don't have clip grooves.
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Re: Reducing the pin hole size of a press fit rod

Post by Dave Koehler »

naukkis79 wrote: Thu May 13, 2021 12:49 pm
Super_Stock wrote: Sun May 09, 2021 6:49 pm Thanks Dave,
Using the steel bush allows me the option to use a budget piston that does not have retainer clip grooves. What size interference fit do you think I should use between the bush and the rod? The same as you would normally use between the pin and a rod, 0.0015 inch ?
You could just use floater pins and teflon buttons on pin ends with pistons that don't have clip grooves.
Not a bad idea but it depends on whatever cheapo piston he opts to use.
Some of the slipper skirt, straight pin wall side pistons may not have enough meat for support. A bit of outboard support is desired.
Another idea is that most KB hyper pistons have pin locks, correct?

But yeah, a floater deal makes more sense
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Re: Reducing the pin hole size of a press fit rod

Post by DCal »

It boggles my mind how far some will go to not buy the correct pistons. The next suggestion will probably be to use Locktite . There are piston companies out there that will build a correct piston at a reasonable price. Any CR you want, any CH, ring set etc. That is just my suggestion on any part that go below the deck, anything above the deck is accessible by leaning over the fenders.
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Re: Reducing the pin hole size of a press fit rod

Post by Dave Koehler »

The OP wants to try it. That should be enough. Sillier things have been done around here.
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Re: Reducing the pin hole size of a press fit rod

Post by Super_Stock »

DCal wrote: Thu May 13, 2021 1:17 pm It boggles my mind how far some will go to not buy the correct pistons. The next suggestion will probably be to use Locktite . There are piston companies out there that will build a correct piston at a reasonable price. Any CR you want, any CH, ring set etc. That is just my suggestion on any part that go below the deck, anything above the deck is accessible by leaning over the fenders.
I think I've already run trough all the things I could do..Sure I could fill in a form, throw a few bucks around and have a nice set of pistons turn up on the doorstep, but that's not the point of the exercise.
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Re: Reducing the pin hole size of a press fit rod

Post by Super_Stock »

naukkis79 wrote: Thu May 13, 2021 12:49 pm You could just use floater pins and teflon buttons on pin ends with pistons that don't have clip grooves.
Lycoming have a good way of doing that where the stepped buttons go right into the pin..The pin needs to rotate freely or the buttons wear out fast.
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Re: Reducing the pin hole size of a press fit rod

Post by C.A.R.E. »

I know this is a old post, but I just read it. I thought someone may benefit from my work. I’ve done this many times when using flat top 351 Cleveland pistons in a 400M Ford motor. ( cheep flat top for 400M to get a reasonable Comp ratio) I have PPPC make me some steel pin bushings to press fit the honed O/S 400 rods (.978 ?) and will finish to press fit on 351C (.912) pin. About .036 wall thickness. The bushing was chilled to press fit rod with .002 interference fit and finished to a interference pin fit of .0014. Heated rod with bushing installed in a rod heater and assembled piston as normal. Has worked great. Remember round rod pin hole and quality bushing is a must.
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