Machining Piston Pin Holes from .990 to 1.094-Any Potential Issues?

[Al K]

OK,here's the deal...Machine shop can't get bushing material to bush my rods down to .990";not a big deal,IMO. But...my Venolia pistons are .990 pin size and I don't want to drop big buck$ on new slugs. Seems to me that machining the material out for the larger pins shouldn't be a big deal-or is it?

The pin hole isn't near the ring area,so I wouldn't be removing material there. You guys see any potential problems?

 

[XCELLR8]

Yes there are issues if you do not get the center-lines in line. Valves, compression height, and locking up in the cyl bore.

 

[RustyRatRod]

Don't do it. Not only for the reasons above, but also you limit yourself to press fit. I would be flat out runnin the other way if a machine shop told me they could not get a chebbie size wristpin bushing. Here's what you need right here:

http://www.summitracing.com/parts/ros-b1094

 

[Meep-Meep]

I just had some 440 rods bushed down to .990" for a 451 I'm working on. Probably used the bushings above.

But if you must enlarge the pin bores I'd take the pistons to a machine shop that is not an automotive machine shop. Someone with a mill that can rough out the pin bores and get them all the same and straight. Then let the automotive shop hone them to fit (leave about .004"). The cost of that operation might make you look really hard at bushing the rods.

 

[bigblock]

Just get the right parts!

 

[rev.ronnie]

You would also need to re-machine the lock grooves. I usually do them first so you don't have to re-reference where they go.

Gary at Rocker Arms Unlimited can make any bushing you need. Better yet, send him the rods and a pin, his work is outstanding.

 

[Al K]

OK;I checked out the bushings Rusty listed from Summit. My questions now are: 1) they list these as being for a 1.097" bore,and I was under the impression that RB rods were 1.094" inner bore. Misprint/typo? Am I missing something here? Will I need to open up the bore the extra .003"? and 2) the bushing inner bore is listed as .997,and the pins are .990";is .007" an appropriate clearance for these? I appreciate the help,guys;as usual. If these aren't what I need(due to the dimensional issues listed),I'll be checking out the guy Rev.ronnie recommended.

Oh;two weeks and two days without a smoke. I seem to be doing OK.

 

[XCELLR8]

OK;I checked out the bushings Rusty listed from Summit. My questions now are: 1) they list these as being for a 1.097" bore,and I was under the impression that RB rods were 1.094" inner bore. Misprint/typo? Am I missing something here? Will I need to open up the bore the extra .003"? and 2) the bushing inner bore is listed as .997,and the pins are .990";is .007" an appropriate clearance for these? I appreciate the help,guys;as usual. If these aren't what I need(due to the dimensional issues listed),I'll be checking out the guy Rev.ronnie recommended.

Without having a bushing in my hand to put a caliper on it, it will give you my opinion. The bushing should be an interference fit so it stays in the rod. Then you have the stack up that happens during assembly. You press the bushing into the rod then the inside diameter shrinks down due to the force of pressing. So the .997" ID of the bushing should turn into ~.994" after pressing into the rod. That would only give you .004" for clearance to put your .990 pin into. That is only .002" per side to get oil to lube the pin and bushing "since it is a floating pin system". I hope you understand what I was saying.

 

[Hemirunner]

.007 is WAAAYYY too much. You won't get a 1.097 bushing to go in a 1.094 bore so you won't get .003 shrink and even if you did, .004" clearance is still way too much on a rod to pin. I'm guessing you have 2.375 journals if you're still messing with chrysler 1.094 rods. Rods are cheap. By the time you get done messing around buying bushings and paying machinists, you could just order the right rods.

 

[RustyRatRod]

That's an incorrect measurement. The bushings are correct. Rodney's got several sets. He's used them before. The bushings come small on the ID too because they have to be finished sized to the exact pin that will go into them.

 

[Hemirunner]

That's an incorrect measurement. The bushings are correct. Rodney's got several sets. He's used them before. The bushings come small on the ID too because they have to be finished sized to the exact pin that will go into them.

Ahh incorrect measurements would explain it all. I have a sunnen rod hone and dial bore gauges for resizing rods. I've done a lot of pin fitting lol

 

[RustyRatRod]

Then you should know that preinstalled measurements mean nothing. Nominal I believe is what they call it.

 

[Hemirunner]

Then you should know that preinstalled measurements mean nothing. Nominal I believe is what they call it.

I do, and listing a .997 bore isn't Nominal, it's just plain incorrect. Listing the bore as .990 and supplying it .001 or .002 undersize to allow for pin fitting would be considered nominal. Pre-installed measurements mean everything, especially if they're incorrect.

 

[RustyRatRod]

I cannot agree any stronger. It's just a mistake big as all hell.