WRIST PIN FIT?

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CFD244

CFD244

"I LOST MY ID IN A FLOOD"
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Hi Folks

So I tore into a 1970 340 that I picked up knowing that is was .030 over TRW 2332P. The bores were pretty nice with no wear, and the rod and mains were .010.

Unfortunately, the main and rod bearings looked like ****, but the crank looked ok (to be determined).

What I found, regarding rods was that whoever built this thing used pressed in pins, and I found 2 rods with different forging numbers. 1 of the assemblies looked really good. The rod rocked back and forth between the skirts, and the pin slid sideways back and forth to the point where the piston contact with the small end stopped the movement. On the other 7 however, all of the ends of the pins were bluish from heat and the rod/pin would not slide back and forth in the piston, and it took a lot of effort to rock the piston from skirt to skirt.

My question is.....how are the pins supposed to fit in the pistons? I know that they are pressed into the rod, but should they be a "slip fit" in the piston? Even without a rod, the pin needs a light press to remove them from the bare piston.

I am hypothesizing that the builder may have ruined the piston holes on a press while trying to assemble everything.

What are your thoughts?

Thanks
 
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Supposed to be a slip fit. No tighter. Being blue from heat certainly isn't a good thing.
 
CFD244 said:
That's what I thought....Hoping to save the pistons, but I guess not.
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From what you said some were to tight. I would think that could be saved. Did I misunderstand?
 
Are they bushed rods or press fit? The blueing would indicate press fit, where the rod is heated to install the pin. Common
 
But the pins should slide into and out of the piston with no effort, if not mounted on a rod.
 
replicaracer43 said:
Are they bushed rods or press fit? The blueing would indicate press fit, where the rod is heated to install the pin. Common
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I agree, but I've never had to heat them that hot and wouldn't like it if somebody did that to mine.
 
The pins do not slip into the piston. I pressed one out, and there was a a tiny bit of galling on it. Out of the 8, 1 seemed to be right. That's why I thought the installer maybe buggered up the holes. If anything, I would think the pin would have to be cooled to aid in pressing, not heated.

I would suspect to make the pin fit, the piston holes would need to be honed or reamed for the slip fit.

BTW......There were marks around the piston hole that looked like some grinding. I'll post a couple of pics tomorrow to see what you all think. I'm checking Summit for a new set of Sealed Power 2316's

Stay tuned.........
 
CFD244 said:
The pins do not slip into the piston. I pressed one out, and there was a a tiny bit of galling on it. Out of the 8, 1 seemed to be right. That's why I thought the installer maybe buggered up the holes. If anything, I would think the pin would have to be cooled to aid in pressing, not heated.

I would suspect to make the pin fit, the piston holes would need to be honed or reamed for the slip fit.

BTW......There were marks around the piston hole that looked like some grinding. I'll post a couple of pics tomorrow to see what you all think. I'm checking Summit for a new set of Sealed Power 2316's

Stay tuned.........
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We're talking about heating the small end of the rod for the pin to slip through. The pins should be a slip fit in the pistons. I would maybe let the shop look at them. They may be savable.
 
A 1970 340 would have left the factory with full floating piston pins and 2 scallops on the piston tops. The rod small ends would have been bronze bushed.

A machine shop should have the correct reamer, hone, lap or scraper for your situation..
 
CFD244 said:
Hi Folks

So I tore into a 1970 340 that I picked up knowing that is was .030 over TRW 2332P. The bores were pretty nice with no wear, and the rod and mains were .010.

Unfortunately, the main and rod bearings looked like ****, but the crank looked ok (to be determined).

What I found, regarding rods was that whoever built this thing used pressed in pins, and I found 2 rods with different forging numbers. 1 of the assemblies looked really good. The rod rocked back and forth between the skirts, and the pin slid sideways back and forth to the point where the piston contact with the small end stopped the movement. On the other 7 however, all of the ends of the pins were bluish from heat and the rod/pin would not slide back and forth in the piston, and it took a lot of effort to rock the piston from skirt to skirt.

My question is.....how are the pins supposed to fit in the pistons? I know that they are pressed into the rod, but should they be a "slip fit" in the piston? Even without a rod, the pin needs a light press to remove them from the bare piston.

I am hypothesizing that the builder may have ruined the piston holes on a press while trying to assemble everything.

What are your thoughts?

Thanks
Click to expand...


There are two kinds of wrist pins, floating and press fit...

Floating pins have a clip on each side to keep the wrist pin in position, and the rod can slide from side to side between the piston ears on the wrist pin...

Press fit pins are press fit to the rod and can't move in the rod, but the pin can slide to where you can touch the rod between the ears of the piston....

Either one the wrist pin should be able to slide side to side in the piston... When installed in the engine, the crank journal and bore position keep the rod form sliding side to side in the piston...

With either wrist pin, the piston should be able to be rocked back and forth (Gently by hand) where you can touch one piston skirt to the rod, then the opposite skirt to the rod with no resistance.... Otherwise there will be too much friction when the engine runs and may cause galling in the pin bore of the piston and possible breakage....

If the rod has turned blue, it has been overheated above 520° and weakened the microstructure of the rod....
 
CFD244 said:
That's what I thought....Hoping to save the pistons, but I guess not.
Click to expand...

We did it once on a 440 that someone had messed with. Rod ends were a little bluer than I would have liked and the pins wouldnt quite slip-fit in the pistons. We reconditioned them all. Unfortunately I dont have infor to report about how it tunred out because that project is still "in progress". They seem (feel) quite proper now tho.
 
The reason some guys have to turn the rods blue to get the pin to slide in is because they refuse to pin fit the rod. You can’t leave that out.

If nothing else the pin ends shrink just from all the heat cycles. Some of these rods have been rebuilt more than once and every time the rod is heated to get the pin in, the hole shrinks when it cools.

You only need .0007-.0009 press fit on a .984 pin. Any more than that and you have to overheat the rod to get the pin hole big enough to get the pin in.

I’ve also seen too much press actually get loose. You can use too much press fit and cause the final clamp load to be less. Many miles or some detonation or both and the pin will get lose in the rod and it will slide over and dig nice troughs in the bore for you.
 
So, here are the pics. It took everything I had on a 10 ton press to get the pin out. As you can see the piston on the left is free to be acted upon by gravity. The other 7 are like the one on the right. Why would these pins be so tight in the piston? There is no evidence of the small end of the rod being heated. Just the pin??? Have a look at the bearings. I suspect that would be a function of the piston/pin's relationship.

Edit: And the grinding? For balancing??

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IMG_0012.JPG
 
That is awful, throw ALL that junk in the garbage and buy a nice set of rods and pistons would be my advice
 
A set of icon pistons and a scat I beam would be a affordable replacement for that mess. Lighter, and stronger
 
Now one more thing you need to consider, is who ever built that, looks like the were not "as skilled" as they should be, so I would be very cautious of the actual finished bore size, because those pistons would have required more piston to wall clearance than a modern forged piston, so you may not be able to just drop in a different piston. And based on the quality of work, I seriously doubt they had the equipment of skill to make the bores round and straight. If it were sent to me, I'd probably plate hone it to .040, new icon pistons and know it was right. That's my free 2cents
 
replicaracer43 said:
Now one more thing you need to consider, is who ever built that, looks like the were not "as skilled" as they should be, so I would be very cautious of the actual finished bore size, because those pistons would have required more piston to wall clearance than a modern forged piston, so you may not be able to just drop in a different piston. And based on the quality of work, I seriously doubt they had the equipment of skill to make the bores round and straight. If it were sent to me, I'd probably plate hone it to .040, new icon pistons and know it was right. That's my free 2cents
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I hear you. I'm already on the phone with the machine shop!
 
Without a proper fixture for pressing out piston pins, what usually happens during that process is the piston gets distorted, and is then basically junk.

Also, with the galling shown in the one pic, it was likely tight enough so that the piston skirt is slightly collapsed now.
Easy enough to tell with a mic.
 
PRH said:
Without a proper fixture for pressing out piston pins, what usually happens during that process is the piston gets distorted, and is then basically junk.

Also, with the galling shown in the one pic, it was likely tight enough so that the piston skirt is slightly collapsed now.
Easy enough to tell with a mic.
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Thanks for your input. Rods and pistons going in the pile to build another Hyundai.:( So much for my low budget build.

Just trying to get the car on the road and trying to minimize machine shop time. Would these Speed Pro pistons (L2613F)and a set of reconditioned floating pin 340 rods require balancing? Hoping to put it together myself.

Thanks
L2316F.jpg
 
It might be “close enough” if it’s a factory 340 steel crank that still has the factory balance.

I’m sure that combo of parts has been assembled without balancing before.
 
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