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Old 01-23-2021, 12:08 PM   #1
Michael_Velling
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Default Connecting Rod (Insert) Question for rebuild

Hello, i have a question about the connecting rods with inserts.

I want to have the crankshaft ground to the correct size and then install the connecting rods with new pistons. Of course, the cylinders will be ground to the correct size for the new pistons.

Is it possible to do this so easily?

Thanks

Michael
Germany
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Old 01-23-2021, 01:00 PM   #2
Jack Shaft
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Default Re: Connecting Rod (Insert) Question for rebuild

Yes, its that easy.I would provide the new rods with inserts to the machinist so he can fit them correctly to the crankshaft journal. Its important to work with the actual parts. Have pistons available to fit when boring as well.
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Old 01-23-2021, 06:49 PM   #3
Gene F
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Default Re: Connecting Rod (Insert) Question for rebuild

The original Ford crank should under no circumstances be cut with 90 degrees where the journals meet the bosses. If your machinist does this the crank will eventually break. I speak from experience!

A Scat crank...now that's likely a different situation.
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Old 01-24-2021, 02:07 AM   #4
Michael_Velling
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Default Re: Connecting Rod (Insert) Question for rebuild

Thanks a lot for those informations. I will order today some parts.
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Old 01-24-2021, 09:00 AM   #5
Jacksonlll
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Default Re: Connecting Rod (Insert) Question for rebuild

I have a stupid question. Is the wrist pin a press fit into the piston? Something must keep it from rotating so the bushing comes into play.
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Old 01-24-2021, 10:27 AM   #6
Jack Shaft
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Default Re: Connecting Rod (Insert) Question for rebuild

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Quote:
Originally Posted by Jacksonlll View Post
I have a stupid question. Is the wrist pin a press fit into the piston? Something must keep it from rotating so the bushing comes into play.

Its a slip fit as you know,piston expansion from heat keeps it tight.

Gene the proper name for what you describe is the 'fillet' the radius cut where the crankshaft journal meets the throw
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Old 01-24-2021, 05:36 PM   #7
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Default Re: Connecting Rod (Insert) Question for rebuild

Something’s not right. When something expands, it does so photographically, everything gets bigger, so the wrist pin hole would get bigger. I don’t think the wrist pin would expand more than the piston. Something must tighten it.
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Old 01-24-2021, 06:06 PM   #8
Gene F
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Default Re: Connecting Rod (Insert) Question for rebuild

Yes, thats what my engine rebuilder said, when my crankshaft snapped.
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Old 01-24-2021, 10:47 PM   #9
bbrocksr
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Default Re: Connecting Rod (Insert) Question for rebuild

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Originally Posted by Jacksonlll View Post
I have a stupid question. Is the wrist pin a press fit into the piston? Something must keep it from rotating so the bushing comes into play.

The wrist pins are called full floating pins because they move/rotate in both the rod and the piston.
Bill
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Old 01-24-2021, 11:04 PM   #10
daren007
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Default Re: Connecting Rod (Insert) Question for rebuild

If your machine shop is “cutting” your crankshaft look for another shop. Crankshafts should. Be ground on a grinder not cut on a lathe.
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Old 01-25-2021, 07:10 AM   #11
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Default Re: Connecting Rod (Insert) Question for rebuild

Thanks Bill. I'm not an engine guy and always wondered if that wrist pin rotated relative to the piston.
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Old 01-25-2021, 07:21 AM   #12
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Default Re: Connecting Rod (Insert) Question for rebuild

When buying new pistons, the pins come already in the pistons. They are a press fit. When I say "press" that means they are pressed with your thumbs or the heal of your hand. It is a very snug fit- not a just slide in.


The sleeves in the rods should be honed to fit the pins at a machine shop. They are not quite as tight as the pins in the pistons. All the rotation should be betweeen the Pin and the Sleeve in the rod.
You do not want the pin rotating in the piston and wearing on the alumninum piston When everythin inside begins to heat up the pin thru the piston wil tighten up leaving the rod and the brass sleeve to do the rotating.
Well. maybe not rotating, but rocking back and forth. ken


gotta stop now and go to shop and start assembling another engine.....
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Old 01-25-2021, 03:14 PM   #13
d.j. moordigian
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Default Re: Connecting Rod (Insert) Question for rebuild

Quote:
Originally Posted by Michael_Velling View Post
Hello, i have a question about the connecting rods with inserts.

I want to have the crankshaft ground to the correct size and then install the connecting rods with new pistons. Of course, the cylinders will be ground to the correct size for the new pistons.

Is it possible to do this so easily?

Thanks

Michael
Germany
Install the bearings in the rods(all of them) and torque them. Using a "dial
bore" measure it on the vertical. Then, with those figures SUBTRACT the
number from what clearance that you want AND that's what you grind the
crank too.........make sense?

djm
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Old 01-25-2021, 04:23 PM   #14
bbrocksr
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Default Re: Connecting Rod (Insert) Question for rebuild

Quote:
Originally Posted by kenparker0703 View Post
When buying new pistons, the pins come already in the pistons. They are a press fit. When I say "press" that means they are pressed with your thumbs or the heal of your hand. It is a very snug fit- not a just slide in.


The sleeves in the rods should be honed to fit the pins at a machine shop. They are not quite as tight as the pins in the pistons. All the rotation should be betweeen the Pin and the Sleeve in the rod.
You do not want the pin rotating in the piston and wearing on the alumninum piston When everythin inside begins to heat up the pin thru the piston wil tighten up leaving the rod and the brass sleeve to do the rotating.
Well. maybe not rotating, but rocking back and forth. ken


gotta stop now and go to shop and start assembling another engine.....
The wrist pin does rotate in the piston as well as the rod, that is why they are called " Full Floating". As the piston expands the pin bore gets larger not smaller.
As for wearing on the aluminum most modern engines use a press fit pin that rotates in the piston only.

Bill
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Old 01-25-2021, 04:30 PM   #15
Jack Shaft
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Default Re: Connecting Rod (Insert) Question for rebuild

Quote:
Originally Posted by kenparker0703 View Post
When buying new pistons, the pins come already in the pistons. They are a press fit. When I say "press" that means they are pressed with your thumbs or the heal of your hand. It is a very snug fit- not a just slide in.


The sleeves in the rods should be honed to fit the pins at a machine shop. They are not quite as tight as the pins in the pistons. All the rotation should be betweeen the Pin and the Sleeve in the rod.
You do not want the pin rotating in the piston and wearing on the alumninum piston When everythin inside begins to heat up the pin thru the piston wil tighten up leaving the rod and the brass sleeve to do the rotating.
Well. maybe not rotating, but rocking back and forth. ken


gotta stop now and go to shop and start assembling another engine.....
Yes sir..'rocking back and forth' is called oscillation
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Old 01-26-2021, 11:08 AM   #16
katy
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Default Re: Connecting Rod (Insert) Question for rebuild

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Originally Posted by bbrocksr View Post
As the piston expands the pin bore gets larger not smaller. Bill
How does the co-efficient of thermal expansion in the aluminum piston compare to the co-efficient of thermal expansion of the steel wrist pin?
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Old 01-26-2021, 03:18 PM   #17
Jim Brierley
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Default Re: Connecting Rod (Insert) Question for rebuild

Some modern engines have rods that require a tight press fit, and all motion is done on the piston-to-pin area. I did this years ago while putting Chevy pistons in a B block. The press fit holds the pin, so no wrist pin locks are used. I was told that wouldn't work but was dumb enough to know better. I made steel bushings and tack welded them in place in the rods. It all worked great, and I had modern pistons and rings.
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