Mopar 383 Connecting Rods

[Larry Hill]

Does the cap grinder cut the cap 90* to the bore? At .0006 taper per inch, it would taper .0072 per foot. That's a lot.

It might take truing the mandrel a few times to get rod to size using a slightly lower stone pressure.

If accepted size is 2.5000 to 2.5005 is any size on or between good or is there a taper tolerance " Tapper not to exceed .........."

[Tom Broome]

Originally Posted by HP HUNTER

You have two rods you're honing..........there's .0025 to hone to size on both rods, one rod has .0005 taper the other has .0007 taper. How do you set these two rods up on the already trued mandrel?

Please pardon, I adjusted your post for clarity.
Okay, I'll play. We're just having fun here........Right?
Let's assume you cut the mating surfaces and are resizing the rods in your example.
Let's again assume you cut the mating surfaces enough that you started from a dimension smaller than you currently have (-.0025). And you honed the rods to this dimension.
Once again, let's assume that you find the taper begins at the surfaces you were holding together, and progresses outward on both rods.
And yet again, let's assume that you have been flipping this pair of rods over every half thousandths or so. You do flip your rods over don't you?
Still yet again, let's assume that you have not been over-stroking the rods beyond the honing stones too much.
One more assumption, let's assume you are honing those rods with the beams riding on separate torque bars, not the same bar.
There are still a few more things to assume, you did deburr the bolt holes at the parting line, you did make sure that the cheeks of each re-assembled rod was...were...are... flat. Because, after all that work you don't want the pair of rods you are trying to hold together to be a couple of "rocking horses".


Answer: When that happens to me, I push the "OFF" button and walk away for a while. Because it's a clear case of operator error.
What did Dirty Harry say?

[HP HUNTER]

[QUOTE=Larry Hill;602288]Does the cap grinder cut the cap 90* to the bore? At .0006 taper per inch, it would taper .0072 per foot. That's a lot.

It might take truing the mandrel a few times to get rod to size using a slightly lower stone pressure.

If accepted size is 2.5000 to 2.5005 is any size on or between good or is there a taper tolerance " Tapper not to exceed .........."[/QUOT


The cap cutter would be dialed in @ 90 degrees, setup with the horse shoe.

How would the rods be put on (position) the mandrel at the start of the honing?

Chevrolet BBC rods from the factory sometimes the mating surface is not 90 degrees to the sides, which will cause taper when the mating surfaces are cut.

[HP HUNTER]

Originally Posted by Tom Broome

Please pardon, I adjusted your post for clarity.
Okay, I'll play. We're just having fun here........Right?
Let's assume you cut the mating surfaces and are resizing the rods in your example.
Let's again assume you cut the mating surfaces enough that you started from a dimension smaller than you currently have (-.0025). And you honed the rods to this dimension.
Once again, let's assume that you find the taper begins at the surfaces you were holding together, and progresses outward on both rods.
And yet again, let's assume that you have been flipping this pair of rods over every half thousandths or so. You do flip your rods over don't you?
Still yet again, let's assume that you have not been over-stroking the rods beyond the honing stones too much.
One more assumption, let's assume you are honing those rods with the beams riding on separate torque bars, not the same bar.
There are still a few more things to assume, you did deburr the bolt holes at the parting line, you did make sure that the cheeks of each re-assembled rod was...were...are... flat. Because, after all that work you don't want the pair of rods you are trying to hold together to be a couple of "rocking horses".


Answer: When that happens to me, I push the "OFF" button and walk away for a while. Because it's a clear case of operator error.
What did Dirty Harry say?

"let's assume that you find the taper begins at the surfaces you were holding together, and progresses outward on both rods"



If your saying, and I think you might be, the first rod with the taper tight (facing the operator) would go on the mandrel first, the second rod with the taper tight up would go against the first rod. So the tight side of the housing bore would always go against each other until the taper is gone, typical flipping would start from there.

[Rich Biebel]

Originally Posted by HP HUNTER

You have two rods your honing..........theres .0025 to hone to size on both rods, one rod has .0005 taper the other has .0007 taper. How do you set these two rods up on the already trued mandrel?

I never honed pairs of rods and did one at a time.
Focused on the one in my hand and not trying to juggle 2 and work out the taper(s) using two.

Is it better to use the 2 rod method.....?
I don't know its been nearly 30 years since I left the engine machining world and I'm not returning anytime soon. No one in the shop I worked at used the 2 rod method.

If its better I missed the memo back around 1970 something....lol

There is and always was an endless string of potentially poorly OEM machined items in an engine. Starting with the block itself and right on down the line.
Correcting or attempting to correct much of it would be very difficult if not impossible sometimes.

Engine machining has definitely advanced a lot with better machines and fixturing and mostly parts....

I was in a shop yesterday.....Didn't look all that different than where I worked 30 years ago...….Mostly Older machines, heads, blocks and stuff everywhere.....

2 Jaguar heads, A complete out of car Mopar Poly engine and a flat head Ford block just a few things I spotted.....

[Tom Broome]

Chevrolet BBC rods from the factory sometimes the mating surface is not 90 degrees to the sides, which will cause taper when the mating surfaces are cut.

I agree many rods, not just BBC, don't have the housing bore and sides perpendicular to the parting line. My personal opinion is that we often find rods (especially OEM) that also don't have the sides parallel to each other. If that is the case then one side will be closer to "square" than the other.

We understand that we will hone, more or less, perpendicular to the rod sides. The cap cutter should cut the parting line perpendicular to the sides. Therefore we need to prepare the sides, to the best of our ability, before we cut the parting surfaces. Then we need to check the parting surfaces before we cut them. How did we remove the pressed in bolts? Did we twist the forks doing that? Are there burrs or dings anywhere?

Only then do we begin to cut the parting surfaces. Production "guys" will touch off on one rod,or cap, dial in the amount they want to remove, and make their cuts.

I prefer to touch off every rod and cap, every time, and observe the cut surface to see if it's cutting "flat". If not, I turn the part around to square off the other side and touch it again. I pick the best side and cut the amount I prefer.
Then we get to prep our newly machined surfaces. Reinstall the press in rod bolts, again trying not to twist the forks. Reinstall the cap(s), torque the bolts using a procedure we can repeat on final assembly. And make sure the sides are flat so that the rods don't "rock" as we hold the pair on the hone.
After that, it's up to the hone operator to do his job. The prep work is "just machining", the honing is where the "touch" comes into play.

All in all, it's not easy, or cheap, to do the job right.
Then if we want to have "fun" let's do some rods that the need to be "saved". You know....the blue ones.

[Tom Broome]

Originally Posted by HP HUNTER

"let's assume that you find the taper begins at the surfaces you were holding together, and progresses outward on both rods"



If your saying, and I think you might be, the first rod with the taper tight (facing the operator) would go on the mandrel first, the second rod with the taper tight up would go against the first rod. So the tight side of the housing bore would always go against each other until the taper is gone, typical flipping would start from there.

Well....what I'm actually saying is that if you have been honing a pair of rods, and the smallest points of the taper begin at the surfaces you have been holding together, and the mandrel is straight....
Let's try to get on the same page. Front rod tapered out towards you. Back rod tapered out away from you. Okay.....Right?
....the rods are tapered from operator error. The person operating the hone is twisting or torquing the rods on the mandrel.

Regarding "flipping" the rods. Sometimes you put the front rod in the rear (opposite the way they run). Sometimes you rotate the front rod 180 degrees and the back rod 180 degrees (opposite the way they run). That's what I do every half thousandths or so.

Flipping the rods not only helps keep the rod bores straight, it helps keep the mandrel wearing straight.

[Tom Broome]

Originally Posted by Rich Biebel

Is it better to use the 2 rod method.....?

No, but you double the length. Makes it easier on the operator.
I like to finish the rods in pairs as they will run in the engine. Does it make a difference? I dunno....makes me feel good.

[Rich Biebel]

This reminds me of the "how to read a mic" argument that went on in the first shop I worked at …..Tony Feil's.....1966.....

2 employees that just couldn't agree on some detail of using a micrometer.....

I was just a green teenager that knew very little...and I don't recall exactly what the disagreement was about but it was bad.....

I wouldn't really mind honing some rods as long as I'm warm and we have music.....gotta have music....and coffee.....and cigarettes for sure back in the day......lots of coffee and lots of cigarettes....lol

[HP HUNTER]

Originally Posted by Tom Broome

Well....what I'm actually saying is that if you have been honing a pair of rods, and the smallest points of the taper begin at the surfaces you have been holding together, and the mandrel is straight....
Let's try to get on the same page. Front rod tapered out towards you. Back rod tapered out away from you. Okay.....Right?
....the rods are tapered from operator error. The person operating the hone is twisting or torquing the rods on the mandrel.

Regarding "flipping" the rods. Sometimes you put the front rod in the rear (opposite the way they run). Sometimes you rotate the front rod 180 degrees and the back rod 180 degrees (opposite the way they run). That's what I do every half thousandths or so.

Flipping the rods not only helps keep the rod bores straight, it helps keep the mandrel wearing straight.

"Let's try to get on the same page. Front rod tapered out towards you. Back rod tapered out away from you. Okay.....Right?"

YES. very few understand this