Connecting rod "offset"?

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FWIW..... IIRC the SCAT rods we got had no 'side' offset.... but the big end widths are .010" or so narrower than stock rods, which helps make up for some of that 'no offset'.
 
MOPAROFFICIAL said:
What is being said is.. 'pertaining to the rods in question'... the thrust side sticks out more, it is offset to one side of the beam.

Say it however you wanna say it... he has no hair, no...he is bald, uh maybe he is hairless, if only I was as tall as I am long, or wide as I am fat...
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I've never thought of it as the "thrust side". If it's made as those 340 rods shown are you'd match them side to side as long as the oil squirt holes line up to lube the cam and cylinders. There's really no thrust side except on the mains...

But if the rods are all machined evenly side to side you'd simply install them as usual and measure your side clearances and you're done.

Those Pankl rods are the same side to side but they are machined so one side goes towards the crankshaft radius.

Racetec will be making the pistons to hang on these rods... Since the original application was a Chevy RO7, and my SBM 383 journals are wider than the width of the big ends when installed, I'll make some washers to fit on to the piston pins so the rod will be centered on the piston... Pretty common deal when mixing and matching used and new parts from who knows how many original applications...
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Krooser said:
Since the original application was a Chevy RO7, and my SBM 383 journals are wider than the width of the big ends when installed, I'll make some washers to fit on to the piston pins so the rod will be centered on the piston...
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I can't say I am sure on this idea.... so you are using the pistons & pin bosses to control the location and side float on the rods? Doesn't that put abnormal forces on the sides of the pistons? Never heard of such a thing... but I sure haven't heard of everything....
 
nm9stheham said:
I can't say I am sure on this idea.... so you are using the pistons & pin bosses to control the location and side float on the rods? Doesn't that put abnormal forces on the sides of the pistons? Never heard of such a thing... but I sure haven't heard of everything....
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Yes, those rods don't have an offset because they are pin guided rods. You have to compare apples to apples. A non pin guided rod has offset.
 
Krooser said:
I've never thought of it as the "thrust side". If it's made as those 340 rods shown are you'd match them side to side as long as the oil squirt holes line up to lube the cam and cylinders. There's really no thrust side except on the mains...

But if the rods are all machined evenly side to side you'd simply install them as usual and measure your side clearances and you're done.

Those Pankl rods are the same side to side but they are machined so one side goes towards the crankshaft radius.

Racetec will be making the pistons to hang on these rods... Since the original application was a Chevy RO7, and my SBM 383 journals are wider than the width of the big ends when installed, I'll make some washers to fit on to the piston pins so the rod will be centered on the piston... Pretty common deal when mixing and matching used and new parts from who knows how many original applications... View attachment 1715123735

View attachment 1715123736
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Cool, doesn't mean **** pertaining to the rods in question and ill probably put you on ignore now...but what the hell.
 
stixx said:
-Those Pankl rods...

Isn't a Pankl rod a titanium deal? They sure look like that...
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Steel.... just a very nice, high quality Austrian made piece that's cheaper(used) than the Chicom rods. Pankl is now part of CP that makes the Carrillo rods and tons of other stuff.
 
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yellow rose said:
Yes, those rods don't have an offset because they are pin guided rods. You have to compare apples to apples. A non pin guided rod has offset.
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These were non-floating...

I bought a couple sets to have on the shelf for future projects. When I bought my broken 383 I thought I might use them on that rebuild but finally figured I didn't want to spend the $$$ money needed to make the engine any "better" than it was... I'll save that cash for the Gen 3 if I build it.

Anyway my old friend Jim Watson (RIP) worked for Roush for nine years in the engine department. He was a crankshaft specialist and was a wealth of knowledge about these rods. Roush uses Lentz rods but he was very familiar with all the brands used in NASCAR.

He told me they haven't used floating rods for several years. The non-floaters are lighter and they don't have to worry about the bushing pounding out in 500 miles. They toss the rods after every race so these things are for sale all over the web and are strong and inexpensive. You just have to adapt the pistons and maybe the crank to what you are building.

If the crank you are using has a large radius you need to modify the bearings to accommodate that radius. You can see that radius on these rods. So the opposite side is where you adjust the side clearance... this isn't anything you guys don't already know.

I spoke with Randy from RaceTec pistons at PRI and he suggested using washers to control the position of the rods with his pistons rather than 'pin guiding'. Got to admit that's a new one on me but it sure is feasible. Maybe I'll just use a traditional pressed fit... don't know.

Back on subject...

I've been working on this stuff for over 50 years and, until now, have never heard the term "thrust" used for rods. Cranks yes... rods no. I'll stand by my opinion that one side is machined to a different measurement to correct the rod side clearance only. The thrust bearing on the mains controls the crank. Any offset is limited to the pistons.

I have seen, and I'm sure you have too, many terms that were once universal to our language now misused either intentionally or in error. That's why we have dictionaries. Rod 'thrust' is one of those terms... IMHO of course.

Automotive Mechanics: Piston designs
 
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yellow rose said:
Yes, those rods don't have an offset because they are pin guided rods. You have to compare apples to apples. A non pin guided rod has offset.
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Thanks very much. This particular idea is all new to me. Is there anything different in the piston design if it is used to guide the rod (via the pin)? I'm just trying to figure out where the forces go and how that effects things....if the rod drifts forward or backwards, something has to restrain it. (Which I assume is the reason for the washers Kooser is referring to...)
Or is 'pin guiding' just what is keeping the rod in an upright position, and the rod big end still works back and forth between the side of the journal and the other rod?
 
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People are reading into terms used way too much.
No one has said the the rods control the crank thrust...There are simply way too many experts looking for a window to flex their far superior knowledge or parts show and tell.

The rods have a side that rides,thrusts, touches etc against the rod next to it, flat machined face...call it or term it whatever you want. Start another thread for your recycled rods that go both ways.
 
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yellow rose said:
As I said...all V-8 rods I can think of off the top of my head are offset. They have to be.

Yes you can flip the piston on the rod if the pin is offset but IMO it's a waste of time. The HP you MAY gain is minimal.
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There is no HP "gain" to reversing piston offset, but the actual effects are very noticeable.
By reversing the offset, you are leaning the rod into the direction of crankshaft rotation earlier in the cycle giving peak cylinder pressure a bit more leverage to work the reciprocating assembly.
The engine will feel snappier and hit the converter harder.
I have done this on all of my own engines (when possible) over the last 40 years and can tell you first hand the back to back difference is profound
 
When u reverse the piston on the rod u r reducing the friction in the cylinder thus freeing up horse power. I have done this trick on many mopars. Yes, it does help performance. White punk is right on. Kim
 
As for con rod offset, u need to have that to keep the rod centered on the pin in the piston as 1 cylinder is ahead of the opposing cylinder. Kim
 
What everybody forgot is the rod has a v groove in it to spray the cam with extra oil so really with the chamfer needing to go to the front the v groove in the rod needs to go toward the cam
 
yellow rose said:
As I said...all V-8 rods I can think of off the top of my head are offset. They have to be.

Yes you can flip the piston on the rod if the pin is offset but IMO it's a waste of time. The HP you MAY gain is minimal.
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early 273 rods are not off set. only ones I ever saw
 
Krooser, y did u delete ur statement? If the pin is centered in the rod on a pressed pin the pin will not be centered in the piston because of the cylinder offset. Kim
 
oldkimmer said:
Krooser, y did u delete ur statement? If the pin is centered in the rod on a pressed pin the pin will not be centered in the piston because of the cylinder offset. Kim
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you guys are using the word offset for two different things and really mixing things up badly . The pin bore in the piston ( or less likely the small end?) is offset to avoid piston slap or rocking SIDE to SIDE looking frum front of engine . Done . Maybe very slight power gain / reducing friction but you will have violent slap , break piston . bad trade . when the plug fires . That is one thing —
it has nothing to do with big end .
But as one person posted the center of big end vs center of rid is moved on the journal front to back of engine to center the rod IN THE BORE front to back under piston . Talk about piston bosses moving the rod back and forth are pure BS . How can it move on rod journal back and forth ? But without that beam offset it ends up as much as 200 to one side , Seems wrong still hits nothing on piston , if full float seems to me would destroy bushing with eccentric load . But pressed pin maybe it’s ok. maybe .
So the reason to use press makes sense to me if straight rods are not centered under piston ? NOT a ” preference” don’t call it “offset” ; call it pin offset or rod beam offset .
Speak english and all that ?
 
The later 645 rods were offset between the big end area and the beam to better clear the bigger crank counterweight of the cast cranks, (read late 340s/360s). Less density than forged steel means more size to allow balance.
 
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