Rod alignment

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Steve.k
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Re: Rod alignment

Post by Steve.k »

We were talking about certain ford stroker kits however using chevy rods it shifts the rod off center. Some say it helps to have then centered.
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Re: Rod alignment

Post by hoodeng »

Some manufacturers use weight add bosses on the top and bottom of the rod to facilitate final weight distribution and final total weight in the rods manufacture.

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Re: Rod alignment

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And if your crankshaft is too light/insufficient overlap, it won't make a difference.
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Re: Rod alignment

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modok wrote: Sat Jan 20, 2018 8:13 pm Rod alignment, is checking that the pin is parallel to the crank pin.

I believe the crank -bearing- not being centered under the cylinder might be called... called "Crankpin offset"?
For average size engines, .040 or .060 off center is quite reasonable. I have only heard of problems reported when the offset was exceeding .100 in some parallel twin motorcycles

The MASS or structure of the rod being, or, not being centered under the piston OR on the bearing.....don't think that has a name, but good question, I DON'T KNOW.....but I can see some indication being inclined to stay stuck to one side might be good. There are a FEW engines that have thrust wear problems ON THE RODS, and the only thing I see in common is they are all LONG rod engines, always wondered why/how that was happening.
Engines with some crankpin offset that had rods with the beam shifted to center the beam under the piston, when the rods are replaced with symmetrical rods, generally no problems result. Never crossed my mind that it might be an improvement tho :D
I build vintage Triumph bike race engines, 360 degree parallel twins....Some guys fuss endlessly getting the crank centered in the cases...This is about .010 " left or right in most cases...I don't bother with it but spend time getting the crank end float correct, near zero end float with the crank located by the right side ball main bearing. When the engine comes up to temperature ,the cases expand and the crank end float opens up...because the right side ball bearing main is clamped to the crank, end float can loosen the interference fitted into the case main bearing ..........
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modok
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Re: Rod alignment

Post by modok »

Sorry to hear some triumph enthusiasts suffer from that. It does not seem to even enter the minds of most to check, they assume it is.....but it probably isn't.
The +.100" offset was because it was spread bore.
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Re: Rod alignment

Post by Steve.k »

The rotax engines we work on are set dead nuts on center. There must be a reason for it. Rotax consistently making high hp/cc.
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Re: Rod alignment

Post by modok »

Id like to know the reason behind why people think there is a reason behind everything. :lol:
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Re: Rod alignment

Post by Steve.k »

IMG_2201.PNG
heres what I'm talking about.
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Re: Rod alignment

Post by modok »

So the structure of the rod, and the pin bushing are off center....is the rod bearing not still in the same spot?

Once I had an idea, that being an H beam rod, I could trim the width of one side of the "H" smaller to account for it not having as much load. I haven't done it, but if somebody requested MAX lightening of the rods I may try it.
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Re: Rod alignment

Post by Mark O'Neal »

Truckedup wrote: Sat Jan 20, 2018 7:02 pm Looking at the drawing above, if the rod was .010" off to one side do you think it would make difference in performance or engine life on a moderately built engine?
No.
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Re: Rod alignment

Post by blykins »

If you're looking for the little end to always be perfectly centered, it's not going to happen, unless it's a piston guided rod setup. With as much side clearance as a lot of these setups have, tied in with crankshaft thrust play, it's never going to be perfect.

As much of a Molnar fan as I am, I lost a little respect for them when their "centralign" graphic was posted on my forum the other day. The graphic (same one on page 1 of this thread) shows the difference between a regular Ford crank with a Chevy rod vs. their new connecting rod design. However, in the right side of the graphic, they deliberately changed the distance in between the pin bosses so that the offset would be exaggerated to the eye.
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Re: Rod alignment

Post by Steve.k »

Mark O'Neal wrote: Tue Jan 23, 2018 1:41 am
Truckedup wrote: Sat Jan 20, 2018 7:02 pm Looking at the drawing above, if the rod was .010" off to one side do you think it would make difference in performance or engine life on a moderately built engine?
No.
In a moderate built engine very little gains i spose. On a 800hp engine 2-3% was seen by centered correctly on pin. Brent why lose respect? Ive talked with builders who say they've seen the rod against piston boss. In that case diagram is forgiving?
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Re: Rod alignment

Post by DaveMcLain »

Steve.k wrote: Tue Jan 23, 2018 10:29 am
Mark O'Neal wrote: Tue Jan 23, 2018 1:41 am
Truckedup wrote: Sat Jan 20, 2018 7:02 pm Looking at the drawing above, if the rod was .010" off to one side do you think it would make difference in performance or engine life on a moderately built engine?
No.
In a moderate built engine very little gains i spose. On a 800hp engine 2-3% was seen by centered correctly on pin. Brent why lose respect? Ive talked with builders who say they've seen the rod against piston boss. In that case diagram is forgiving?
I've only ever seen the rod get against the pin boss on a Big Ford using a big Chevy style connecting rod. I wonder are they worse?
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Re: Rod alignment

Post by blykins »

IMO, they fudged that diagram to exaggerate it. Why else would you change the dimensions on the pictures? The picture to the right makes it look a whole lot worse than it is, because the distance between the pin bosses are different. The rod is meant to work with any piston, is it not? So why change the piston dimensions in the diagram?

It's just marketing I suppose. The cool "centralign" is marketing too. I have never been one to jump on a bandwagon and it seems like the SBF world has been stirred up by the introduction of these rods.

In addition, their tagline is "All Ford stroker assemblies that utilize the SBC connecting rod."

That statement is incorrect, as I showed on my forum yesterday.

I'd like to see documentation of a 2-3% increase from someone else than a connecting rod manufacturer................................
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Re: Rod alignment

Post by Steve.k »

Brent im thinking they went through the trouble of r&d for a reason. Otherwise all you guys could just buy good ol chevy rods and stuff in anything! They would sell a hell of alot more if chevy fits everything.
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