Rod alignment

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Steve.k
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Rod alignment

Post by Steve.k »

How critical do you think rod alignment in terms of centerline on pin relate to hp and/or longevity. We had this discussion before and some well known mfgs say theres gains. Thoughts?
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Re: Rod alignment

Post by pamotorman »

there are builders who say the friction from the crank seals cost HP so i would guess from the friction generated by out of aligned rotating assy. parts would do the same.
Steve.k
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Re: Rod alignment

Post by Steve.k »

IMG_2193.PNG
. This is therory we talking about. Some independent testing reported gains of 2-3% on 800hp engines. Mostly due to more stable piston and ring seal in their view.Note the diagram maybe slight exaggeration but have heard where some rods were out close to this much.
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desoto30
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Re: Rod alignment

Post by desoto30 »

think pin guided rods,,, there would be something
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Re: Rod alignment

Post by PackardV8 »

It's interesting how the theory, practice and importance of piston/pin/rod alignment has changed in the past sixty years.

Some OEM engines designed in the 1950s use a full 3" deep barrel skirt and a piston pin 3.250" long in a 1.5" wide rod small end. Their SAE design paper will state the necessity of all that material to keep the piston and rod square in the bore.

Some of today's better race pistons have only a bit of skirt on the thrust side, nothing on the pin ends and maybe 1" on the off side. The pin is no more than 2" long in a 1" wide rod small end.
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Steve.k
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Re: Rod alignment

Post by Steve.k »

And obviously by the last setup dead nuts center.
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Re: Rod alignment

Post by Truckedup »

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?
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PackardV8
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Re: Rod alignment

Post by PackardV8 »

FWIW, Studebaker V8 rods are forged with an offset of 1/16" (.0625”) Some racers run SCAT piston-guided rods with no offset.
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hoodeng
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Re: Rod alignment

Post by hoodeng »

We deal with a number of engine types that have their own architectural quirks , so there is no set rule of one fix fits all applications .In some engines you are stuck with the manufacturers layout unless you pour a bunch of money into them to correct areas that were passable in a mass produced low stress street application,but now need major realignment to work properly in a high load application ,Some engines afford adjust-ability without major reinvestment.
In my circumstance [HD V2] setting the rod central to the bore in the 90°to pin axis is usually pretty accurate from the manufacturer in engines that were manufactured with a Timken left bearing ,early engines that used parallel roller bearings left and right used thrust washers to contain the crank end-float to .012"- .014" ,these thrust washers could then be changed in thickness to retain the end float but shift the crank left or right to get everything back in the center of the bore ,this process was detailed in the service manual as a standard repair process. After the rod is centered it has to be checked for squareness to the case deck and also adjusted accordingly for true.
I have seen in engines that have been assembled without these action taken pistons skirts with offset wear or diagonal wear ,noted with this wear is rings not seating evenly in the bore , these engines through their life had noted oil consumption or case breathing issues.
So the negative impact on longevity and performance on these engines was identifiable .

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Re: Rod alignment

Post by modok »

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
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Re: Rod alignment

Post by digger »

wouldnt it be nice of the pressure at any given time was perfectly uniform....
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Re: Rod alignment

Post by hoodeng »

That's a gas turbine!!!

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Re: Rod alignment

Post by pamotorman »

Rod alignment, is checking that the pin is parallel to the crank pin. that is what i thought the post was about till i saw the drawing.
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Re: Rod alignment

Post by hoodeng »

You are right , rod alignment in the rod itself is it being parallel in the gudgeon to crank pin plane , vertical plane and twist accuracy.

Rod alignment in the engine assembly relates to its physical location using the bore center and line as a zero reference.

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Re: Rod alignment

Post by Krooser »

Went thru this discussion on another board recently. Some guys insisted the extra material on one side of the rod was the "thrust" side of the rod.
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