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Bronze pin bushing vs. no pin bushing

General engine tech -- Drag Racing to Circle Track

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Birdlab
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Bronze pin bushing vs. no pin bushing

Post by Birdlab » Thu Apr 05, 2012 8:16 pm

I'm hoping for input regarding the importance of running a bronze pin bushing in a steel connecting rod. With a DLC coated wrist pin, would a proberly finished steel pin bore be just as reliable as a bushed rod? If well lubricated, the coefficient of friction is listed to be the same for steel on steel as it is for bronze on steel, so I'm wondering what the benefit is to running a bushing. Are there any clearance guidelines to follow when running with a bushing vs. no bushing?

Thanks in advance

rob vine

Re: Bronze pin bushing vs. no pin bushing

Post by rob vine » Thu Apr 05, 2012 8:39 pm

i do sb chev steel rods for our local dirt track - set pin to rod clearance at .001" with no problem - too tight and the pins gall -

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Re: Bronze pin bushing vs. no pin bushing

Post by TMSJoe » Thu Apr 05, 2012 9:23 pm

rob vine wrote:i do sb chev steel rods for our local dirt track - set pin to rod clearance at .001" with no problem - too tight and the pins gall -
I did a set of stock SBC rods @.001" One ended up getting very lose after a season of 1/4 mi. dirt racing. Now new rods are so cheap I rarely use them in any performance engines.

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Re: Bronze pin bushing vs. no pin bushing

Post by Birdlab » Fri Apr 06, 2012 7:58 am

With a quality aftermarket steel rod and a DLC coated pin, would you rather have a bronze bushing in the pin bore or not? Also wondering why an aluminum rod is usually run with no bushing, but a steel rod is more likely to be bushed.

rob vine

Re: Bronze pin bushing vs. no pin bushing

Post by rob vine » Fri Apr 06, 2012 8:26 am

unfortunately our rules dictate stock rods or i would use aftermarket rods - some tracks dont realize that reworking stock rods is more money than buying a set of scat or similar rods all they care about is that it is stock oem - by the time you buy bolts , resize and full float them , clean and check them , a scat rod is cheaper

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Re: Bronze pin bushing vs. no pin bushing

Post by TMSJoe » Fri Apr 06, 2012 9:05 am

Birdlab wrote:With a quality aftermarket steel rod and a DLC coated pin, would you rather have a bronze bushing in the pin bore or not? Also wondering why an aluminum rod is usually run with no bushing, but a steel rod is more likely to be bushed.
I'm guessing here but I assume you want the pin to survive hence a softer material touching it. I did a 460 Ford with Chevy rods and I honed out the bushing and pressed the pin in the steel rod. The 460 has a bigger pin than the Chevy and the Eagle rod was bushed for the Chevy pin but the bushing OD was smaller than the Ford pin. Press fit worked just fine.

I like bushings because I can re-bush the rods when they wear out. If the question is would I rather work hard to float a pin when pressing is an option then I would press the pin.

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Re: Bronze pin bushing vs. no pin bushing

Post by 540 RAT » Fri Apr 06, 2012 3:21 pm

Birdlab wrote:With a quality aftermarket steel rod and a DLC coated pin, would you rather have a bronze bushing in the pin bore or not? Also wondering why an aluminum rod is usually run with no bushing, but a steel rod is more likely to be bushed.

It is a simple matter of like materials having the tendency of galling each other if they come into direct contact with each other (meaning no lube under extreme circumstances). Thus the bronze bushing in a steel rod with steel wrist pins, to stay on the safe side with Hi Po engines. But no bushing is required for aluminum rods with steel wrist pins because of the different materials. With the DLC coating you may have the option of skipping the bushing in a steel rod. Though ideally, you'd like to see some test data to back-up a decision to skip the bushing. Personally, I'd stay on the conservative side and use the bushing even with the DLC coating.

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Re: Bronze pin bushing vs. no pin bushing

Post by ProPower engines » Fri Apr 06, 2012 4:16 pm

The original GM Z302 had floating pins. GM dipped the rod in copper and then sized the pin end. They lasted for many years of street driving and abuse.
Most if no all import engines are steel on steel with a floating pin and they last for 200K miles with no issues.
And most engines do not have a provision for oiling the pin other that splash. While some do use a piston cooler jet spraying oil under the piston crown others do not and they still live a long life
with the advances in pin coatings available today it would be no problem as long as the surface finish of the pin bore is glass smooth.
Most cases where this comes up is rules against aftermarket rods. All good quality pistons do come with a float option but in most cases a pressed pin is less work and will do the job just fine. If you have to use a stock rod just press the pin don't waste money on floating them there is really no advantage other then ease of assembly.
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Re: Bronze pin bushing vs. no pin bushing

Post by cjperformance » Fri Apr 06, 2012 5:39 pm

i have done many factory Cleveland rods with floating pins and no bushings and have no problems even with uncoated pins. I would not do it in any sort of boosted engine though due to the increased load and possibility of galling.

Ally rods use bushings for service reasons. Far cheaper to change a bushing than a rod.

Id have no hesitation doing a non bushed floating pin if the application allows.

What is the intended use of your engine.?
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Re: Bronze pin bushing vs. no pin bushing

Post by 526 turbo » Tue Apr 10, 2012 1:14 pm

Birdlab wrote:I'm hoping for input regarding the importance of running a bronze pin bushing in a steel connecting rod. With a DLC coated wrist pin, would a proberly finished steel pin bore be just as reliable as a bushed rod? If well lubricated, the coefficient of friction is listed to be the same for steel on steel as it is for bronze on steel, so I'm wondering what the benefit is to running a bushing. Are there any clearance guidelines to follow when running with a bushing vs. no bushing?

Thanks in advance
check out my post on the subject for more infor thx

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Re: Bronze pin bushing vs. no pin bushing

Post by tsanchez » Tue Apr 10, 2012 6:21 pm

Just took my engine apart after 25 yrs and pins look great, they are tapered but dont think it would have made any difference.

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Re: Bronze pin bushing vs. no pin bushing

Post by ProPower engines » Tue Apr 10, 2012 6:33 pm

tsanchez wrote:Just took my engine apart after 25 yrs and pins look great, they are tapered but dont think it would have made any difference.

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Re: Bronze pin bushing vs. no pin bushing

Post by tsanchez » Tue Apr 10, 2012 6:52 pm

AMC

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Re: Bronze pin bushing vs. no pin bushing

Post by ProPower engines » Wed Apr 11, 2012 12:46 am

Done a bunch of 340 rods lately. The have a similar looking big end.
They must have been bushed to last that long.
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Re: Bronze pin bushing vs. no pin bushing

Post by rustbucket79 » Wed Apr 11, 2012 12:47 am

rob vine wrote:unfortunately our rules dictate stock rods or i would use aftermarket rods - some tracks dont realize that reworking stock rods is more money than buying a set of scat or similar rods all they care about is that it is stock oem - by the time you buy bolts , resize and full float them , clean and check them , a scat rod is cheaper
As a machine shop, which rules puts more money in your pocket, working with stock rods, or selling a set of aftermarket rods? :wink: Be thankful of the antiquated track rules, much better than mandating a crate GM engine.

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