Hi!

I am currently building an engine that will use 1.090" full floating pins.

1. If I bush the small end of the rods, after I hone for the desired 0.001" clearance w the pin, I'd end up with bushings that have a wall thickness of 0.031". I fear the wall thickness wont be enough to hold the interference fit over time and might come loose? Whats the minimum wrist pin bronze bushing wall thickness allowed? These are all bronze bushings with no steel backing. I have seen the Eagle H beams or similar do have very thin bushings aroung 0,030" but I wonder if they are press fitted or if they are actually brazed on? My machinist told me a non steel backed bushing thats press fitted and final honed to a final wall thickness of 0,030" doesnt make him too conffortable. He advised against it.
2. In order to install the wrist pin bushings I have, I would also have to open up the small end of the rod to accept the bushing. Thing is the wall thickness of the small end of the rod right now its at 0.168" (see attached pic). If I open it up for the bushing the wall will end up at 0.125". Again, I might fear this might weaken the rod and lead to a majour failure? These are stock reconditioned rods.

DUE TO THE ABOVE REASONS, THAT DONT GIVE ME MUCH PEACE OF MIND.....I WAS THINKING ABOUT OPTING FOR A 2ND OPTION:
Would it be OK just to run a full floating pin steel on steel. No bushing. Is this OK to do? And what pin to rod clearance should I run?

I have to use the parts I have on hand as this is a budget build. I just want to choose the best route so I can have peace of mind about not having an engine that will come apart.

Rod small end wall thickness

If its a budget build just press the pin and be done with it No money spent at all. the rods you have were not designed to be bushed full floating rods leave the as they are

Not enough meat to achieve a proper press fit

Not enough meat to achieve a proper press fit

Not enough meat for a press fit? Do you mean the hole is too large? That would explain your problem.

1. I have never seen a wristpin bushing with steel backing. Ever.

2. There's no way in heck that Eagle or any other high performance rod manufacturer BRAZES a bushing into a connecting rod. Again, I have never seen it done in any application. Ever.

3. If Eagle uses a 0.0030" thick bushing there's no reason why you can't.

At 5000rpm, a stock dimension 440 piston exerts 5000lb of pull on the pin end of the rod. That's assuming an 1100gram piston and pin. If the wall thickness is 0.125 and the length is 1.1", the cross-sectional area of the pin end is 0.275 square inches. That computes to 18,182psi tensile stress.

Using Young's Modulus for 1541 steel of 28x10^6, the deformation of a 1.09" length stressed at 18,182psi is 0.0007". The press fit has to be greater than that. Steel elasticity is not dependent on its tensile or yield strength.

If you wish to float steel on steel, you will need an oiling hole on top of the pin end about 1/8" diameter with a small chamfer. I would suggest 0.001" clearance as a starting point, although others who know much more than I should be consulted first before setting that as ideal. The racing community started out with this as pin oiler, moved to two holes coming up from the bottom sides at an angle, but then moved back to the single hole on top of the rod. That is the latest configuration I have seen.

R.

If it's a drag race type application where you really don't put a lot of miles on the engine I see no problem. I have done it several times. Most stock rods don't have the meat to machine and install a bushing. I usually drill a small oil hole in the small end, to lube the pin, and have the small end honed to fit the pin. from my memory I think we used .001 clearance. Ran a mild 440 this way for many years with no issues. Of course if you are trying to build a 800hp engine, I would say it makes more sense to buy good rods.

He's being too cautious, it's common practice to bore the small end to 1.160" to bush for a 1.094 pin which makes the bushing wall thickness .033". I've run lots of them on the street that way.

Some people run floating pins without a bushing, when doing this it's best to dip the small end in molten tin and then hone to size.

I did it in a small block many years ago with no issue at all. Drilled and chamfered a small oil hole in top of the rod and ran it at .001

Used to do a lot of sb roundtrack motors that way. Hone the rods out for about .001" clearance w/ no bushing and drill the oil hole at the top. Worked good, but these weren't exactly real powerful engines either.

GM did it from the factory on the 1969 Z/28 302 . I also had an L-88 427 that came with the floating pins and no bushings. As said above adding an 1/8" hole with a chamfer was a popular mod. My $.02

Mark

All I can tell you is mine are steel on steel - older build and not sure where along the line this happened as I don't believe that they were floating originally.

Just found major galling on most of the pins and rods. Both are junk. Buying new bushed rods and new pins from Todd Marsh to fix the problem.

All the steel on steel galled pins/rods/piston pin bores I have seen come from inadequate clearances and those using thin pins.
Battleship pins don't flex and maintain their clearance in the rods. When they flex they hour glass and shut off the oil to the rod small end. I've seen a few pin tier modifications do the same thing but many pins are pressure fed in the piston so they last a tad longer.

Steel on steel will work fine with an oil hole for what your doing, BUT, .001 isnt enough clearance when doing that on a 1.094 pin

35-40 years ago most of us ran steel on steel with the 1/8 mod. Most of us also ran that heavy azz Speed Pro or TRW pistons. On rebuilds we had to take our flapper wheels and get the pins cleaned up so we could throw it back together.

My first good Slant had the pins steel on steel. They had the pins coated with something. (Can't remember what) It lasted over 50K on the street and about a bazillion passes. They were beat up when we took it apart, but it had suffered an oil pump failure.

Steel on steel is fine...

I took one motor apart that had the wrist pins floated with the small end of the BB rods steel on steel, can't remember now if they where six pack or LY rods, knurled for oil retention and clearances I'm assuming/. I'm sure the piston where the old heavy forged TRW small dome "race" 440 pistons
I've never saw or heard of anyone else using that type of set up since

Take a look at my calcs, maybe I should have stated conclusions in bold print.

1. The stock rod as measured will have a safety factor of 3 or more with a stock piston at 5,000rpm, with the pin end bored for a bushing. So saying the pin end doesn't have enough meat to bore for a bushing is incorrect.

2. At that stress level the hole will elongate a maximum of 0.0007 inch. A press fit exceeding that will keep the bushing in place. I'm thinking the press fit is more like 0.002". The bushing will remain in place.

This simple exercise in mechanical engineering demonstrates why going steel-on-steel is unnecessary.

R.

Thanks for all the replies.-

At this point I think that bushing the rods is the way to go.

Good thing is the machine shop I use listens to what I ask them and they always do a good job. If I have oddball requests they also go the extra mile to do procedures as I ask them to. Remember I live in LIMA, PERU so race engine machining is not what they do, they just do regular rebuild jobs. I have to walk them through certain procedures like using honing plates, multi angle valve jobs, etc.

Now I have 2 questions:

#1

Now....the machine shop I use would generally just press in the bushings with their interference spec. Lets say 0,002"

But, Since these bushings will end up being about 0,03" thick once proper clearancing is completed, I was thiknig that maybe not just press fitting them, but freezing the bushings and heating the rods would be the best option? Will installing them like this guarantee a better grip than just pressing them?
If its the better way to do it, what would be the intereference to shoot for prior to install? Also, would freezing the bushings in dry ice or just throwing them in the fridge would do the trick???
What about the rods? dipping them in boiling water???

#2

Is it an absolute necessity to use a burnishing tool to achieve clearance once the bushings are pressed in?
I see that they just press in the bushings and they they just hone them to size, but they do not have burnishing tools- I hear burnishing will help achieve a better hold with a thin walled bushing as opposed to just honing to size.
Are burnishing tools expensive? how much would it cost one to do a 1.09" bushing? Does anybody have a link to the appropiate one to do the small end bushings?

Thanks!!!