Steel-on-steel unbushed rod small ends

[BILL-C]

I've built many road race and circle track engines with full floated rods without bushings. Always with very light box style pistons and DLC coated pins. Usually 2.00 long .866 dia. Typically piston guided also. A very smooth pin bore is required.

[MaxFlow]

Done it many times. The old 250 6 cylinder chevy rod. Narrow it at the big end, hone it out and go. No problems. If it does freeze up don't you have a pressed pin? LOL

[Truckedup]

There are some exceptions where a floating pin is good idea to make wear even and/or to allow more accommodation for crank flex, but that would be mostly OLD archaic designs.

Ain't that the truth...The vintage Triumph bikes I race needs the floating pin with a bit of a loose fit in the piston...Otherwise the pin seizes in the piston and then it all goes to crap....
I rebuilt a Ford 9N tractor engine and noticed the cam rides directly on the cast iron block ..............

[Flo]

all of the Japanese 4 cylinder motorcycle engines are steel on steel floating pin. My old Zuzuki GS 1100/1150 only spins to 8500rpm (stock) and the wrist pins are not a week point. Those motors are good to about 60k miles before overhaul.... and mostly the air cooled cylinders and the guides are worn, not the pins/rods.

Current GSXR 1000 spinds what at redline? 14000rpm? Should not be a problem if oilng is secured

[DaveMcLain]

About a year ago I had a 302 Chevy come in that was an original factory build from 1969 or so... Some of those engines came with full floating pins that were supposedly run in a rod that had been sized and specially plated. They were totally 100% worn out. I'd say at least .020 clearance on the pin with most of the wear inside of the rod. I don't know how many miles were on the engine but the crank looked great and there was very little bore wear.

[Warp Speed]

Just about every Cup engine out there runs without a pin bushing. I know we haven't used them in 15+ years.
A polished pin bore and a DLC coated pin.

[pamotorman]

Just about every Cup engine out there runs without a pin bushing. I know we haven't used them in 15+ years.
A polished pin bore and a DLC coated pin.

don't they use full pressure pin oiling thru the rod ??

[Warp Speed]

Just about every Cup engine out there runs without a pin bushing. I know we haven't used them in 15+ years.
A polished pin bore and a DLC coated pin.

don't they use full pressure pin oiling thru the rod ??

No, not any more. It was too tough to properly control the finish of the feed hole. Stress risers would form from the feed hole and the rod would fail in the beam or small end.

[Krooser]

Just about every Cup engine out there runs without a pin bushing. I know we haven't used them in 15+ years.
A polished pin bore and a DLC coated pin.

don't they use full pressure pin oiling thru the rod ??

No, not any more. It was too tough to properly control the finish of the feed hole. Stress risers would form from the feed hole and the rod would fail in the beam or small end.

My wife always complains about failure on the small end...

[engineguyBill]

I have used steel on steel, unbushed rods/pins on many occasions. Have always drilled a small hole and chamfered it, for pin oiling - with no problems.

[KnightEngines]

I'm putting together a SBC with floating pins no bushes today - I don't expect problems.
Done it quite a few times, not an issue.

Just run a little extra clearance than you would with a bronze bush & drill a spit hole in the top of the small end with a chamfer.

[swampbuggy]

OK guys now lets hear the REASON for NOT using a pin bushing ? Mark H., I am gonna guess that it is to eliminate a part that could possibly fail ?

[pamotorman]

OK guys now lets hear the REASON for NOT using a pin bushing ? Mark H., I am gonna guess that it is to eliminate a part that could possibly fail ?

if they are not pressure rolled into the rod they can come loose if just a press fit. the best way is a coarse feed finish in the rod bore and pressure roll in the bushing.

[swampbuggy]

Pamotorman---- that must not be the ONLY reason ???

[pamotorman]

Pamotorman---- that must not be the ONLY reason ???

it adds a expense that is not needed. I used to do it when rod center to center dimensions were not well controlled to get the decks equal and you had to use the stock parts