Allcoupedup

It seems like press fit rods are "normal". What are the advantages and disadvantages of using bushed rods?


Thanks,
Brian

66427-450

My Opinion: For sustained hi RPM use floating pins are superior. For under 6000 or so, press fit is fine.

Ironcross

Pressed fit rods are used in nearly all of GM`s engines. Including all small blocks of any HP and even the LS7 454. The only full floating rod engines were the L88`s and ZL1 both of which are 427`s and easlily capable of 7000+ rpms. The longer stroke of the LS7`s would probably max out at 7000 and quit pulling after that figure, where as many small blocks with press fit pins and the L88`s keep right on revving. :D

SWCDuke

The primary advantage of floating pins is easy of disassembly and assembly on an engine that is frequently torn down. Considerable cost is involved in converting to floating pins and there are "right" and "wrong" ways to do it.

If you're rebuilding a OE engine and don't plan on taking it apart at least once a year, stick with fixed pins.

Duke

JohnZ

302 Z/28's also used bushed "pink" rods with floating pins - the only small-block floating-pin application (so SCCA would accept it as "production configuration" for the Trans-Am Camaros, which spent their whole life between 4500-8000 rpm at wide-open throttle). :thumbs:


[Modified by JohnZ, 12:35 PM 2/24/2004]

Plasticman

Brian,

All the above responses are correct. Pressed in wrist pins are "normal" for street engines, whereas floating pins are used for most racing application due to ease of disassembly and slightly less friction. But, the main advantage to pressed in wrist pins is that it forms a rigid "T" (the top of the "T" being the wrist pin, and the vertical portion being the rod) which is better at keeping the piston/rod aligned with each other in the crank to bore relationship. For longivity, this is a better situation (at the expense of slightly more friction).

Most forged pistons are sold with floating pins (probably since most of these pistons will be used in racing applications). But the stock rods must be revised to accept them.

The use of bushings vs. just honing out the small rod end for the floating pin (with no extra bushing) is a debatable issue. Many a SBC has been built with no bushings (and bushings are softer and likely to wear that much faster). I have never seen wear on a non-bushed rod. Normally the rod ends are just honed to the correct bore dia. (normally .0008/.0010" clearance) for the floating pin, and a 1/8th inch hole drilled in the very top of the rod through to the small end bore (and chamfered at the top of the rod and deburred at the pin bore) to provide lube for the bore/pin.

On the positive side for bushing use, the rod bore can be honed to a reduced clearance of .0005/.0008" due to the increased lubricity of the bushing material, which makes the rod/pin more closely aligned (closer to the rigid "T" of the pressed in pin design).

But for street purposes, I prefer the rigid "T" of the pressed in pin design.

Plasticman




[Modified by Plasticman, 12:07 PM 2/24/2004]

norvalwilhelm

All the 3800 motors in the bonnevilles, buicks , whatever are fully bushed full floating. I regularly tear new motors down and am amazed at the stuff in these V6 engines in everyday street cars.
Full floating pins, slipper pistons, narrow rings, windage tray, roller cams, roller rockers and plastic intakes with really smooth passages.
That said I run steel floater rods in my blown bigblock. I just hone the small end for clearance and double drill the oil holes, 1/8 inch hole in the top of the rod and one from the bottom on an angle from the front. I have never had a rod failure and regularly do them for the local race shop. I have seen rods let go but never a wrist pin.
ON one of my big blocks running in the 7500 rpm range I had 3 pistons on the verge of seizing with pressed pins.
Hone the stock rods, double drill the oil holes and you should be fine. I also like taking things apart a few times while assemblying.