Just daydreaming... bushing pistons instead of rods

[defrag010]

While I was busy boring blocks today (maybe they call it boring because it IS really boring), I got to thinking all about bushings in the small ends of connecting rods, offset bushing them, etc. Then, I was wondering about how you could put a bushing in the wristpin boss on the piston itself and bush the piston to where it accepts a smaller wristpin... like say from a chevy .927" or a ford .912" down to a .866" wristpin. I'm sure you could probably make it work, but the one thing that I couldn't come up with is a safe way to press the bushing into the piston itself without damaging it... and the fact that the soft bronze bushing in the soft aluminum piston is just a recipie for disaster.

For those wondering, I always think of just random things like this, and create scenarios and try to solve the "problem" in my head as best as I can, it keeps my gears turning while I'm busy.

[Ed-vancedEngines]

It is good to think and at times to keep on thinking. lol.

Before you get too far along with the idea of the smaller wrist pins consider this. Would you turn your rod pin on the crank down to .866 ? IN some ways the lowly wrist pin has as much or almost as much stress and load on it as does the crank pin.

Bushing the pin boss on the piston could be a tough thing to do, for the same reasons they are not bushing the wrist pin end of aluminum rods. The heat expansion rates of the two different metals could result in a mess with more than plenty of extra clearance at exactly where you don't want it.

Ed

[defrag010]

yeah, that's the only real reason I think it wouldn't "Work"... I bet if you found a way to press in an iron or steel "bushing" and hone the inside of that out to a thousandth or so larger than the wristpin, it might work. The circlip would keep the sleeve from exiting the piston on the outside, and the side of the connecting rod small end would keep it from coming out the inside of the piston... If you could just find a way to press a hard metal "sleeve/bushing" into the piston pin boss and get it to stay there under power, it would work.

Or, you could make it "double floating"... the iron sleeve floats inside the pin boss, and the wristpin floats inside the iron sleeve.. and you use the circlip to retain it on the outside of the boss, and a clip to retain it on the inside of the boss. This would be just like how journal bearing turbos hold the bronze bearings in the center housing.

As far as wristpin load vs. rod journal load, I don't know.. I'm just using sizes that are common for wristpins. I'd assume that wristpins are made of a harder alloy than crank journals, so they will take a little more load.

[Keith Morganstein]

While I was busy boring blocks today (maybe they call it boring because it IS really boring),

What machine are you using? With my old VN777, it's always exciting because one mistake is the difference between a good job and junk.

I think you could bush pistons if you had to for some oddball application where you made parts work together, but that is the only reason I can see for it.

[Speedbump]

I know it's not the subject of the thread but I got a good morning laugh at Kieth's comment about the 777. Early on I got into the habit of keeping my finger on the off switch until the cutter was firmly in the bore and the catspaws could be engaged. It was never "boring" as I had the bar try to leave twice in my illustrious career. Thanks for the grin .

[BLACK BART]

Since we are just daydreaming and this is not the norm or practical for that matter, here's an idea. What if you made the bushings out of aluminum and either staked them or welded them on the ends after installing but before honing? Of course this is more work, but they would have the same expansion rate and bearing qualities as the original piston and they should stay put.

I like thinking of weird stuff like that too. CJ




SB Mopar .984" to SB Chevy .927" is a popular conversion and may be worth it if you had more time than money.

[OldSStroker]

yeah, that's the only real reason I think it wouldn't "Work"... I bet if you found a way to press in an iron or steel "bushing" and hone the inside of that out to a thousandth or so larger than the wristpin, it might work. The circlip would keep the sleeve from exiting the piston on the outside, and the side of the connecting rod small end would keep it from coming out the inside of the piston... If you could just find a way to press a hard metal "sleeve/bushing" into the piston pin boss and get it to stay there under power, it would work.

Or, you could make it "double floating"... the iron sleeve floats inside the pin boss, and the wristpin floats inside the iron sleeve.. and you use the circlip to retain it on the outside of the boss, and a clip to retain it on the inside of the boss. This would be just like how journal bearing turbos hold the bronze bearings in the center housing.

As far as wristpin load vs. rod journal load, I don't know.. I'm just using sizes that are common for wristpins. I'd assume that wristpins are made of a harder alloy than crank journals, so they will take a little more load.

IMO, the idea is to get mass out of the system without compromising strength. Bushings don't carry load as efficiently as the parent metal. They mostly go along for the ride. Many bushed rods use extremely thin (less than 1 mm) bushings, but if you eliminate the rod bushing completely by using a DLC coated steel pin you can make the pin end of the rod smaller (less massive) which decreases your inertia loads without compromising strength. It isn't much, but every little bit helps at exteme rpm.

If you have a minimum rod weight rule, transfer the pin end mass to the cap where it can do some good. I have yet to see a minimum pin end rod mass rule. If you want lighter but stronger pins, use a piston properly designed for a shorter pin of the original diameter.

Jon

[Larry Widmer]

We're building a VW 4-cylinder diesel into a 5-valve turbo race engine. The stock VW pistons have bronze pin bushings, and so do the rods. It's the first time I'd seen anything like it and most of the people I know that work in the high performance machining industry are amazed when they see it.

[dwilliams]

Back in the mid '90s there were some vendors selling 330 Ford stroker kits using some OEM rod (I think they were Ford Escort CVH) and bushing an off-the-shelf .927" piston down to fit. I knew a guy who bought one, and it had held up to half a dozen track events when I lost track of him.

I once did a 500 Ford stroker with pistons bushed down from Ford to large Buick pins. I made the bushings from 6061-T6 aluminum, pressed them in with Loctite and .015 (yes, fifteen, not one and a half) thousandths interference fit (being thin, they swaged right down), made a conical tool to stake them into place, honed them to size, and drilled two oil holes in the bottom of each pin boss.

[Masher Manufacturing]

Back in the mid '90s there were some vendors selling 330 Ford stroker kits using some OEM rod (I think they were Ford Escort CVH)

I'm pretty sure the rod was a 1.6 Ford " Kent " found in early Pintos and English Fords. These motors werethe spec motor for Formula Ford road race cars.

The CVH is a 81 up Escort motor.

[jimivice]

Daydreaming is good especially when you are boring, it is the opportune time, unless you are using the VN777. Whoever said boring wasn't boring was correct, I don't know how many times I waited for the bar to move or get kicked off the block. Boring bars are unforgiving, there is no turning back. If the mike is set wrong or the cutter is misslocated by the time you notice the problem, it is too late. I don't know if there would be a benefit in bushing pistons. I think reducing pin diameter is going in the wrong direction. The common trend is to shorten the Compression Hgt. to either accomodate a long rod or stroke. The skirt is shortened and the pin shoved into the ring lands. If aluminum rods are being used, the top of the pin ends have to be machined to fit the piston and/or the piston has to be machined to fit the c.h.. You take away from the integrity of the rod and piston, even if the pin diameter is reduced. If pin diameter is reduced the wall thickness has to be increased and there will no substantial wgt. saving. I believe in reducing riciprocating wgt.. How much is to much? Do you sacrifice stabilility for weight? The jury is still out on the effect of rod length and power, it is the subject of debate. There has to be compromise. I favor a taller c.h., longer skirt, shorter rod,larger diameter pin and heavier piston. I think this would improve ring seal and structurial integrity of the assy. In the quest of weight savings other factors are ignored.

[Stef]

We're building a VW 4-cylinder diesel into a 5-valve turbo race engine. The stock VW pistons have bronze pin bushings, and so do the rods. It's the first time I'd seen anything like it and most of the people I know that work in the high performance machining industry are amazed when they see it.

To quote from SAE 970840 "Friction and Lubrication Characteristics of Piston Pin Boss Bearings of an Automotive Engine":

"Pin boss friction force can be significantly reduced by including bearing material in the piston boss, and this should allow further weight reduction and improved lubrication"

Combined with decreasing pin surface roughness there are reasonable reductions in frictional losses to be had I think.