Using rods narrower than the main journals or stock rods?

Let me see if I can explain this:

Had a guy tell me today that I could use a thinner rod than my stock rod, and use spacers on the piston pin to keep it centered on the crankshaft?

That sounds so wrong to me, but is that an acceptable thing to do?

 

Sounds like a recipe for disaster.

 

Only if it's a lawn mower

 

Ain't never heard of that ....

 

Is this for a Trabant engine?

 

They are called piston guided rods. Its been done for years.

Ideally you use pistons made for this purpose, eliminating the use of spacers.

 

you get a lot of oil splattering
around in the crankcase and
probably low oil preassure
and higher oil consumption
due to all the extra oil squrting
up in the cylinders
Why using them?

 

On race engines with limited use. Also a little more to it than just using spacers on the piston pin.

 

Well it would open up, some rod choices as of now I have 1 choice, stock rods. They are forged but still......

 

Oil hole placement is critical, as are bearing clearances.

 

Chevy, Ford V8? Most are fine, especially with good bolts. Exceptions would be early 265/283 rods with narrow beams.

 

I guess I could have the journal ground a little under, leaving a lip to catch them??

They are ford 300 rods, but I am putting a blower on it. hoping to make some serious torque.

 

They other thing is I am shooting for a daily driver, lol.......I want it to be reliable as possible.

 

What i heard so are the 300 rods good rods
i had not run a set by my self thoug
and with a blower you dont stress the rods
as much as with high rpm

 

NO!

How much side clearence are you talking about?

 

As others have said this is done on race engines. The idea being there is less friction between the SE of the rod and piston if it is machined for it or spacers than there is if the BE of the rods are against each other and there is less reciprocating mass.The inside of the pistons (pin towers) need to be machined parallel to each other though as they are now a bearing surface. Also, you will probably need con rods that force feed oil to the pin.

I think most of the time there is also piston oil squirters used when it is top guided and you don't see it on the street much.

 

This shows the difference between a "normal" piston and one made specifically for piston guided rods.

 

tell us more about your combination, there might be other options

 

I would never do that. I would buy the right parts for the job.

 

I's a Ford 300 inline six, with the exception of 240 rods there is nothing else off the shelf that will fit...........

 

Seen the concept done on ford 4 cylinder kent engines by racing /hot rodders when the datsun 520B cranks were swopped over into them the bore spacing on datsun was slightly differant so rods were centered on pin piston using teflon spacers, no need for oil squirt holes as theres plenty of it splashing up .Didnt have any thing to do with a free -er reving engine theory , thats a differant engineering requirement ,dealt with by narrower journal cranks and rods to free up frictional losses. Theres some who have used a narrow big end rod and used a wide big end bearing shell to keep oil pressure not ,to center the rod --thats still done by spacers on the pin. If the bearing shell is too narrow for the intended journal it can have excessive oil bleed off, low oil pressure , so might need to run a high CAPACITY pump.THese are short term engines so no idea how suitable the method is for a high milage road car.

 

seems a little over kill for a dd.replace the rod bolts with arp and you should be ok.im sure crower or oliver or another custom rod company can make rods to your specs.wont be cheap

 

Man this thread is makin my head hurt. Why would you try this ?

 

I'd stick with the correct pieces.......

4TTRUK

 

I am running a blower.......thats why I am looking for something better than stock.

 

Piston guided rods are no problem, if one knows how. But in this case, not worth the expense of custom pistons and custom rods.

IIRC, there is a heavy duty truck 300" crank, C5TZ-6303-D and heavy duty rods C5TZ-6200-A. Guaranteed you won't break those. We used to hang 302" Chevy Z-28 forged pistons on them.

BTW - Rods are plenty strong under compression. so torque doesn't hurt rods. However, RPMs do; the inertial forces trying to pull the rod apart go up by the square of the RPM. Lots of torque at 4,000 RPM, no problem. Just double the RPMs at 8,000, the intertial forces are four times as great, but not from torque, just all that flingin' around fast.

How's your head now, Hank?

jack vines

 

Stock rods can't be all that bad. http://forums.subdriven.com/showthr...d.-Yes-that-s-the-old-145-hp-van-truck-engine.

 

Try
http://www.cliffordperformance.net/index.html


Posted from the TJJ App for iPhone & iPad

 

Interesting article, but the following copied from it is pretty much wrong:

By contrast, most typical V8 engines send a piston down the hole every 90 degrees. On the negative side, that means the six's crank must rotate a full 120 degrees before there is another power stroke. But on the positive side, each power stroke has 30 degrees of extra time to put energy (i.e., torque) into the crankshaft. That's why straight-sixes generally deliver more low-end torque than comparably sized V8s—all other factors being equal.


It doesn't matter if it's a single cylinder Briggs & Stratton or a 28 cylinder Pratt & Whitney R-4360 Wasp Major, the crankshaft rotates 720 degrees to complete the four stroke cycle, with each of the four cycles lasting approximately 180 degrees of crankshaft rotation (let's ignore valve overlap and use the textbook example of the four stroke engine). To say that the power stroke on a six is 30 degrees more crankshaft rotation than that of a V8 is ignorant.

 

I don't understand something here: runs thru the traps at 5200 rpm on a 3800 to 4200 stall converter into a 3.25:1 rear gear turning 28" - 29" slicks. I don't have my calculator handy, but his MPH should be much higher!

The 300 is a stout engine, especially with the truck forged crank. Blueprinted stock rods with ARPs will handle the combustion pressures, provided it is correctly tuned - but that applies to any engine.