racerdude5
Well-Known Member
Pros and Con's of each?
Personal Experiences?
Reliability and Performance Differences?
Personal Experiences?
Reliability and Performance Differences?
Press Fit vs. Full Floating Wrist Pins
- Thread starter racerdude5
- Start date
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moper
Well-Known Member
Pressed pins can walk out and hit the bores, especailly with rpm and load. They just don't handle the abuse as well as having some oil between the parts and some room to wiggle. I know there are those that float pins in rods without bushings. Personally I wouldn't but it has been done. I have run pressed pins pretty hard before but not really really hard...
If fits are within specifications, both are good. I'm with moper, if you are going to run floating pins I want a bushing between the rod and pin. Floating pins can be assembled and disassembled at home. Pressed pins, not so much...
floaters have two pivot points if thats what you call it . much better for higher rpms
It's been argued back and forth for decades. The general idea was in high performance engines, the full floating pin allowed a little acceptable movement of the piston in the bore and relieved stress.
Both are acceptable. If you go full floating have the rods BUSHED. Some people do not and simply have the little end of the rod honed until the pins float in the rod. Although people have done it and gotten by, you need two different metals there. What the pin slides into must be softer than the pin itself or the rod and pin will gall and seize. Lastly, bushed rods need a hole drilled straight through the top of the small end and into the pin bore for splash lubrication of the wrist pins. That's about it.
Both are acceptable. If you go full floating have the rods BUSHED. Some people do not and simply have the little end of the rod honed until the pins float in the rod. Although people have done it and gotten by, you need two different metals there. What the pin slides into must be softer than the pin itself or the rod and pin will gall and seize. Lastly, bushed rods need a hole drilled straight through the top of the small end and into the pin bore for splash lubrication of the wrist pins. That's about it.
racerdude5
Well-Known Member
Is there a particular difference between the rods for full floating pins and pressed pins?
No. In fact, there are 318s, 340s and 360s that all use the same casting number rods. The only difference is that the 340 rods are bushed for floating pins. All small block rods are virtually the same, except the early 318 and the 273 rods. They were the same length of course, but much smaller and lighter. They were also bushed. Some people prefer them for a lighter reciprocating assembly. I have two sets myself I am just sitting on really for no reason. I'll probably never use them. lol
I think that it's more of a manufacturing issue than a "performance" issue.
With press fit rods, you have to control the temperature or you can overheat the rod and make it weaker.
If you use floating pins, you have to worry about a missing/loose clip.
It's not an issue when you are hand building single engines at a time, but when you have to put hundreds, and thousands together, it can become a challenge....
With press fit rods, you have to control the temperature or you can overheat the rod and make it weaker.
If you use floating pins, you have to worry about a missing/loose clip.
It's not an issue when you are hand building single engines at a time, but when you have to put hundreds, and thousands together, it can become a challenge....
moper
Well-Known Member
"I think that it's more of a manufacturing issue than a "performance" issue. "
I agree - but it's not the assembly. It's the additional time of a full floater, and the extra cost of installing the pin bushings in a rod, and the clips in the piston. Simply put the old engines using pins were the way it was always done, until the bean counters got with the eingineers and figured out it was overkill for an engine that has to last through a car loan. So the later performance engines kept the floaters, the standard duty stuff went to the cheaper pressed pin for the sake of money. Like you say - one bushing is half a cent. The clips are about the same for two clips. Times that by 8, and times that by 600,000 for each displacement engine they made and it's significant.
I agree - but it's not the assembly. It's the additional time of a full floater, and the extra cost of installing the pin bushings in a rod, and the clips in the piston. Simply put the old engines using pins were the way it was always done, until the bean counters got with the eingineers and figured out it was overkill for an engine that has to last through a car loan. So the later performance engines kept the floaters, the standard duty stuff went to the cheaper pressed pin for the sake of money. Like you say - one bushing is half a cent. The clips are about the same for two clips. Times that by 8, and times that by 600,000 for each displacement engine they made and it's significant.
racerdude5
Well-Known Member
So here's the question. Full floating or pressed fit for 6500 rpm 318 at about 400 HP? Which forging? Magnum vs pre-73 273/318 vs pre-73 340 vs post-73? I'm on a budget so it's crucial to keep cost to a minimum but I still want the best that I can get for the money.
moper
Well-Known Member
Find a set of 273 rods. They're light and already have pin bushings. And you can get them cheaply... like a free engine you can keep the forged crank and turn in the rest for scrap.
Yup. They are light. I got 2 sets.
madscientist
Banned
For all the screwing around you can buy an aftermarket rod. Don't waste your time bushing a stock rod.
skrews
Well-Known Member
this
^^^^ This,. A Scat 4340 rod, at around 325-350, is hard to beat. Ask a local machine shop, to Magnaflux/ resize/add rod bolts alone , will net you a 250-300 bill. Buy the good rods, end of story.
pishta
I know I'm right....
LA rods came in 2 designs. The original 273 casting and the heavier duty beefy 340/360 '4bbl' casting. Magnum rods work but are dimensionally thinner on the little end (its so slight you wonder why they did it) but its a factor when you try and put stock magnum pistons on an LA rod, they dont fit! Or they are so close that they dont allow the piston to center in the bore. All factory floaters were bushed. Ive never seen a floater without a bushing for said reasons. Pressing a pin out of a 360 is tough, I used a 20 ton and it spiked to 11 tons before the pin gave way, and no one will guarantee the piston will survive this. My machine shop also had a "hell of a time" pressing a magnum pinned piston onto a 360 rod. Not sure why but he said that combo was 'F'n tighter than the norm...'. Specs say all the Mopar 318 pins are the same OD, .9842.. LA or magnum.
<<< Some aftermarket pistons do not come with lock grooves, make sure you check before you go floater!!>>>
<<< Some aftermarket pistons do not come with lock grooves, make sure you check before you go floater!!>>>
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yellow rose
Overnight Sensation
I can't think of a reason why you would even bother with a press fit rod and piston. Buy an aftermarket Rod, get a stronger, lighter Rod with 7/16 cap screws instead of 3/8 bolts and the rods will already have the bushings installed.
Here's a question.....are the pistons already cut for spirolocks/snap rings? If yes then float the piston, (see if RRR will give you a set of his 273 rods he'll never use) if not, press it. For your stated goal, my opinion is it's a coin toss, your stated rpm is not all that great, nor is power level. I get low coast/budget, I don't see $325-$350 as being "inexpensive", and even with "NEW" rods you should still have the big ends checked for size. I know you can spend a whole lot more than that and I have. I was not letting coast be my guide, I was going for a whole lot more than 6500 rpm and 400 hp.
If I were you, I'd look for a an unmolested donor, pull the rods; date codes/size on the bearings will be the tell of prior work, have the big ends checked for size and if in spec put it together, I'd start with the rods in the "teener" you already have.
FWIW, my own "mean teen" as I call it, got put together with 273 rods that were pulled form one engine and poked into another, only passing thru the wash tank along the way; Desk Top Dyno said it made 450 hp and I bounced it off a 7400 rpm chip more than once.
Just my opinion............
yellow rose
Overnight Sensation
To screw around and correctly rebuild a set of rods is almost as much as new rods. And you still end up with STOCK RODS. That's crazy. If you think any OEM put connecting rods in their basic passenger car,
surface transportation they did not. They used what they engineered to make it past warranty and then build in a factor and called it good.
Don't step over donuts to pick up dog poop.
OP asked for opinions, I gave him mine.......I grant you that Mother Mopar didn't spend lots of money in design, materiel, construction of their rods....in comparison to other factory offerings though, they are are stout....I am of the opinion that if the big end is checked and is in speck to yield a good crush, there is little need to go any further.....I have never seen a broken rod bolt, I've seen broken rods, but not bolts. A mag inspection is a good idea, but I have also by-passed that on more than one occasion with no ill effects. A while ago a member from Oz posted a question about how much a stock rod could take.....he claimed he was pushing upwards of 700 hp on a stock rod in a boosted turbo application....I commented that I thought he had already defined for us what a stock rod would take.......he could have been lying, who knows....what I took away from all of it was that hp is not your first enemy in engine death, it is rpm, YR you yourself have stated in the past that anything less than 8000rpm is nothing........so the OP's 6500 estimate is just off idle to you and I think is well with in the capabilities of a stock rod.
Again, my opinion......
yellow rose
Overnight Sensation
I didn't disagree with your opinion. I disagree with the cost side of it. I've seen Rod bolts break. Especially stock Rod bolts that have a billion cycles on them.
By the time you buy good bolts, cut the cap and Rod, size for clearance and replace the bushings and hone them to size, you are almost at the same cost as a new set of rods, with 7/16 capscrews, and made from 4340.
From that point of view, the money side of it, the stock Rod is loser.
BTW, Stock eliminator guys were allowed to use aftermarket rods. Newer engines were coming with lighter rods, the OE stuff was failing (it's hard to keep the big end round with a 3/8 bolt no matter how good it is) and you have to add more clearance to make room for the big end going out of round.
Money should not be the reason to not buy aftermarket rods.
Pay once.
Cry once.
You gotta have it (money) first, for it not to be a reason...................
yellow rose
Overnight Sensation
Damn. If 50 bucks you don't have, because I can go on the web right now and find rods for 350 bucks and you'd be lucky to CORRECTLY rebuild a set of stock rods for that, then you need to go golfing.
What's your labor burden?
............. 4 years later! Old post.
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