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Discussion Starter #1
Does anyone know how, or have a source for, machining a set of pistons to accept spiral locks so I can convert a full floating setup? :2huh:

I have found a nicely priced set of H-beam rods for my boat’s 460 and I want to run TRW’s coated forged pistons, but they only come for a press fit pin (i.e. the groove isn't machined in the piston for the locks). :bawling:
 

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Baby Huey
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Find a good set of Manleys that are set up for fully floating and have Polydyn coat them.
 

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The advantage of the full floating wrist pins is that you have bearing surfaces on both the piston and the connecting rod whearas you would only have a bearing surface on the piston of a ‘press fit’ arrangement.
 

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Discussion Starter #6
From what I found on their website a few days ago, Manley doesn't offer any ford pistons except for the modular engines. :bawling:

I'll look into the Polydyn coating, etc. thanks. :thumbsup:
 

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Discussion Starter #7
tbirdbrain said:
The advantage of the full floating wrist pins is that you have bearing surfaces on both the piston and the connecting rod whearas you would only have a bearing surface on the piston of a ‘press fit’ arrangement.
Exactly. Normally I wouldn't worry about it, but with a marine engine you can easily see 5000 rpm.... for 20 or more minutes!! :beek:

That is VERY tough on any engine, then factor in that this is a big block... The better I can build it, the longer it will last. :thumbsup:

These are the rods I'm eyeballing:
http://cgi.ebay.com/ebaymotors/4340-BB-Ford-429-460-H-beam-6605-Connecting-Rods-ARP_W0QQcmdZViewItemQQcategoryZ33623QQihZ010QQitemZ200070957871QQrdZ1

Good price IMHO. And the coated TRW pistons are about $350. So for $700 I can get a very solid bottom end... if I can get the TRW's set up for the spiral locks. :D
 

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Alright guys, let's talk about this then. In a conventional pressed-pin application, the pin is pressed into the rod end, and the piston floats on the pin.

How about a little further explanation of how you suppose you get an increase in bearing area by full floating the wrist pins? The wrist pin bores in the piston are still seeing the same load on the same area.

In fact, the pin itself is subject to an increased bending moment as a function of the clearance that is present between the rod and the wrist pin. This clearance allows for additional deflection of the wrist pin, and an associated increased bending moment.

The advanatage of a full float pin is primarily two fold:
- Decrease in friction for the engines rotating assembly
- Ease of assembly and disassembly

You will also have a wrist pin that rotates around some so that it won't be loaded in the same place every single combustion cycle, but this effect is small.

There is a possible additional con, but I'll go into that in another post.

Mike
 

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Toombs said:
How about a little further explanation of how you suppose you get an increase in bearing area by full floating the wrist pins?
ok i'll do this nicely. You don’t get to count the interference fitted ‘pressed in’ wrist pin intersection as a bearing surface. The ‘bearing’ surface for this conversation being the material relationship and friction and not the structural loading.

You do have reduced potential friction as a result of the ability of the wrist pin to move more freely. The mechanical load on the bearing surface or in the case of a friction/interference fit parts would be the same obviously.
 

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tbirdbrain said:
ok i'll do this nicely. You don’t get to count the interference fitted ‘pressed in’ wrist pin intersection as a bearing surface. The ‘bearing’ surface for this conversation being the material relationship and friction and not the structural loading.

You do have reduced potential friction as a result of the ability of the wrist pin to move more freely. The mechanical load on the bearing surface or in the case of a friction/interference fit parts would be the same obviously.
Listen, there's no need to get testy. I fully understand what you're saying, I just asked for clarification to make sure we're on the same page, that's all. Now I've gotten that clarification, and I agree with your statement. Intelligent discussion can happen without a pissing contest. Let's be cool people :D

My comment was made because mechanical loading of the parts is of paramount concern.

Let me also preface this by saying that we run full float wrist pins in our racing engines as well, so I'm not against full floating the pins, but there are things to consider.

When you've seen engines fail from excessive RPM and loading, what typically fails? The wrist pin? Not typically. Piston below the wrist pin? Also unusual. Most failures (at least ones that I've witnessed) from this type of loading accur at the small end of the rod.

Now if you're going to run an aftermarket rod that's designed for use with full float wrist pins from the drawing board, have at it. What bothers me are when people talk about converting to full floaters. In order to do this, a signifigant amount of material must be removed from the rod pin bore to bush the bore. This is taking material away in the worst possible area.

Additionally, consider that the static force on the rod from a pressed pin exceeds the inertial loading that the rod sees. If it didn't, the wrist pin would walk. The signifigance of that is that if the small end of the rod is preloaded from the press fit to a loading that exceeds the inertial loading then the small end of the rod isn't cycled. Which means fatigue failure in this area is out of the question.

Again, I'm not saying that I'm against full float wrist pins, as long as the rods are designed for that. Or at the very least, the above has been considered before boring and bushing your press fit rods to make them full floaters.

tbirdbrain - I agree with what your saying, I'm not arguing with you. I like that we have a place to discuss these types of things.

Mike
 

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Discussion Starter #13
Now that everyone is so happy, can we get back on topic?!?!?!? :leftright

I said nothing about converting a rod to full floating, my original post was about converting a piston to accept the spiral locks so I can use the better rod.

Does anyone know how to do this or do you have source to have it done. I've hit up all my machine shops and none of them can do it. :bawling:
 
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