A standard 2.3L piston is already 0.3mm short, thus giving an additional .0118" of deck clearance.
A FelPro Perma Torque Head Gasket is .055" thick when compressed.
That is adequate for running an aluminum rod with a minimum deck clearance of .060".
It is wise to know the thickness of the compressed head gasket and also know exactly how much material was removed from the deck of the block when resurfacing.
The same should be done when resurfacing the head.

I'm sure Mike at R&R http://rrconnectingrods.com/store/sp...rods-p-58.html will answer any questions you may have about dialing in the perfect rod center-to-center length if your combination of deck resurface, and compressed head gasket is not enough to provide the required .060" deck clearance.
Getting custom pistons is not wise IMHO.

 

Just keep in mind that you don't want the actual running clearance to exceed 0.060", or you will lose your quench area.

 

Ted,

Whats the method for checking rod stretch without taking off head or pan?

 

Agreed, position is significant in rotating situations. But at the end of the rod, the movement is essentially linear and not rotating. I don't see it significantly affecting anything with position and would think total weight would be more important.

This thread has inspired me though. For a class on fatigue, I will be researching the fatigue life of various aircraft grade aluminum alloys and the difference between the methods of manufacturing (plate stock billet, forged to shape billet, cast, and extruded billet).

From what I have been seeing, I think fatigue life is going to be the most important thing here. I think even a 6061-T6 rod would have the strength to hold up to huge loads. The 6061 rod would likely fail in no time though from fatigue. All these claims of "custom 25% stronger alloy" means just about nothing. 7075 is a LOT stronger then 2024, yet 2024 will hold up better in most situations of cyclically loading because it has a higher resistance to crack propagation.

 

Mike will also tell you that rods expand/grow but dont "stretch". If it stretches at all it has already failed and is likely on the wrong side of operation.

 

Yep, they will expand and contract with use and heat cycling. When they don't contract, that would be "stretch", and is a telltale sign that they've reached the end of their useful life.

Take a minute, think about it, and tell me how you would do it. It's a good little mental exercise.

That is correct. But given the high G-loads on the wrist pin and piston at high crank speeds, think about how the mass on that end of the rod is reflected in inertial loads applied longitudally through the beam of the rod.

It's just a physical property of aluminum, and there's no getting around it. Metallurgically speaking, it's a matter of drawing the best compromise. That's why titanium rods exist - they're lighter and don't have the fatigue life issues, but unfortunately, that comes at a cost.

 

Excellent discussion, I hope it continues.

It’s not just aluminum either; EVERY material will fail eventually from some form of fatigue. It’s nature, Thermodynamics 101.

Titanium actually has as many if not more down fails as aluminum. Titanium is VERY susceptible to fatigue cracking. It's also a metal that likes to grab other metals and Fretting fatigue is a huge issue with it. The benefit though is the strength to weight is better than aluminum, and it is more stable under varying temperatures.

Different aluminum alloys have MUCH different toughness characteristics though. Toughness carries with it the ability to resist crack propagation. Also, manufacturing process and design can have a HUGE impact on fatigue life. Crack nucleation is going to happen in EVERY material on EVERY design. The difference between all the materials out there is how cracks will propagate and the difference in design will control the affect that a crack has on the item.

I've got a spread sheet around that should be interesting for this discussion. Let me modify it a bit to make it relevant to this discussion and I'll post up some computational data.

 

I did some initial calcs and piston jerk is showing some interesting results. Jerk is the rate of change of acceleration. It's comparable to an impact event.

I'm thinking my time step may be too course and it's causing some serious errors at certain parts of the calculations. Looks like I need to write something in matlab instead of Excel to make this easy on myself. That should make it easier to calculate approximate piston wall loads too.

 

Bringing this back from the depths of 2009...

03whitegsr,
What does jerk have to do with the force applied to the connecting rod? Jerk does not affect the load the connecting rod takes. F=ma right?

 

Steel rods stretch during running. I dont know about aluminum. But steel stretches. At 8,000 rpm there is typically .025 of rod stretch.

http://www.rbracing-rsr.com/squishcalc1.html

 

I think Aaron was talking specifically about aluminum rods in that instance.

 

I was.

Stretch is permanent elongation and is damage to the rod.

I believe that the link is using the word "Stretch" to interchange with Expansion which I do believe happens. In aluminum rods you want more on the order or .020 or so extra clearance because of this. Where that .025 buffer might be fine on steel, we use .050 for aluminum. When you take the engine apart and remeasure the rods they are still exactly the same length they were new.

Anything other than that means the rod has exceeded the modulas of elasticity and became fluid at some point. That is not good and means the rod (or truly rods if there were even one in the same motoro) needs to be taken out of service. The easiest way to illustrate this is if I crash my quad or streetbike my clutch lever and/or brake lever get stretched the opposite direction of the crash.

 

R/T Ernie, jerk as I mentioned is similar to an impact event. Think energy/time. The higher the energy or the shorter the time, the larger the impact and the more damage done.

Frequency effects come into play as well.

Damage is all that matters here and the more damage done to the rods, the shorter period of time they will last.

Also, I did a bit of research related to aluminum rods. There are several different methods to produce the rods used that I have come across.

Rough shape forged, fully machined
Extruded billet, fully machined
Plate billet, fully machined

When it comes to fatigue, the residual stresses left in the material has the most significant impact on fatigue life of equal materials. Every material deformation/removal process will leave behind residual stresses.

Tensile stresses are the enemy, as localized tensile stress will want to help propagate cracks. Tensile stresses will also help form cracks in the first place. Surfaces also have the highest stress intensity as there is an incomplete material field that leads to roughly 55% higher stresses. Thus, cracks are most like to form first at the surface and then propagate perpendicular to the applied load.

Compressive stresses on the other hand help close cracks and are great for fatigue life. However, you can't simply induce high levels of compressive stresses and be done with it, because physics forces a balance to take place and inducing compressive stress in one location means a tensile force is also induced in a surrounding area to balance in energy. Shot peening for example induces a compressive residual stress at the surface of a material. However, it also creates a layer of tensile residual stress under the surface of the material which can lead to sub-surface cracking. It becomes a balance, induce enough residual surface stress to reduce surface crack formation, but not so much that it leads to sub-surface cracking.

With regards to the base material used, each has good and bad sides.

Forging induces HUGE amounts of residual stress, with very high levels of internal tensile stress in localized areas. This is the bad side of forging. However, it also forces the material to flow around the open areas and forces internal voids closed. This reduces the number of end grains available for corrosion to attack and internal voids for cracks to form. A very good thing. It also produces a preferential grain direction to help carry hoop stresses in the rod big end. When you machine the entire surface you remove a lot of the surface compressive stresses induced by the forging process (bad) but also reduce the internal tensile stress (good). Also, most forgings are post processed to reduce the internal stress levels. (very good)

Extruded billet, depending on the dies and the process method used can have very high internal tensile stress in the middle of the material, and may show tensile residual stress on the surface as well. It's also a completely directional grain boundary system. Cutting the rod big end leaves a large amount of exposed grains to corrosion. The grain flow produces a non-isotropic material. If properly oriented during machining though, the grain direction is good for strength through the beam, although the tapered beam profile leaves more exposed end grain.

Plate stock has high compressive stresses on the surfaces before machining, but again, much gets machined away and leaves tensile stress through the internal material. Directional grain flow. Often the grain is very carefully controlled though, they have plate processing very well refined. Similar non-isotropic material properties as extruded material.

One down fall to many of the extruded/plate formed products is they do not undergo stress relief processes because while the stresses are often high, they are predictable and uniform. Forgings on the other hand are almost always stress relieved because of the very high residual forces left behind. The stress relief process reduces the internal stresses left behind that help form and propagate fatigue cracks.

All that said, from what little I've seen on aluminum rods, it still seems to be the fastener and the cap mating surfaces that are the weak areas and where cracks are most likely to form. These issues will likely dominate over material, forming process, post-treatment process, etc.

 

Kind of wish I had kept on this thread earlier, I could've answered your question back then, but better late than never I suppose lol.

One of the main reasons the shorter r/s ratio Honda GSR/Type-R can rev as high as it does is because of the valvetrain setup...the rocker arms are physically attached to the head so they can't fly off, and they make use of dual valvesprings to avoid valve float. Earlier Honda 1.8 liter dohc engines (B18A1/B1/B20) all used a similar rocker arm setup as the Evo/DSM heads do, just without lifters. They used valve lash adjustment to keep a set distance and hopefully keep the rockers on the seats...as long as you kept the rpm below 7500. A lot I feel had to do with spring pressure though, as once you hit a certain rpm the valve spring cannot keep up with the rocker and the valve floats and the rocker's would pop off. Pretty sure the same can apply to high rpm Evo's as well, I know I've seen it happen in older 4g63's before.

The only Honda motor AFAIK that has even as close a R/S ratio as the 4g63 is the Honda 1.6 liter B16A/A1/A3/A2 models, at 1.74:1 ratio. 160hp in n/a form, but less than 100 ft/lb's of torque.

 

A Honda B18C has a 87.2mm stroke, as opposed to a 2.3L 4G63's 100mm stroke. A 2.3L 4G63 hits a piston speed of 25m/s at only 7500 rpm, while the Honda doesn't hit that figure until a much higher 8600 rpm. That single factory inherently gives the Honda the potential for better high rpm efficiency and durability.

As for the R/S ratio, the Honda B18C is as such probably because Honda wanted to keep some low speed efficiency in this small displacement motor to make it reasonably snappy for regular street use.

In contrast, the Honda F20C has a R/S ratio of 1.82, and with an 84mm stroke, it doesn't get to 25m/s piston speed until almost 9000 rpm. With it's big, high flowing head, it's all about high rpm VE, which is why it makes so much hp.