Archive through May 16, 2006

[rbedell]

I have an inquiry for the members.

I have five cubs and have worked on three of their motors. In each case, when working on these motors, I have had to replace the Aluminum Connecting Rod. I have read numerous times, on different forums, where rods come apart and do various types of damage. I got to thinking, that is there some reason for this type of failure? Are the aluminum connecting rods the “weakest link”? Should these rods be replaced anytime the motor is torn down for a major overhaul, even if they look good? Is there a better connecting rod? Is there some tip or suggestion to reduce the failure of these rods discounting proper installation and proper lubrication?
I am looking for comments, suggestions and insight to this.

 

[kmcconaughey]

Steve, nice job on the pump bracket!

 

[dfrisk]

ROLAND - The correct answer to all your questions is "Yes". As an old R/C racing Buddy who was also a VERY GOOD certified diesel mechanic for all brands used to say about Our billet alum. conn. rods in Our R/C engines..... "They're a wear part.... replace them and throw the old one's away! He did make His very cute wife a nice pair of earrings out of a pair.... They are about an inch long...engines run up to 40,000 RPM... A pretty stressful environment!
WYATT - Your 169 only has 34 cid..... not 7000 like the other LP engines You used to design....

 

[digger]

I was asked to post a pic of the riveted brake pads I make and how I attached them, so here it is.

 

[taweivoda]

A few years back a member had a post of a power steering conversion he had made for both a hydro and non-hydro tractor. I can't seem to locate the information.

Does anyone recall who the poster was or how I might contact him?

 

[kmcconaughey]

Terrence, I've been around here since 1998 and I don't recall that. Not saying it wasn't posted but I don't recall it and I don't see it in a quick browse through my archives. I recall hydraulic lift mods for non-hydros and power steering mods for hydros but not power steering mods for both a hydro and non-hydro tractor. If you can narrow down your "A few years back" to a year and season I might be able to do a search of my archived photos but with tens of thousands of photos it's quite a task to search through.

 

[jgeorg]

Charlie, what are you using for the replacement pads?
Thanks, John

 

[digger]

John I buy the material buy the roll and punch the pads out using dies I got from a grump in Kentucky.

 

[jgeorg]

They looked too good to be hacked out by hand.

 

[dfrisk]

CHARLIE - I thought that riveting die looked like some grumpy old fart down south made it....
Nice work!

 

[stanner]

Terrance, Kraig
dunno who originally posted it, but here they are

 

[dkirk]

Roland B.,

You ask a very interesting question. Dennis is correct in the “yes” answer concerning all points, but here are some personal observations on the subject.

Aluminum is a widely used engineering material with many benefits. It is the material of choice by small engine manufacturers for connecting rods used in virtually all utility-type industrial engines made today because of it’s light weight/volume, ease of forming, and low cost. Typically, these rods are made via die-casting and in quantity, are very low in cost to produce. The properties of aluminum make it a good bearing material; hence no special inserts are required. The light weight makes it attractive for lowered inertia forces, thus reducing transmitted vibrational forces when compared to a steel rod. This is especially important and desirable in single-cylinder engines.

But, the real down-side is lack of a strength fatigue limit. Aluminum, like all non-ferrous metals (brass, lead, etc.) has no fatigue limit. Fatigue is when a component fails subject to alternating stresses being applied. A connecting rod is a perfect example of a part subject to fatigue loading; high compressive stress on the compression and power stroke, then tensile stress on the exhaust-intake stroke. This continued “working” of the part in service will ultimately fail it. Thought of another way, the aluminum rod continually gets weaker as the hours (number of cycles) are built up. The new rod may have a tensile strength of 45,000 psi, but after several million cycles (and this can vary greatly) its strength will go to zero! You can guess what happens then.

 

[dkirk]

The die-casting process can trap air bubbles in the metal structure (Swiss-cheese syndrome). The uneven cooling of the process can lead to large grain structures forming within the casting, and these combined with entrapped air can produce a metal structure that will fail rapidly in fatigue. These potential accumulated faults produce crack formation zones (stress risers) that, once subject to tensile loading in fatigue, will quickly allow a crack to form and propagate through the material, resulting in failure. With a die-cast part, the surface may appear perfectly fine, but it’s what lurks under the surface that is the unknown variable. This material variability is the main reason that some die-cast rods run for thousands of hours and others fail in a few hundred. For a lawn mower engine, a few hundred hours is the product’s design life.

However, all that negativity being said, there are some aluminum alloys and forming operations that can produce satisfactory connecting rods that have predictable fatigue characteristics. Most metallurgists will agree that high strength aluminum alloys do have a fatigue strength limit of about 8,000 psi. Using a forging or machining from billet alloys produces the required shape. Both of these operations are more costly than die casting, but the material properties that result in the finished part are highly consistent, with no surprises inside. Connecting rods made in this manner are stronger initially, and fatigue more slowly than the die cast material. And if the engine designer selected suitable rod area cross sections such that the 8000 psi stress level was never exceeded, the rod could be good for an infinite life. But it should be noted that a 4140 alloy steel connecting rod would have fatigue strength ten times higher than the aluminum part and, if properly designed, would weigh the same! It would cost more though.

When overhauling a Kohler with unknown history, it’s always good practice to replace the connecting rod. A visual inspection will not reveal when a die-cast rod is at the end of its service life. For the K301 to 341, the forged aluminum K361 rod is the logical choice if maximum reliability is desired. It’s pricey at around $100.00 but is excellent insurance against failure.

Hope some of this rambling clarifies things.

 

[jschrage]

A quick introduction and a couple of questions.

I've been reading this forum off and on for a number of years, with plans on getting a 149 that was given to me working again. Seen lots of great advice.

The 149 hasn't seen work for 8 or 9 years. It now runs, and moves, I'm left with getting the mower working before we loose the kids in the tall grass. (It's a long story, but I've been mowing with a string trimmer for the last few years, and want to avoid that this year).

Now for the questions:
1) All the set screws in the implement clutch came out except the last. I notice the FAQ says use a carbite bit to drill it out. Does anyone have any tricks to this that make the job any easier? If I simply drill out the middle, is that enough to get he clutch off?

2) If you were going to bring a mower back into service that had been sitting out for 10 years - what would you do. Obviously I'll make sure nothing is seized, and clean and regrease and greasable parts. What else should I be doing?

Any help appreciated.

Thanks

 

[kfass]

Besides the link at the top of this page, where is the other Cub Cadet FAQ page again?

 

[digger]

Ken F.
http://cubfaq.com/questions.html

 

[kfass]

Thank you sir.

 

[wcompton]

Denny-
7000? That wasnt' even a mid sized engine, the biggest one I worked on was 17,398 cubes. . . . and going back to David Kirk's explanation, those engines had forged 4140 rods that were fully polished and stress relieved. Good stuff!!!!

Oscar-
Nice mockup. Do you know if Cub Cadet will have to "erase" the IH logo like it had to in it's 40th anniversary literature?

 

[owill]

Wyatt --

don't know the answer to that question -- keep your fingers crossed.

 

[mkopishke]

The good news is I got those dang blasted bearings on the shaft. I had a put the crank in the fridge on the coldest settings and then cooked the bearings and even then it was tight.

I get the deflection all set on the bearing plate, go to snug up the bolts and snap the head off one. I'm going to get the easy outs out tomorrow, I hope it will come out since it's not in the very tight at all, then again easy outs never seem to work for me...

Bad luck...