I'm in the process of converting a Kioritz 21.5cc and have discovered that they used roller bearings on the crank. What's the general feeling, should I forget this engine or just go ahead and use it as is with the rollers. Anyone tried this --- RCIGN1 ???

No reason to forget it based on ball vs. roller. Rollers will handle a higher loading while balls will typically handle higher RPM. The RPM range of these engines won't really be an issue with rollers so start cuttin'!

Read this thread, I believe that this engine is the same as yours even though it is called a "McCulloch".

Read post #24 first.

http://www.rcuniverse.com/forum/m_16...tm.htm#1696802

You will need probably 1 ballbearing at least if it's for an aircraft!

Quadra 35-42 been using rollers since day one. Still work fine with few problems.

Could you post a pic? I once had a 21cc engine that really didn't look like the other Echo/Kioritz engines, but it was and I decided it wasn't worth converting. I eventually used the cylinder & piston as a "big bore kit" for my Kioritz 16cc. (Don't go there either, as it worked out well but was a very involved project.)

Anyway, the one I had, had a small lightweight crankcase that looked attractive, (light), but it only had one bearing in the crankcase and the other crank bearing was mounted with bend over tabs in a piece of aluminum that was part of the weedeater mechanism and overall metal that I needed to cut off. I could have machined the crankcase for another bearing, but it just wasn't worth it for a 21cc engine.

Good luck,
AV8TOR

Its simple rollers won't take side thrust, ball bearings will. The old Quadras get by because they use a bronze thrust washer on the crank to take the side load.
A ball bearing on the "front" of the engine or a thrust washer is a must.

Don't know how they get by with it, but the new US 41 engines have roller bearings and no thrust washer, just steel crank against the front roller bearing...

Thanks for the responses, I'll probably go ahead with this thing,,,,I'm into it now !

AV8TOR, It's pretty well cut up but I'll try to get a picture of the bearing setup. This one is not like the one you described, it seems to be pretty well built. No metal tabs good castings.

Neither will a simple ball bearing- unless it's specifically designed for side loading (thrust). See: [link]http://www.nsk-corp.com/page.asp?ID=252[/link] and note "Angular contact". While a standard ball bearing will take a moderate amount of side load, this is not the specific type of loading they are designed for- unless the bearing in question is indeed an angular contact bearing.

That being said, you'll need to determine if the engine has an adequate provision(s) for thrust loading. This notwithstanding, rollers are fine and will support a higher axial loading than ball bearings- albeit with a lower top RPM limit.

A bearing engineer told me a standard ball bearing will take half its radial load in thrust...
If a ball will take 3000 radial it should easily take 1500 side, way more that the 15 or so lbs put on it by a prop.....

I think the real question is how long will it take a side load? No doubt a standard BB will take side load- to a limited degree- but what the life of said bearing will be? Well, that's another story. There's a reason your typical, older automobile uses tapered roller bearing on the wheels; these will accomdate both radial and side loading- and both loads will have a high limit.

Regardless, good discussion that brings up some good questions.

Old Wisconsin single industrial engines had tapered roller brgs. for mains. Could rebuild them 3 or 4 times, rings, rebores, before the brgs. had to be replaced. Most of the time just reshim them and go again.

Sam,
It is also important to know how much thrust they take, - in a model aircraft situation this is not great and a standard ball bearing works well.
Of course an angular thrust type would be a better but more expensive solution, - but unnecessary.
Only 1 ballbearing is needed, and I believe that this engine, ( if it is the same as mine ) has castings made to allow room for ballbearings originally, which helps.

Willdo,

Yep, I'm sure a standard BB would work fine in a limited thrust (i.e., model aircraft) situation; just wanted to clarify that there is indeed a difference between the two types of BB's and that this is something needs to be considered when retrofitting bearings.

Was down in Christ Church a couple of years ago, pretty nice place- like to go back sometime.

The most common crankshaft ball bearing is the 6202 bearing. It is also the most common auto alternator bearing around.
I've replaced bearings by the bushel basket in engines cause they were rusted, the engine swallowed something, they were packed with 10 year old dried oil. I replaced a couple caused they were wore out and had to much play.
Don't lose any sleep about the side load model engines place on the ball bearings.

Went to Christchurch last year, you have probably been there as much as I have! Yes it is pretty nice and the people are friendly.
Was in Seattle in 1989, it's not unlike Auckland with it's tower and all the water around.

OK, what is a side load? There is torsional, radial, and thrust. So which is it?

Side load, or thrust, is what the prop, pulling on the crank, does to the bearing...
Radial is what the piston, pushing down on the crank, does to the bearing...
Don't know how torsional applies to a bearing, it's usually the twisting force applied to a shaft, as in a torsion bar..