mtcarey

My Feedback: (2)

When installing bearings, would it be advisable to
Immerse the bearings in lubricant (Marvel Mystery Oil)
While in the refrigerator to reduce condensation and rust?
Is this oil good for lubricating the piston and cylinder before?
assembling?

Shredz

I'm new to this hobby but know a bit about bearings.

The odd thing about chilling a bearing to reduce condensation and rust is the moment you bring the bearing out of the fridge, it's attracting moisture from the warmer ambient air which would promote corrosion. The oil on the bearing would prevent moisture from reaching the bearing surface, but I would chill a bearing to shrink it for an install into a boss, or I'd heat the boss for a contact fit but I'm unclear as to why you would do this for the reasons you've stated.

Hopefully someone can shed some light on this practise? Now I'm curious.

Volfy

My Feedback: (23)

The refrigeration bit I have no idea. Does this mean you have to be standing a walk-in freezer while you assembly the engine? Seem like a thoroughly nonsensical idea to me.

This cooling of the smaller part and heating of the larger part for a better fit is another bad idea. Problem is, as soon as the parts make contact, heat transfer will occur - with steel this happens very quickly. If the temp differential is great enough, you might end up with local distortions and thermal stress cracks because of it.

Bearings are either slip fit or press fit, both should be done "dry" as you put it. If it is press fit, it should be done with a press so as to drive the bearing in evenly without damage.

You can buy engine assembly lube if you must use something labeled as for just such a purpose; otherwise, just about any oil is fine for assembly RC engines, with the same precautions as for afterrun oil selection.

Ernie Misner

Greetings ! Put the bearings in a ziplock back while in the freezer.
If the bearings are new they will have a very effecient coating of protectant on them anyway. It's after you remove them from the freezer and they start warming up that they would attract the most condensation anyway. I wouldn't worry about corrosion happening in such a short time- you'll be lubing things good when you get them pressed into place and putting it back together anyway. Boca Bearing has good info that comes with their bearings. They just say to put the case in the oven at 350 and the new bearings in a plastic bag into the freezer.

Ernie

Spicoli

I am no expert on bearings but the book I bought on Saito engines basically says the same thing as Ernie.

JWN

My Feedback: (42)

I've replaced bearings in several engines and always done it as Ernie desribed, but I don't even worry about the zip lock baggy. Just heat the case, drop the bearings in and slide the crankshaft in place. You can do it quite quickly, even with gloves on and I've never had a problem with the bearings not seating or aligning properly.

John

Flyboy Dave

My Feedback: (21)

Once the chilled bearings are seated into the heated
case....the heat transfer takes place rather quickly. If
you watch the inner race of the bearing, the frost will
dissapear in about 20 seconds, and they are dry.
Moisture isn't a problem. A few drops of 3-in-one oil,
in the bearing, and your ready for the remainder of the
assembly.

Ernie Misner

When I put new bearings in my OS 46SF, it turns over (by hand) just slightly tight as compared to when I still had the old bearings in it. I haven't fired this engine up yet but I was wondering if this is normal until it runs a little. It's not overly tight or anything mind you, but just doesn't have that loose feeling you would expect from an older engine. Thanks for any input -

Ernie

Rudeboy

Could just be the polymer seal in the front bearing... I'd put it on a test stand, fire it up and keep a hand on the case. If the case doesn't get too hot: nothing to worry about. The friction will probably disappear after the engine has run for few minutes.

Ernie Misner

Thanks Rudeboy. These bearings are a high speed/high heat set from Boca. Supposedly they have a phenolic race..... think that would take a little breaking in?

Ernie

Flyboy Dave

My Feedback: (21)

Ernie....did you put a prop on it, and pull all the free
play out of the crankshaft (forward that is).?

Ernie Misner

Hi Dave - As I recall I put an oversize prop on the shaft first, then a washer and prop nut, and "sucked" the crank all the way foreward to seat the bearings. Still, I can't feel any any end play in the crank after it's all put back together and I think maybe there should be a hair. I was hoping that running it would simply free things up.

Ernie

Flyboy Dave

My Feedback: (21)

I'm thinkin' that rear bearing isn't seated all the way,
and you have a slight "load" on the inner races. Is there
a proper gap between the prop collar and the front of the
case ?

Ernie Misner

Hi Dave, there's no visible gap there. Do you think the engine would have to be totally disassembled to seat the rear bearing? Could I try tapping the back of the crankshaft?

Thanks - Ernie

Flyboy Dave

My Feedback: (21)

That's what I thought Ernie....Leave the prop base washer
on, use some washers, and the prop nut to hold it so it
doesn't pop off. Heat the motor up real good....I use the
toaster oven. Give it a couple sharp raps from the back,
until the gap in the front apears normal. You can hear it,
and feel it when the bearing hits home.

Heat the motor until "spit dances on the case"....like when
you put a little spit on your finger, and touch it to a hot
iron. I use a dowel rod and a small hammer to strike the
bearings, or the crank. You're gonna have to hit it sharply
to get it to seat.....

Lemme know.....Dave.

Rudeboy

Tapping the back side of the crank... make sure you've got a good base to tap on... I mean, put the mounting lugs of the engine ON a vise (not in) so you've got something to take up the impact.
Be carefull tapping on a bearing... you might just put a flat spot on it somewhere... that would be the end of it... When I do this I use wood between the crank and the "tapping device"...

Shredz

Wow! How about that.

The bearings I work with are a bit larger- I've done some that are 18 inches across....we heat them with an induction heater and can get them hot enough to slide them onto a shaft with about .005" clearance. When they cool, the inner race is tight on the shaft (interference fit). I've used a torch on case bosses to get an outer race of a bearing to seat the same way.

The theory is the same, big and small.

When these small bearings (bushings) are installed like this, is it necessary to ream the surface at all, or are you ready to go?

Ernie Misner

Hi Dave and others - thanks SO much for the great advise. I will re-heat the engine and seat that rear bearing once again. I am sure (now) that's the problem.

Ted, we're talking small ball bearings here, not bushings.... although some model engines do have bushings. Replacing those bushings would be a whole different topic.

Thanks again!

Ernie

Ernie Misner

Just curious here..... what WOULD happen if I started the engine up and the rear bearing was not fully seated? Any chance it would then "seat itself", or would it just cause premature bearing failure?

Thanks - Ernie

Flyboy Dave

My Feedback: (21)

Ernie...I doubt that it would pull itself into a full seated
position, and could create unwanted heat in the bearing.
When you pull the backplate off, you might be able to
reach in there with a 1/4 drift....and strike the outer
race cleanly. Peek in there and see if one side is "high",
and adress it there first. It should however, be pretty darn
straight if it is in there that far.

Rudeboy

The first thing that is likely to happen when your rear bearing isn't seated properly is that your crankpit will rub on the backplate... you should feel that pretty good (speaking from experience here...).

If that isn't the case, it is probably in all the way. If there still is tension in the bearings it could just as well be the front bearing that is the culprit.

I'm just going over the options here...

Volfy

My Feedback: (23)

It really does sound like the bearing is not seated correctly.

The instructions by bearing manufacturers to use to "freeze small part and heat big part" to install a press-fit bearing has never sat well with me. Besides the thermal stresses I mentioned earlier, it leaves no room for error on that fateful first try. If you drop in the bearing and it falls into place perfectly - good. However, if it so much as to sit a tiny bit cockeyed, the contact between the two parts will cause heat transfer to occur very fast and the interference fit to take effect instantly - possibly distorting the bearing and damaging it.

Now I understand the reason they say to do this is mostly because they do not expect the average modeler to own a press. However, if a press is not available to drive in a press-fit bearing, I much prefer clamping the work piece in a vise and then striking a hammer on a deep socket sized to fit on the outer bearing race. If you sample automobile service manuals, that's usually the suggested alternative method if a press cannot be used.

Very often, the act of removing a bearing will destroy it. This may or may not be the case with every RC engine.

Ernie Misner

>> It should however, be pretty darn
straight if it is in there that far...............

Yep, it is in there most all the way, probably just a few thousands or so lacking from being fully seated Dave.

I think what I will probably do when I get back to that project is pull the carb and backplate and put it in the oven at about 250. Remember these bearings have a phenolic race (from Boca Bearing) and can't take too much heat according to the poop that came with them. Anyway, warm it up good and give the crank a pop from the back with a hammer and wooden dowel.

Do you think I should pull the piston and sleeve out again? Thanks for all the great info!

Ernie

Flyboy Dave

My Feedback: (21)

If you can't sneak in the back with a drift, and get it
home....you'll hafta' pull the liner, piston and rod and
crank....and get after that bearing....

You could just heat the case around the bearing with
a propane torch....and as soon as you get it seated....
blast it with some compressed air to cool the bearing.

Ernie Misner

>> If you can't sneak in the back with a drift, and get it
home....you'll hafta' pull the liner, piston and rod and
crank....and get after that bearing..................................

Okay Dave, assuming that I pull the crank and go straight for the bearing, when tapping directly on the bearing...... does one have to be careful only to tap on the outer race? Like using a socket or something that only contacts the outer part? I suppose it's remotely possible that there could be a small piece of crud behind the bearing also. Thanks again,

Ernie