[floyd]

How many guys have changed a set of glow engine bearings only to find you have end play when you grab the prop and move it side to side with a hand on each blade. It'll almost feel like a click back and forth. Best to check with the engine having just been ran. Another way I check for play is by removing the rear cover and rock the crankshaft back and forth with one hand while watching the bearing. Try it in a couple of different spots on the crank. I've seen so many engines that when you do this you'll find a spot where the crank turns but the rear bearing doesn't move at all. That's the end play that I'm talking about.
Cheers Floyd

[RAMJET]

Floyd you are correct the bearings need to be checked when the engine is hot , knowing what is normal is the first part of knowing if you have a problem . All bearings have clearance or they would not move freely , Depending on the quality of a bearing some more then others . A $2 bearing will likely have far greater clearance then a $20 bearing because it's built to far less restrictive tolerances . Having a small clicking noise in a hot bearing is no problem as long as the bearings are smooth .To understand why , the outer race of a bearing is far larger then the inner race so it will expand more then the inner race when hot , this will cause the bearing to have greater clearance hot then cold , how much more once again depends on the quality & type of the bearing . But all metal bearings will loosen up when hot , completely normal .. cheers Roger

[floyd]

Not one of my own glow engines have any play in the bearings. The minute I feel that click in the prop out the engines comes for a bearing job. I don't use regular bearings, I use C3 rated when I can get them or Abec3 rated. The old OS FSR engines used to use a 6902 AC3. Only YS still use a C3 rear bearing, every other engine manufacturer use the cheapest bearings they can buy, including OS. Cheers Floyd

[stegl]

You can have the same bearing with OD , ID and width but this is were other design specs come into play where the balls could be larger for tight play and others with smaller balls with more play to allow for heat expansion , preload or whatever operation requirements. Also shielded both sides , one side or no sides and with different materials .
All in the bearing number.
https://www.bearing-king.co.uk/artic...ur-bearings-c3

AC3 bearings (angular contact - check the design)
https://www.skf.com/ca/en/products/r...-ball-bearings
I don’t believe AC designated bearings would be appropriate for use in model engines as there are pushing
Forces when starting ( using electric starter) and pulling when running .

[RAMJET]

Originally Posted by floyd

Not one of my own glow engines have any play in the bearings. The minute I feel that click in the prop out the engines comes for a bearing job. I don't use regular bearings, I use C3 rated when I can get them or Abec3 rated. The old OS FSR engines used to use a 6902 AC3. Only YS still use a C3 rear bearing, every other engine manufacturer use the cheapest bearings they can buy, including OS. Cheers Floyd

OK now the story has changed LOL, Before you edited your post you said it was your engines that had the problem after rebuilding them . As you weld most of your cranks and force the bearing over the weld ,one can only assume your using high clearance bearings .

[RAMJET]

Originally Posted by stegl

You can have the same bearing with OD , ID and width but this is were other design specs come into play where the balls could be larger for tight play and others with smaller balls with more play to allow for heat expansion , preload or whatever operation requirements. Also shielded both sides , one side or no sides and with different materials .
All in the bearing number.

I agree 100% and getting the wrong bearing can cause a bit of play but as long as they are smooth and the play is not excessive it's not a problem .. Now if you don't balance your props that will cause things to wear pretty quick . cheers ..

[darkith]

It’s important to note that C3 is not the same as Abec3 or Grade 3.
Abec3 or Grade 3 refers to *precision* (the dimensional tolerance/accuracy in the construction). with ABEC ratings higher is better, and the range is 1,3,5,7,9. Other grade systems may differ.
Cx ratings refer to clearance between the balls and races, in the design. Higher is looser (more play), and ranges from C1 to C5. C2/C3 is generally middle of the road and considered “normal”.

So, you can have a high precision (Abec7) bearing with *lots* of internal clearance (C5), perhaps for heat expansion, because it lubed with a thick film oil, or will be in a press fit housing that compress the outer ring. The bearing would have lots of play when dry, but be very accurate in construction and should last a long time if the design was right.

Or, you could have a lower tolerance bearing (Abec1) with tight clearance (C2) for cases where you want tighter preload, but don’t expect much usage, so cheap tolerances/variation and possible noise/wear aren’t a design issue. Maybe a light duty router spindle when you don’t want much runout, but the design life isn’t many revolutions.

There’s still a lot of room for variance, as Abec and clearance ratings don’t specify materials, hardness, cage type, seal type, etc.
In general, going up in ABEC rating shouldn’t hurt anything (as long as all other factors stay the same), but costs money. Clearance ratings can bite though, as too tight a clearance may not allow sufficient lubrication film, or thermal expansion, or alignment tolerance as the design calls for.
Obviously, too loose a clearance or too low a tolerance will probably lead to wear, noise, and/or premature failure.

[RAMJET]

Originally Posted by darkith

It’s important to note that C3 is not the same as Abec3 or Grade 3.
Abec3 or Grade 3 refers to *precision* (the dimensional tolerance/accuracy in the construction). with ABEC ratings higher is better, and the range is 1,3,5,7,9. Other grade systems may differ.
Cx ratings refer to clearance between the balls and races, in the design. Higher is looser (more play), and ranges from C1 to C5. C2/C3 is generally middle of the road and considered “normal”.

So, you can have a high precision (Abec7) bearing with *lots* of internal clearance (C5), perhaps for heat expansion, because it lubed with a thick film oil, or will be in a press fit housing that compress the outer ring. The bearing would have lots of play when dry, but be very accurate in construction and should last a long time if the design was right.

Or, you could have a lower tolerance bearing (Abec1) with tight clearance (C2) for cases where you want tighter preload, but don’t expect much usage, so cheap tolerances/variation and possible noise/wear aren’t a design issue. Maybe a light duty router spindle when you don’t want much runout, but the design life isn’t many revolutions.

There’s still a lot of room for variance, as Abec and clearance ratings don’t specify materials, hardness, cage type, seal type, etc.
In general, going up in ABEC rating shouldn’t hurt anything (as long as all other factors stay the same), but costs money. Clearance ratings can bite though, as too tight a clearance may not allow sufficient lubrication film, or thermal expansion, or alignment tolerance as the design calls for.
Obviously, too loose a clearance or too low a tolerance will probably lead to wear, noise, and/or premature failure.

Good job and well said David , I tried to get away with being a little more vague just to give a basic Idea of what was likely happening . thanks for the detailed information . I don't know how he can expect any bearing to last after putting weld on 75% of the cranks and forcing the bearing over it ..How would the bearing ever sit true , we are talking microns for trueness and he's dragging a welding rod across the crank to cause burrs to force the bearing over on most of his engine to take the click out LOL . what does it matter what bearing you use after doing that ..after doing that you would need the loosest bearing you could get just so they would not bind . sure they wont click because the bearing are no longer sitting true . That fore sure will take all the play out but will trash the bearing in no time .. .. Crazy IMO .. cheers ..

[volksman]

before i get jumped on what floyd could be describing is the oblong in the lower rod bushing. have many enginges i can wiggle the crank end cold but not hot. like its supposed to be. 2 dollor and 2 thousand dollor bearings are two different things.

[floyd]

When you run an engine with a bad bearing the crankshaft will usually spin inside the inner race of the bearing because the bearing doesn't want to spin. At least that's what I'm seeing. So the crank wears right on the spot where the bearing rides, that's what I'm tightening up. I'm not forcing anything I'm pressing them in. I have a press to install my bearings in the crankcase, I don't heat or cool the bearings or the crankcase. I use the same press to install the crank. Cheers Floyd