Magnum engine bearings

I've heard people say on this forum that bearings are a problem in Magnum engines. What bearings do they put in them, and what bearings should you use to replace them? I've called around, none of the regular bearing suppliers carry the C3/C4 clearance bearings that we need for our engines. Yeah, I could order from Boca, but that's overseas for me, and they're fairly expensive.

In the past, for Fast Combat, people would replace the stock Fox bearings with riveted cage bearings, or bearings with plastic retainers (not too common back then). This was because the cage had a nasty tendency to come apart and the bits and pieces grind up the rest of the engine. Is this what happens in Magnums? I thought it was a problem only in high RPM engines.

Incidentally, I found a source for Magnum parts - I have an older .36XLA with a broken crank, and was glad to see they stock those instead of just the cranks for the newer engines.

Anyone know of a bearing supply place with C3/C4 clearance bearings that do mail order? I also need some 6801/C4s for my F2D motors.

Near as I can tell from Hobby People's site, the old .32 and .36 use the same crank as the new .36. So far, they don't show an XLS .32. The process of digging out part numbers is a bit of a hassle, but you can do a search for "Magnum .36" and click on "parts" in that frame, do the same for Magnum .32, you get a different order number, but same Mfg. #. The picture of the .32 is the old case, .36 is the XLS, but also called the XL in some places. A little funky, but they do seem to stock parts.

What brands of bearings can you buy locally? Steve

LAST EDITED ON Nov-09-04 AT 02:36 AM (CDT)
 
I can get NTN, NSK, THK, Fafnir, SKF.. (I wonder what's with the 3 letter names..) Mainly Japanese, though I think SKF and Fafnir are Scandinavian.

I remember someone mentioning, on the forum, about two years ago, that they changed the crank when they went to the square fins. I was annoyed because the crank I broke was in an older Magnum. In any case, the Magnum parts are available here:

http://www.hobbyoutlets.com/magnum/

For F2D motors, I would say buy them from Mejzlik or Jari Valo. That way you are sure they are the correct clearance and highest quality. At the rpms these motors run you can't use anything less than the best.
Pat MacKenzie

HI
I have 100s of bearings for the 32-36 Magnum, very High quality c3 series Phenolic cage ...rears are $8.00 plus s&h
call or email if you need them
randy 678-407-9376 [email protected]

FYI: the c3/c4 designations are in relation to the internal bearing clearance. a normal clearance bearing is a c2, c3 is a greater than normal clearance, c4 is greater internal clearance than c3. i'll dig out my old skf literature and maybe i can lay some more trivia out there. i can't remember what the s and k stand for, but the f stands for fabriken. imho, nsk has the best bearing on the market today.

SKF is/was a division of Volvo, but way outgrew the parent company. Now that FoMoCo owns Volvo, dunno if they also own SKF. Steve

Yup, it's radial play or clearance. From looking around at various web sites yesterday, and from what I was told by one vendor, "Standard" is between C2 and C3. And according to Henry Nelson, you have to actually measure the C3 bearings because the spec is so broad (it overlaps "Standard" by quite a bit) to know if the bearing is usable or not (probably this applies mainly to racing engines).

Took another look at one of my Kozjols last night - the bearing has a brown plastic cage that fills the gap between the two races. Looks like a shield - you can't see the balls. The bearings on both engines feel smooth, no grittiness to them at all, so maybe they're OK to use, even though one engine blew the lower end of the rod recently and the piston crowns and cylinder heads were frosted (the consensus on the Combat-L list was preignition, caused by too few shims). The front bearings are held in by a retaining ring with left handed threads - interesting.

So back to the original question - what's wrong with the stock bearings in Magnum engines? Do they come apart after some use, or do they wear quickly, or something of that sort?

Still looking for ball bearings, and found this web site. It's got to be the most annoying animated page I've come across:

http://www.kgbearing.net/index.html

Do this with the sound turned way up....

>Still looking for ball bearings, and found this web site.
>It's got to be the most annoying animated page I've come
>across:
>
>http://www.kgbearing.net/index.html
>
>Do this with the sound turned way up....

especially when there's no "SKIP INTRO" selection ...

I'm intrigued by this engine in two ways - stock for stunt, modified for Fast Combat. It sounds like replacing the bearings might turn it into a decent combat engine, too, and you've used one for that before. I believe you said the crankshaft finally gave out. I wonder if some oven treatment might fix that problem, too.

The engine is popular for stunt, and tongue mufflers are readily available - that might make it the engine I'm looking for - something to invest in, and have plenty of spare parts for both interests.

Isky, can you tell me more about the combat experience you had with it? I know it won't compete with a Nelson, but does it approach Fox Combat Special standards?

It'll blow the crank in 5-10 runs with a large venturi. Up until then it probably will run about the same performance as a stock Fox Mk VI 95-100 mph, depending on the plane, prop, and weather.

You'll know when the crank is starting to go because the needle valve setting will go crazy. You won't be able to find a good setting. Then another flight or two, the crank will let go. If you look close you will be able to spot the crack before the shaft breaks and flys out.

>It'll blow the crank in 5-10 runs with a large venturi. Up
>until then it probably will run about the same performance
>as a stock Fox Mk VI 95-100 mph, depending on the plane,
>prop, and weather.
>
>You'll know when the crank is starting to go because the
>needle valve setting will go crazy. You won't be able to
>find a good setting. Then another flight or two, the crank
>will let go. If you look close you will be able to spot the
>crack before the shaft breaks and flys out.

Sounds like you've experienced this first hand. Does the crank respond to oven treatment? That worked for all the broken cranks when the Mk III came out.

LAST EDITED ON Nov-18-04 AT 08:27 PM (CST)
 
I dunno if heat treatment would help, you might perhaps harden it up by encasing it in charcoal during the heat treatment. That's what they used to do to '03 Springfield receivers.

Mine broke after about 10-12 runs. Mind you, this was with an open venturi (or rather, NO venturi), and the crank had been retimed (it broke, as you'd expect, where the valve cutout was). The main problem with using this for Fast Combat is the diameter of the shaft - it's o.d. is 12mm. The Mark IV had a 1/2" shaft (close to 13mm?), the Mark VI and Wylie 15mm and the Mark VII and Nelson 17mm. So the hole you can put in the middle will be smallish. Mine ran pretty well, more or less like a stock Mark IV, despite what Dirty Dan might say. Took four kills with it at the 2001 Nats before the crank broke. Note that when it broke, it was AFTER scoring a kill in the match! (After that I went to a Mark VI, which suffered a bent crank after a midair with Phil, and after that a Wylie, which was my downfall - didn't want to start right away, ran inconsistently, even spat out a plug.)

I agree, why do we think the Magnum bearings are poor? Anyone??

>I agree, why do we think the Magnum bearings are poor?
>Anyone??

This is one of those things easily blown out of proportion. Still, I was there when one of Keith Varley's Magnum 36s graunched a rear bearing, happened to be in the area when PTG did the same thing earlier in the year.

Of a sudden they're all bad. *Not!*

Others report no problems whatsoever. Must be a West Coast thing.

Look, for seventy bucks, buy it, run the tar out of it. So what if 200-plus flights later you lose the rear bearing? Maybe even the piston/cylinder, in a worst-case scenario the head as well.

It was still one of the best Stunt engines you ever had, it was certainly the best 35-40 sized Stunt engine you ever owned. And it was only $70.00!

On the other hand, if your needs include absolute reliability, and I agree with this line of thinking, buy the engine. While it's coming, look up your engine on the Boca Bearing site, order some spiffy bearings, you'll be set.

Incidentally, while my own Magnum 36 fitted with replacement bearings front and rear, this only due to generosity of Derek Moran. Even having seen Keith and Phil have failures--both had spare engines, of course--it had been my plan to use stock bearings.

FWIW, Phil's observation is that 3-blade props seem to hasten/cause the rear bearing failure; 2-blade props are no problem. Keith Varley's experience is that 2-blade props (APC 11-4 or similar Bolley) perform as well as 3- in most situations.
Derek Moran

What's the failure mode? And does replacing the bearings really help? If there is nothing wrong with the original bearings, and they are failing after 200 flights, there's no guarantee that the new bearings are going to last any longer than that. Unless they _are_ better than the original ones.

Isky,

Give this guy a try...

Paul is in the UK...prices IMO were CHEAP...quality is good!

http://www.rc-bearings.com/

L8R

Eugene S. Chernosky
AMA 639635

LAST EDITED ON Nov-19-04 AT 05:54 AM (CST)
 
I don't think he stocks that particular bearing, though (1801 C4 with phenolic/polyamide retainer). I did find his site very informative, though. He talks about ABEC ratings, among other things.

BOCA is expensive. Henry Nelson and Tomas Mezjlik do have the bearings I want (for much less than BOCA, incidentally), but they are overseas, and I want to see if I can find some locally. Besides, once I start researching something, I usually go on until I finally have to quit out of frustration.. (pretty close, in this case)

While I might not buy anything from BOCA soon, their web site is also an interesting source of info. For instance, you can figure out the diameters of shafts for various kinds of engine. F2D engines are typically 12mm, Fox .36 and .40 sized ones are 1/2", Pylon Racing .40s and the Nelson .36 are 17mm, Jett .60s go up to 20mm. The secret to the Nelson's light weight is partly the rear bearing (it's a relatively thin 1803 - 26mm o.d., while the Pylon 40s use one with a 30mm o.d.). There are a few gaps in their engine lists, though - no Fox Mark VI, no ASP .15.

I have had to replace bearings in one magnum engine(rear bearing, Pro 25) and the balls in the bearings were not spaced equally in the bearings. Engine was off e-bay and bearings were so rusty that they would not turn. Rust was not the bearings fault, but the arrangement of the balls in the bearing was.

Walt

Heh.. Now I'm almost curious enough to open up my .28 and have a look at the bearing to see if the balls are unevenly spaced..

Incidentally, the Magnum uses a locking collet under the drive plate. This was, to me, something new (Foxes and OS Maxes and clones don't have this feature) so it took me a while to find the correct tool to remove the drive plate. The correct tool was a battery terminal puller that I got from Sears.