Hobbsy

My Feedback: (102)

I just ran mine for 30 minutes: my home made bronze bushings are actually tighter than the lower end bushing. I did good.

Webra SilverLine .40
Fuel== Wildcat 10% with 18% full synthetic, I know, I know, but t it's all I own and it ran fine on it
Plug===Taipan idle bar
Prop===Bolly 10.5x6
Muffler==LA .46
Max rpm===10,810
Idle== best at 2,150

BrickitSAM

Can you post some pictures?

Anyway, finally got around to getting the bearing sizes, the rear bearing is 12x28x8, the front is 7x19x6, I looked at boca bearings and could not find the right ones, I am afraid I'll order the wrong type, I did go to Avid though and found these 2, Rear and Front, they look like they will work, anyone have any suggestions? I'm also going to get some for my trx 3.3 also.

Hobbsy

My Feedback: (102)

https://www.bocabearings.com/products/mr6001-zz-c3c-2300

https://www.bocabearings.com/products/mr607-uu-1454

BrickitSAM

Thanks! that helps a lot, I'll order those.
Should the front bearing have a rubber seal right? this engine has something (don't know the name, slipper?) that fits over the shaft and sits flush with the case, I think it will get in the way of the bearings with a seal.

1QwkSport2.5r

The Avid bearings are more than adequate. I've used a dozen sets of their bearings in engines and prefer them to RCBearings.com.

metal shields, rubber shields, or no shields at all - doesn't matter. They all work the same exact way.

Nitrovein

The engine will work the same with any seal (in the front, remove for the rear), but it's never a bad idea to get rubber seal as the will be better at stopping things from getting in.
Especially if you're going to get some for you car engine as well.
The large Avid bearing you listed isn't for engines, it has wrong play, you should use the ones marked C3.

1QwkSport2.5r

I question the need for C3 fitted bearings in anything but a high performance engine. It's been said by other well respected engine guys that C3 specific bearings are just not necessary in the majority of sport glow engines. I've used C3 and C5 and haven't noticed a difference in performance. In some cases, a Looser fit is desired for higher rpm potential. Even the metal ball retainer vs. phenolic retainer argument is moot most of the time because the bearing just doesn't get spun fast enough to make the retainer fail.

Nitrovein

Here is one online source how to determine what to use as far as clearance goes.

aspeed

That chart just confuses old guys like me. I would have been confused when younger too. Which bearing has the most clearance? The C 5, or the C 3? I have heard for years that the larger clearance is best, as the case shrinks down on the bearing, minor misalignment and heat also make the bigger clearance desirable.

Nitrovein

It's;
C1 = Less clearance then C2
C2 = Less clearance then CN
CN = Normal clearance
C3 = Greater clearance then CN
C4 = Greater clearance then C3
C5 = Greater clearance then C4

aspeed

OK, so either one has more clearance than a standard. The Fora uses C3 on front and C4 on the rear. They rev pretty high.

1QwkSport2.5r

It was preached to me that phenolic ball cages and C3 fit was the only way you can go in sport engines. I don't believe that to be true for every engine. I've used C3, C4, and even a few C5 bearings in average sport engines. In some cases, certain sizes were unavailable in C3. So am I supposed to put a premium brand C3 bearing in the engine that costs as much or more than the engine it's going into? I'd bet $10 that if you put a C3 bearing into a tightly machined crankcase, your C3 fit might go from C3 to CN or C2 just by installing it, and running the engine with that scenario present would ruin the bearing pretty quickly.

I'm not trying to be snarky here despite it looking like I am. Just making a point. Aircraft sport engines do not require anything hyper sensitive or special in the category of crankshaft bearings. Look at bushed engines.

Nitrovein

The whole point of posting that list was to show what happens when installed, what to think about and so on.
I have tried my fair share of bearings as well, different brands in different engines, matched and assembled my own and so on, there is difference in how it works.
But this is out of the realm for this thread, I think... So my suggestion to the OP is to play it safe and follow the mfg recommendations to avoid problems, a few $ extra spent in the right place isn't waste of money, it's an investment.
Yes bushed engines works well, so did wood wheels, if you catch my drift.

1QwkSport2.5r

I get where your coming from and I have the utmost respect for your knowledge. I just don't think in this particular case (a Webra .40 with baffled & ringed piston) that there is a big deal which bearing fit is used. Other more high strung engines - I'd think differently about for sure. In those situations, I would invest in good bearings. WIB are at the top of my list if I can find a supplier stateside that will sell them singly.

Hobbsy

My Feedback: (102)

Bushed engines still work well, there is no difference in performance between a ball bearing equipped engine and a bushing engine when all else is equal. Some companies made engines both ways and the prop data was always the same.OS LA engines thrive on full synthetic oil. I personally only use BOCA bearings and have no clue as to their C rating. I'm not advocating ignorance, and as Tim alluded to, it just doesn't matter for 90% of our little engines. That's a western Pa. Farm Boy speech if there ever was one.

1QwkSport2.5r

My comment on bushing crankshaft engines is the amount of play in the crankshaft - often the radial and axial play in a bushed crank is greater than a higher clearanced bearing and they still run well albeit a bit messier.

aspeed

We ran Supertiger .15s in Goodyear racing, and the BB was replaced with a bronze bushing from the factory. There was no measurable difference in speed. It got you into the plain bearing stock class. I checked a Norvel .15 PB and BB and the BB was 1,000 rpm higher. Not really that much, but the liner was the better porting, and the PB had holes for bypass ports. (big mig) What is the most popular engine? Small block Chevy plain bearing. Billions of miles so far. Cox and Fox well the jury is out on them. I have seen a lot of leaky crankcases that would not hold a setting without 30% oil. I try not to use them at all. Love those LAs though. The carb is the limiting factor when comparing those to more performance type motors. The hole is very small and matches the porting arrangement well.

Nitrovein

Most of the time I would rather bet on loser fitting like bushed engines or the larger C3 fitting, it will most likely be more chock resistant.
In airplane engines where you typically run higher lube content as well, I would say it's less likely to be a problem (noticed) with too lose fitting.
I've had some (too) lose bearings in car engines that didn't run well, so that can without a doubt also be a problem, not denying that.

Anyhow, run what you like, I will!

BrickitSAM

Ok, reading all this I'm confused, should I stick with C3 or go with C4-C5?

aspeed

Whatever is cheaper.

Nitrovein

Run C3.
Bearings sold for engines are C3 (at least all I ever seen).