Preface

Bearings seem to be a common problem in engines. Having been helped by several club members over this issue I have been researching  some of the specifications regarding bearings and wonder what others may add to this thread.

Firstly I feel that pointing the finger at fuel or engine tuning may be a little premature as I feel there are several factors associated with the performance of them. I have a Kyosho .21 buggy engine that I have to say at least, "ringed out" and leaned several times and the bearings are still a tight as the proverbial.... Is it the engine design, or are these just better bearings?

Bearings have various criteria associated with them. Material type used, RPM, sheilds, seals temperature and ratings. Then comes the engine design and this is where I seem to be a little bewildered by how the front bearing is to get lubrication from the oils in the fuels when leaning down a long straight.

I have ordered two types and grades of bearings from bocabearings.com a leading provider from the US. Both are double sided rubber sealed and greased. The engines I will be using are budget SH based and I have ruined front bearings in these engines in under 5 hours of use in both. It seems to be a consistent attribute.

I aim to use these cheaper engines to get a better understanding of how and why these critical components fail. As the engines I used and the fuel I use is constant it will be interesting to see what eventuates from my trials.

I'd like to thank the members that helped with their advice and its been much appreciated. For now I will continue using the engines and determine whether its the bearings, my tuning, fuel or the engine itself.

Findings

 26/3/08

[ Click here ] to go to their great website. There's a lot of information to learn about bearings, the package arrived within a week of shipping and their range is very comprehensive.

I ordered hi performance bearing from boca bearing in the US and in the mean time I visited statewide bearings at Virginia and installed some cheaper affordable NSK bearings into my older SH  engine. I can not recommend you use the NSK as they are not spec'd for this task and I am prepared to ruin my SH .15 engine for the sake of this exercise.

I fired her up and after a bit of tuning she purred along merrily and I began running her in on my street  ( much to the dislike of my neighbours) The bearings were both sealed and Ive left seals on (not shields) as per advice from the boca bearing website. Temperatures were below 100c and I run three tanks continuously up and later than night took it to the work bench. for an inspection.

 The seals on the bearings looked fine and not distorted, there was no play in the crank shaft and the performance was an improvement of 200%. I am now heading to the track for a more vigorous test sessions to see how the seals hold up.

The concern I have is that as per specs, RPM are reduced when packed greased seals are left in place. And these are in no way hi performance / hi rpm bearings.. will be interesting to see what happens next.

26/03/08 pm

SH .15 Engine with NSK non spec bearing

[ Click here ] to see a large image of the NSK bearing seal after a more vigorous track session

So having returned home, I found a package in the mailbox from bocabearings.com.  it was a kit for set for the LRP Team Spec 2 .12r I use for club racing.

The front bearings are much the same in appearance as most front bearing, though the rear bearing seemed to have differences between it and the old original.

The new rear bearing from bocabearings.com

LRP TEAMS SPEC2 Z.12R with spec bearings (BOCA bearings)

[ Click here ] to see a large image of the bearing supplied by bocabearings.com. it's just installed.

Original bearing in the LRP. Note the bearing cage is completely encapsulating where as the boca version is exposed on one side. This would seem to be better for lubrication. The other side (not shown) has a synthetic material that binds the cage for what I assume to be extra strengthening.

Original bearing - LRP TEAM SPEC2 Z .12R

[ Click here ] to see a large image of the original LRP bearing. NOTE: The insect was probably getting high on the methanol!

NSK non spec bearing update - 13/04/08

After several practice sessions and a Saturday club meet I returned home and checked my SH .15 engine's bearings and found that the rear bearing once again had failed. Taking into consideration that it was not a spec bearing, I must mention that nor was the front bearing and it is still in good working order. The rear bearing has minor play and because of the nature of this experiment I removed the seal to display my findings.

[ Click here ] to see a large image of the original failed NSK rear bearing.

Fuel Change

There is evidence that the new fuel being used leaves far less residue, this could be due to the oils used. A hypothesis is that cheaper smaller .12 engines combust and exhaust the fuel less efficiently than a larger or more engineered engine. This is my assumption as the the cause of the residue left on the previous bearings. Hence if using cheaper engines it may be wiser to use less castor oil and more synthetic oil so that the engine may combust and exhaust efficiently.

Seals

Against advice and only for this exercise I left the seals (not shields) on both bearings. As you can see in the following pictures the seals on these budget bearings seemed to hold up quite well. The front bearing is still in good working order and and marking on the seals was the outer seal (marking subject to removing three shoe spring clutch) . The inner seals seem to be fine.

[ Click here ] to see a large image of the NSK bearing seals.

[ Click here ] to see a large image of the flip side of NSK bearing seals.

Conclusion

As this engine was old, compression low and a limited amount of time to do this study my findings are not entirely conclusive. What can be deduced is that fuel does make a difference and this is dependent on the engine you are using. Leaving seals intact seems to make little difference and as I tested using budget non spec bearings I am surprised as to how little they deteriorated.

Finally, during the course of this exercise I must accept that the crank shaft and the balancing might have a major role in the deterioration of bearings. One can not expect to have a sub $200 AUD engine to be engineered and machined to a precision that can perform at RPM's over 30k, you may be lucky, but one should not depend on luck with racing. It's just fact that you get what you pay for. Hence I have personally concluded, I will be investing in more precision engineered engines in future. As the cost of maintaining a budget engine and the labour that it requires is far greater than the additional outlay of buying a higher quality engine.

DISCLAIMER: The information within this document is not founded on a high level of engineering or science and may not be used in law as an action of liability to myself, QRCCRA, engine and bearing manufacturers, suppliers and retailers. It's a personal posting of my findings within the boundaries of my working environment and technical skill. I would be happy to accept any suggestions or comments from manufacturers or end users as to improve this document and to better understand the key elements of engine management.