Bearing damage

[Tom Foley]

I have been experiencing a type of bearing failure that's called spalling. There are different types of this condition caused by different circumstances . The VAC 91 is a notorious bearing consumer if you run the hell out of them like I and others do . The bearings I have been using for the most part are the Boca Bearings High Performance plastic retainer type . Now switching to the SKF bearings and hoping for some longer life . The VAC 91 engines are beasts and seem to run with anything . I am running 18 % oil in my 60 % fuel
Thinking of going to 20 % . Take a look at the photo closely . Same size bearings as MAC 67 and .84 CMB 80 HR , 67 HR and VAC 91 . By the way I never run the boats except at open water before a race and during the race .

 

[John Beardslee]

Tom, what type oil are you using? I use 18% Klotz 80/20 then add another 2oz of Benoil/caster per gallon.

 

[john v]

Castor would be a good choice

 

[RaceMechaniX]

Thom,
Can you pop out the retainer and take some pics of the inner raceway? Spalling usually happens to the raceway more so than the ball itself in my experience. Is just one ball damaged or multiple?

-Tyler

 

[dr gary turner]

Is the Spalling D/T heat load or poor lubrication? All 3

Caster with its high h flash point helps with heat but it has a high viscosity and probably doesn’t lubricate as well as a low viscosity oil.

I am just starting to run a Vac 91 in a resurrected CS so interested in those with experience with Vac 91

 

[dr gary turner]

Vac 91

 

[Al Hobbs]

Higher viscosity means bigger molecules, therefore more space between metal surfaces.

 

[dr gary turner]

Yep, but is there less penetration between those surfaces?

I have been running 14-16 % low viscosity oil 60% nitro in 101s.
The bearings seem to doing very well.

 

[dr gary turner]

Castro seems to help my motors that are prone to pre- ignition especially 101s

 

[dave roach]

NO 1 problem Don't use bearings with the plastic retainer.

 

[Tom Foley]

Tom, what type oil are you using? I use 18% Klotz 80/20 then add another 2oz of Benoil/caster per gallon.

Std Technology fuel , Klotz techniplate and castor .

 

[Tom Foley]

NO 1 problem Don't use bearings with the plastic retainer.

Lol all high.performance bearings including the original have the polymide or plastic retainers .

 

[Mike Hughes]

NO 1 problem Don't use bearings with the plastic retainer.

Why do you say that Dave? Care to give us the why?

 

[Tom Foley]

Is the Spalling D/T heat load or poor lubrication? All 3

Caster with its high h flash point helps with heat but it has a high viscosity and probably doesn’t lubricate as well as a low viscosity oil.

I am just starting to run a Vac 91 in a resurrected CS so interested in those with experience with Vac 91

Don't think it's heat as not burning plugs , not even close

 

[Tom Foley]

Thom,
Can you pop out the retainer and take some pics of the inner raceway? Spalling usually happens to the raceway more so than the ball itself in my experience. Is just one ball damaged or multiple?

-Tyler

Using what minimal.magnification I have it appears to be one in this bearing . I think it's the quality of the bearings or corrosion.

 

[Jeff Lutz]

The main reason for the big bearing failures in Vac .91’s is the case fit that it goes in. The upper half of the bearing is only held by a small amount of material and is hanging out a lot. Unequal interference fit and the bearing is not staying round. A K90 had a big bearing of the same ID and OD but was .03937” thinner (16002) . Smaller than the Vac but no bearing problems at all. The crank on the K90 is longer but that is not why the bearings survive, it’s case fit is full round and proper. You will probably get a little more life out of the SKF. Jeff Lutz

 

[Mark Bullard]

Very interesting. Jeff maybe on to something about half of the outer race hanging out of the housing. Our motors use the method of tight fit on the outer race and slide fit on the inter race. This is the standard fit for this kind of app. Spalling is caused by ball skidding or the ball locking up and sliding in the races. Now the running clearance changing in the outer race would be a problem at high speed. But there is another idea. Oil with castor with anything over 30 percent nitro will separate the castor and cause the parts of the bead to clump together. This could also cause ball skid. You can see what I am talking about by looking at your fuel for the little white things floating in the fuel. And they will be very small. I have not used any caster in almost 40 years. I have not lost a bearing in years unless they had a lot of fuel thru the motor. Lets face it, the balls are hit with a hammer x number of time a minute. I have been using pure Klotz sysnthetic 22% for the same time. No castor .

 

[Stephan Peterson]

Just wondering if you have dunked the boat, you would be surprised how much particulate is suspended in some of the water we run in. Could this start the process of hurting the bearing while turning motor over to get the water out ?

 

[Tom Foley]

The main reason for the big bearing failures in Vac .91’s is the case fit that it goes in. The upper half of the bearing is only held by a small amount of material and is hanging out a lot. Unequal interference fit and the bearing is not staying round. A K90 had a big bearing of the same ID and OD but was .03937” thinner (16002) . Smaller than the Vac but no bearing problems at all. The crank on the K90 is longer but that is not why the bearings survive, it’s case fit is full round and proper. You will probably get a little more life out of the SKF. Jeff Lutz

Yeah I love these engines and will replace bearings every 3 outings as necessary. This may be a combination problem as well . After every race I remove engines and remove the intake housing and dump all the needles and hand out the engines so I'm not sure what more I can do except add oil and keep changing them out . Takes 30 minutes for both engines .

 

[Tom Foley]

Is the Spalling D/T heat load or poor lubrication? All 3

Caster with its high h flash point helps with heat but it has a high viscosity and probably doesn’t lubricate as well as a low viscosity oil.

I am just starting to run a Vac 91 in a resurrected CS so interested in those with experience with Vac 91

I change bearings every3 -4 (races) . Sometimes the bearings look and feel good but if you look at them magnified under good light I have seen the beginning of surface degradation on some of the balls .