Front main bearing weear and SC applications FYI
 

When we pulled apart a SC engine a few months ago, I carefully reviewed a front main bearing from this SC application and found considerable wear on the new front main bearing due to SC belt tension. I read somewhere that it is recommended to have 200 lbs tension on the SC belt...is this true?

In an effort to modify the Munck bracket to minimize the unbalanced front bearing load, I have found a few tensioning methods that would reduce the forces considerably. But the lack amount of space would require complete redesign of the bracket..is it worth it...I do not know. I have a call into a old Ford friend to see what he knows of any additional engine design requirements for factory SC applications, and belt tensions.

I am very surprised that no one has mentioned this before....I know engines have been apart after SC usage...did anyone look at the front main bearing for wear?

I do not know "if" a failure will occur or what the failure mode will be, best case is a worn front main bearing and seal leakage...can become a routine maint item..., worst is crank deflection and fatigue failure. The engine had about 5000 miles on a new bearing.

My suggestion is to use the absolute minimum tension, with the widest belt with maximum "wrapage" of the belt onto the pulleys that you can get away with and still make the desired power.

A few years ago, I posted the drawbacks of cutting the air pump and AC belts and the effects on crank/front main bearing wear. When I pull an engine apart, I can always tell if the belts were properly tensioned and balanced, or accessories were missing!

Maybe someone can begin an oil testing routine to see if the wear levels off after some amount of time...

Regards,
Marc

A sampling of one is just that.

It does make sense that more upward strain on the crank would cause greater bearing wear. If it turns out to be a real issue, I'm sure redesigning tensioners to also place an equal load downwards (or side-side) would do away with the danger.

The one sample you're looking at, is perhaps the very worst example.

Actually, a sample of one can be significant...the primary factors are belt tension, mileage and number of units in operation....lets see if some more data shows up.

And it is most likely an average sample....the engine ran at less than 6 lbs for at least 90% of it short life, and used the typical tensioning method.

Hope this helps.

Marc

I'll assume this was a FAST installation?

No, it seems to be a combination of many parts ...whose I do not know...but I am not sure why it matters?

Marc

There are hundreds of aftermarket SC kits on the market for as many different models of automobile. This is nothing I have ever heard of. There has no mention of front crank bearing strengthening in what I have read about the design of the Ford GT. Additionally I can't imagine that the crank bearing would wear more quickly that a much smaller SC bearing would.
Kennebell gets over 885HP from the Autorotor with only 6 rib belt. There aren't even 8rib pulleys made for the Autorotor because there is no need for them. One reason that this is possible is that the change in rpms of the rotors is very low compared to other types of SC. Generally a positive displacement rotor will spin at a range of 1200 to about 13000 rpms through the engines rpm range. The impeller of other types of SC will range from about 6000 rpms to over 50,000 rpms.
For the Autorotor SCs 500N or or 112.4 pound-force should not be exceeded for belt tension.
If there is ever a need with my systems 2 SC pulleys can be mounted together and 2 6 rib belts could be run. And the way I have designed my crank pulley will allow up to 18ribs dedicated to driving the SC in a very extreme application.
HTH,
Andy K

Why WOULDN'T it matter? :(

Marc,

I appreciate your input but I get the distinct impression you are trolling with this thread. Engine wear in general is a function of simply running the engine - they are all going to wear out at some point. But so many car manufacturers put SCs on their cars either as OEM equipment or as an aftermarket upgrade that I am convinced they are safe power.

Now if you are simply giving a heads up regarding belt tension that is a whole different animal.

now, im worried about my unbalanced PS pump and Alternator belts. (without AC and smog pump attached) what type of tension should we use on those. just enough to keep them from squealing?

MK

Interesting that nearly every new engine uses a serpentine belt like this.. www.wjjeeps.com/serpentine www.thesaabsite.com/95/954cylbeltreplacement.htm and "OH MY GOD the sky is falling" note how it only pulls up on the front of the crankshaft !! Marc I believe in your previous comments to Doug Hillary you had stated that you had done many,many oil analysis reports it would seem that this supercharged GTS deserved such treatment as well.

I have rebuilt my S/C motor after about 10,000 miles and found that the front main bearing was indeed worn......but it was worn in the direction of the alternator, not the S/C. It must be that I don't run a smog pump to off-set the alternator. When I put it back together I did not tighten the alternator belt as tight this time.

Not being hampered by facts, I can discuss the subject freely...

Lets see:
Weight of the crank - straight down, all the time.
Compression, from zero up to 180 psi on 12 square inches times two cylinders, down at 45 deg from vertical.
Combustion, from zero to what, 350 psi at least, on 12 square inches times two cylinders, down at 45 deg from vertical.

And, opposing this, one cam drive belt and one supercharger belt, both pulling more or less up.

Looks like the supercharger belt should help main bearing life more than hurt it.

Guys, why shoot the messenger?

The way I see it, Marc was only reporting his findings, proposed a possible cause and has asked a few questions.

Sharing information is what these forums are all about! Lighten up and lets try and keep it on a positive note!

Bailey, was your post supposed to be a fun light hearted jab between friends? I really hope so, as it makes you look like a jerk, which we all know your not!

As a more-involved-than-using-the-menu means of subscribing to this thread....

I agree with T_MaX. Let's ask questions and look for answers.

Marc? Why are you going deep into the engine anyway?

I think there is much history on why one vendor would post something potentially protecting his or her own way of doing things. Nothing abnormal there, but nevertheless you'd have to be blind not to see that. Jim is correct, there is definitely need for more than **one** test case .. cmon Curtis, do you think the car in question warrants the conclusion that the bearing is subject to supercharger strain?? Even Blown Beast with I think the most powerful car here has seen wear as Marc said, in the direction of the alternator. NOT in the direction of his aggressive supercharger.

Personally I appreciate this type of information-sharing, however AGAIN Curtis ... there is history here.