Radial crankshaft load at flywheel 2

[amorrison]

My understanding is that in automobile engines the back crankshaft bearing will only last "minutes" if the engine power is "taken off" by a chain or belt due to radial forces.

The only engines that have bearings designed for radial loads seen to be snowmobile engines with CVTs.

Can these bearings be "upgraded" or are there other solutions?

Thanks

 

[patprimmer]

I have seen many engines driving roots type blowers of the front by a belt drive.

These blowers can consume several hundred horse power to drive them and the front of the motor normally has a much smaller main bearing than the back.

Regards

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[FoMoCoMoFo]

I agree, most engines would require a large load for alot of minutes to do damage.

 

[FoMoCoMoFo]

you would obviously want to put this sprocket or pulley as close to the bearing as possible.

 

[patprimmer]

An external support bearing to eliminate cantilever on the rear main would also help a lot. Look at American drag racing blower drive crank supports for ideas.

Regards

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[patdaly]

Many of the older Combines used belts driven off the back of the crankshaft to turn the Hydro pump. They were typically Automotive based Gasoline engines and when they blew, standard junkyard engines were used to replace them.

I would say you would have to have an excessive load for it to do any damage.

 

[thundair]

if the design intent was to belt/chain drive off the back, I am not sure that they used plain bearings or ball. At any rate if you could add one there it would be a great improvement..

Are the loads defined well enough to calculate failure..

Cheers

I don't know anything but the people that do.

 

[patprimmer]

Drag race snout supports are sealed roller bearings set in an outrigger that is mounted to support posts bolted to the block. I am sure a web search will show photos in a suppliers catalog

Regards

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[Fabrico]

The crank itself is also not designed for that kind of load, on either end. Although it's just as often done to accommodate high speed vibration, many small block race cranks have "big block" snouts because they break off.

Industrial and agricultural applications always have some form of bell housing with an additional bearing.

 

[amorrison]

Supercharger snout picture here

http://www.intense-racing.com/Merch...en=PROD&Product_Code=MSS-90x&Category_Code=IF

and a less elaborate one here

http://www.blowerdriveservice.com/categorynarrow.php?category_id=3418&company_id=101011

Nothing found for power takeoff at crankshaft rear yet.

 

[patprimmer]

This shows a fairly poor picture of a crank snout support.

http://www.kenlowe.com.au/99344-26001.htm

Regards

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[patprimmer]

Here is a better picture.

http://www.rcdengineering.com/crank_bs.html

You should be able to re dimension this principal to bolt onto the bellhousing mounting flange

Regards

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[patdaly]

The reason for BBC snout sizes on a SBC is for those Supercharger applications that require more drive Hp than the stock SBC crank can handle. Countless units running 6-71 and 8-71 blowers run for years without breaking cranks. I rip the teeth out of a 36 MM wide 8 MM pitch belt on my BBC anytime I miss a shift point on my setup ( takes some power to do that )and I have neither a crank support nor a broken crank. From the best estimates it takes right at 200 Hp. to drive my particular Centrifugal.

As for the difference between front and back, I can see no reason you should treat it any different than you would a front drive.

What we really need here is a more specific load and application.

 

[amorrison]

Here is a cross section of a Packard engine. The geared output crankshaft bearings (ie. having a radial load) do not look to be anything special.

http://www.enginehistory.org/Packard/jpgs/Merlin V-1650-1 sectional - a.jpg

http://www.enginehistory.org/Packard/jpgs/Merlin V-1650-1 sectional - b.jpg

More general Packard information here.

http://www.enginehistory.org/packard1.htm

 

[Fabrico]

Larger snout cranks are extremely common on stock cars too. But the point was that it was just one more reason why a stock crank can't work without additional support, not that it would be inadequate with support.

 

[patprimmer]

The OP wants to drive off the flywheel end.

I mentioned snout end because that is the end superchargers are normally driven from, and it is normally the weakest end as the flywheel end is normally the highest loaded drive end. The snout is normally only used for ancillary drives, but still survives with a substantial load of a supercharger.

I mentioned crank snout supports as an example of how to increase load bearing properties of the crank by making it a supported beam rather than a cantilever.

I think that topic is now covered and we should try to keep it relevant to the OP's question.

Regards

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[FoMoCoMoFo]

life expectancy will depend on what engine, how much load and how exactly it's taken off.

 

[Fabrico]

amorison4, you can refer to the front of the crank all you want. Unless I am looking wrongly at your link to the Packard drive arrangement in which you suggest that there is nothing special,

http://www.enginehistory.org/Packard/jpgs/Merlin V-1650-1 sectional - a.jpg

It clearly shows that the crankshaft is completely separate from the drive unit and bolts to it. The drive unit has ball bearings on both sides of the drive gear.

Fomo..and patdaly point out correctly that it will depend on how and how much. I would state again that the crankshaft is not designed for this and may have problems regardless of support.

 

[tbuelna]

"My understanding is that in automobile engines the back crankshaft bearing will only last "minutes" if the engine power is "taken off" by a chain or belt due to radial forces."

What is the configuration of the engine? Vee, opposed, in-line
How many cylinders?
What is the rear main bearing size, material?
What is the duty cycle and torsional characteristics of the driven element?
What is the direction and magnitude of the belt/chain tension load on the crank end? Is the sum of the forces at any instant better or worse than before?

It just may be that the belt or chain drive and driven load characteristics help to reduce the torsionals in the crankshaft and/or helps to offset inertia loads in the journal bearing, thus prolonging crank and bearing life.

To get a good idea of how difficult and complex a problem this is, read up on the development issues the aircraft piston engine manufacturers worked thru during WWII.

 

[Tmoose]

1 - The acceptable bearing loading probably ought to be kept to a few hundred psi.
2 - The direction of a continuous belt or chain pull needs to be generally away from the point the oil is introduced to the bearing. Note this is probably NOT done for typical passenger accessory drives handling a few dozen Horsepressure, or as others have mentioned, hundreds of HP supercharger drives for supercharged race engines
3 - Some passenger car V-8s (Ford 302?) have had service bulletins about noisy knocking front main bearings if the radial clearance is tending toward 0.003 inch (which is often an acceptable new tolerance)