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Radial crankshaft load at flywheel
2

Radial crankshaft load at flywheel

Radial crankshaft load at flywheel

(OP)

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  

RE: Radial crankshaft load at flywheel

2
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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RE: Radial crankshaft load at flywheel

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

RE: Radial crankshaft load at flywheel

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

RE: Radial crankshaft load at flywheel

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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RE: Radial crankshaft load at flywheel

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.

RE: Radial crankshaft load at flywheel

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.

RE: Radial crankshaft load at flywheel

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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RE: Radial crankshaft load at flywheel


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.

RE: Radial crankshaft load at flywheel

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.

RE: Radial crankshaft load at flywheel


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.

   

RE: Radial crankshaft load at flywheel

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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RE: Radial crankshaft load at flywheel

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

RE: Radial crankshaft load at flywheel


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%20V-1650-1%20sectional%20-%20a.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.


RE: Radial crankshaft load at flywheel

"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.

RE: Radial crankshaft load at flywheel

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)

RE: Radial crankshaft load at flywheel

Tmoose

A  very good point. Typically on V8s Supercharger drives pull directly against the oil hole as the supercharger is normally mounted over the valley.

Most after market high performance V8 top main bearing shells have an oil grove to distribute the oil feed over 180 deg and this would overcome that problem in that case. It is to long since I looked at an OEM bearing shell to remember.

Regards

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RE: Radial crankshaft load at flywheel

I think lots of top main shells are often grooved, stock. With a single feed oil to the rod journal that would provide rod oil approximately when it was at BDC +/- 90 degrees. On a generic 4 stroke On the power stroke the "bottom" of the rod oil clearance would be open.  On the exhaust stroke decelerating the piston the "bottom" would also be open.  

On cranks from badly maintained engines the rod journal wear is primarily on the "underside" of the journal, which is where the rod would be pushing at BDC.  My theory is the hydrodynamic oil film starts pretty thick around 90 degrees BTDC when the oil is new and cool, but the film  getting thinner and thinner as oil is squeezed out, (and sheared oil warming and getting squeezed out even more)until the oil film is thinner than the abrasive chunks, and if the oil level is too low, then the contact becomes metal to metal, taking the inserts down into the copper without really failing.

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