Underdrive pulley

[Irish Pride]

If I remember correctly the first UDP's used a smaller crankshaft pulley that didn't have a true harmonic balancer in them and the result was crankshaft breakage. The next version used the stock crank pulley and larger P/S, Alternator and water pump pulleys

Every underdrive crank pulley is exactly as you described. I've been running one on my 91 for 10 years with no issues. The SHO V6 is internally balanced so it doesn't need a balancer. Anybody that's had a crankshaft break was because of something else.

 

[Jim Leyden]

There is a HUGE difference between an internally balanced engine and an externally balanced engine.
That being said, all engines, internally balanced or externally balanced have a HARMONIC balancer. It has absolutely nothing to do with balancing but has everything to with eliminating harmonics in the crankshaft.
As far as being "because of something else" I had a Sho Shop balancer on my '95 and broke the crank. Don Donaldson also experienced a broken crank as did do enough other people that the UDP's were redesigned to eliminate the problem. That being said, both Don and I were running highly modified engines with greatly reduced rotating mass which makes harmonics an even worse problem.
Think of it this way.
If every engine manufacturer in the world could save some bucks by using a solid front crankshaft pulley, what do you think they would do?

 

[Irish Pride]

3.3 High Compression with light weight pistons that regularly sees 8K. Been running an Underdrive Crank in various forms for 8 years on this engine. I've had a Hypertech pulley, an unknown brand pulley, and currently have the SHOSource pulley. Zero issues with my setup.

If solid crank pulleys cause so much chaotic damage why do so many manufacturers offer them for performance upgrades in so many applications?

 

[Jim Leyden]

Same reason they made Slick50
Because people will buy them.
Doesn't matter if it doesn't work as long as money keeps rolling in.

 

[Irish Pride]

Were not talking about snake oil. Slick 50 doesn't cause main bearing failure. Using Slick 50 won't destroy your engine. If it did you better believe that no one would be buying it.

If someone with a fresh engine build knew he was going to snap his crank by adding a solid crank pulley do you really think they would use it? If crankshafts were snapping left and right there would not be a demand for underdrive pulleys.

There are a few threads on the forum discussing this and by doing some poking around you can see it is not a wide spread problem. I'd like to know how many UDPs SHOSource has sold over the years and how many have caused documented crank damage.

I understand there is a use for a Crankshaft Damper in certain applications. I wouldn't use a solid pulley if I were boosting my SHO but that's going above and beyond. A modded or stock SHO will have no issues with a solid pulley.

 

[Greg Millard]

If I remember correctly the first UDP's used a smaller crankshaft pulley that didn't have a true harmonic balancer in them and the result was crankshaft breakage. The next version used the stock crank pulley and larger P/S, Alternator and water pump pulleys

I bought my SHO it had a smaller underdrive pulley (I believe that’s what it’s called) so the alternator will spin slower and the power steering pump spins slower too and it has the rev limiter taken off. The question is how do I push the idle up so my battery doesn’t keep going dead. Oh and is there already a thread on this?

Doubtful the prob would be alternator - if you'd like to check place a voltmeter (meter or gauge) & watch it asr is increased -anything over 12.5 volts and look elsewhere including run a load test on your battery but it sounds like you have a drain in your system - start pulling one per night measuring volts (before & after) until you find the one which avoids the drain - have fun be patient.chrres Retrogreg

 

[Night Runner]

Doubtful the prob would be alternator - if you'd like to check place a voltmeter (meter or gauge) & watch it asr is increased -anything over 12.5 volts and look elsewhere including run a load test on your battery but it sounds like you have a drain in your system - start pulling one per night measuring volts (before & after) until you find the one which avoids the drain - have fun be patient.chrres Retrogreg

I figured the problem out later after a while. My alternator was on its last leg