About 15 years ago I asked the guys at the Crower booth during the SEMA show in vegas about stroker cranks. They stated that they can do cutom cranks for anything. I am curious if anyone here has ever gone the cusom crank route vs offset grinding route?

Some have. Randy Gummelt's dragster has a custom crank. Big bucks, and for most of us, not necessary.


Lawrenceville, GA

I believe Gummelts crank alone cost about $1800. As Charlie says, they are not necessary. J. Mummert in CA offers stroker kits made from factory cranks. For any reasonable application they will do nicely. The Gummelt crank was for an all out supercharged dragster application. Besides, extremely long stroke crank assemblies are not possible on a Y-Block due to lack of clearance.

Paul

Moldex offers custom billet steel cranks for the Y.  While they can be machined with a variety of crankshaft flanges and snouts, journal diameters, and strokes, they are expensive.  Very nice pieces and allows considerably more stroke capability than what offset grinding is capable of.  Lead times when ordering can be reasonably long depending upon the time of year they are ordered though.

Lorena, Texas (South of Waco)

I have a follow up question then for those who can answer with more than speculation:

Wouldn't a new crank be preferable to an offset ground original due to recipercating weights being designed for the additonal stroke?  I understand you can ballance the crank either way. 

Ted, you mentioned that you can possibly get a larger stroke in a newly produced crank than what offset grinding allows.  I was under the impression that interference issues would trump max stroke either way.  Can you clarify this for me?

I am interested to know if the max stroke with a custom crank would be significantly larger than that of an offset ground?

Getting a new moldex crank with a 3.64 stroke is an easy bolt in and I believe alot stronger being they are cut from billet steel. Mines a 3.66 stroke and this helps the torque a bunch!

-Gary Burnette-

Key considerations in offset grinding a stock crankshaft for additional stroke will include the stroke of the crankshaft you’re starting with, the current journal size, the journal size being targetted for, the width of the connecting rods that will be used with the resized journals, rod to camshaft clearance with the increase in stroke, and oil hole placement in the journals before and after offset grinding.  When starting out with a good standard journal 292 crankshaft, the stock stroke (3.3”) can be increased to:

3.380” with a 2.100” journal

3.480” with a 2.000” journal

 

For a good standard journal 312 crankshaft, the stock stroke (3.44”) can be increased to:

3.520” with a 2.100” journal

3.620” using 2.000” journals.

 

A custom crankshaft raises the bar in that up to 3.800” stroke is doable with the 2.00” journals but requires some serious rod clearancing at the top of the rod bolt thread area to provide adequate connecting rod to camshaft clearance.  Keep in mind that when going with a smaller journal, the connecting rod cross-sectional measurement (in most cases) also decreases which helps with cam to rod clearance when increasing the stroke.  When going with Honda rod journals (1.889”), then a 3.750” stroke is reasonably effortless without any connecting rod modifications.  Going to a 3.800” stroke with the Honda journals requires some slight clearancing at the top of the rod bolt area on the rods to insure a minimum of 0.050”-0.060” rod to cam clearance.  Going for more than 3.800” stroke on a Y is not for the faint of heart but indeed doable.

 

Here’s a link to the build up of Randy’s dragster engine which uses a 3.800” stroke crankshaft.  This particular article has a picture of the connecting rod as it’s being modified for additional rod to cam clearance.

http://www.eatonbalancing.com/blog/2007/12/09/blueprinting-for-an-eight-second-y-block/ 

 

And here’s a link going into some more detail on the Moldex crank that was used in the same engine.

http://www.eatonbalancing.com/blog/2007/12/10/building-the-foundation-for-an-eight-second-y-block/ 

Lorena, Texas (South of Waco)

Ted, where would one go to purchase rods for a combo w/a 3.75 stroke for intance? Ballpark $?

There are several aftermarket rod manufacturers that offer a variety of off the shelf rods that are suitable for custom or non-stock applications.  Crower, Eagle, Oliver, Probe, and Scat to name just a few.  You essentially pick the rod for the journal size you want and then work the custom crankshaft specifications into and around the connecting rod.  For the aforementioned 3.750” stroke and Honda rod journals, then the Eagle H-Beams (#CRS6300HJ) work nicely in that they are 6.300” long and considerably lighter than stock while being capable of some very good horsepower numbers.  Price for a set of these typically runs in the $550-$625 range depending upon where you shop.

If offset grinding a 292 or 312 crankshaft, then many of the aftermarket 2.000” or 2.100” journal offerings for a scrub will work but you’ll need to narrow the rods at the bearing beam portion and use the narrower than stock rod bearings that are available.

Lorena, Texas (South of Waco)

Ted, a while back you wrote an article for Y-mag regarding rod and main journal overlaps in cranks.  As I recall the amount of overlap in Y-s resulted in some extra strength.  I have been wondering for a while how much the overlap can be decreased before weakening occurs.  Take a 312 crank with mains ground down to 292 size, there is some decrease, and then progressively more of a reduction should rod journals be taken down to 2.1, 2.0 or even 1.88.

I saw a picture of a crankshaft from a Plymouth 230.  They have huge strokes, and the main and rod journals were widely separated.  These motors probably would come apart at 4000 rpm.  Apparently this doesnt correlate with stroked 292/312s because they often turn high rpms.

Mike

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.