With a 3.50” stroke and 6.250” rod, the compression height (wrist pin location) for a piston at zero deck and with a 9.750” block deck height would be 1.75”.

 

If you’d like to play with other compression height (CH) values, here’s the basic math formula.

 

CH = Deck height - (stroke divided by 2) – (rod length) – (amount piston is in the hole)

Lorena, Texas (South of Waco)

 

I havent given the block a check yet to see if it has previously been decked, but assuming it has not, and that it will have a .005 cleanup, is .015 too much to take off an old NOS flattop piston, or, what is the max. safe limit for material removal from the piston top?

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.

What is safe will vary from piston to piston. Most of the original pistons I've seen from various engines are pretty thick so a .015 cut should not be a problem. Aftermarket pistons may not have so much room for error because their use is more clearly defined.

I did have to cut about .015 off of my probe flat tops, which are about .200" to begin with. So far, so good. If I'm not mistaken, Hoosier is using the same pistons with more cut off the top in his supercharged race car and it is doing great.



I think you will most likely be ok if you have to take .015 or so off of the piston.


Lawrenceville, GA

Thanks Barry, Hoosier, Ted and Charlie, and Jepito for starting the thread.  Wouldnt have hijacked it but it looked like the original question was covered.  So I have a plan , a 319 cu in project!

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.

Sounds like you have a plan but I’ll add the following.  The number I use for the stock deck height is 9.775”.  Cast pistons are normally very robust in their deck or top thicknesses so taking off up to 0.150” isn’t a problem unless it gets the top piston ring marginally too close to the top of the piston.  Measuring the piston for deck thickness before doing anything is of course recommended.  A minimum of 0.200” of piston top thickness is also desired after all modifications have been performed.  As Charlie mentions, many of the better aftermarket forged pistons are already at 0.200” deck thickness so not much room to modify on those but cast pistons are typically much thicker in that area.

Lorena, Texas (South of Waco)

Then the 9.750 figure must be after decking.  I had to deck the block that is in use .028 to get .004 in the hole.  There was align honing, plus the rods being resized made them .004 shorter, all added to the shorter(?) comp. height piston, left the piston .032 down.  With 9.775 being the stock height, there is a lot more wiggle room and theoretically decking alone could have the piston at zero.  I've seen deck heights referred to before, but didnt have reason to remember them, so thanks for the figures.

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.

Our Probe pistons are set-up for 3.48" stroke, .927" pin (sbc) and 6.200" rod  2-350-6.200-2.000 Scat.

We made the pistons that way so you could start with .030" under crank and still end up with standard rod bearings.

Pistons will also work with 292 crank offset ground to 2.00 journal.

They will also work with 312 crank offset ground to 2.00" journal and 3.61" stroke and 6.125" rod

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Since there is a NOS set of .060 over 292 pistons on hand, this mini stroker idea seemed feasable, and wouldnt require having to take  so much deck off like happened the last engine when  .028 was removed.  I was standing within a foot of the block as the mill made multiple passes across the deck.  After the 3rd or 4th pass a crack showed up at the rear DS dowel hole, going from it to a water hole.  Didnt show up with maging.  I was kind of sick because this was about the end point for block work.  The crack didnt go to the bottom of the threads but it was on each side, meaning coolant might work into the valley. So a wicking ceramic sealer was used, and studs were installed.  I put the engine together wondering if the effort would prove futile, but it all worked out. 

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.

The quick and easy idea of using an Eagle rod with 292 piston has dead ended.  Eagle doesnt make pressed pin rods in the 6.250 length.  I had hoped they did so that the small end could be bored out for a Ford bushing.  The onely way left to do this seems to be what John suggested, having the piston machined for an SBC pin and clips.  That sounds expensive and I dont know where it could be done.  Also sounds like there is a lot of room for error(s).

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.

What about a bushing which reduces the rod to the ford pin size?


Lawrenceville, GA