Hi all,

I have some questions regarding a 272 stroker I’m hoping you might be able to help answer.

What do I have to do to stroke a 272? I’ve been looking at Mummert’s CR-312-BU rods. I know I’d have to get the crank offset ground, but I’m wondering if the piston to valve clearance will be ok using the current piston.

Bit of a back story-

Engine- (rebuilt less than 500km or 800mi)
- 20thou over bore with forged pistons (all the supplier had)
- block deck machined so pistons are flat to deck
- eczG heads with all new valve train, valve guides oversized intake valves and hardened seats, positive valve stem seals, 1.54 rockers.
- B manifold modified to dual oval opening
- Mummert Y270S cam
- MSD distributor

So this engine has less than 800mi on it and I’ve developed a ticking noise that increases with rpm. I initially suspected I’d wiped a lobe on the cam but now I’m thinking I may have done some bottom end damage due to oil starvation from hard braking (I don’t think I have my sump baffles low enough to stop oil sloshing) and the oil pressure light came on a few times.

I haven’t pulled the pan to have a look because I’ve got a few other projects in the go and don’t have the space, and if I’m going to pull the engine out (easiest for me due to space and time) I want to do some work to it (mainly for enjoyment).

Now, I know the obvious solution to more cubes is to use a 292 or 312, but the 272 is what I have and I’ve already spent the time and money on it, plus 292 aren’t as common here in Aus compared to the US, so I’m sticking to what I’ve got.

I know we all like pictures so here are a few.










Thanks, Dennis.

56 F100 - 272 Y Block
NSW, Australia.

To get any stroke increase with the 3.300" crankshaft, you will need to cut the rod journal down to a smaller diameter by keeping the current outside of the journal and cutting the inside of the journal to the new dimension.  Usually that is accomplished by going to the small block scrubrolet early rod journal diameter of 2.000".  There are several connecting rod suppliers that make a 6.250" forged rod with the 2.000" journal and .927" pin bore size.  Usually the rods will have to be narrowed to the Y block journal width.  Using your current pistons would be very difficult to find a rod the correct length, especially after changing the stroke of the crankshaft.  Each crankshaft stroke increase is determined by the already size of the journal and how much it would take to clean up the journal at a 2.000" diameter, or a .010" under 1.990" journal.  The crankshaft grinder would be the person to tell you if they can actually make that happen.  Joe-JDC

JDC

272, 292, and 312 pistons all have the same compression height, with the exception of the Heavy Duty 292 truck pistons. Where did you source your pistons? Do they have the same compression height? Considering that you already have Mummert's stroker rods, which do not have to be narrowed, there's no need to consider using SBC rods. Are your pistons flat-topped or domed? Do they have the short skirts (312) required to clear the additional stroke that you're seeking? What size intake valves? Unless you've cut the block and head decks more than a combined .030-.050, and you are going to use shim gaskets, not composite, piston-to-valve clearance with the net valve lift & Duration @ .050 of the 270-S cam, shouldn't be a problem. Considering you've bought Mummert stroker rods & cam, have you run this by John?  Hopefully your machine shop has the expertise to make it all work. 

Thanks Joe, good info there. It’s all just a bit of a hypothetical at the moment seeing if i can get it to work with least amount of complications. I’ll have to contact a crank grinder and have a chat.

55blacktie- I haven’t got the rods, just been looking around at the moment. Pistons are flat top, not sure about the short skirts but I’m guessing not, as they are 20thou over 272 std size. I actually got the pistons years ago from a fella named Cusso Bill here in Aus, never met just did an over the phone sale. The intake valves are 2inch, had to go up a size due to a machinist error. I can remember how much came off the heads and deck as it was a quite few years back now.

Thanks for the info so far.


Thanks, Dennis.

56 F100 - 272 Y Block
NSW, Australia.

A 312 crankshaft with the factory 6.252” long rods using your existing 0.020” over pistons will net you 287 cubic inches.  For the 312 crankshaft, you will need to turn the mains and rear seal area down to the 272/292 sizes.  If the Mummert stroker rod is 6.252” long but uses the 2.000” journal, then offset grinding a 272/292 crankshaft so it has a 3.44” stroke is very doable and still use your stock 0.020” over pistons.

As Joe brings up, if offset grinding a crankshaft for additional stroke, then you will end up with a smaller than stock Ford journal thus requiring some kind of aftermarket rod.  For rods using a non-Ford Y wrist pin, that will require another set of pistons so you can match both the wrist pin diameter and the wrist pin compression height to whatever connecting rod you choose to use.  For most stroker Y builds, I will use a 6.350” long rod but the connecting rods are available in a variety of lengths both shorter and longer.  I use a 6.750” long rod in my roadster Y engine so that shows you the extreme to which you can go.

Lorena, Texas (South of Waco)

Thanks for all that info Ted. I haven't done a stroke’er before and I'm just dipping my toe in the water with these questions, but as always there is alway far more to learn than expected. I’m going to have to go back to the drawing board. I was hoping to gain a little more cubic inch, but obviously using the same pistons will limit me. Maybe I’ll look at stroking my other 272 which is next on the project list and maybe look at something a bit more radical in terms of stroke and piston.

Do you have any recommendations on brands/piston rod combinations that you use to get the most out of a 272 stroke’er?


Thanks, Dennis.

56 F100 - 272 Y Block
NSW, Australia.

For most Ford Y-Block (FYB) stroker builds using modified FYB crankshafts, I will use an Eagle 6.350” long rod with a custom piston.  Most of the custom pistons I use for FYB builds are sourced from Diamond Pistons, JE Pistons, and Wiseco.  While I have used FYB crankshafts offset ground to a 2.100” journal, best bang for the buck comes with making the journals smaller thus making additional stroke available.  The actual rod length is not much of a concern but I prefer it to be longer rather than shorter.  The longer the rod, the less the propensity for detonation as determined by the quality or octane of the fuel.  The longer rods do put the wrist pins closer to the top of the piston.

More food for thought.

If attempting to retain the factory pistons with the 0.912” wrist pin diameter, you are limited to using a connecting rod that accommodates the 0.912” wrist pin.  If using a stock replacement or shelf piston, you are likely going to be limited to the oem style rings which add a considerable amount of drag or friction to the engine versus using pistons that incorporate more modern ring designs.  Going the custom piston route allows the ring package to be upgraded to modern ring or metric designs and this by itself can be worth 25-30 HP.

Option 1: The factory ECZ or C1TE connecting rod with its 6.252” length will work with a 312 crankshaft while maintaining factory rod journal diameters and the available and common under sizes.  That combination will require that the main journals and seal diameter on the 312 crank to be cut down to the 272/292 sizes.  If trying to retain the factory rear oil deflector on the 312 crankshaft, the machine shop doing the grinding must use a narrow rock.  Shops that do not have the narrow rock will typically just remove the rear oil deflector from the crankshaft so that the wider grinding rock can be used.  For myself, I prefer leaving the rear oil deflector on the crankshaft intact if at all possible.  If using a factory piston, then the piston skirt to crankshaft counterweight clearance must be checked and if necessary, modify the piston skirts accordingly.  Using 272/292 pistons with the shorter rod will sometimes get into a crankshaft counterweight clearance problem depending upon the piston manufacturer.

Option 2: The work around to using a 312 crankshaft and still use a factory piston (including your existing 0.020” over pistons) will be to offset grind a 272/292 crankshaft to the 3.44” stroke and 2.000” journals and then use John’s rods which allow the use of the factory 0.912 wrist pin diameter.

Option 3: Use an offset ground 272/292 crankshaft.  If grinding to a 2.000” journal, those crankshafts can be offset ground to as much as a 3.48” stroke.  Any commercially available SBC aftermarket connecting rod can be used but must be used with a piston with an appropriate wrist pin location (aka compression height) and 0.927” wrist pin diameter.  The journal widths on the crankshaft will need to be widened along with the connecting rod big ends being narrowed.  I target for a 1.810” journal width and then narrow the rods so that they are 0.895” wide.  Custom pistons are the norm here but the caveat here is that the pistons can be ordered to be used with the more modern piston ring designs which provide some free horsepower over the older stock rings.

Option 4: Use an offset ground 312 crankshaft.  If grinding to a 2.000” journal, those crankshafts can be offset ground to as much as 3.620” stroke.  If the crankshafts have been previously ground undersize, then the actual amount of stroke that can be achieved will be limited.  Any commercially available SBC aftermarket connecting rod can be used but must be used with a piston that has the appropriate wrist pin location (aka compression height) and 0.927” wrist pin diameter.  Custom pistons are the norm here.

Option 5.  Use an aftermarket billet crankshaft which can be made with strokes up to 4.300” and are available in a variety of connecting rod journal diameters.  For many of these, I use the Honda 1.889” rod journal diameter.  The 4” stroke is the most common stroke for this stroker combination and for those, I have used up to a 6.750” long rod.  For strokes in excess of 4.000”, a custom-built connecting rod is used.  Custom pistons are the norm here and wrist pin diameters are dependent upon the connecting rod being used.  I have used wrist pins as small as 0.866” pins on some Y stroker builds.

Here’s the link to a past thread discussing some of the nuances in ordering custom pistons.
http://forums.y-blocksforever.com/FindPost160000.aspx

Lorena, Texas (South of Waco)

Thanks Ted for all that great information. This is good, thanks for adding the 4 options and the link. Option 2 or 3 would probably be the way to go for me. I don’t like my chances of finding a 312 crank in usable condition here in Australia without the premium price tag attached. However, after reading this I’d be better to find a bare 292 block and stroke that using the spare 272 crank I have and go with custom pistons to get the best bang for buck.


Thanks, Dennis.

56 F100 - 272 Y Block
NSW, Australia.

Hello  Noticed  YB builder and crankshaft grinder gets a 3.625" stroke from a stock rod  sized 312 crank. That  (possible) with STD 2" rod journal, must be under sizing rod journal? Also  is there a  way  to (re) radius rod journal all the way around without a wider journal width, didn't think so.