Piston support at BDC

[69Stu]

I have just started mocking up my new engine, a 2332, (my first stroker motor) and I am checking how much of the piston comes out of the cylinder at BDC.
I am using JayCee long barrels, Wiesco pistons and 5.500" rods, and 15mm of the skirt on the piston is below the end of the barrel, but all of the gudgeon pin is within the barrel.
Is this acceptable, or should I get the case and barrels machined so that all of the piston is within the barrel at BDC?

Thank you.

[69Stu]

Maybe this picture will help to illustrate my question.

[Mike Lawless]

You're fine with that. Although you're probably OK, make sure you check the crank counterweight to bottom of piston. It can get close with short rods.

[69Stu]

Thanks Mike,

The crank counterweight to piston clearance looks OK, but it will get checked again several times before final assembly.

Would it hurt to drop the barrel into the case a bit more?

[Jon]

I would drop it in until you have the squish height where you want it. And then check for clearance for rod and crank.

[Mike Lawless]

Wouldn't hurt at all. As JHU points out, you can sink it till your deck height says no more. Not so far that it interferes with bottoming the barrel, and again as JHU says, check the rod and crank clearance, especially right there where the case is notched.

Have fun!

[69Stu]

Thanks for the advice. 

[Zach Gomulka]

How much deck do you have now?

[69Stu]

I haven't done the final measurements yet, but it looks as though by taking approximately 19mm out of the length of the barrels I will end up with a 1mm / 0.0040" deck height.
This will also drop the skirt of the barrel 5mm further into the case, which is about as far as i can go before there will clearance issues with the rod bolts.

[Mike Lawless]

Sounds like you have long barrels then. If the case bore allows it, if it were me building this, I'd sink the skirt of the barrel as deep as the case allows, maybe only leaving .020 - .030" short of bottoming out before the mating surface seats against the case deck. If the bottom needs additional clearance then go ahead and notch the barrels so you have about .060" rod to barrel clearance.

I was thinking you had stock type barrels and were concerned about the support with those.

My current combo probably has much less piston support than you have as I have a high deck case and stock length barrels with a 5.7" rod. I buzz the snot out of it and there hasn't been any scuffing on the skirts of the piston at all

[Fiatdude]

I'd stick some longer rods in it -- or get a set of pistons with the pin lowered there by raising the piston in the barrell

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[Taylor]

My personal opinion is that it is not the .590 that sticks out it would be what % of the piston is .590?

[69Stu]

My personal opinion is that it is not the .590 that sticks out it would be what % of the piston is .590?

Good point, cant answer at the moment as I am at work, I'll have a measure up later. But as previously stated, the gudgeon pin is still fully inside the barrel, so the majority of the piston is in the barell.

I'd stick some longer rods in it -- or get a set of pistons with the pin lowered there by raising the piston in the barrel

Yep, I can see how that would help, but I already have quite a bit of money tied up in these parts.

Sounds like you have long barrels then. If the case bore allows it, if it were me building this, I'd sink the skirt of the barrel as deep as the case allows, maybe only leaving .020 - .030" short of bottoming out before the mating surface seats against the case deck. If the bottom needs additional clearance then go ahead and notch the barrels so you have about .060" rod to barrel clearance.

I did think about notching the barrels to clear the rod bolts, but was not happy with the idea of removing barrel material at the point where the piston skirt would run.
Is it not defeating some of the advantage of having the extra barrel length?

[69Stu]

My personal opinion is that it is not the .590 that sticks out it would be what % of the piston is .590?

Just had a measure.The 0.590" equals 23% of the piston height.

[Taylor]

That's not too bad. I would cut the step out of the case and run the cylinder as far down as possible. Even if you just run the cylinder down shy of the rods. Your not looking for piston support as have enough. What you're looking for is to keep the rings sealed against cylinder wall.

[Taylor]

As a side note:
Even if you ran the cylinder down real far you would only have to notch the side of the cylinder for the opposing rod. the meat of the cylinder ( top and bottom ) would still be there to support the bottom most part of the skirt thus giving extra support to the piston and keeping the rings from getting upset.

[neil68]

My 2332 cc set-up:  OEM mag case, Mahle slip-in 94's, 5.5" rods, 84 mm crank.  I haven't had any problems and have opened the engine every year while swapping camshafts.  I elected to minimize cylinder shims and go with copper head gaskets in order to keep the barrel down inside the case more.  Here's a picture and it appears similar to your's:

[Airspeed]

The piston in an original 964 engine sticks out further with a lesser rod ratio, so I would not worry about it.