Forged alum. pistons 45- advice, deck height?

[AdminGuy]

I'm looking at getting some forged pistons (+0.050) for a 45" sport scout. I want tough stuff for the extra 12" cube stroke. I need some advice in regards to ordering them. I'm cutting down a set of chief 74 wheels (Yes, all Ingin, why not). Havn't done this yet. Stroked 57" w/ stock rods, stock 640 cams. Barrels are square bottom reinforced cast.
Stock Bore: 2.875, Stroke 3.5, Piston clearance 0.003".

What should the deck height be? Rod center to deck height piston. I think I'm doing this backwards. I should be measuring the clearance from an assembled state. I want to avoid shimming up the barrels. advice?

Specs: Flat top, 3 ring plus oil control ring, no t-slot(forged), spiral locks, wrist pin oilers cut,

Cam-ground (.006-.010): Bottom -.005, top-.007, ring lands .020, ring joint gap .015-18
Pin fit Piston: push fit, Pin fit rod(honed): 0.0015,

Any technical advice appreciated.

[AdminGuy]

What... is the air-speed velocity of an unladen swallow?

What is the expansion rate of a modern forged aluminum piston over an older style? Wouldn't this allow for tighter tollerances? Not much -but a little tighter I would think.
Is the barrel operating temperature of a flat head around 250-300 degrees F? Just a guess. Do you have one of those fancy digital thermal heat guns?

[T. Cotten]

Forged pistons are denser, and therefore expand more. So more clearance is needed than a conventional cast T-slot piston. When .0035' might be spec'd for a cast piston, .007+ might be expected for a comparable forged piston.

Please note that the piston is usually not where the fuse gets lit. Things that increase heat cause the pistons to gall, such as advanced timing, misaligned rods, or the classic evil manifold leak.

Pistons don't need to be overkill bandaids on even a 6 to 1 flatty. Consider that the market-leading oriental producers have cast 10 to 1 OHV pistons in good service without widespread disasters. From that perspective, the difference between 45" and 57" is still negligeable.

The intake valve of a 45" HD has been rated at 400F, so you can expect the combustion chamber portion of the cylinder exceeds that by a great margin.

Your deck height can only be assessed by mock up. Try using modeling clay in the combustion chamber to give you a measuresable "squish-height"
.060" would seem optimum.

[AdminGuy]

Barn Swallow

Opps- I got that backwards.

Ok, so stock piston (t-slot) clearance - 0.003, Bonn - 0.0055"
Solid piston clearance - 0.005, Bonn - 0.0075, Forged -0.008"

Forged not really nesessary due to compression ratio. I forgot about that. Being low it's more forgiving. I can understand a few more practices now.

I was trying to avoid dummying it up. But by the looks of things I'll have it appart and together 4 or 5 times before I'm done. Might as well start here. My plans for work avoidance have failed miserably.

I'll have to get some peek MANAfold seals from you. Makes sense. Good job. And thanks for info.

Any cam prefs for a 57"? Should I phone Max? hummm...Maybe I should. It'd be interesting to get his perspective. I'll play 50 questions with Kenny and maybe Robin also. I'll post some info back here. Maybe it will save these guys a few phone calls. Ron Link? Should I call him? Ya! humm...anyone else? Fasst Jim?

[T. Cotten]

I must plead ignorance when it comes to Indian cams.

Without FasstJim's page on cams in the VirtualIndian archives, I wouldn't even be able to identify the differences.

I do know that at least four different grinds are currently reproduced!