Deck Height

[Deye76]

Is there a way to determine (mathematics) if a piston, on a given build, will be down, or proud, short of assembly?

[RoadKingRon]

Never have tried, but you could measure from the wrist pin center while on the rod with the cylinder bolted to the case. You would need the piston measurements from top of piston to wrist pin center. Rod would have to be on top dead center and aligned properly. I am sure someone will now have a easier way.

[Faast Ed]

I believe they would be coming off the assembly line at zero deck, if there was a way.

[Rusty Steel]

Seems like RoadkingRon is thinking mathematically.   

For a given rod length and stroke, and known piston height you could get an approximant but not an exact without measuring after assembly. Mathematically. YMMV.

RS

[roadglide65]

Is something like this what your looking for??

http://www.rbracing-rsr.com/squishcalc1.html

[Wingnut]

Try this.   

"The sum of the square root of two sides of an isosceles triangle is equal to the square root of the third side."


The Scarecrow

(after he got a brain)

[Herko]

Sure it can/could be done.
Factor in the block height, rod length, compression height etc., one should be able to do so.
With that said, if all is measured in your shop from the ground up, your golden. I for one do not have a good true and highly accurate way of measuring block height or a crank center to cylinder base dimension.

So, for us device limited guys, seems the trick with these Harley engines is getting a "solid standard" on the dimensional specs.
And, apparently HD doesn't publish and entire set of blueprint specs either.
If so would like to see "that" document published.
This is one of those areas where a lot of hearsay and conjecture get displayed but with the best of intentions.
On occasion there's even different specs within the various online/off line calculators.

Block height for example. Not typically spoken in the Harley world.
So, next best might be a crank center to case deck dimension plus cylinder height.
Well, best I've heard is 6.000 +/- .002 for the 96 motor.
Then depending on where you read or hear, cylinder height is 4.937 or 4.938.
We're up to .003 already. Gets sloppy in a hurry.

There's a lot of "the ones I've measured have been x.xxx"
This is good but what will the next guy say?
What are the "intended" engine blueprint drawing specs?

I say intended because we all know some of HD's tolerance surprises.
One example, the 2007 rod lengths early on.
Another one...what's the intended production CC size of the combustion chamber for a given model of engine? Again, with the best of intentions, you'll hear variances here as well.

Many thanks to all the guys that have taken the time to measure certain things the "right" way with the "right" high quality instruments known to be calibrated properly. This type of spec arrival is the best we have in most cases.

JMHO

[POORBOY]

I agree with Herko

[longshooter]

I will take a little different slant on the question, if I may. When you say "short of assembly" I will assume that you are already at the
teardown stage and have new pistons in-hand. If so, then you should be able to snug down the cylinders, measure deck height with the old pistons still on the rods. Remove the pistons and measure compression height and compare it to the compression height of the new pistons. Any difference can be added or subtracted from your original deck height measurement to calculate new deck height and determine how much, if any, needs to be shaved from the cylinders for zero deck. Course, I could be all wet. The hell do I know? It's nuts and bolts.

longshooter

[Deye76]

Herko, you pretty much summed up what I was thinking, especially around crank centerline to deck dimension. I'm just curious, ahead of teardown/re-assembly, if I'll have to trim the cylinders.

[Don D]

Then measure it before teardown (torqued with bolts and spacers) and then compare the piston compression distances of the new VS the pistons you take out. Add or subtract as applicable and there is your answer

[02FYRFTR]

Yes measure for deck heigth before tear down.  Have your local machine shop finish grind to a .927" dia X  8.000" long straight wrist pin.  Slide wrist pin through the pin holes on the new and old pistons and measure the drop between them.  Use this dimension plus the previously recorded before teardown to correct the cylinder or piston heigth accordingly.

[Deye76]

Thanks fella's.