Help: Setting Deck Height... For Dummies

[Toasty]

So I'm at that stage of my GS550-650 swap where I need to start reassembling the top end. I was researching here and other sites on how to check and set the deck height.


So if what I read is correct I need to:

* Lay down the base gasket on the block
* Put pistons onto crank, lower cylinders onto the pistons
* Use spacers to torque cylinders to spec
* Set engine to TDC
* Lay straight edge on top of piston and measure clearance to the top of the cylinders.

I'm guessing I use this convenient flat spot for the straight edge.

Is this right? From what I read from Suzuki Don in another thread is that the optimal deck height for this swap is .02 - .04"?

When setting deck height, do I need to install the oblong rubber o-rings along with the base gasket? Do you set the squish band when doing the deck height or is that a separate step? Since the 650 pistons still have the old piston rings on them, should I keep them on there until everything is set and then install the new ones?

Maybe unrelated: If I need to check squish band by putting on the cylinder head, torquing, and using clay while turning the engine... Can I use the old head gasket while doing this? I don't wanna torque down the new gasket any more then I have to.



Edit: I used this thread as a visual guide
http://www.bigboyzcycles.com/showthread.php?t=92

 

[Guest]

Assemble the bottom end with block and pistons and get a baseline for where the piston deck height is now.

Measure from the deck down to the piton around that ledge.

Idealy you want the piston to be as close to 0 deck height.

For squish between piston and head I've herd different things, I'd aim for 0.043 to be safe. Someone will chime in with a how much and why.
I just aim for 0 deck height and use the head gasket thickness as the squish zone.

CC the combustion chamber and see what you have in there, then CC the piston dome from the flat edge to the tip of the dome.
You can squish the piston into some play-doe or clay to get an impression and then fill it to find out how much cc's the dome takes up.


With those two numbers. Subtract the head cc's from the piston cc's to see what you get. You can use an engine calculator and figure out what the compression ration is going to be.

http://www.cbperformance.com/v/enginecalc.html
Just punch in the cc's
bore
stroke
deck height
and see what it gives for compression to see if you have to modify anything.

 

[gearhead13]

That thin area around the edge of the piston is where you measure height compared to the block to get deck height. 0 deck height is when that part is even with the top of the block. Most head gaskets are .043" after being torqued. That much clearance is needed to keep the pistons from hitting the head at high rpm.

 

[boontonmike]

My question is why are you over-analyzing this swap. There is no need to be doing these things. This is a proven swap done my a multitude of members here with no issues.

Now, If you are doing this for the fun and learning of the process then more power to ya.

 

[rapidray]

As an engine builder, I measure deck height WITHOUT the base gasket in place. I do it with the block clamped down, just as you described, but then add in the difference after. Ray.

 

[trippivot]

As an engine builder, I measure deck height WITHOUT the base gasket in place. I do it with the block clamped down, just as you described, but then add in the difference after. Ray.

Yep X2 no gasket - no rings installed lightly clamp cyl-s down and measure at the wrist pin area - rock it and average the measurements (if you are weary of the piston offset) . you'll use a verneer - or dial gauge and stand-- because we start with the piston sticking out of the bore - and you only need accurate no need to be super precise.

sling out for a 1000/1100 is .040" - the 550 probably is a little less- so as mentioned before .043 as a final product is great ! but because copper base gaskets are .005 , .010 , and .020 -- and most copper head gaskets are .046 the combination can be set slightly dangerous or safe ..

CC'ing the combustion chamber assembled is overkill for a street engine but if the deck height is safe just grease a piston at final assembly and use a graduated barrett "turkey baster and a hose"-- something like 18 or 20 will probably have you at 9._ _ something -- give or take a couple of points -- the difference being a few thousthousand-ths of safe deck space