Adjusting Deck Height, 3.3 turbo rebuild
 

Is .035" or .889mm sufficient deck height using (1) copper ring?

It's an 87 930, stock flat Mahle pistons.

Or should I get the oversize .5mm rings?

Thanks!

Anyone?

Glenn:

.035 is not quite enough,.......I shoot for .038-.040.

Q: Do you have the cylinder well clamped down and are you using a dial indicator to measure this?

Steve,

Thank you.

No, it was measured my just pressing the cylinder down firmly. Measured with a vernier. My dial hasn't arrived by mail yet.
I'll clamp it down with the head nuts and re-measure. Appreciate the feedback on the height!

Glenn

Tightened down a bit, I get .032" Even less.

Wish they made a .4mm

Can I double up, re-using my old copper ones?

G

Glenn:

IMHO,...This is not a measurement done by "Kentucky Windage" given what is at stake here: detonation or piston contact. It really must be done right with the correct tools to get accurate, repeatable values.

The most accurate way is to properly clamp the cylinder down and take deck height measurements with a decent dial indicator and stand.

Base gaskets are made in .25mm, .5mm and 1mm. In some cases, one machines a tiny bit off the cylinder bases to get the right gasket stack to hit the targeted value. In a pinch,.......you can re-anneal the old gaskets if thats the only alternative but I would not do that, especially in a turbocharged engine.

Steve,

Got, it. Thanks. And I had pizza tonight, no KFC. The by-product may STILL be windage.... ;)

I tried mocking it up with 3, .25mm gaskets which yielded just over 1mm gap. Much better. The machine shop got all the cylinders to the same height so I should have expected to make up for it somehow.

I think I'll get .5mm gaskets to add to my .25 ones, and use the dial indicator.

I won't re-use any old parts.

Oh man,..I'm glad I'm here,....... :) :)

Too much deck height is just as undesirable as too little and this is especially important in a 930. I go the extra mile to get it spot-on. Given the variances in stock rod lengths, head volumes, and perhaps a decked case, sometimes the cylinders get trimmed a tad.

Carry on, Sir!! :)

Thank you Steve!

Guess I've got more work to do. Hope it doesn't involve more machining but it might. :(

G

Glenn,
Steve has a very good point. The cylinders have to be clamped down with sufficient torque so you get accurate real time measurements. The copper base gaskets I received had a thin film of adhesive on each side which would of thrown off my measurements if the cylinders were not tightened down on the spigot bores.
Yes, you can use two base gaskets to get the desired deck height, but other places like EBS Racing and probably Steve sell the .5mm base gaskets.

I glue solder on the piston squish area at the front and back. Assemble, turn the engine over, disassemble, and measure the solder. Seems pretty accurate to me.

Thanks Dave and David.

I might try David's/solder method. That seems the most accurate method. I guess I could mock up one P&C, bolt the head onto it to flatten it, and rotate the thing while using the solder method.

When I mocked it up with the 3, .25mm gaskets I clamped down the cylinders, tightening 2 head nuts per cylinder maybe 10-15 ft/lbs. The additional set of .25mm gaskets luckily didn't have that glue either. I swear I was getting different readings, at different points around the piston, when using the vernier caliper. Did you guys experience that at all?

I'm going to pick up the .5mm gaskets, maybe even the 1mm ones - and give it another go with better measuring tools. I even tried using feeler gauges, pushed right up against the cylinder - as I noticed that my "flat" pistons had a slight crown. I took the P&C's off again.

It sounds like the goal is 1mm gap, slightly less than suggested in Wayne's book.

You should use an area directly above the wrist pin on the left side and on the right side of the piston closest to the barrel of the cylinder at TDC. This will minimze any effects of the piston rocking in the barrel and throwing off your measurements.

That does make sense, Dave.

I'll try the solder method tomorrow when the .5mm gaskets are in.

What deck height did you end up with?

G

I had 0.031" with the .25 mm base gasket, changed to .5mm which took it to 0.408".

Got it. Thanks.

I'm eager to get past this point, but I also know it's not worth rushing.