3.2 Deck Height base gasket issue

Classic11 · 10-07-2019, 05:25 AM

Hello, I am building a stock 3.2 and I am in the process of measuring deck height with the acid core solder. I only have the 1.5mm solder (3mm only available in solid). My motor was all original and as far as I could tell never apart before, factory used 0.25mm on cylinder 1,2,3 and 0.5mm on 4,5,6. I installed new copper gaskets in the same location and when I measure deck height I cannot even get the 1.5mm to compress. I took the 0.5 out and installed 0.25 and I may get the slightest compression of the solder right on the wall, see picture below and I measure 1.45mm.
Are there thinner gaskets? Don't thing running with no gasket is a solution. My heads and cylinders are original and were not surfaced. What are some typical measurements for a 1984 3.2? How much can they vary?
Thanks for you support.

r lane · 10-07-2019, 10:11 AM

I have never checked the stock deck clearance but .060'' sounds about right. Having a .020 shim on the motor must mean that it was done post factory. Anomalies happen but cant imagine the factory mixing and matching base shims. Start by measuring the cylinder heights and check the script on the base of the cylinder to see whether they all match. Bob

cmcfaul · cmcfaul's Garage

never heard of different size gaskets on the same motor.

Chris

Classic11 · 10-07-2019, 04:52 PM

Casting date and all matching. Just checked a cylinder that had a 0.5mm gasket originally with a 0.25 gasket and 3mm solder and got 1.75mm deck height means it was 2mm before. I cannot see any signs this motor was apart before. I guess I will install the 0.25 gasket all around and make sure they are all similar. Anybody measures a 3.2 stock? Would be courios about results. Are the coated Reinz gaskets really not as good compared to the copper only porsche gaskets? I will orede63 more porsche 0.25 gaskets anyway just curious. Thanks

Eagledriver · 10-07-2019, 06:26 PM

You are not measuring deck height. You are measuring piston to head clearance. Deck height can be measured with a depth guage or caliper. The height is from the top of the cylinder to the top of the edge on the piston.

-Andy

Eagledriver · 10-07-2019, 06:28 PM

I have different size gaskets on each side of my engine. The case isn’t machined perfectly symmetrical.

Classic11 · 10-08-2019, 03:52 AM

Eagledriver, i know i am measuring piston to head clearance in the end, deck height is tough to measure with a caliper on the 3.2 pistons since they are anything but flat on the top. What motor do you have and what sizes did you end up using?
Anybody measured piston to head clearance on a stock 3.2 before? What is a "good" measurement?
Thanks for the replies

r lane · 10-08-2019, 09:27 AM

Measure all the pieces correctly, that will tell you what you need to do. Bob

Classic11 · 10-10-2019, 04:22 AM

I re-measured all cylinders with the stock (original porsche) 0.25mm base gasket and here my results:

#1 --> 1.58
#2 --> 1.48
#3 --> 1.53
average of 1.53mm
#4 --> 1.35
#5 --> 1.55
#6 --> 1.45
average of 1.45mm

I think the average for each side is important since i do believe that the cases are not 100% symmetrical as Eagledriver mentioned and for sure the measurement itself is not super consistent, depending on how close you get the solder to the wall and where you measure it definetely can change.
I conclude that i will go with the 0.25mm stock shim rather than the 0.5 that was installed. Any feedback or results that you can share?

r lane · 10-10-2019, 06:56 AM

I should clarify, pull a straight edge across the cylinder spigots on the case to see if that area is warped. Put a light behind the straight edge. then measure the height of the cylinders (a leveling plate and height gauge is the best way, but if you get a proper feel for a Vernier, you can get close), then measure the rods center to center. I am assuming the crank is standard. Stroke, cylinder height, rod length, and pin position in the pistons and case integrity are the specs that need to be determined. Being off .23mm on piston to head for a street engine is I think no problem. Bob

Neil Harvey · 10-10-2019, 10:26 AM

Measuring Piston deck height on the engine is a hit or miss thing, so accept that there will be some error included. You have to accept that the crank stroke maybe different, the rod CCL could have some differences, is the pin bore parallel with the BE bore, and is the piston pin bore straight to the deck. Production engines will have a certain amount of tolerance built in and typically this is quite big. You have to make sure you are at true TDC by splitting the dwell over the top, and have zero rock in the piston.

The best way to do this measurement is at the very beginning before you even assemble the engine.

Lap the case half's and measure their deck heights. Make sure they are equal and parallel to the parting line surface. Then make sure all the cylinders are the same height, plus add in any base gaskets you will use. This becomes your "block" deck height.

Now have each crank measured for the same stroke. It hard to change this, but at least know of any differences. If you have had your rods rebuilt, their CCL should be noted and given. Measure the compression height of your pistons and again, there may be some differences. Use the max/min numbers in your calc's. You need can then do some simple math to find what your piston deck height is.

As for finding out the piston to head clearance, at home. I can see how this could be difficult. How I would approach this would be, first look at the piston and see where its largest part of its dome is situated on the chamber. This where you should expect the closest the piston will come. I would add base gasket thickness so that the clearance is at least another 0.040" or more. This will ensure if you use any sort of compressed material, you won't fully compress it and end up with a worthless measurement. You then figure into the thickness that is left, you have to remove that extra base thickness added.

Typically, unless you are running some aftermarket piston, the piston will clear the chamber OK. They are well tested and used by many without issues. I think the biggest concern should be the pocket depths if you have changed the cam or its position.

If the engine is already assembled, up to fitting the cylinders, maybe do this. Remove one cylinder and add in multiple base gaskets of an known thickness. Now the piston should sit proud of the cylinder. This may make the use of a depth mic or caliper easier to measure the difference. Then remove the added base gasket thickness you added from this measure number.

It about making is simple and as error free as possible.

Eagledriver · 10-14-2019, 09:05 PM

The edge of the piston has a flat area. Measure the distance from the flat area to the top of the cylinder with a caliper depth guage. Sharpen the tip of the depth guage if needed. Measure at the 3 o’clock and 9 o’clock position. The 6 and 12 position varies from the piston rocking on the wrist pin.

-Andy