Deck height clearance help
 

Hi. I was checking the deck height on my 72 t before installing my heads. Measuring the depth along the cyl wall with my vernier I'm getting .63mm .I've measured three cyls, and they seem to be consistent. B.Andersons book says min.89mm and Wayne says 1.25 to1.5 . The end of my guage is a little large for the contour of the edge of the piston so maybe I have a little more. My pistons are stock T and are somewhat flat but still are slightly domed.
I tried the solder measurement but it didn't seem to work. The base gasket is .25 mm. I have'nt changed any components other than new guides and valves in the heads and piston rings. The original base gaskets were also .25 mm.
The cyl bore is 84 mm and when I measure the combustion chamber width on the head I get 85.25 mm. Is this normal for a T motor? Because the piston cannot touch the mating surface of the head,should I be concerned? Do I need to assemble everything and make sure valve clearance is ok?
Your thoughts would be appreciated.


Clarence

naive question, did all these parts come as a motor from Porsche? if so you should be cool, other wise...seems you say they did so I would guess you should be cool

take a look at how big .89-.63=.26mm is, that is pretty small, so if you "maybe I have a little more" that may be all you need.

I am no expert here for sure, so hopefully someone else will chime in

Jim

Re: Deck height clearance help
 

You need to do this on every motor, regardless of the deck height measurement.

In this case, your vernier caliper is not specific enough to make an accurate measurement of 1/2 a millimeter...

-Wayne

I use (at least) a couple of cylinder hold down "nuts" to hold the cylinder down. If I'm going to be taking stuff apart before final assembly I use an old gasket so I don't kink a new one. (Measure it with a micrometer to make sure it isn't squished of course.)

I measure the deck height at 4 places along the edge of the piston.

If you can't get the end of your depth gauge in there, maybe you can get creative using a ball bearing? I made a tool so I could use a dial indicator.
-Chris

OK Chris, I'll bite. How do you use a BB to measure less than 1 mm? Also, what's the DI tool like? I'm approaching this op in a 3.0 assembly and haven't done it before.

I can't remember if the SC pistons have a flat area (like a running track for ants) around the outer rim of the piston but if they do, you would need something that would reach to the top of that. A depth micrometer is too fat to fit in there. I was thinking that if you had something of known size that would fit along the edge of the piston you could measure to the top of that. Hmmm, you'd probably need Jo blocks to space up the depth micrometer anyway. My thoughts were that (unworn) ball bearings are very round and uniform - possibly uniform enough to use for measurement. A doubt a BB would be round enough.

Here's a drawing of what I was thinking of:
http://forums.pelicanparts.com/uploa...1104459607.jpg

On the right side the tip of a depth micrometer (lime green) is too fat to reach the top outer edge of the piston.

On the left side small red ball bearing is used and the measurement is to that instead. Probably a stupid idea.

Slight less stupid was my deck height tool:
http://forums.pelicanparts.com/uploa...1087523787.jpg

See this thread for more info: 3 things I learned on my latest rebuild

-Chris

OK. I get it now. Not stupid at all. Using gage balls is very common in part inspection. Metrology-grade balls can be purchased, however many times a standard grade BB works fine. Holding the ball is place would help, but that ought to be doable. Thanks for the info.

Thanks for the replies I'll have to get a more precise measurement. I like your ideas Chris.
Wayne I guess I didn't consider assembling the top end and timing the cams only to take it apart to seal it up but you are right about the valve clearance check. Better a few more hours to be safe.
Thanks

Clarence

I thought to use putty or clay but it was too hard to measure. So
I used a two-part epoxy putty that I bought at Home depot instead of solder. You just roll the two parts together. The cure time is slow so you have plenty of assembly time. Having said that I siliconed the sufaces that it touched so it didn't adhere to anything. It stayed in place better than solder and dries hard as a rock. It was easy to check with a dial caliper. I mixed up two batches per cylinder.
And if you'e real anal you can save them and pass them down to your children or make ear rings for your wife.
I'm always thinkin' of ya Alice!!

When I get back out to the garage I'll get the name and edit this post.

Indeed, that is the way the professionals do it, particularly on a high performance engine where the tolerances and clearances will be close.

-Wayne