Ah-ha, I'm following you now. I'm not for sure what the uncompressed thickness of a gasket is....but if I had to guess, I'd say .015-.015".

If you are able to see aluminum thru the clay on the video, this motor was doomed from the start - head gasket or no, there was inadequate clearance from day one.

BTW, do you know how far your pistons sat in the hole?

The composite gasket crush is about 0.004" but the important issue is what is the actual clearance now. It will not have changed from his Assembly to now even if it has been dis-assembled. Pick 1 piston rod assem. and put it back in a couple of good holes to check clearances. Use clay and a wipe of grease on valve head to keep from sticking to clay. Roll engine through 2 or more full revolutions with valves properly adjusted on that hole. Torque head etc.... to return all to as run condition. Remove head and then cut clay along contact area to expose a visual thickness side view, then use a depth mic. to determine thickness at lowest point.

Steel rod engines should have a min. of 0.080 or the 0.100" mentioned earlier is good also. What it does have is the real issue. Just make sure you reference piston chosen to front of block in each hole measured. Valve lash cold should be about 0.010 tighter as a good ballpark #. Cam timing with chain and gears will be repeatable as 1 tooth off would not run right at all and if gear driven tooth count will tell if possible to assemble wrong. Jeff C

Here are the actual motor specs...

72 block with 9.480 deck height
Block was decked .015
4" stroke
4.040 bore
6.2 inch rods
JE 232459 pistons with a 1.280 compression height
Felpro 1011-2 gasket
CC 35-781-9 cam .696/.683 lift

The numbers say that the pistons are .015 out...

I was thinking that could be part of your problem as well. I agree, the numbers say that the pistons are .015" out of the hole.

With the pistons out of the bore and such a large lift, I don't see how this combo really had a chance from the get-go.

Is it possible that the builder did not take the .015 decking into account?!? :eek: That's not .0015 (thousandths); .015 is a significant amount.

Gosh, if I EVER have an engine built by a local source I will tell the guy "Show me the clay!" Lots to be learned on this thread...thank you for sharing.

-Dean

For a quick check on the cam timing---both lifters should be aprox the same ht out of the lifter bore when the cylinder is at tdc on the overlap stroke--in the old days this was where we started on setting the cam timing---
IF the lifters are not aprox equal , your cam timing is way off

You said that he had a .215? number on the indicator---if that was on the intake valve( and 000 on the exhaust) you can see that by splitting the number you would have .100 on each valve, which would be more than enough.

Jerry

Um....actually, .015 is fifteen thousanths; .0015 is one and one-half thousanths. Either way, it wouldn't have made a difference, because those gouges in the piston tops are deeper than 14 thousanths of an inch.

As regards where the piston is sitting assembled - you will need to know exactly the dimension between the TDC stroke centerline and the top of the deck (deck height), and then know what the assembled piston/rod combo is. Compression height of the piston is that dimension from the centerline of the piston pin to the top of the piston; the measurement of the connecting rod, center-to-center, plus the compression height of the piston, as measured against the aforementioned deck height, will tell you exactly where the piston is in the hole. All kind of moot, since there is no doubt whatsoever that the valves were hitting the pistons, meaning the cam was the wrong choice for the short block as assembled.

However, there might be some real credibility to the crank key issue - since the valve was contacting the piston, this means there was a BIG load put on the cam to stop turning as all lash was removed and something had to make up for it....either by flexing or by going to the weakest link which just might be the crank key. I am surprised that maybe a pushrod didn't bend - actually, I'm kind of surprised they ALL didn't bend - but strange things do happen.

Still. All in all, your builder has some serious explaining to do, especially since you have a video showing that there was no clearance at the time of the build.

Uh.....what?

Post number 11 he says the guage read .2100----I don't know what else would give him a reading like that except ZERO on the exhaust and .210 on the intake---


If he simply takes two lifters and puts them in ANY cylinder and turns that piston to TDC on the overlap stroke, the lifters should be pretty much equal if the cam is timed anywhere close to correct specs--

This whole thread is spinning around without knowing where the cam is timed---that needs to be verified first thing--then with checking springs and the head assembled with compresswd gasket, and Zero lash on a pair or lifters, turn the engine thru the overlap stroke and check for clearance very carefully at every point from 20 degrees before to 20 degrees after tdc, the actual clearance can be measured with feeler guages---no difficult computations or computer symulations are required---

If he wants he can PM me and I'll give my number so I can explain it

Jerry

Stuff Happens, replace or repair the parts and put it back together making sure you check clearances. Make sure the push rod guide plates are lined up properly.
Here is what happened to my AFR heads after who knows what happened. This was with a solid roller and pro Magnum rockers.

http://www.cobranet.com/coppermine/a...G_0004%7E1.JPG


BTW the best engine builders of reliable sb engines are Nascar engine builders and sometimes they blow them up after 10 minutes.
Like I said first off stuff just happens.Internet trouble shooting rarely works.

:LOL: :LOL: I think you are the one that needs to check his math. .015 is 1.5 HUNDRETHS.

Now we know why some motors that are built go kablooie like this one.:rolleyes:

turnpike gets the cigar this time!

Im just glad I can still build my own, hate to have to pay some of this lot to do it wrong!

Jac Mac

So; .001 is one-one hundreth?

Oh. OK. Tenths/hundreths/half-hundreths, not tenths/hundredths/thousandths.

Got it.

And the NASA guys use hundred millionths!!!

In the machining trade numeric values less than one are expressed in "thousandths", i.e., .010 is read as "10 thousandths", .100 is read as "100 thousandths" (not 1 tenth), whereas .0001 is read as "1 tenth" ( as in 1/10th of a thousandth).

I never said that. :rolleyes:

Let's both agree to agree that the clearances on this particular motor were a tad tight. ;)

was that modeling clay or silly putty????

Scotts right---auto engine machining is discussed in thousands---we recently had an marine engine where the customer gave us a diminsion but misread/mis stated the diminsion and we couldn't come up up with compatible parts for days before we figured out that he had left out a digit.

Jerry