Thread: Help Me Pick Some Heads For Christmas Present

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Wow how a couple months blows by!! I had to re-read my own thread to get back on track here. My how life gets in the way of these builds.

In any case, we're off high center and moving again on my son's truck project. We've pulled off the heads to verify a few things:

1. Verified a 4.00" bore x 3.48" stroke
2. Piston deck height of 0.032"
3. Head Gasket thickness of 0.039" compressed (Felpro#7733PT2)
4. Stock heads with 76cc chambers

Using a dial indicator to ensure TDC I am confident that my piston desk height is accurate but I'm confused about a few things I'm seeing:

1. Since the mileage of this engine has been in question from the get-go (This is a 1973 truck and odometer says 21k miles) I'm looking for evidence of any level of rebuild. Though the bore is still at 4.00" I'm seeing markings on cylinder wall as if its been honed (see photos).
2. Also the current pistons have 4 valve reliefs (see photos) which is excessive for these two-valve stock heads
3. Lastly, the current head gasket is a Felpro#7733PT2 (link: https://www.summitracing.com/parts/fel-7733pt2 ) which is for a 4.125" bore and used for rebuilds

I'm still not sure about what is considered stock specs for this motor (i.e. piston type, piston deck height, etc.) so all of the above points are confusing and need some insight to ensure making the correct parts decisions moving forward. Thoughts?
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1. I don't understand. What happened to the nice new heads you had ?
2. 0.032" + 0.039" makes a squish/quench of 0.071". Too wide. Use the 0.015" shim gasket with the 0.032" piston deck height for a squish/quench of 0.047".
.

Looking at the carbon build up on the pistons says that your piston to head clearance is too close-also 4 valve reliefs are common in those type pistons so that they can be used in bothsides of the block for valve relief and wrist pin offset----------where on the piston did you measure for clearance??????? and how did you do it for tdc? use a positive stop method??????

Originally Posted by techinspector1

1. I don't understand. What happened to the nice new heads you had ?
2. 0.032" + 0.039" makes a squish/quench of 0.071". Too wide. Use the 0.015" shim gasket with the 0.032" piston deck height for a squish/quench of 0.047".
.

The new heads are still in play. The notes and measurements above are from the current engine setup. I'm just confirming what this 'stock' engine has so I can make sure that 1) I know exactly what I'm working with and 2) can accurately calculate which head gasket thickness I'll need in order to achieve as close to possible SCR of 9.5:1 and quench of 0.040-0.045".

Using the engine's current measurements of 4.00x3.48", 76cc stock chambers, 7cc valve relief volume (approximated), 0.039" gasket thickness, and 0.032" deck clearance I calculate a SCR of 8.34 and 0.071" quench which I agree is ugly.

Now if change to the new heads and plug in the new variables of 67cc chambers & 0.015" gasket, I get a SCR of 9.57 but my quench is 0.047" which is more squish/quench distance than I want right???

Bottom line is I'd like to make sure that I'm ordering the correct head gaskets that keep me within the 9.5:1 & 0.040-0.045" quench range that you all have advised me on.

Originally Posted by jerry clayton

Looking at the carbon build up on the pistons says that your piston to head clearance is too close-also 4 valve reliefs are common in those type pistons so that they can be used in bothsides of the block for valve relief and wrist pin offset----------where on the piston did you measure for clearance??????? and how did you do it for tdc? use a positive stop method??????

Jerry,
The carb is set up has a pretty rich mixture set up (previous owner did this) and was probably run by the prior owner like this for who knows how long. More evidence of this can be seen inside the tale pipes and with fuel mileage so I'd say that this is contributing to the carbon buildup.

As far as how I measured the piston deck height? I used a dial indicator located directly over the wristpin centerline and at the highest point on the piston top to locate TDC. After finding TDC I used two methods to confirm piston deck clearance, 1) straight edge over wristpin c/l and feeler gauges and 2) dial indicator differential between deck and highest point on piston (again at wristpin c/l).

With all those vertical scarches and carbon build up (looks like result of oil) you are in for a rebuild needing at least CK10 type hone job to an oversize-pick the pistons to give u the results your looking for and keep the present heads-----

Originally Posted by jerry clayton

With all those vertical scarches and carbon build up (looks like result of oil) you are in for a rebuild needing at least CK10 type hone job to an oversize-pick the pistons to give u the results your looking for and keep the present heads-----

I'm hoping to get a few more miles out of this motor before needing a rebuild. Current diagnostics aren't too bad with compression across all cylinders between 159-162psi (less than 2% delta) and cold leakdown loss of 10-11%

Well I guess I've answered my own questions at this point but was hoping a few more minds would have chimed in for piece of mind.

I guess I'll go ahead and order the 0.015" head gasket which has a 4.100" bore. Im gathering that although this exceeds the recommended quench range I really don't need to be playing this quench game so tightly. Neither do I need to be so concerned with the bore size of the gasket itself and that a slight oversized bore on the gasket is preferable as to eliminate potential hot spots.

Off to bolt on the new heads....

I'm still scratching my head on these hone marks, I can't believe these are the original hone marks. Wondering if the previous owner did a re-ring & hone job at some point. This would explain the solid diagnostic values stated above. The piston slop also very very little. Hmmm?

What direction would you guys go if the budget is tight/non-existent? Bolt on new heads and run it as is for as long as I can? Pull the pistons and inspect rings, skirts, bearings, etc?? Other options that don't involve a full rebuild?? I'm not seeing any significant evidence of oil consumption so I'm inclined to just run it for now but I'm all ears.

Get it back on the road as cheap as possible, retune the carb and get some miles out of it.

Have you checked the cylinders for taper or out of roundness???????

I have not as I don't have the proper tools on hand for that. I may see if I can check one out from a friends tool case.

Edit: From what I'm reading I would need a torque plate to properly measure so I guess this is out the window.

This morning I was able to verify bore roundness/taper and though Im approaching 75% of allowable limits, I'm still within allowable tolerance. With that said, it doesn't really matter what the previous owner did. I know now that this block is down to its last ~50k miles and will run it as is (no rebuild) until it gives.

Should have the decks prep'd and heads on in the next couple days. I'll post pics as progress develops

You guys sure deserve more updates than I'm giving but here's a quick one. Been raining off and on here so we've been using the last few weeks to prep parts and paint as weather allows. Heads are installed but waiting on rocker set and manifold bolts to finish install. Getting ready to repaint the engine bay and re-wire parts of harness that need to be beefed up. After that we should be ready to put the motor back in and begin tuning. Getting excited!

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Well....tomorrow is the BIG day!!
My son's first hotrod & bike show which is being held at his high school for the athletic booster club (STABC). I'm sooooooooooo excited for him!! The two of us have worked very hard to get everything done before this date and its paid off, we're ready!

I plan to post progress photos as well as car show pics so I'll wait until Sat night/Sunday to post. With that said, I would like to thank all those who have contributed to and educated us in the process of this truck build. No way we could have done it w/o you and I'm super happy to have found a board like this that paves the way for families like ours. Good stuff!

More to follow....