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During my winter rebuild, I felt it was my duty to "help the economy" by purchasing a custom ground solid roller cam for the GT. Since my pistons were already .002 above deck, I fully expected that my new cam might have some piston-to-valve (PTV) clearance issues. The valve opening and closing events, when combined with the .655" valve lift, proved that I was indeed right. Thanks to a little advance research, I was able to implement a low buck approach in order to deal with this common cam swap problem.

A little technical information: Basic PTV clearance consists of 2 different concepts. The most obvious is that the valve must have sufficient clearance when it is opened by the cam so that the valve does not hit the piston. The standard recommended allowance for the intake valve is .080” minimum clearance and for the exhaust valve the specification is wider at .100” minimum.

The second concept is that due to the piston rocking in the bore, a possible side-to-side valve movement in the guide, and normal expansion from heat, the notch in the piston must have .060” additional radial clearance beyond the diameter of the valve. As an example, a valve with a 2.08” head should have at least a 2.20” diameter pocket in the piston. (2.08 + (.060 x 2) = 2.20)

So I used my piston stop, a degree wheel, light checking springs, and a degree wheel to first check PTV clearance.









I found that the 2.08” intake valves had over .100” of PTV clearance, which was fine. The 1.60" exhaust valves measured only .080”, which is less than safe for a motor. I had no choice but to notch the pistons deeper and wider. On the net I found that it was possible to purchase (or even rent) a professional notching tool from Isky or buy one from Lindy. Instead I decided to take an low buck approach and simply make my own.

This notching tool consists of a cheap intake valve, a good adhesive, a locking collar, and a strip of cloth backed 50 grit belt sanding paper. Because I wanted to make sure that I had sufficient radial clearance, I ordered a 1.72” diameter (11/32” stem) Chevy intake valve. (1.60 + (.060 x 2) = 1.72)

For this tool, it doesn't matter if you use an intake or an exhaust valve--generally an intake valve will be cheaper. Total cost of the 1.72" valve was under $5 at Autozone. A huge 2.21” (11/32” stem) BB Chevy intake valve was less than $10 and would have been used if my 2.08” intake valves needed clearance:



A link to this Melling catalog is here: http://www.mellingengine.com/Portals/5/pdf/pdf_catalog/valve-progressive-size-chart.pdf.

I found a dis-guarded sanding belt at a friend's woodshop and I already owned the Loctite industrial super glue. Quick dry 2 part epoxy is a suitable substitute.

I cleaned the head of the valve with lacquer thinner and then put an ample amount of the industrial super glue on it. I placed the valve face down on a strip of the sanding paper and then slid several sockets over the stem of the valve for additional weight. This assembly was left to dry overnight:





The next morning I took a pair of industrial shears and cut the excess sanding paper from around the valve face:






I installed the valve into the head (using a little lube on the stem) and temporarily retained it with a locking collar:





Note that the oversized head of the valve will always remain above the valve seat and it will never touch the seat.

Next I prepared the block. I rotated the crank until the piston was in the location where the valve was at its closest (in my case 15BTDC) and taped off that cylinder, leaving the subject valve relief untaped:



I installed an old head gasket on the block that was the same thickness as the one I was going to use when the block is final assembled. Then I installed the head on the block using 3 head bolts torqued to 50lbs.

I pulled the valve stem up as high as it would go, then I loosened the locking collar so that I could slide a .025” feeler gauge between it and the valve guide. This gave me a way to determine approximately how deep I had notched the piston:



Next I chucked up my cordless drill to the stem of the valve. I slowly spun the valve while adding moderate pressure to the drill. It took approximately 2 minutes to sand the piston away enough so that the locking collar would touch the top of the valve guide.

Before I removed the head, I used a shop vac to gather up as may loose filings that I could through the ports. A vacuum is a very important part of this process because it helps to remove the loose flakes:



I then removed the head and checked my work:



As you can see, not all of the filings can be removed through the ports with the shop vac. Again I used the shop vac and cleaned up the block and the head, followed by a clean rag. Next I reassembled the head with the checking springs and checked my work again by measuring PTV clearance. This time I found that the position of the locking collar did not allow for enough clearance, and I still needed another .010” to reach MY goal of having at least .105” exhaust PTV clearance. Again I reassembled the head with the cutting tool and lock collar. The head was reinstalled on the block and this time I used a .010 feeler gauge to set the desired depth:



I spun the valve with the drill until I had zero contact at the collar. The head was removed and the clearances checked. This time I was happier with the results. Here are before and after photos of the piston valve relief:





Satisfied with the clearance, I removed the tape-using the shop vac to catch any filings. I also took the time to rotate the piston down and then thoroughly wipe out the cylinder bore with a rag:



I moved on to the other 7 pistons and repeated the procedure. Once I had checked and clearanced all 8 pistons, I wanted to remove some of the sanding scratches that the sand paper left on the piston. The deck of the block was fully taped (as was the open areas of the block) and then I used a fine sanding drum on the dremel to smooth the deck and taper the sharp edges:





Here is the final product (which is a lot smoother in person than this closeup photo appears):



After I cleaned up the block, pistons and heads, I reassembled the head so that I could do a clearance mock up using clay. I put a little strip of clay on both valve pockets and then I installed the head on the block:



The valves were adjusted to zero clearance and then I rotated the crank 2 full revolutions. The head was removed and I laid the smashed putty on a flat surface. It was cut into strips to check the thickness of the impression and to verify the radial clearance:





CONCLUSION:
It goes without saying that there are times in our hobby when you spend a few more bucks than what was anticipated in order to get the desired results. There are also times when a simple idea and a little research can reap these same results, without breaking the bank. I am happy to report that with a little patience and attention to detail this inexpensive procedure can get you out of a predicament, plus give you the satisfaction that you used old fashioned hot-rod ingenuity instead of modern technology in order to resolve an undesirable situation.
 

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Dennis, you make it look easy, thanks!
 

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Dennis I welded the file to the valve and it worked well. Probably because I did not think of this. These are ideas that at one time I would have considered too crude to do to "my" engine. Just wondering if you have also relaxed your ideas as to what is an acceptable risk to take. Nice job.
 

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Discussion Starter #6
Thanks guys it was a satisfying endeavor. It probably takes a little more time than using a "real" cutter, but I'd rather put the $$ I saved into something that can make me go faster. (Caution: Drag race mentality.) ;)

By far the proper way to notch the pistons is to mark the true valve center on them with a centered punch (I have one.) There is no machine shops locally that are equipped to handle the machine work on a Bridgeport. I could have built a nice piston vice fixture and done it at work, but it just seemed way too involved. Who knows how many times I might have assembled and disassembled the motor to get the clearances right. This is one case where the "backyard" technique made the most sense to me.

Dennis I welded the file to the valve and it worked well. Probably because I did not think of this. These are ideas that at one time I would have considered too crude to do to "my" engine. Just wondering if you have also relaxed your ideas as to what is an acceptable risk to take. Nice job.
I cannot take credit for the original idea as I found out about it on another site. I certainly considered your idea as well as "tuliping" a valve by cutting the head into 3-4 equal pie pieces and bending each down at an angle to make another type of cutter. They were both backup ideas in case I couldn't make this work. (Obviously Latamud knew it would work.) I wish I could have followed your idea of using a different head as a guide but unfortunately my AFR's have relocated valve spacing (I verified this with an old Ford head.)

Yes, using any type of cutter in this style will have its risks--primarily from uncleaned debris or by notching the piston too far. Still, this is a common procedure in the performance world and has also been done by those who are leaders in our hobby. One of them even recommended using shaving cream over the ring lands instead of masking tape . . . . .

Admittedly I am somewhat of a risk taker in this hobby--I do much of my own work without any formal training. When I come up with an idea I actively research it and weigh the pros and cons. Then I decide on a plan of action and if it sounds feasible, I jump on it. That is the essence of true Hot Rodding--coming up with ways of doing things yourself without overextending the credit card.
 

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I had a problem with valve reliefs not being wide enough.

I had the engine on a stand, and simply rotated it upside down so the filings would just fall to the ground, and carefully opened them up with a die grinder.

It's not the prettiest, but it works just fine. You've just got to be CAREFUL, as if the burr BITES, it can take off across the block's deck. A slower drill and light pressure are what I used.

I've heard of people taking an old valve, cutting it radially, bending it down a little, and using the valve's metal to do the cutting. I would probalby use a cutoff wheel to cut a 45º or so section out of the valve head, bend the leading edge down a bit so it would bite, then sharpen it a bit. Of course, I've never tried that method, and it might be easier said than done!

Dennis's results came out nice. With that method, the only thing I would change (since it looks like the engine is out anyway) would be to turn it upside down on the engine stand for the grinding. I did some grinding on an engine once on a couple of intruding stainless fasteners. I tried to catch all the dust, but it didn't work, and I ended up having to replace all the bearings. I find it MUCH easier to contain chips than grinding dust.

Good Luck!
 

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dennis, i want to thank you again. i have become a fan. this is the tool i made. had a guy at work in the machine shop form the head on a lathe, used a drill rod for the shaft and a piece of tubing to make the collar, 36 grit & super glue. did the tape and the vacuum thing almost exactly as you did. not as pretty as yours. funny. how does that ole saying go....
 

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You're my hero, Dennis. And your timing is impeccable. I degreed my cam and checked my PTV clearance tonight on a 306 build and ,well, The PTV is non-existent. Not so much a relief depth problem as it is a radial clearance problem. They "just" hang up on the edge of the relief. I'm going to give this a shot!
 

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Discussion Starter #10
Thank you guys--glad that the technique is being used. :)

I found that most of what I needed was radial too-I needed more clearance toward the center of the piston. I wonder how many people measure using the valve drop test and call it good without doing the clay test for radial clearance?

Using a .120" larger diameter valve for notching pretty much takes care of that issue.
 

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Any feel for how long the belt sanding paper will last, how many notches before it needs replaced? Obviously, your mileage may vary.
 

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Discussion Starter #13
I used 2 disks. The first wasn't worn, but I tried to speed things up on the 4th piston by bearing down fairly hard and it lost a disk. The 2nd disk finished that piston and all the remainder. Both were a little worn, but still usable.

I used 50 grit because it was free and would expect that 36-40 grit would cut faster and last longer. It would also leave deeper grooves. The 50 grit never clogged.

As a side note, I first tried to eliminate the 50 grit scratches by following up with an 80 grit (belt sanding roll) disk but it quickly clogged--that is when I reverted to the Dremel.
 

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Does anyone know of a way to notch the pistons while they are out of the block? I suppose if you take an initial measurement from one cylinder you could rig up something on a drill press. Notching in the block is too risky for me but I don't ride roller coasters either!
 

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Awesome work Dennis!! This is the method I use as well...with only a few differences. I do use 36 grit, simply for the ease of cutting and the larger particles it seems to leave (not a lot of dust). Another difference is I leave the paper about 1/8" larger than the valve. This helps make a nice blend at the base instead of a sharp cut. The final real difference is that I use a 3m scuffing disc (picture green scrubby, only round and 1.8" larger than the valve head) glued to the valve head to 'polish' the cut. This takes the scratches out from the 36 grit, and leaves a VERY nice, very smooth, lightly turned appearance. Smaller differences are I used an old 1.78" SBF intake valve I had laying around from some 289 heads for the exhaust, and a 2.24" 351c 4v valve for the intake. I, like you...feel that radial clearance is JUST as critical as depth clearance.

Here's a picture of how mine turned out. Note, I didn't need to do the exhaust on this one...only trim up the intake for radial:



The roughly circled area is the area I cut.

Anyhow, again...awesome write up, and thank you for taking the time to let everyone know how this stuff works in such a clear, and concise manner =D.

Cris
 

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Carbon can more easily stick to a rough surface and sharp edges can heat up and cause preignition.
 

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Carbon can more easily stick to a rough surface and sharp edges can heat up and cause preignition.
Exactly...it's an anti-detonation/preignition tactic! It's the same reason that, before you assemble a motor you put a light bevel on the edges of all the reliefs to round them off a bit. Just one more step towards the safe running of these motors when they're going to be abused with either compression, rpm, load...or any combination of the above.

Cris
 
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