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Author Topic: Piston to valve clearance checking methods  (Read 30404 times)
woody
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« on: June 03, 2006, 12:30:30 pm »

I will outline 2 methods for checking piston to valve clearance. One may be better than the other for you. One involves having to remove the cylinder heads and the other does not. If you are working with the motor in the car then the removal of cylinder heads method may not be to your liking. Read on.

Piston to valve clearance is the relationship is just that, the distance from the valve to the piston during the most critical time in the engines cycle, that time is the "overlap".  No other time during the engines cycle is the piston closer to the valve than in the overlap. Overlap occurs at the end of the exhaust stroke and the beginning of the intake stroke. This the time when both the intake and the exhaust valves are open simultaneously, as shown below.



A lot of people have used the max lift number when calculating piston to valve clearance and that is probably the single worst method. When the valve reaches it's maximum lift point the the piston is actually furthest away traveling down the cylinder bore drawing the intake charge in. The minimum clearances I always have used were .080 on the intake valve and .100 on the exhaust valve. For people using an aluminum rod, I would allow more clearance as the aluminum rods stretch when in operation.

If you still don't grasp the "total valve lift possible Piston to Valve problems" concept, perhaps the following animation and graph will clear your doubts. The animation starts in the power cycle, the exhaust valve is the one that opens first......

Click Please

Click Please

PtV "Danger" Area Enlarged

NOTE: The two graphs above DO NOT take into consideration the valve reliefs on the piston crown.

The first method is using clay, although clay can be a pain in the ass as it likes to stick to the piston and takes a little practice to get correct.



To use the clay method take a 1/4th inch amount, cover the valve reliefs on your piston and rotate the engine one full cycle. Make sure it's 2 revolutions past top dead center. Take the head back off and peel the clay away. The best benefit of clay is that you can use an x-acto knife and cut it into sections and measure exactly where the thinnest area is, if there is any. Remember .080 and .100 minimum thickness.

The next method takes a little practice but is great if you dont want to take the heads off the car, although it will be necessary to replace the intake and exhaust valve springs on one of the cylinders. I use a checkign spring, but if you don't have a dedicated light weight spring, take a trip to your local hardware store. Remember the spring only has to have enough pressure to keep the valves fully closed and return an open valve back to it's closed postition.



Ok let's jump forward, you have replaced the intake and exhaust valve springs with lightweight springs. Now you want to adjust the rockers to zero lash. What is important here is if you are using a hydraulic type cam, wether it be a hydraulic roller or flat tappet hydraulic cam. Do NOT preload the lifter. All you want to do is take all the movement out of the pushrod WITHOUT collapsing the plunger in the lifter. Make sure you do this adjustment when the lifter is on the base circle of the cam which is at top dead center on the compression stroke.

So now we have the valves ready for measuring. You will need feeler gauges set to 0.100 thousandth's. Start with your piston at top dead center and rotate one full revolution in normal operating rotation. Keep your eyes open now, as the piston starts traveling back up the bore the exhaust stroke starts to occur and the exhaust valve will start opening. Watching the valve train you will notice the exhaust valve opening till it's fully open. As you are approaching top dead center you will notice the intake valve starting to open before the exhaust valve is fully closed. This is the area of overlap, usually about 10-15 degress before and after top dead center. Both the intake and exhaust valves are open and the piston is near the top.

During this overlap point is when you want to measure the piston to valve clearance. The piston is so close to to the top that you can push down on the nose of the rocker and actually feel the valve making contact with the piston. Now with your feeler gauge set to 0.100 insert the feeler gauge between the valve stem tip and the rocker arm. If you can insert the gauge at 0.80 for the intake and 0.100 for the exhaust then you have enough piston to valve clearance.



It may take you some trial and error  before you can identify the prescise overlap period at which you need to check the clearances, but this is a good way for someone that does not want to take off the heads.

I highly suggest you go through the steps above several times, it is VERY easy to miss the overlap, resulting in very unaccurate measurements. Work slow and this process can be accomplished by just about anyone.

Final note, if your measurements are say less than 0.10, for example there is .090 clearance on the intake you can retard the camshaft and play around with that but remember that will also affect performace charactersitics of the cam.

If you have any questions, feel free to post them.


* Overlap_Cycle_2.JPG (30.32 KB, 495x415 - viewed 11180 times.)
« Last Edit: August 01, 2009, 10:09:58 am by Joel5.0 » Logged

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« Reply #1 on: July 04, 2006, 11:49:35 am »

Just wanted to say, great tech post!
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« Reply #2 on: August 06, 2006, 09:28:22 pm »

Where do you buy the clay and what ype is it?

How are you measuring the clay ? With a dial caliper?
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« Reply #3 on: August 07, 2006, 03:06:34 am »

Well the clay can be bought at a local hobby shop or general dollar has it.  I measured mine with the dial calipers or as the picture above indicates the light spring and feeler guage is tricky but saves from removing the heads.
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« Reply #4 on: October 10, 2006, 01:50:16 pm »

Hey Woody!! Don't shot me for asking this as I'm a novice for sure....when checking piston to valve clearance instead of using clay could one use "Silly Puddy"?  You know that wonderful kids toy we all had when we were little.  It's a lot less messy than clay..Thanks.
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« Reply #5 on: October 12, 2006, 06:38:24 pm »

Hey Woody!! Don't shot me for asking this as I'm a novice for sure....when checking piston to valve clearance instead of using clay could one use "Silly Puddy"?  You know that wonderful kids toy we all had when we were little.  It's a lot less messy than clay..Thanks.

We tried using " playdoe" and found that it actaully doesn't stick enough.
it was hard to make it stay in place, would imagine silly puddy would act the same.
diffenantly use modeling clay or some such.
« Last Edit: October 12, 2006, 06:40:39 pm by r.barn » Logged
Matt Paul
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« Reply #6 on: October 13, 2006, 01:05:06 pm »

Wellfare cheese works the best you can slice it to the thickness you need and it sticks very good on the piston and leaves awsome imprints.
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« Reply #7 on: October 13, 2006, 01:09:38 pm »

Wellfare cheese works the best you can slice it to the thickness you need and it sticks very good on the piston and leaves awsome imprints.
LMAO on floor
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« Reply #8 on: October 13, 2006, 04:09:21 pm »

Wellfare cheese works the best you can slice it to the thickness you need and it sticks very good on the piston and leaves awsome imprints.
LMAO on floor LMAO on floor
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Jayber
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« Reply #9 on: October 13, 2006, 10:06:58 pm »

Just wanted to add if you are doing the clay method make sure to either use the OLD head gasket or no gasket and add in the compressed gasket thickness to your figure.
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« Reply #10 on: November 04, 2006, 12:22:49 am »

Woody--- When checking P2V with clay, are you suppose to use either a "solid" lifter or a checking spring?

This is something i was told recently. I was told to use a solid lifter instead of a hydrolic lifter when checking p2v with clay. OR that you should use a checking spring.

The reason for this is that there would be "too much preload" on a hydro lifter and not give a accurate imprint in the clay.


   WTF
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« Reply #11 on: November 04, 2006, 07:51:54 pm »

Woody--- When checking P2V with clay, are you suppose to use either a "solid" lifter or a checking spring?

This is something i was told recently. I was told to use a solid lifter instead of a hydrolic lifter when checking p2v with clay. OR that you should use a checking spring.

The reason for this is that there would be "too much preload" on a hydro lifter and not give a accurate imprint in the clay.


   WTF
You could always figure in the amount of collaspe of the lifter. I used the stock lifters when I did mine. I also, primed the oiling system before I rotated the engine through the cycle. Not to difficult, one hand holding the drill trigger and the other turning the motor.
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« Reply #12 on: November 04, 2006, 09:44:46 pm »

Or make you own checking solid lifters......I have two I prepared following the procedure below.

Quote
Need a solid roller lifter to check piston-to-valve clearance on your hydraulic roller cammed 5.0L or 5.8L Ford?

Save a couple bucks and make your own out of an old stock lifter. The lifter at left (below) is a disassembled stocker. To turn it into a checking lifter, you trash the spring and flip the main plunger 180 degrees until your lifter looks like the one in the center.



The lifter on the right (above) is the finished product, marked with a yellow band so it won't get mixed up with its hydraulic cousins.

Do It Yourself Checking Roller Lifter

So you want to check piston-to-valve clearance on your hydraulic roller cammed small block Ford, but don't have the cash for an expensive solid checking lifter? Then do what hot rodders have always done: make your own. It's actually pretty simple: just take the lifter apart, grind .020 in. off the main plunger, remove the spring, flip the main plunger around, and reassemble. Presto -- a solid checking lifter.
Courtesy of http://www.trickflow.com/articles/stroker_1/#

Added: and to clarify some questions.....
You could also flip the plunger and not grind the .020" off, the snap ring will be a little difficult to install but it will work. If you intend to use the lifter in your build, disassemble it, flip the main plunger to its original position, reinstall the spring and reassemble the lifter. That's how I prepared the 4 lifters I have for degreeing cams, checking valvetrain geometry and PtV.
« Last Edit: December 19, 2007, 05:52:51 pm by Joel5.0 » Logged

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« Reply #13 on: November 05, 2006, 07:12:00 pm »

So your saying that i DO need to checking with a solid lifter?
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« Reply #14 on: November 05, 2006, 10:55:34 pm »

For best accuracy.

Yes.

However, a straight up solid roller lifter might have a different body height.  I'd do what Joel suggests above.

Cris   
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