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Measuring piston to valve clearance

 
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66step
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PostPosted: Thu Dec 30, 2010 2:12 pm    Post subject: Measuring piston to valve clearance Reply with quote

I am not new to rebuilding engines but...
This is my first performance build and I would like some instruction on how to use clay, and what kind of clay to use, to measure piston to valve clearance.
Once the clay is compressed how do you go about reading the thickness? Do you use some kind of depth gauge?
I cannot find anyone who has actually done this although MANY people say they have built hotrods over the years.
I have a gen-1 350 decked, Vortec heads that started at 64 cc and were shaved to 57 cc. I'm running an Edelbrock 2201 hydraulic roller cam with .548 exhaust lift. The heads were massaged to be able to run .660 lift so I'm not worried about that. The pistons are hyperuetectic .030 over flat-tops with 4 valve reliefs advertised at 6cc.
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clay
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1972 Chevrolet Nova

PostPosted: Thu Dec 30, 2010 8:24 pm    Post subject: Reply with quote

Quote:
what kind of clay to use

Just go on - use me and abuse me Very Happy . It's a pretty easy thing to do - you just need a few details and you will have no problems. First clean the piston with carb cleaner, brake cleaner, alcohol, acetone, etc. - anything that will get you a grease free surface. You can use Playdoh but it won't stick very well. Modeling clay is the better choice as it will stay stuck to the piston. After cleaning the piston, make a ribbon of clay about 1/2" in diameter by about 3/4" or so long and lay it in the center of the valve relief oriented at 90* to the crankshaft. Then kinda sorta push is lightly down into the valve relief but don't really squash it too much. Take what is left outside the valve relief off becaue it will get mashed between the head and piston and it really serves no purpose other than it makes the engine hard to turn through T.D.C. Put a light coat of grease, oil, Vaseline, etc. on the valves. Mock everything up with the camshaft in your desired postion - most likely 4* advanced. Now comes the iffy part - hydraulic lifters. If you have never filled them with oil I would try to adjust the rockers with the plunger fully bottomed. If you have pumped them up with oil, it's anybodies guess how much they will collapse. The ideal situation is to use a solid roller fo the clearance check. Turn the engine through 2 complete revolutions to open and close both valves. Pull the head and hopefully you will have a nice pretty indention in the clay. Take a razor blade and slice down the middle of the clay and measure the thickness. I usually use the depth rod on a dial or digital caliper. You can use a scale just as easily. Get a 6" machinist scale - they are graduated in 1/8ths, 1/16ths, 1/32nds, and 1/64ths. With a magnifying glass you can measure within 0.010" - 0.015" - 1/64th is roughly 0.015" which is most likely close enough for your application. It depends on the pistons. The old 4 valve relief TRW forged pistons had pretty shallow reliefs whereas the SRP's and JE's I have used have ample reliefs. Seems like the minimums are 0.080" intake and 0.100" exhaust. Exhaust is more critical because it is trying to close and if it is in a little bit of a valve float situation, it can hit the piston. The intake is basically chasing the piston going away from it so most likely any valve train flex will actually increase piston to valve clearance. Hopefully you will have plenty and won't have worry about the exact amount of clearance. Sorry for the long post - just trying to cover as much as I can. If I left out anything or you have any more questions, feel free to ask. Welcome to Smokemup. Clay

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SMOKEmUP
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PostPosted: Thu Dec 30, 2010 9:36 pm    Post subject: Reply with quote

+2 to what Clay said.
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MufflerBearings69
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PostPosted: Thu Dec 30, 2010 10:00 pm    Post subject: Reply with quote

Good info about using a solid lifter for checking- not sure why nobody else puts that in their texts...
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66step
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PostPosted: Thu Dec 30, 2010 11:37 pm    Post subject: Valve Clearance Reply with quote

Should I check all 8 or is one enough?
Also, if I bottom out the "pumped up" lifter, since I don't have a solid on hand, will that work?
Thank you for the info. Detailed is more what I was looking for so a long post it wasn't.
Thanx for the welcome as well.
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af2
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PostPosted: Thu Dec 30, 2010 11:47 pm    Post subject: Re: Valve Clearance Reply with quote

66step wrote:
Should I check all 8 or is one enough?
Also, if I bottom out the "pumped up" lifter, since I don't have a solid on hand, will that work?
Thank you for the info. Detailed is more what I was looking for so a long post it wasn't.
Thanx for the welcome as well.


You didn't like the well informed post Clay wrote???
You probably will hate mine! LOL
Get a solid lifter to measure and throw the so called pumped up lifter in the garbage.

Welcome to Smokemup!! Razz
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10sec.et
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PostPosted: Fri Dec 31, 2010 12:17 am    Post subject: Reply with quote

could he take the hyd lifter apart and put a solid shim in it such as a piece of wooden dowel ?
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squeeezer
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PostPosted: Fri Dec 31, 2010 2:53 am    Post subject: Reply with quote

for hydraulic lifters
I use a super low tension spring in place of the valve spring
i use a bendix spring out of a chev starter it happens to be 1.5"x 2.0" and use dial indicator

for clay i do use a solid lifter

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clay
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PostPosted: Fri Dec 31, 2010 7:41 pm    Post subject: Reply with quote

Quote:
could he take the hyd lifter apart and put a solid shim in it such as a piece of wooden dowel ?

That's a good idea. You could probably take the internals out except for the actual pushrod seat and just bottom it out and that would work too. You could stack washers, a wooden dowel as you mentioned, basically anything. Unless you had the block decked, there will most likely be some difference from front to back on each side but only something like 0.010" to 0.025" because usually the factory decks aren't parallel with the crankshaft. Hopefully you won't be anywhere close enough for this to make a difference. Clay

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jeep_406
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PostPosted: Fri Dec 31, 2010 9:15 pm    Post subject: Reply with quote

I thought it was humorous that the first response about claying piston to valve clearance was , in fact, from Clay

I checked clearance many years ago and had a huge number. Then it dawned on me that I was using a hydraulic lifter. Felt pretty foolish. Fortunately I was alone. But you do something like that once and you it usually cures you from a repeat performance.
I think Clay covered everything well. The only thing I would add is that I degree the cam in before checking Piston to Valve clearance.

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