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Too Little P to V Clearance

2184 Views 13 Replies 11 Participants Last post by  89lxcoupe, 
T
I just installed a comp cams .230/.236 duration, .562 valve lift. Springs= Eddlebrock 5767 which are recommended for stock heads. I had the heads rebuilt (D3VE), then I ported the exhaust. Timing chain is a 9 position. At the zero mark my number was 108 for intake lobe centerline, 106 is specified. Setting timing 2 deg advanced my centerline is 105 deg. Regardless, my piston to valve clearance is .022 intake and the exhaust hits before full lift. Pistons are SRP .015 below deck with eyelashes. I painted the eyelashes with a sharpie, put on a head, gently rotated the valves to make a light impression, seems like they are positioned correctly. I quadrupled all my procedures including checking intake valve timing @ .006 before and after TDC. Both are reasonably close. Does anyone have any insight into the Piston to valve issues?
A handfull of years ago I ran an eddlebrock RPM cam (234/244), stock valve train and the above springs and was able to wind to 6,000 with no problem although this was with a different set of stock heads. Why these issues with a smaller cam?
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Paul Kane
Did you actually see valve head impressions in the valve pockets after painting them with a sharpie?

Assuming proper setup of that camshaft, I find it hard to believe that you could have p-to-v problems with flat top pistons and the D3VE head (which puts the valves 0.100" higher over the piston than most other heads). Are you sure you are not experiencing retainer-to- guide interference?

Paul
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T
If they are stock height valves with no work done to the head then .530 lift is all they can take for cam lift.
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S
too little P to V clearance is a problem? I always thought too much space between the P and V was a problem...


OH, you are talking about Pistons and Valves... nevermind ;)
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Filucky
SLOWnSTEADY said:
too little P to V clearance is a problem? I always thought too much space between the P and V was a problem...


OH, you are talking about Pistons and Valves... nevermind ;)
Click to expand...
Good one.. :)
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R
I agree with Paul ... You must be trying to do something which isn't correct. With your components the piston to valve clearance shouldn't even be close when running.
MAXIMUM lift has absolutely NOTHING to do with running piston to valve clearance. Maximun valve lift is only considered if you're concerned about having an engine which is a "free wheeler" which means that the valves will NEVER touch the pistons even if the timing chain or belt or something else breaks in whatever controls the valve timing.
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D
If you have too much P to V clearance,I suspect previous boring and stroking with a tool larger than the one your using.
Russ
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White Lightning
Minimum intake clearance is .060". Exaust is .120". Have the heads been shaved?
Rob
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T
Thanks guys....

I don't think it could be the retainer to guide interference because I could push the valve down (with checking springs) every few degrees untill I could feel the piston as the valve opened. Also I had an Eddlebrock cam with .581 valve lift on a previous stock head and it had lots of room. I'm thinking I made some simple mistake but it making me nuts. The shop did take a shave off the surface of the head to correct a .005 warp. Other than that I don't know the history of the part. I appreciate all your comments.
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bosshoss
If you are using stock valve train your pushrods could be to long and holding your valves open, or your checking lifter could be higher than the stock one, or your pistons could be in backwards.

Just idea's definitely sounds weird tho.'

dkp
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P
ok, i'll take a shot

I've seen it b4...... either used number 5 instead of number 1.... or maybe using the exhaust instead of the intake during your degreeing process..... just an idea.

sean
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T
Stock Valvetrain

Thanks for the help. The pushrods and rockers are stock at this time, I am using a solid lifter for testing purposes. The tracking over the valve stem looks ok. My next attempt is to throw on a junk Eddlebrock head and see what happens. This should eliminate (or point a finger at) this aspect. I work nights so my response in this forum is the best I can do.

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bosshoss
So when you install the stock rocker and pushrod are you tightening the bolt all the way or just enough to get zero lash?

dkp
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8
i'm guessing retainer to guide clearance or piston backwards ! somewtimes you can see the spring collapse and see if the retainer is close to the guide.
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