valve to piston clearance

[fishman]

I installed a roller solid cam in my 383 for the last race of the year...when i did piston to valve clearance i got if i remember right with zero lash...exhaust was 28 thou and intake was around 50 thou....anyways i tore the heads off and the intake to get send out for porting, i noticed on each piston the exhaust valve has made an impression in the build up on the piston and i can see a shiny round ring from the outside of the valve....whewwwwww no bent valves but it has to be damn close...the fix this problem what do u guys recommend...

1 going to a thicker head gasket

2 taking the motor apart and fly cutting the piston

3 or dropping the exhaust rockers to 1.5 from 1.6


Thanks any input would be greatly appreciated

[Wolfplace]

I installed a roller solid cam in my 383 for the last race of the year...when i did piston to valve clearance i got if i remember right with zero lash...exhaust was 28 thou and intake was around 50 thou....anyways i tore the heads off and the intake to get send out for porting, i noticed on each piston the exhaust valve has made an impression in the build up on the piston and i can see a shiny round ring from the outside of the valve....whewwwwww no bent valves but it has to be damn close...the fix this problem what do u guys recommend...

1 going to a thicker head gasket

2 taking the motor apart and fly cutting the piston

3 or dropping the exhaust rockers to 1.5 from 1.6

Thanks any input would be greatly appreciated

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First, you must be praying to the car Gods a Lot,,,
Don't know what your lash is but assuming about .020, .048 ex clearance is just crazy.
I would opt for the 1.5 rocker
Going to a thicker head gasket is not normally a good idea.
You could also advance the cam as you have "extra" on the intake.
I have no problem with .040 to .050 on the intake but .080 is sort of my self imposed limit on the exhaust & this is with a fair idea that the valvetrain is under control & this is with solids.
You need more with hyd lifters if you are not running them at zero.

[bigjoe1]

Whatever the check clearance is, as soon as the engine starts, the cam retards at least 2 full degrees from dynamic loading ect. I have found you can run the intake very close( 010 to 015) with a big race roller cam, BUT, even with super duper roller springs, 060 is about as close as I dare on the exhaust side. I never see any real gains with high ratio rockers on the exhaust side any way. JOE SHERMAN RACING

[fishman]

thanks guys...so how much will i gain by going to 1.5 rockers from 1.6...20 thou as a guess not sure....

[FordManVT]

You'd have to find the place in the rotation (probably 10 to 20 degrees BTDC) where clearance is least, and then measure the lift at that point. So even 1.5 rockers may not solve your problem, as lift would need to be .352" at the valve to lose .022" to give it the same clearance as the intake valve.

Although more time consuming, I would go for the fly cutting as long as you know the piston is thick enough. .050" would give you plenty of clearance, and unless your pistons were made to be ultra-light, I don't see that being an issue.

The pistons in my engine have .118" reliefs.

[Baprace]

Fishman, standard generic small block roller with .420 lobe lift x 1,5 rocker = .630 valve lift, same lobe .420 x1.6 ratio rocker = .672 lift

[fishman]

with 1.5 rockers i have .594 lift and with 1.6 rockers i have .633....so am i right with 1.5 rockers i would gain .039 thou......?

[Ed-vancedEngines]

Changing the rocker ratio to a lower ratio could help some. Not becuase of reducing maximum lift. Maximum lift has no bearing whatsoever pertaining to valve to piston clearances.

Changing rocker ratio while not affecting the actual total duration by much, it will alter the effective duration once the valve leaves the seat. If the ratio is increased the valve leaves the seat harder and starts moving quicker, so your measured lifts at all points in low and mid lifts will show an increase as measured, and will actually hold the valve open longer, because the valve opeing events will start sooner and will close later.

Let me try to explain this a little better. Let us say that with your 1.60 rockers, your measured lift at .250 will be earlier in the duration cycle, than it would be as measured at .250 with the 1.50 ratio. That same measured lift with 1.50 would be at a later point in the engine's rotation.

Am I making any sense?
It still seems that I am not doing a very good job of explaining this. In your degrees of engine rotation it will only be where the valve lifts are during the points of overlap that will be closer to the piston. Maximum lift means nothing. The valves get closer to the piston at 5 deg to 20 deg before and after TDC. Those are extreme examples that would cover anything used in the amount of camshaft retard or advance. Usually it would be closer to 10 deg to 12 deg, but it is still good to cover all the bases.

The long and short of it is that at valve overlap where it gets the closest to piston, a lower rocker ration should give you some more available valve to piston clearances.

This is not accurate becuase it is only an average that I worked out for me to use years ago;

Advance cam by 1 deg = .007 increase of Ex & decrease of In V/P clearance.
Retard cam by 1 deg = .007 decrease of Ex & increase of In V/P clearance

I just use this as my rule of thumb as an average to get an idea with. Each application will vary some.

If this engine is run only as Normal Aspirated AND you have a fairly thick margin you could cut down the face of the valve some. I suggest a minimum Intake Valve margin of .060 and a minimum Exhaust Valve margin of .075. IF guys that do this all the time tell you different listen to them instead.

With a normal aspirated engine I am a tight quench fanatic, but you can play with head gasket thickness some and still keep a quench effect.

It is possible to cut valve notches deeper while piston is still in the block if that is necessary.

That is a few options for you to think on.

Ed

[Wolfplace]

Changing the rocker ratio to a lower ratio could help some. Not becuase of reducing maximum lift. Maximum lift has no bearing whatsoever pertaining to valve to piston clearances.

Changing rocker ratio while not affecting the actual total duration by much, it will alter the effective duration once the valve leaves the seat. If the ratio is increased the valve leaves the seat harder and starts moving quicker, so your measured lifts at all points in low and mid lifts will show an increase as measured, and will actually hold the valve open longer, because the valve opeing events will start sooner and will close later.

Let me try to explain this a little better. Let us say that with your 1.60 rockers, your measured lift at .250 will be earlier in the duration cycle, than it would be as measured at .250 with the 1.50 ratio. That same measured lift with 1.50 would be at a later point in the engine's rotation.

Am I making any sense?
It still seems that I am not doing a very good job of explaining this. In your degrees of engine rotation it will only be where the valve lifts are during the points of overlap that will be closer to the piston. Maximum lift means nothing. The valves get closer to the piston at 5 deg to 20 deg before and after TDC. Those are extreme examples that would cover anything used in the amount of camshaft retard or advance. Usually it would be closer to 10 deg to 12 deg, but it is still good to cover all the bases.

The long and short of it is that at valve overlap where it gets the closest to piston, a lower rocker ration should give you some more available valve to piston clearances.

This is not accurate becuase it is only an average that I worked out for me to use years ago;

Advance cam by 1 deg = .007 increase of Ex & decrease of In V/P clearance.
Retard cam by 1 deg = .007 decrease of Ex & increase of In V/P clearance

I just use this as my rule of thumb as an average to get an idea with. Each application will vary some.

If this engine is run only as Normal Aspirated AND you have a fairly thick margin you could cut down the face of the valve some. I suggest a minimum Intake Valve margin of .060 and a minimum Exhaust Valve margin of .075. IF guys that do this all the time tell you different listen to them instead.

With a normal aspirated engine I am a tight quench fanatic, but you can play with head gasket thickness some and still keep a quench effect.

It is possible to cut valve notches deeper while piston is still in the block if that is necessary.

That is a few options for you to think on.

Ed

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Ed,
You are of course correct that total lift has almost nothing to do with p/v clearance except indirectly because as you go up in lift the normal practice is to also increase the lift everywhere with either the rate of lift or with more duration.
But if you decrease the rocker ratio you will increase the p/v clearance by about the amount in difference of lift at each point in the lift curve not just total lift.
You also decrease the duration at the valve very slightly at each lift point or more aptly move it.
The only place you do not change the duration is seat to seat.

So, if you go from 1.6 to 1.5 & the closest point to the piston is with the valve .250 off the seat (on overlap) you should pick up very close to .016 in clearance ignoring the timing issue which may also increase the net gain.

[fishman]

You guys are the best...thanks alot...i am a sponge absorbing all of this

I have a couple questions on your answers

1.. cutting the valve is one way u say off gaining clearnce...is that a safe practice or is it done all the time.

2 changing the cam postion on advancement notch will gain clearnce...can somebody explain this as i am quite not sure how it works...like 108 degree cam...110 etc......i am new at this and learning

3 flycutting the piston the piston has to be taken out of the block to this or not and does it change any balance issues...my piston r light weight mahle only weigh 495 grams for a 383 stroker.


thanks alot guys

[Wolfplace]

You guys are the best...thanks alot...i am a sponge absorbing all of this

I have a couple questions on your answers

1.. cutting the valve is one way u say off gaining clearnce...is that a safe practice or is it done all the time.

2 changing the cam postion on advancement notch will gain clearnce...can somebody explain this as i am quite not sure how it works...like 108 degree cam...110 etc......i am new at this and learning

3 flycutting the piston the piston has to be taken out of the block to this or not and does it change any balance issues...my piston r light weight mahle only weigh 495 grams for a 383 stroker.


thanks alot guys

=
Just consider what the valves are doing.
On overlap the ex is closing, the intake is opening
If you advance the cam you will lose intake clearance as it will be open further.
The opposite is true of the ex
If you retard the cam the intake will not be open as far so you will gain intake clearance, lose ex.

On flycutting, they can be done in the block, Isky makes a tool to do it but I am reasonably sure those pistons are not real thick in the pocket so you may want to call Mahle before whacking on them

You can run your intake quite a bit closer than what you have if it is not a hyd cam with preload.
So, you can both use a 1.5 rocker & advance the cam a couple of degrees & see where you end up.
How are you checking your clearance?
If you are using checking springs you are going to gain some with the real springs too.

[fishman]

I have been checking clearance by putting putty on the piston then putting the head back on with old head gasket and tighting the head down and then set the valves, turn the motor over by hand then take off the head and mic the compression of the putty......if there a better way

[MaxFlow]

I nice way that I have done for years is to use solder. bend it in a little D shape and tape it to the valve relief. Roll the engine over and you will be able to mic the clearance very accurately. You can also do this through the spark plug hole alot of times. Stick the solder inbetween and roll the engine over.

[F1Fever]

Did one the other day with a red WD-40 tube.I placed it completely across the valve notch and it was close real close (so tight I couldn't pull the tube out at 8* BTDC IN/Valve), my buddy kept saying it was ok, never done it that way before, .. your opinion, safe or not? bent valves in the future?

[FordManVT]

When checking PTV clearance (part of degreeing the cam), I use a checking spring and a dial indicator. I rotate the engine to the position I wish to check, setup the dial indicator (with extension) parallel with the valve over the retainer, and set it to .100". Then I need only press the valve down, and read the dial. If it reads .030, I know I have .070" clearance.