piston to valve check info

[grumpyvette]

this is an old post I got asked to repost

 

I still use the strips of modeling clay about 1" square and .2" (two tenths thick) but one thing everyone forgot to mention so far is that you need to spray the piston and valve and clay strips with WD-40 to ensure the clay does not stick to any parts, otherwise the clay will tend to stick to the valve and piston allowing them to push the clay between them durring the compression of its surface by the valve (exactly what its there for) and PULL ON THE SURFACE of the clay as the valve moves away durring seperation (because the clay tends to stick ever so slightly as the parts pull away from each other if you don,t)which tends to give a false slightly greater than correct clearance measurement

most people tend to tell me Im wrong about that untill they try it both ways yeah the differance is usually minor but five to 10 thousands differance is not rare if the parts are clean and dry versus sprayed with an oil mist

 

One of the easiest and quickest methods thats a bunch

more accurate than the clay-method , would be to use

 

Acid-core solder (usually .120" thick )

or

Resin-core solder (usually .090" thick )

 

READ THIS LINK

 

http://www.fordmuscle.com/fundamentals/pistontovalve/index.shtml

 

 

 

With the solder-method , you don't actually need a degree wheel

..just the harmonic balancer timing marks and a 6" dial caliper

 

Turn the engine over till you are coming up to TDC-Overlap

with both the exhaust valve on its way to closing, and

the intake valve beginning to open

 

Turn the engine till you are about 1/2 inch from TDC ,

then rollout and straighten a piece of acid-core solder about

6 to 8 inches long ....then with headers off , look thru

#1 Cylinder's exhaust port with a penlite...take the solder

and place it thru the spark plug hole , placing solder

across the Exhaust valve piston notch...then hold solder at that

angle while someone slowly turns engine over to TDC-Overlap

and then past TDC until you "feel" you can pull out solder .

 

as you turn the engine over at TDC the exhaust valve will

touch or squeeze the solder to the valve-to-piston clearance

...as you keep turning engine past TDC-Overlap,

the solder will be released

 

remove the solder and look for indentation ...measure with

dial-caliper ..and this is the valve-to-piston clearance !

No clay mess , no clay spring-back , very much accurate than clay-method

 

Cut a new piece of solder ...and just repeat for intake side !

 

Note=>can use solder method to check total deck heights accurately !

----------------------------------------------------------------------

 

the best method would be to use a 1.000" dial indicator and

magnetic stand ....bolt a 1/8 thick small plate to valve cover

bolt hole then stick the indicator in place on the steel plate .

(sometimes a SBC fuel-pump cover works great)

 

attach a degree wheel and pointer and find true TDC ,

then turn engine over till 10 degrees BEFORE TDC-Overlap

to measure Exhaust clearance . (8 -to- 12 deg closest points)

 

at 10 deg BTDC ...place the 1.000" dial indicator's point on

the flat part of the spring retainer , zero the indicator,

and with the set-screw backed out of the adjuster nut, take

a wrench and turn the adjuster nut till you force the valve to

bottom out against the piston's exhaust notch ....read how much

the dial indicator traveled ...thats your Exhaust clearance

 

back-off Exhaust adjuster nut back to ZERO point on dial indicator

 

now, repeat the same proceedure on the Intake side ...but this

time turn engine past TDC-Overlap to 10 degrees AFTER TDC

then check Intake clearance .

--------------------------------------------------------------------------

 

Note : You should always check valve-to-piston clearance with

a fully assembled valvetrain with the real springs in place

and every rocker lashed ...and ONLY turning the engine over in

the direction of rotation (ClockWise).

 

using light checker type springs will make you flycut pistons

approx. .030" more than necessary ...in other words, what ever

valve-to-piston clearance you check with lite-springs, when the

engine is fully assembled with the real springs, it will have

approx. .030" more clearance !

 

using lite-checker springs will be a "SAFER" way to check and will

be a good method to use for a beginner engine builder !!!

 

-------------------------------------------------------------------------

A professional engine builder would use the real springs and watch this

effect upon the cam-twist, Jesel belt distortion, pushrod flex , ETC.

 

A professional engine builder would check each and every Cylinder's

clearance..and have detailed computer records of things like

1- Piston Intake and Exhaust flycut valve notch depth

2- Piston Valve notch flycut radius , angle + tilt, center-to-bore location

3- Intake and Exhaust valve seat depths on heads, valve margins, etc.

 

and other things like

4- Total Valve-Notch-Depths

 

to check the Total Notch Depths ...just place each piston at TDC ,

then place dial indicator zeroed on the top of the valve stem ,

push the valve down till it rests ontop of the piston notch ,

then record this distance !

 

(need to have springs off , and 2 rubber O-Rings holding up valve

in guides ...when you go to check distance)

 

As you gain experience and information, you can easily know in advance

what the ballpark valve-to-piston clearance will be with known cam lobes and

rocker ratios , along with cylinder head's valve depth readings , and

piston flycut data .

 

 

I try for 0.080 on the intake and 0.100 on the exhaust as absolute minimums but am far happier with 0.120 thousands (just under 1/8") or greater on both!

Ill always trade increased clearance to gain reliablity for a slight loss in compression,keep in mind that if you get to tight on those clearances you will be locked into that cam timing and dropping it back (RETARDING the cam) for greater high rpm power or (advancing the cam) for more low rpm torque becomes next to impossiable in some cases while you tune the engine combo!

[awd92gsx]

Solder crush tests are also what we use when we rebuild trannies. Probably fairly common I suppose.

[grumpyvette]

http://www.auto-ware.com/software/eap/eap.htm

 

theres software like I use in the engine shop but its reasonably expensive.............and I still check MANUALLY because I don,t trust software, yeah its usually close, but not exactly correct

[Guest zfan]

Piston to valve clearance, live and learn! I didn't do that one time and was lucky that I di not completly frag the motor. I check it and re check it now.

 

Mike