All Small Six Piston to Valve Clearance

[clochard68]

Was wondering if anybody has some information what the piston to valve clearance of a stock 200 with log head (any year, either small log or large log, stock cam) is.
I am aware that it all depends on lift, rocker ratio, cam advance/retard etc... I just wanted to know if anybody here has Maybe measurements already taken. Since the falcon handbook suggests that .090 can savely be milled off of a log head, I assume that there will still be enough piston to valve clearance after milling?

If anybody has numbers on different combinations (larger cams, ...) it would also be great to hear!
Thanks

 

[chad]

I assume U want the deck hight & how far dwn the hole. Those may B easy to find. Ck the above archive:

Classic Inlines

along w/'the Handbook' a general 'go to' for those in the know.

"...with log head (any year, either small log or large log, stock cam) is....'
those don't matter as the piston is pretty much stuck on the crank (by the c.rod)...

* deck hight = CL of crank to mating surface of block (to head). Ur deck may have been machined to eliminate warp or "to deck the block" a
mill pass for compression change in competition vehicles (ofter for the 200 as it's a lill rev'er, not to the 250 as it is kept for the
long stroke).
* dwn the hole = area left btwn piston top & mating surface of block (to head).

Here is one of the cases where a Q is asked w/the answ embeded in it. It would B easier if the prob was announced and the offerer (more experienced) were allowed to solve w/o initial constraint.

 

[clochard68]

Hello chad,

I didn't mean the deck height, what I am looking for is the minimum piston to valve clearance between the intake valve and the piston. As the relative position of the piston to the valve is given with the grind of the cam and if the cam is advanced or retarded in relation to the crank there are some variables that come into play.

So the clearance may differ vastly from modified engine to modified engine, hence I was asking for some numbers of any given head/cam/valve size/head gasket/... combination just to get a feel of how much distance we have in the 200.

Min. distance should be .080"...
I hope that clears things up.
Regards, Martin

 

[pmuller9]

I don't remember anyone here ever checking the piston to valve clearance as everyone assumes there is plenty even with performance cams and flat top pistons at zero deck.
I've always did a quick check by bolting the head on with a couple shims in place of the head gasket and run the cam around using light springs on the valves so I could check the clearance with a dial indicator on the valve stem.

 

[drag-200stang]

I can not imagine that with what you are doing that there will be a clearance issue, but please check like Paul posted.

 

[chad]

knowing exactly what U mean:
"...the deck hight & how far dwn the hole. Those may B easy to find. Ck the above archive:
Classic Inlines..."
this gives U what U want w/a stock (known) compression chamber. All could have changed. Y we CC a head & measure from CL etc.

 

[pmuller9]

knowing exactly what U mean:
"...the deck hight & how far dwn the hole. Those may B easy to find. Ck the above archive:
Classic Inlines..."
this gives U what U want w/a stock (known) compression chamber. All could have changed. Y we CC a head & measure from CL etc.

Chad
The piston to valve clearance has to be measured directly with the camshaft, pistons and head installed.
The minimum clearance usually occurs around 10 to 15 degrees before and after TDC.
The best way is to use light valve springs that can be depressed by hand and a dial indicator on top of the valve stem as the crankshaft is turned slowly.

 

[wme013]

I'm a fan of light springs, no head gasket and a lump of clay on top of the Piston. You don't know when the minimum occurred, but you do know the absolute amount of clearance

 

[pmuller9]

You don't know when the minimum occurred, but you do know the absolute amount of clearance

With continuous tapping of the valve head against the piston as you turn the crank and watching the dial indicator you certainly know when and how much.
The dial indicator is much more accurate than trying to measure clay thickness.
I've seen error where the clay thickness was not measured in the correct spot.

 

[clochard68]

I'm a fan of light springs, no head gasket and a lump of clay on top of the Piston. You don't know when the minimum occurred, but you do know the absolute amount of clearance

That's also what I was planning to do before I get the head to the machine shop for milling. Did you by any chancewrite the clearance down when you checked it? Was it significantly greater than 0.08?

I will measure it on my setup as well when I am finished with porting and the head is clean enough for a mock-up...

 

[chad]

yup"...with the camshaft, pistons and head installed...." that leaves out the 'drop of the valve' into the cc. All Im saying is there is some knowns U can wrk w/then U gotta figure out the unknown. I like the dial indicator idea above.

 

[bubba22349]

Was wondering if anybody has some information what the piston to valve clearance of a stock 200 with log head (any year, either small log or large log, stock cam) is.
I am aware that it all depends on lift, rocker ratio, cam advance/retard etc... I just wanted to know if anybody here has Maybe measurements already taken. Since the falcon handbook suggests that .090 can savely be milled off of a log head, I assume that there will still be enough piston to valve clearance after milling?

If anybody has numbers on different combinations (larger cams, ...) it would also be great to hear!
Thanks

Isn’t usually a problem on the Ford small six’s and you should have lots of clearance. But you can get a theoretical valve to piston clearance measurement by measuring the height from top of the valves to the the heads deck surface, than add in the piston top to block deck height measurement and your head gasket thickness, finally subtract your cam lift measurement this would all be at TDC and the cam lift isnt even going to be anywhere near that much when at TDC. Best of luck

 

[drag-200stang]

When I started hotrodding my 200, I was in high school with no money...No way was there money for the right tools, at that time everything was expense...Had a couple drill bits and used a rat tail file to make the holes larger for the torque strap...Put engine in by hand and took some clay from one of mom's flower arrangements for clearance checking.
Just for fun you could pop a coupe of the valves that you have in and put a straight edge across the head deck and measure how much travel you have..If you use a larger valve head later of course it will change the numbers.
Bubba ninja ed me .

 

[wme013]

I've seen error where the clay thickness was not measured in the correct spot.

That's why I do it with out a head gasket, if you do a poor job measuring the clay, the missing head gasket gives you a margin of error

 

[clochard68]

I did measure the clearance with clay on the weekend, as best as I could. Maybe it's somewhat helpfull for somebody in the future:

The piston to valve clearance without head gasket (!) is around 3/8 of an inch on the intake valve.
(Calliper measurement is in millimeter, on the photo the pushrod is on the exhaust, not the intake valve, measurement was taken with the pushrod on the intake side)

Here are the exact specifications:
1968 small log head, chamber 53cc
standard intake valve, head Ø1.649
Rocker Arms Unlimited rolle rockers with 1.65 ratio
standard dished pistons with 7cc dish
EDIT: piston to deck height: 0.034 to 0.036 measured --> piston compression height of 1.500" with aftermarked .030 over pistons (dish 6.5cc)
stock cam (Duration 240° and 106.5° LSA, these are the measurements I got when I degreed the cam) installed with 4.5° of advance, with 1.65 roller rockers, the max lift of the valve is 0.381"

 

[drag-200stang]

What is going on with the #2 cyl. rocker roller pin?
Thank you for checking the piston to valve clearance. We had a guy say that he could not change the cam timing because that valve clearance was to close, So I am thinking what? not on a SB6.

 

[clochard68]

What is going on with the #2 cyl. rocker roller pin?
Thank you for checking the piston to valve clearance. We had a guy say that he could not change the cam timing because that valve clearance was to close, So I am thinking what? not on a SB6.

Do you mean the pin on the tip? I think it is supposed to be like that, they are all flush on one side and stick out on the other, I will attach a photo as soon as possible...

I have to say I was surprised how much of clearance there is, and the head gasket will even add more. Good to know that a higher lift cam in the future will not be a problem

 

[drag-200stang]

O yeah, you can put a lot more cam in it.

 

[clochard68]

Here is the picture from the other side, and one from the underside.

Is the pin not seated properly?

 

[drag-200stang]

Sorry What I thought I saw was the pin not pressed in all the way but I now see it was just the reflection making it look that way yes it is OK. Think that is what Slip Mahony would call an optical contusion.