checkin p/v clearance questions

ECU5.0 · Aug 5, 2005

alright, im getting my heads back tomorrow and before i install them i need to check the piston to valve clearance. i know how to do it, im just wondering if i can use the old head gaskets that came off the motor to do it instead of using the new ones? also, im going to be running 1.7 rockers on this motor but the ones i am using are on my car right now. is there anyway to use a stock rocker and figure in the extra lift? i also need to know what kind of thickness am i looking for in the clay when i do measure it? thanks for any help guys

vristang · Aug 5, 2005

You could probably do the math to figure out the p/v clearance with a 1.7rr, but why would you. The entire point of actually checking it is to KNOW, not estimate. It won't take that long to pull some of the rockers from the other car do the job and put them back. Worth it in my opinion. But that's just my opinion, I could be wrong.

I have always used an old head gasket, just make sure it is still in good shape. Don't use the one that came off the block in pieces.

I will let someone else answer the actual clearance question. Every time I have checked it I ended up with about .200" clearance so I didn't worry about it.

ECU5.0 · Aug 5, 2005

any other opinions

ECU5.0 · Aug 5, 2005

Modular2v · Aug 5, 2005

check it without the gaskets 1st...if it clears without the gasket, it will definetly clear with them

ECU5.0 · Aug 6, 2005

does anyone know when its too close for comfort? a minimum clearance? and how would i figure clearance with the 1.7s if i used a stock rocker?

CrazyCobra · Aug 6, 2005

ECU5.0 said:
does anyone know when its too close for comfort? a minimum clearance? and how would i figure clearance with the 1.7s if i used a stock rocker?

.060" is the absolute minimum, however .100" is recomended. I would not estimate the clearence by calculating the 1.7 ratio, use a 1.7 and measure it.
good luck.

Michael Yount · Aug 6, 2005

Minimum clearance depends on how much risk you're willing to take. In a racer where every HP counts and you're rebuilding components regularly, you might go with less. General rule of thumb is .080"-.100" intake; .100-.125" on the exhaust side. As recommended above, pull a 1.7 rocker off your motor and use it for your tests. Also, be sure you have a solid lifter to replace the hydraulic lifter --- the force of the valve spring will cause the spring/plunger in the hydraulic lifter to depress throwing off your p to v measurements.

Michael Yount · Aug 6, 2005

...by the way, with that cam, the 1.7's vs. 1.6's will cause you to lose something on the order of .005"-.010" of p to v clearance.

ECU5.0 · Aug 6, 2005

alright, thanks for the help guys. now all i ahve to do is find a solid lifter...crap

Michael Yount · Aug 6, 2005

You can make one out of an old one by tack welding the plunger in place; or you can disassemble one of yours - and replace the spring with a solid piece that holds the plunger all the way up. Once you're through measuring intake and exhaust, put it back together the way it was before.

ECU5.0 · Aug 6, 2005

i think i have an old one layin around somewhere. ill get my buddy to weld it up. thanks for the help mike

ECU5.0 · Aug 10, 2005

alright, so went against everyones suggestion to use one of the 1.7 rockers off of my car to check the clearance and went ahead and used a stock 1.6 rocker. ive got right around .25 clearance on both intake and exhaust. does this sound right or no? the cam is advanced 4 degrees. no i didnt use a degree wheel but i lined up the dots on the cam and crank sprockets for 4* advanced. thanks for any input

edit: after rereading what it is supposed to be im a little concerned that my cam is way off in the timing. or am i just worrying myself

vristang · Aug 10, 2005

ECU5.0 said:
alright, so went against everyones suggestion to use one of the 1.7 rockers off of my car to check the clearance and went ahead and used a stock 1.6 rocker. ive got right around .25 clearance on both intake and exhaust. does this sound right or no? the cam is advanced 4 degrees. no i didnt use a degree wheel but i lined up the dots on the cam and crank sprockets for 4* advanced. thanks for any input

edit: after rereading what it is supposed to be im a little concerned that my cam is way off in the timing. or am i just worrying myself

I had about .200" clearance so if you messed something up, I would like to know cause I probably did it too. More likely though we are both right as I don't think there is too much to really screw up.

To find the clearance change I would do this...

Multiply the cam lift by the rocker used to check clearance (1.6).

Multiply the cam lift by the 1.7 rocker.

Subtract the 1.6R lift from the 1.7R lift.

Subtract that difference from the .250" clearance that you already measured.

After illustrating how to do this I still recommend against it. The rocker ratios are probably not exact, due to manufacturing tolerances, even if this is small it is variation.
If you are still over .200" doing the above calculation you should be ok. But I still don't understand not checking it with the correct parts. Maybe you still plan to do this later, before installing the new motor?
Good Luck Dude

ECU5.0 · Aug 10, 2005

well the problem is....i started doing this at like 1 and didnt really want to tear my motor down just to do it and than have to put it back together so i can be at work by 4 just to tear it down again on friday night when i start pulling the old motor.

edit: just did some calculations and im still over .200 with the 1.7s. i doubt there is enough variance in the rockers that i have to cause a problem. i just subtracted the valve lift with the 1.6s from the valve lift with the 1.7s and got .030 and .039...so i should be good to go. i might recheck them with the 1.7s this weekend

Michael Yount · Aug 10, 2005

Don't understand your math -- if you read the post, subtracting peak lift differences between 1.6's and 1.7's won't tell you anything about changes in p to v. At peak lift the pistons are way down the cylinders -- the clearance issue occurs during overlap - the valves are barely open.

Nevertheless, if you measured correctly and have on the order of .200" clearance then the rocker swap is completely safe. At worst with that cam you'll only lose .005 - .010" with the swap.

My E cam with 1.7's on a stock piston (reliefs) installed on a 110 CL had .110" clear intake; .210" clear exhaust.

ECU5.0 · Aug 10, 2005

Michael Yount said:
Don't understand your math -- if you read the post, subtracting peak lift differences between 1.6's and 1.7's won't tell you anything about changes in p to v. At peak lift the pistons are way down the cylinders -- the clearance issue occurs during overlap - the valves are barely open.

Nevertheless, if you measured correctly and have on the order of .200" clearance then the rocker swap is completely safe. At worst with that cam you'll only lose .005 - .010" with the swap.

My E cam with 1.7's on a stock piston (reliefs) installed on a 110 CL had .110" clear intake; .210" clear exhaust.

i didnt really understand my math either. but i figure with the measurement that i got with the 1.6s there wont be a problem with 1.7s. thanks for the help guys

vristang · Aug 11, 2005

Now that I think about it that's not right.

So how are you coming up with .005-.010? I would like to know as I will be swapping out the cam and rockers fairly soon. I will need to consider valve clearance changes between 1.6 and 1.7 RR.
Appreciate the help.

Michael Yount · Aug 11, 2005

Minimal valve to piston clearance with the TFS stage 1 cam being used likely occurs somewhere around zero to 10 ATDC. At that point, depending on the cam timing used, the lifter is somewhere around .050-.070" lift (lobe lift) which means the valve lift is somewhere around 1.6 times that; 1.7 times that with the other rockers. Do the math --- 1.6X.050" = valve lift of .080"; with the 1.7's that's .085" valve lift. There's your .005" difference - at the same point of minimum clearance, if you bolt on the 1.7 rocker, it's gonna hold the valve open .005" more at that point -- so you'd lose that much p to v clearance.

You need to measure your engine -- the differences can vary due to valve train geometry, stiffness of the rocker, variation from cylinder to cylinder, etc. But as you can see, even with variations, the reduction in p to v due to rocker ratio change with most milder street cams is relatively minor. In general -- rocker ratio change usually will neither cause a p to v problem -- nor solve one for you. As cam duration increases - and intakes open sooner/exhaust closes later - the differences will be greater. If in doubt - measure yours. But if you've got .200" to start with - a simple 1.6 to 1.7 rocker change isn't gonna come anywhere close to causing a problem. You're looking for .080"-.100" clearance on the intake and .100"-.125" clearance on the exhaust for safety. You can see - the change in clearance with the rocker swap is AN ORDER OF MAGNITUDE smaller than the clearances needed.

Rick 91GT · Aug 11, 2005

Michael Yount said:
Minimal valve to piston clearance with the TFS stage 1 cam being used likely occurs somewhere around zero to 10 ATDC. At that point, depending on the cam timing used, the lifter is somewhere around .050-.070" lift (lobe lift) which means the valve lift is somewhere around 1.6 times that; 1.7 times that with the other rockers. Do the math --- 1.6X.050" = valve lift of .080"; with the 1.7's that's .085" valve lift. There's your .005" difference - at the same point of minimum clearance, if you bolt on the 1.7 rocker, it's gonna hold the valve open .005" more at that point -- so you'd lose that much p to v clearance.

You need to measure your engine -- the differences can vary due to valve train geometry, stiffness of the rocker, variation from cylinder to cylinder, etc. But as you can see, even with variations, the reduction in p to v due to rocker ratio change with most milder street cams is relatively minor. In general -- rocker ratio change usually will neither cause a p to v problem -- nor solve one for you. As cam duration increases - and intakes open sooner/exhaust closes later - the differences will be greater. If in doubt - measure yours. But if you've got .200" to start with - a simple 1.6 to 1.7 rocker change isn't gonna come anywhere close to causing a problem. You're looking for .080"-.100" clearance on the intake and .100"-.125" clearance on the exhaust for safety. You can see - the change in clearance with the rocker swap is AN ORDER OF MAGNITUDE smaller than the clearances needed.

I usually shoot for .080" int .100" exh, but I have run tighter, a lot tighter...depends on the entire combo and intentions.

checkin p/v clearance questions

ECU5.0

Banned

vristang

ECU5.0

Banned

ECU5.0

Banned

Modular2v

ECU5.0

Banned

CrazyCobra

New Member

Michael Yount

Mustang Master

Michael Yount

Mustang Master

ECU5.0

Banned

Michael Yount

Mustang Master

ECU5.0

Banned

ECU5.0

Banned

vristang

ECU5.0

Banned

Michael Yount

Mustang Master

ECU5.0

Banned

vristang

Michael Yount

Mustang Master

Rick 91GT

Mustang Master

Similar threads

checkin p/v clearance questions

Banned

Banned

Banned

Banned

New Member

Mustang Master

Mustang Master

Banned

Mustang Master

Banned

Banned

Banned

Mustang Master

Banned

Mustang Master

Mustang Master

Similar threads

Privacy & Transparency

Privacy & Transparency