Ok I curently have a 351w im putting into my mustang and I am wondering if I put after market heads and flat top pitons with vavle reliefs and mild street cam. when or what part do i need watch for to insure proper valve clearance. My deck clearance stock is .023 with stock pistons that is does this change with aftermarket pistons?
valve clearance question.
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txstang84
15 Year Member
Best way to tell is to mock it up with a dial indicator and checker springs or at least clay it up and measure...
How big is the cam? What kind of heads? How big are the reliefs? Got any pictures?
How big is the cam? What kind of heads? How big are the reliefs? Got any pictures?
If you have a hyd. roller cam, then the question really is about duration and not lift. You can run over .600 lift with stock pistons and have no piston to valve clearance issues at all if the duration is kept under 220* at .050 and the LSA does not get to crazy. A flat tappet camshaft is a whole different animal, because with lift comes duration, you cannot get away from it. That is the beauty of a roller cam, hell you can have .700 lift if you want, just watch the duration.
The hyd roller cam set up will cost you more $ up front, but you will ALWAYS be able to make more power with a roller cam than with a flat tappet type. The other nice thing about a roller set up is that you do not have to worry about camshaft break-in or pre-lube ect, with the roller cam, you can just start it up and let it idle, and never wear out a thing. Also a roller cam will still look like brand new even 100K later.
txstang84
15 Year Member
Bullitt makes a good point-but it's always a good precaution/idea to check clearance regardless of what "should" fit without interference...
txstang84
15 Year Member
Well, if you want to retrofit, you have two options I know of...first is the link bar lifters. I can't recall how much they cost, but I know it's somewhere north of $300 for the set. That will allow you to run standard 5.0 type grinds. The other way is to tap the block, install the spider and run with stock type rollers, but then you have to run a reduced base circle cam to keep the oil holes in the block for the lifters...either way you're looking at somewhere north of $300, but the link bar lifters, I believe, are the preferred (and much easier) method.
As for measuring p/v clearance...if you dial indicator the clearance and determine it to be within acceptable tolerance, you don't need to clay it...The dial is more precise anyway.
As for measuring p/v clearance...if you dial indicator the clearance and determine it to be within acceptable tolerance, you don't need to clay it...The dial is more precise anyway.
If you want to run rollers in a flat tappet block, your only real option is to run retro fit link-bar lifters. DO NOT run a reduced base circle cam. Talk to any good cam grinder, they all hate reduced base circle cams.
The dial may give you a more exact measurement, but IMO clay is the better method. While clay may not give you an exact measurement down to the last .001", it does give you an idea of what your valve radial clearance is, which is something that the dial won't do. Plus the clay method is so mindlessly easy, anybody can do it without special tools, and you can generally get a measurement within +/- 5 or 10 thou, which is close enough to know if you have the proper clearance or not.
To the OP: Always, always, always check, regardless of what method you use! Here is a brief how-to of the clay method that I used while building my motor. If you have any questions, shoot me a PM.
http://www.stangnet.com/mustang-forums/threads/checking-piston-to-valve-clearance.837135/
The dial may give you a more exact measurement, but IMO clay is the better method. While clay may not give you an exact measurement down to the last .001", it does give you an idea of what your valve radial clearance is, which is something that the dial won't do. Plus the clay method is so mindlessly easy, anybody can do it without special tools, and you can generally get a measurement within +/- 5 or 10 thou, which is close enough to know if you have the proper clearance or not.
To the OP: Always, always, always check, regardless of what method you use! Here is a brief how-to of the clay method that I used while building my motor. If you have any questions, shoot me a PM.
http://www.stangnet.com/mustang-forums/threads/checking-piston-to-valve-clearance.837135/
txstang84
15 Year Member
[/quote]
Please notice I didn't say the reduced base circle cam was a good idea, just the other method...
Also, I can't personally think of a time where the radial clearance will be less than the edge clearance unless the valve reliefs aren't cut evenly; which is a possibility. If the radial area of the valve is nearer to the piston than the edge, then the valve will run into the reliefs first and you'll still get your measurement by using the dial and checking spring, thereby negating the need for clay. I used the clay method numerous times and it does work-not saying it doesn't, and if you don't have the dial, it works fine. If you have the dial indicator though, there's no need to pull the heads off again just to measure a squished piece of modelers clay. JMO...
txstang84
15 Year Member
Yea I understood you on the cam thing, I just wanted to make it clear for the OP.
As for PtV, valves and valve notches are never in exactly the same place unless the pistons are designed for the specific heads or your machinist cut the notches for your setup. In a worse case scenario, you could have. 005" radial clearance with the sidewall of the notch, but you'd never know because the dial method only checks clearance parallel to the travel of the valve (axial). What happens when you run that motor and parts start to warm up and move around?
I just prefer the clay method because it gives you a 3D image of what is going on in the combustion chamber. The dial method only gives you part of the story.
Who checks valve clearance 
So the pistons are .023" in the hole? That is the most Ive ever seen from a factory motor. Do they have valve reliefs or a dish? What year is the motor?
All the guys are right, the link lifters are $350+ depending on your needs, Lunati makes a decent lifter for a street car set-up that doesnt have crazy spring pressures. The valve springs measurements will truly determine what cam you can go with...
What haed are you looking at?
So the pistons are .023" in the hole? That is the most Ive ever seen from a factory motor. Do they have valve reliefs or a dish? What year is the motor?
All the guys are right, the link lifters are $350+ depending on your needs, Lunati makes a decent lifter for a street car set-up that doesnt have crazy spring pressures. The valve springs measurements will truly determine what cam you can go with...
What haed are you looking at?
txstang84
15 Year Member
Yea I understood you on the cam thing, I just wanted to make it clear for the OP.
As for PtV, valves and valve notches are never in exactly the same place unless the pistons are designed for the specific heads or your machinist cut the notches for your setup. In a worse case scenario, you could have. 005" radial clearance with the sidewall of the notch, but you'd never know because the dial method only checks clearance parallel to the travel of the valve (axial). What happens when you run that motor and parts start to warm up and move around?
I just prefer the clay method because it gives you a 3D image of what is going on in the combustion chamber. The dial method only gives you part of the story.
Delving farther into the hypothetical
Unless this is something you've personally witnessed/experienced-not just heard about, that's one hell of an "if"...for your valves in motion to only have 0.005" of clearance [anywhere during travel] without being detected during a thorough dial check, the valve reliefs would necessarily have a very irregular shape (not the typical scalloped or gibbous moon shape we're all used to seeing). Any radian of the valve "at risk" of being contacted during said movement would be far enough from the longitudinal axis that you're talking about unless you're dropping the valve .800" into the chamber *and* the reliefs weren't cut big enough for the diameter of the valves...now, I'm not that well traveled an individual, but I don't know anyone running a cam larger than about .650"-.670"...and those are few and far between. Furthermore, if you're running something that gargantuan, there's a very good chance you're not running off the shelf pistons, and there was very likely custom machine work involved. The part of the valve to which you're referring doesn't go as far into the chamber as the edge due to valve angle (23*), so, unless you're dealing with an incredibly specific/irregular/abnormal combination, this academic discussion is basically moot for most of us plebians, but it seems as though we both suffer from the same disease of wanting to clarify our points to one another for the OP...so-for the sake of argument, just use the clay and measure at the thinnest point taking care not to *stretch" the clay during measuring.Rick: didn't some of the smog years have the pistons sitting down in the hole more than what most of us would accept as normal?
As far as radial clearance it is what most guys miss when adding a large valve cylinder head, they clear the notch depth but can contact radially or right at the edge of the eye brow when the notch is shallowest. I know my old Holey 2.02 cleared fine but with a little float up top contacted just at the edge of the relief (I never knew it).
So when I notched the pistons for the larger cam I opened it up radiallt to properly fit a 2.05" valve.
Jeff, yes they do leave them in the hole but I normally see .010"-.015", but Ive seen decks crooked as well. I have a 74 here that was .014" high in the front, .010" low in the rear. 9.506" nominal height
So when I notched the pistons for the larger cam I opened it up radiallt to properly fit a 2.05" valve.
Jeff, yes they do leave them in the hole but I normally see .010"-.015", but Ive seen decks crooked as well. I have a 74 here that was .014" high in the front, .010" low in the rear. 9.506" nominal height
txstang84
15 Year Member
I guess I've been incredibly lucky then. Granted the last time I put a 302 based engine together, I used clay, but the smallest measurement was still in excess of .100"...and that was with 202 valve heads and about .560" lift and 230ish @ 050 duration.
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