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By slumlord444 - 11 Years Ago
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I have the specification somewhere but thought someone here would know it off the top of their head. Since I switched cam, heads, and rocker arms I need to make sure I have enough clearance. The old modeling clay on top of the piston thing. How much clearance do I need?
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By miker - 11 Years Ago
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Well, Ted will know better than most. This spec from RHS is interesting, as it has different clearances for intake and exhaust, and more for aluminum rods. Assuming you don't float the valves, I'd guess.
http://www.racingheadservice.com/rhs/piston-to-valve-clearance-guide/
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By Ted - 11 Years Ago
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For valve to piston clearance minimums and steel rods, I use 0.075” for the intakes and 0.090” for the exhaust. You’ll find that 0.090” (Int) and 0.120” (Exh) are also accepted values for this. The difference in intake and exhaust values is a result of the timing chain stretching at rpm and causing the camshaft to retard thus putting the exhaust valve closer to the pistons as the rpms increase.
As a general rule, I find that for each 4° the camshaft is moved, you’ll get a change of ~0.025” in valve to piston clearances. If the cam is advanced four degrees, the intake valve clearance reduces ~0.025” while the exhaust increases ~0.025”. If the cam is retarded, then the inverse occurs.
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By slumlord444 - 10 Years Ago
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Ted, I am using the Isky custom grind cam that you had used in an engine in a YBlock Magazine article last year. It is installed at 4 degrees advance per your specs on that engine. I am having difficulty getting an exact valve clearance measurement with modeling clay but it is a little tight for my liking. As I understand it if I retard the cam 2 or 4 degrees it will give me al little more valve clearance. This would put it at 2 degrees advanced or at the stock location. What are the downsides to retarding the cam to gain piston to valve clearance?
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By charliemccraney - 10 Years Ago
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Is that 4 degrees advanced according to a degree wheel or 4 degrees based only on the change of the crank gear position? Hopefully it is by the degree wheel. Mine is set in the 8 degrees advanced position according to the crank gear but my cam is still 1.5 degrees retarded for some reason so it is important that you are determining that measurement by a degree wheel.
If it is not being used in the exact same engine, then it is possible that some other setting is required. Retarding the cam shifts the power band up slightly. If you chose the right cam, then straight up should function fine and 2 degrees advanced will shift the power band down to help the low end a bit and is a preemptive measure against timing chain wear. It certainly doesn't prevent wear but as it wears, it retards so advancing the cam initially helps to keep it in the ballpark as miles are accumulated.
Note what he says in the second paragraph. When you change the relation of the cam, one valve increases clearance while the other decreases. If both valves are tight, then you may need to change some other aspect of the engine. You didn't say if it is one or the other.
In your post a couple days ago, when the valve was hitting the piston, you were not using head gaskets. Make sure head gaskets are in place and take into account the fact that they crush when torqued. Or, find a way to mimic the crushed head gasket thickness - use an old gasket, washers or shim stock the same thickness.
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By pintoplumber - 10 Years Ago
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Have you degreed your camshaft yet? From what I've read, you haven't. You need that as a baseline to start. My cam from the factory was 7 degrees advanced. Found that out from degreeing it in. Ended up using the 2 or 4 degree retarded keyway.
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By NoShortcuts - 10 Years Ago
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Consider scrolling through this article on Ted Eaton's web site, Slumlord.
http://www.eatonbalancing.com/blog/2012/06/30/head-gasket-volume-calculation/
Ted's article is about the cc volume displaced by different y-block cylinder head gasket manufacturers' designs. In providing that information, Ted lists the linear distance measurement around the different y-block combustion chamber head gasket configuration perimeters, BUT ALSO lists the thickness dimension that the different manufacturers' head gaskets end up compressing to after the heads have been torqued in place.
The compressed head gasket thickness is a factor in your engine's assembled valve to piston top clearance. As an example, the BEST Gasket regular cylinder bore head gasket compressed thickness is listed as being 0.046 inch.
I hope this helps you with determining the valve-to-piston clearance you have with the cam, rocker arm, and timing set installation combination that you're using. 
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By Ted - 10 Years Ago
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When checking valve to piston clearance, head gasket thickness and valve lash must be taken into account. Checking V/P clearance with no head gaskets and zero lash can bias the measurement results by as much as 0.070” which is more than significant as this is potentially the amount of clearance being sought.
Charlie has pretty well nailed it in that the engines operating band is effectively changed when changing the camshaft phasing. Retarding the camshaft will see a drop in low end torque but you’ll also see an increase in the top end horsepower numbers. Cranking compression will also reduce when retarding the camshaft and that’s simply a result of the intake valve closing later. There are limitations to how much advance or retard can be performed before overall performance simply falls off.
At just two degrees of cam timing change, these will not be big differences though and may not even be felt when driving the car. The biggest reason for initially having some camshaft advance is to compensate for timing chain stretch as the chain and gears wear. As the chain stretches, the camshaft retards and it’s not unusual for a heavily stretched chain to retard the camshaft 6° or more. I have by design installed camshafts with as much as 8-9° of advance on stock engines depending upon the intended usage of the engine. It’s an accepted practice for most engines to install the camshaft 4° advanced with a new timing chain to compensate for future chain stretch and wear. Used chains can typically tolerate less camshaft advance due to the initial stretch in the chain having taken place.
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By slumlord444 - 10 Years Ago
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This is all great info. I will re check the valve to piston clearance again taking in to account the head gasket compression and then retard the cam 2 and 4 degrees and see where the clearance ends up each time. I will advise of the results when I get done tinkering. And yes I will degree the cam and re check everything.
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By slumlord444 - 10 Years Ago
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I spent the afternoon playing with the cam advance and checking valve to piston clearance. Went 2 degrees at a time from straight up all the way to 6 degrees advanced. The best piston to valve clearance I could get was .060 to .065 not including the compression of the Best gasket would make it a little less. This was at the 4 degrees advance that I started with. I am pretty sure I will have to cut reliefs in the pistons for the intake valves. Got lots of clearance on the exhaust valve. I am thinking .030 to .040 would be more than enough. Does anyone here think that would be a problem with Ford flat top pistons? I need to talk to my local machine shop to see what they think and what it would take to have them do it. It can be done with an old head and a valve modified into a cutter but I am not sure if I want to try this at home. One problem using an old head is that the valves on the Mummert heads are spaced slightly differently. That could be an issue. Also I think the valves are slightly larger. I need to degree the cam and do a final check before doing any cutting but I think I am going to have to go that route. Could probably get the clearance I need by going back to the stock '57 Rocker arms but I hate to give up the Sharp Roller rockers for a lot of reasons.
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By slumlord444 - 10 Years Ago
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Still playing with degreeing the cam. Determined TDC. Talked to my machine shop today. Will need to pull the pistons, remove the rods and rings and take them to the shop to have the relief's cut in the pistons. Still not sure exactly how deep I need to cut the reliefs but I am sure that .040 will be more than enough. May be ok wit .030. Anybody know for sure if this will be a problem with the stock flat top pistons? Machine shop will be able to measure to check for sure but would like to have an idea before I take it all apart.
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By Ted - 10 Years Ago
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You’ll need to check your piston deck thickness to see exactly what is currently present there. I like a minimum of 0.200” piston deck thickness after any cutting is performed to the piston tops. Any less than this makes it marginal if the tune up errs to being on the lean side and/or too much ignition timing. It’s important that the exact TDC be located as any errors in this will be transferred to the cam degreeing in process. If eyeballing TDC, then that could be off several degrees due to the piston sitting stationary for a period time due to the connecting rod having to change directions at TDC. I generally find that any valve to piston clearance problems will take place at ~10° from TDC rather than right at TDC.
Which camshaft do you have? I find very few problems with Y engines and V/P clearance when dealing with 0.535” valve lifts or less. This is both with iron heads and aluminum heads. As mentioned earlier, it’s important that head gasket thicknesses and valve lash be compensated for in those checks. Also remember that ‘chain elasticity’ will have the camshaft retarding itself as the rpms increase. That’s the reason you typically have more exhaust clearance than intake clearance in the checking procedure.
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By slumlord444 - 10 Years Ago
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The cam is the Isky S662. with .528 lift. Using Harlland and Sharp roller rockers. Pulled a piston and took it to local machine shop and he measured the piston thickness. Don't recall exactly what he came up with but he was comfortable going up to a .100 relief cut in the piston. He likes .080 valve to piston clearance. Isky says .100 and Ted likes .075. Think I am going to have him make a .050 relief cut. That should give me .090 to .100 valve to piston clearance with out making the top of the piston too thin. Rather have extra clearance rather than too little. Will take the pistons to the machine shop. tomorrow. Will also re check the clearance after the relief's are cut. Local shop has been around for a while and does a lot of stock car engines as well as the usual machine shop work. Got a lot of good references on him an had him drill and tap the main bolt holes, deck the block and hone it sometime back and was happy with his work and rates. Thanks again all for the info. Learning a lot of interesting things on this re-build.
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