First engine build valve clearance

az97cobra

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This is my first engine assembly so I'm a little green obviously but I bought a Teksid block and some PI heads to put into a 97 mustang. I put a scope down the plug hole and I see what appears to be a small ring or imprint on the piston where one of the valves would be. The cam is a comp cams XE274H I believe from the cam inscription part number. On the comp cams website it suggests that the lift is .5
Intake Valve Lift:0.5
Exhaust Valve Lift:0.5

From what i researched the stock cam had .505 and .535 lift
I used a H591CP speed pro piston which has a dish but is not fly cut.
Unfortunately I did not think the piston to valve clearance would be an issue so didn't check the clearance but is it reasonable that there is a clearance issue? I turned the engine over a number of times and never felt any resistance after the rebuild. Or is it more likely that it has jumped a timing chain gear tooth or I didn't line it up properly? I made sure I followed instructions and lined up the markings on the timing chain so it's hard for me to see how that is the issue. The imprint is on every piston though.

thanks for the thoughts
 

lwarrior1016

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I think it’s safe to say that you have an issue. Typically, comp 270’s are about the biggest you can go without reliefs. That being said, you can degree the cams in to get maximum clearance. You were probably fine with everything cold and not running, but once the oil pressure gets up in the lash adjusters and everything gets hot and swells, then clearance goes down.
 

Silver95bird

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The dish doesnt matter, it hits on the outer edge, which is the same on all modular pistons.
A 274 is the largest low lift comp cam, i forget the duration, but rheyre definitely big enough they should have been degreed and measured. Theres a ton of variation and slop in factory timing gears, which makes matters worse.

Do a leak down test to see if the valves are still sealing. Likely one or more is bent.

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az97cobra

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Well its bad news but at least I know now its possible. It's not a very large imprint but I know that no amount of contact is good. Looks like I'll probably be pulling the engine then. It was fun on the track while it lasted, all of about 20 laps.:(
thanks for the comments
 

96blak54

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We have ways of making clearance for the valves when you ready for the next build
 

Addicted

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Dish does matter. Study the way the valves angle comes down to the piston. The valve will reach the 10.5cc faster than 17cc or 18cc dish. Blak knows this, he's one of the best at this. Listen to him. Same cam, same ICL, but will have 2 different ptvc clearance between the 2 different pistons. Search the forums and you might find an example;).
 

Silver95bird

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Dish does matter. Study the way the valves angle comes down to the piston. The valve will reach the 10.5cc faster than 17cc or 18cc dish. Blak knows this, he's one of the best at this. Listen to him. Same cam, same ICL, but will have 2 different ptvc clearance between the 2 different pistons. Search the forums and you might find an example;).

it doesnt hit in the dish. it hits on the outer edge of the piston.
i have not found modular pistons with varying compression heights, though I'd be very interested to see them. Thats the only way PTV would change with a changed piston in a modular.

It could be 10cc's or 100, it doesn't matter. I'm sure I'm not the only person who has seen it with their own eyes.
12e92d4c0a287e8f970d745f801ab137.jpg


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Addicted

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it doesnt hit in the dish. it hits on the outer edge of the piston.
i have not found modular pistons with varying compression heights, though I'd be very interested to see them. Thats the only way PTV would change with a changed piston in a modular.

It could be 10cc's or 100, it doesn't matter. I'm sure I'm not the only person who has seen it with their own eyes.
12e92d4c0a287e8f970d745f801ab137.jpg


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I thought the same thing until I personally did it. If you look at how the valve comes down, it comes at an offset angle. Between my 2 pistons showed here, a 18cc and 10.5cc, there's over .050"-.060" more clearance with 18cc. My MHS camshafts have .085" on a 18cc and .035" on NPI's, and my intake valves margin are even machined down .045". 20200525_043646.jpg 20200525_043606.jpg
 
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Silver95bird

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Wow. That's a big difference.

Less meat. In exactly the worst possible place to remove it, right near the rings, where the pistons usually give out first.

Proof again that Ford designed these for anything but performance.

Would be even more amazing if cutting a valve relief in a stock PI piston wasn't significantly weakening an already weak area. I'm surprised people get away with that.

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Silver95bird

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I looked around for some of that info from Nick - but so many forums he was on and unfortunately he's gone now. Could you share a link ?

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Addicted

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Big debate this is, but I can't turn my face to real world experiences. I understand why the majority of people went with what others have said. I went went hours looking at websites but when I run across it I will show you. Ive personally logged just in the past 3 weeks about 20 hours of PTVC checking, and around 50 hours last year. I'm a nerd with this stuff. The valve does hit the outer edge of course, but the place of the valve thats hits is the lower right of the base circle, now add a wider edge, and the the bottom part of the valve base circle will hit.
 
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Addicted

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I looked around for some of that info from Nick - but so many forums he was on and unfortunately he's gone now. Could you share a link ?

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It was WMBURNS who said it, I was thinking it was Nick, but WMBURNS is a mad scientist, you got to read his stuff. My forum reading reading blurred. I edited my post, dont want to put something someone didnt say.
 
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Addicted

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This is my first engine assembly so I'm a little green obviously but I bought a Teksid block and some PI heads to put into a 97 mustang. I put a scope down the plug hole and I see what appears to be a small ring or imprint on the piston where one of the valves would be. The cam is a comp cams XE274H I believe from the cam inscription part number. On the comp cams website it suggests that the lift is .5
Intake Valve Lift:0.5
Exhaust Valve Lift:0.5

From what i researched the stock cam had .505 and .535 lift
I used a H591CP speed pro piston which has a dish but is not fly cut.
Unfortunately I did not think the piston to valve clearance would be an issue so didn't check the clearance but is it reasonable that there is a clearance issue? I turned the engine over a number of times and never felt any resistance after the rebuild. Or is it more likely that it has jumped a timing chain gear tooth or I didn't line it up properly? I made sure I followed instructions and lined up the markings on the timing chain so it's hard for me to see how that is the issue. The imprint is on every piston though.

thanks for the thoughts
I like the AZ name, oddly familiar hmmm..;). Your speed pro's have a thicker edge than others, so there's where people get the confusion.
 

az97cobra

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The valve is contacting the piston outside the dish as you can see from the pic. Seems like the contact is very close to the edge but I don't know how wide the raised portion of the piston is since it can't be measured now.
 

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az97cobra

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What made you suspect something was wrong?
It's been burning some oil and i was investigating that. It would appear that this issue with valve clearance would be unrelated unless the valve bent enough to damage the valve seals. I'm kind of thinking that's not the case which implies there's more than one problem :(
 

96blak54

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Piston to valve contact pretty much is engine catastrophic to all components.... especially the the heads. The valve guides prematurely worn, valve seals tracking a wobbly valve stem wear out fast....then their is the valve seats....the got beat to death from a bent tulip and no longer concentric
 

Addicted

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The valve is contacting the piston outside the dish as you can see from the pic. Seems like the contact is very close to the edge but I don't know how wide the raised portion of the piston is since it can't be measured now.
That stinks brother:(. If it the same piston you say it is it should be a wider edge than most, almost double the width. Hope you get it figured out.
 

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