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Discussion Starter #1
So I bought a take off head with low miles, very clean and I sent it out to have the valve seals replaced and deck the surface to clean it up.
The tech decided to check the valve lashings and on the intake side on the last 4 valves, is coming up with numbers like .05mm so he brought it to my attention. The shop manual says .11mm to 0.18mm.

I read some post and a few measured what I have and asked for the right spec. But I'm curious to see what others think about making spec now while it's at the machine shop vs just running the head the way it is.

I told the tech to continue measuring and lets see what I get, and will lean towards tipping valves to make spec. Maybe there all close to the same and they can be done in one or two sweeps.
 

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Cut the tips. The valves on these seem to have what looks like a LOT of clearance but they NEED it. When you run close like that the engine will center up cams in the cam caps and that clearance then lets the cams move around up and down to vary the actual clearance at valve and another reason why the clearance is so big. If you have measured .002" clearance then not unusual to have .000" when running, and that will make cylinder miss. Best way to burn exhausts there is too. I for one look at the first .002" as invisible, it does not exist in real running. The cams flopping around in the clearances negates it.

Intakes and exhausts set slightly different there and open them up. The valves get radically longer when hot, another reason so loose. That .002" disappears in that too.

Each valve cuts different to as needed, they are close to same when new but cutting and seat recession changes ALL that.

When I do them I put intakes in the middle of the clearance range and exhausts toward the wider end, the exhausts recede in the seats over engine lifetime to close up a bit, that equals it all out. All valves then live forever.

Of course, yours and do as you will.
 

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You ARE cutting valves here right? At least the exhausts, they almost always need it, the intakes often can be lapped back in. All valves MUST stay in the proper hole though.
 

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Discussion Starter #4
You ARE cutting valves here right? At least the exhausts, they almost always need it, the intakes often can be lapped back in. All valves MUST stay in the proper hole though.
Yes, cut or machine the valve tips.
Measure the lash or clearance of each of the 16 valves, mark it on the deck and see what I have.
Then remove the intakes first and trim them down to the calculated value.
.1mm intake was suggested by the shops contact at Cosworth in the UK, and .18mm for the exhaust measured cold on the bench.

So your saying that once the cams spin up and rotate, that gap will pretty much go to .0mm or so?
That when the cylinder head and cams gets hot, the expansion rate of the aluminum head and steel cams will close the gap, and that's why I need a larger lash value? To allow for thermal expansion, thus reverting back to almost 0mm when rotating at operating temperature.

I get what your saying about the exhaust valve lash, and the exhaust valves expanding in length so increasing lash will not affect how much the valve opens in distance.

They told me that getting the valve lash right on an over head cam engine in which there really is no adjustment through the caps was a big deal. I can't get shims or valve caps for it anymore.

On the side:
The cylinder head looks really good and very clean, well except for the valve lash. But the tech measured 96% sealing value; he called it coefficient of restitution. So far he took it apart and replaced the valve seals, and took measurements of each valve and guide to check for wear, in which none was detected.

I decided to stick with the stock valve angles and not do the professional valve job, so I guess dialing in the lash will be my professional valve job. 3 angles is good enough for this project, and would rather buy the adjustable cam sprockets instead.
 

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OEM zetec valve clearance is .004"-.007" intake and .011"-.013" exhaust. You are begging for trouble with that 'Cosworth' exhaust setting. .18 mm. is only maybe .007", or too close. The exhaust valves will stretch easily .005" hot putting you at that .002" or nothing figure, burn valve city. The valve itself will lose a thou simply running into the seat.

For those that have trouble with it.........the valve clearance is lessened real world by how loose the cam caps are on that type head. Another reason they are so big.

'...coefficient of restitution.'

?????? you got an uninformed bullsh-tter there. Restitution is something you pay back later for damage done, I would not have used that term at all.

Yours and do as you will. I have a zetec running that had the clearances set to those numbers on a bench grinder that now has over 130K on that work. Still runs peachy. I lapped the intakes myself and the exhausts were cut.
 

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Discussion Starter #8
Is this a stock warmed over build , Race , Turbo what are you doing with this head ?

Tom
I'm just doing a stock build, but trying to make small enhancements in efficiency and durability.
But I am taking the valve lash seriously, realizing it will contribute to my goals.
I was thinking the same thing about needing more space in the lash. And I need to double check if the measurements were metric or in inches.
 

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Discussion Starter #9
OEM zetec valve clearance is .004"-.007" intake and .011"-.013" exhaust.
I should of taken a picture of the measurements recorded. I'm looking at your numbers above and that seems to be what was measured on the intake side of the last 4 valves. Like .005", .006" - .005 - .007

Metric conversion for intake as per image below
0.11mm= 0.004in
0.18mm= 0.007in

Metric conversion for exhaust as per image below
0.27mm= 0.011in
0.34mm= 0.013in

I think I see what is happening here, perhaps this is simply measurement confusion.
And his exhaust spec is not even close. I was thinking that Ford should of had this taken care of already and that this valve train should of been in spec already.

Alright, I'm going wait till Monday and double check all the facts next.
Thanks for the feedback, it's makes sense now and I think all is within spec already.




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Stock clearances is all you need , your not going to burn a Valve with stock specs , I have Built hundreds of these Engines with stock valve clearances and never burned a Valve

Tom
 

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X2. Listen to Tom on this, he knows his sh-t. Normally I set in the middle and did on the intakes as the seats are pretty stable. I moved out a bit looser toward the exhaust bigger spec as the exhaust seats recede over time and I want the max valve life I can get, the exhausts tend to go up in the head with wear and the extra makes up for it. The valve seat recession is more than the tips wear since the springs are so weak; the cam lobes virtually do not wear either.
 

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Discussion Starter #12
Stock clearances is all you need , your not going to burn a Valve with stock specs , I have Built hundreds of these Engines with stock valve clearances and never burned a Valve

Tom
That's the plan. But I think I missed the time window with the Wuhan
 

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Discussion Starter #13
So I finished my cylinder head project finally. Well it turned into more of an engine overhaul project actually. The idle belt tensioner was my last issue I had with the engine making strange noises, that sounded like a bent cam or something.

Ended up going with the Cosworth specs, because I really didn't get much say on the subject as my vendor just did it that way, Specs of .010/.011" on the intake and .014/.015" on the exhaust. I have the original head still that I can play with as well, so If this takes a downtown for the worst, I can just change the head again. But I'm currently very happy with the results, and how it drives now.

AMC, I get how the valve seats wear, and the valve sort of gets taller because the valve material is harder than the seat surface. But perhaps the tighter tolerence prevents the valve from hitting the seat as hard resulting in a longer lasting seat. I don't know nor do I have the experience or the benefit of time on my hand to see the results at the moment. The vendor builds high performance engines and one of the guys worked for Cosworth for 20 years building racing engines, and this is the spec that came directly from Cosworth engineers.

But what a journey it's been, and how much knowledge and experience I have picked up from it. When I first ran the engine it sounded and ran great, then after a week it started making strange noises. Ended up re torquing the ARP head studs, and re timing the cams again which cleaned up the noise.

So I changed the head, changed the front crank shaft seal, washed the inside of the intake manifold, cause the air ram ports had like 1/8" of thick EGR residue on the inside and a pool of gunk on the bottom. Put all new gaksets on, re manufactured CM5051 injectors, and installed my Jet Hot coated exhaust manifold. And replaced the sensors with mostly NTK and some Motorcraft ones. Also pulled the oil pan and resealed it as well with Ultra Black. Did a transmission service using ARP AT216, and changed the power steering fluid with AT216. Finally did the brakes with Motul 5.1. Now on to the A/C to fix the leaks.

Used a stone to clean up the block surface. Ran a couple of cans of B12 to and from Vegas to clean up the cylinders before I pulled the head. I didn't touch the pistons.
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Installed the ARP head studs, and Mahle MLS gasket.
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Set the cam timing using the tools, mark my work with paint markers.
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The old cylinder head, I'll clean it up and build another one. This was the source of the puff puff noise from the exhaust, and perhaps low cylinder pressure in #2. It's not cracked as I thought it was, but looks to be in decent shape at 110K hard city miles.
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So that's it for the engine. Gonna fix the A/C and then onto the outside of the car to make it look nice, then flip the car later in the year.
 

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'But perhaps the tighter tolerence prevents the valve from hitting the seat as hard resulting in a longer lasting seat.'

Absolutely not. It is the now-crap fuel quality that does the recession thing. The lack of lead. Ethanol in it if used makes it even worse. Tighter tolerance only gets you burned valves faster. You hold slightly tighter on race stuff because it is intended you will be back into the engine quick to catch closer valves before they burn. It also increases power infinitesmally. What Cosworth does, if something happens they will not tell you the flipside of the coin. Just that 'We're Cosworth and we make no mistakes!' BTDT with other known brands. Laughing to self just thinking about it.

The clearance I gave is Ford's and why the engines go to death usually with never yanking head to have to fix valve issues or adjust shims. No need to. 'Longer lasting seat'? I don't think so. The extra clearance is what stops them from burning early. The super weak springs add to that.

'...the valve sort of gets taller because the valve material is harder than the seat surface.'

How does that even make any sense? The valve gets taller, especially the exhaust because it gets MUCH hotter, the seat is part of the head and as such gets coolant exposed to the surrounding area. There is a radical difference in temperatures from the valve to the head material itself. The valve gets hotter and that makes it get longer. Why intakes do not grow in length as far as the exhausts do.

Yours and do with it as you will, they all go that way. I should tell you I have one engine running right now with the valves cut exactly as I said and it has well over 150K miles on it since the work and still running fine. So, proven out I think.
 
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