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Discussion Starter · #1 ·
I have some 164 heads rebuilt by the same crew who rebuilt on for another car for me. Those earlier heads had proper valve clearance set up when they came back from the shop. I was happy. I was spoiled. When the second set came back, I didn't check tolerances and I'm about to install onto a block. However, one intake clearance is ~3 mils under... #5 valve intake clearance is 0.015"-0.016" and it should be 0.0188" minimum. (That's still under 0.019" so I call my under 0.016" clearance 3 mils short.)

If I had shims in hand I'd fix that. This is the only intake of the six to be out of spec. Being on the #5 cylinder (front bank), it is readily accessible -later- to be adjusted. And with new tappets, I'm not certain but what the clearance might open up by a half of a mil during use, anyway. I just don't know at what level 2 to 3 thousandths of an inch sub-spec clearance on an intake valve will cause grief.

The only reason I can see for the intake valve lash to be so large when the exhaust valve spec is 0.009"-0.010" (these are rounded, too) is that the intake valve is larger and more heat pours into it during the power stroke, so it has to cool longer against the valve seat. But the exhaust valve lives a life so much harder than that of the intake that it -would- -appear- to me that 0.0188" is a generous accommodation.

Any comments here?
 

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1990 164QV Euro spec & 1991 168B
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You say what? I say if head not yet installed make number 5 same as others now before you install and cam easier to remove to install a thinner shim.

I have shims a go go what thickness do you need to get that 0.003" extra clearance?

I know you don't know that until cam and cam follower removed and installed shim measured unless you installed it and recorded thickness.

As for intake and exhaust clearance differences me thinks it is same as apples and oranges since intakes direct lobe profile to flat tappet cam follower via shim cap direct to valve stem interface much different than from exhaust indirect lobe profile via flat tappet, push rod and rocker arm acting on exhaust valve stem.

Set up is an engineering marvel to me and I R just a wrench not an engineer so it works and I can accept that.

Let me know what size shim cap you need if you want to open up clearance on number 5.

Happy New year.
 

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I agree with Steve. Why not take it back to the machine shop and get them to fix it, unless you got the work for free:)
 

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These engines keep their clearances very well, especially the intakes. I am pretty sure my original engine has never had the intakes adjusted. Checked regularly per Alfa spec but never changed. For that matter I am not sure the exhausts ever needed changing either.

Hardened valve seats and unleaded fuel means valve seat wear is minimal these days. Both the cam faces and the shims are hardened steel.

I say you MUST get that #5 clearance up to snuff because too tight is a potential problem from the first time you fire it up and the valves reach operating temps. Too loose just increases the hammering on the cam face and shim which is a very modest risk, too tight causes exhaust gas leaks which can erode the hardest valve rim in a surprisingly short time. We are talking plasma effects here.
 

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Discussion Starter · #5 ·
Michael,

I just want to mention the engine's cycle in this regard. The power stroke happens, the exhaust valve opens, the piston passes BDC, and then the exhaust stroke happens. The intake valve opens something like 33 degrees before TDC with pretty well quenched combustion gases -- still -hot- as blazes, but no longer burning, and with as much of the combustion energy extracted as the engine can manage. The intake valve opens when the exhaust gases are hustling out the exhaust port and with the prospect of a dynamic rarefaction wave scavenging the exhaust from the cylinder. The intake valve closes ~74 degrees after BDC (wow!). The intake valve is vulnerable to hot exhaust gases only at its opening.

Low clearance on the valve results in slightly greater opening with slightly early opening and late closing. The tone wheel for the crank angle sensor has 58 teeth on it with a gap equivalent to about 3 teeth (61 teeth effective circumference). I measured the difference between 11 and 15 mils clearance as 2 to 2-1/2 teeth on the tone wheel, and the difference between 1 and 3 mils as 1 tooth. I measured 55-1/2 teeth between the 1 mil gap points on the cam lobe. Putting these together, I estimate the open to close rotation on the crank (not cam) as being about 54 tone wheel teeth, or about 319 degrees. It should be 287 degrees. If I add 4 mils to the clearance, I'd expect the open to close time to drop by about 2 teeth on each side to get 50 teeth duration, or about 295 degrees. One tone wheel tooth counts for 6 degrees so I'm off the nominal cam duration by only one tooth (circumstantial evidence that my absolute accuracy is at the one tooth level, and I'm not totally out in the woods). I conclude that the 4-ish mil small clearance results in something like 12 degrees early opening and late closing. The valve opens at higher exhaust pressure, potentially pushing to before the rarefaction wave can reduce the exhaust port pressure to below the intake manifold pressure.

How significant this is for the opening event, and how much more exposure to high temps the intake suffers, is the issue. As a reference, 12 degrees is 1/15 (6%-7%) of the 180 degree span between BDC and TDC. I'd guess it -could- matter, and would be of greatest concern for long hill-climbs. It looks like I'll be pulling the cam and visiting Steve for a thinner shim. It's been a year or more since I had the heads done, and I should have checked the clearances -long- ago. I also should have had an S block built up out of the pieces I have here.
 

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1990 164QV Euro spec & 1991 168B
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Michael come on over. I have factory puller to pop cam hub loose from cam taper.

So much easier to do with head off engine to set valve clearances.
 

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Mr. T, it sounds like your'e doing a lot of overthinking to try to convince yourself that you don't need to fix the issue.

I have no idea whether the 0.003 will make a big difference or not. I have found, however, that when I find myself trying to talk myself out of doing something the right way, it usually means that I should really go back and do it the right way.

Personal experience only, YMMV.
 

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The intakes hold spec really well, so may as well get it to spec and not worry about it, probably ever again. Exhaust valves are the ones that usually need checked/adjusted over time. I think making them all the same is more of an issue than whether the one tight valve clearance would work OK or not.
Charles
 

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Discussion Starter · #9 ·
I recognize that sometimes specs are set by what is achievable or what is customary, and not -always- by what is needed. I was analyzing the problem from my physicist's first principles standpoint to see what the spec meant in real life. In materials science, 6% in heat dissipation might mean a factor of two in lifetime. But these things are generally empirically determined. I thought someone who knew from a real-world standpoint of having experienced failures correlated with tight valve clearances might chime in. The measurements I made were targeted at helping -me- understand the issues, and deciding based on the needs. I quite truly didn't want to dismount the head one more time and throw away another head gasket., but better to do it now than in 5k miles. If I pull the head again, I'll build up that other S engine to put them on, rather than putting them back on the tired L block I had installed into the '91 164S as a holding action a couple of years ago. The front cylinders aren't getting full compression anyway, even with the new S head, and I take that to mean the rings are leaky. I pulled the engine to replace the clutch and thought I'd take care of an overheating problem at the same time. The overheating seems to be due to poor compression on #6 (30 psi[!] only) with the old L head. Cylinders 1-3 still are over 200 psi, but 4/5/6 are 170 +/- 10 psi dry. I'd have pulled the engine this summer anyway, given the problems, but I considered limping along with the L block until then. It would probably have been a poor choice.

But I understand something more about the sensitivity of intake valve clearances now than I did before, and I hope it was at least entertaining for some of you.
 

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"4/5/6 are 170 +/- 10 psi dry"

You should check the cylinders wet with oil, as dry numbers are not accurate.
 

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Always we then hear a "Now for the rest of the story" so, now am I to understand you have head with one intake valve below spec installed?

If only 0.003" under spec valve clearance will not cause a low Compression Condition.

Redo compression check with some WD-40 or light oil sprayed into cylinders and with all 6 plugs out and throttle open. Record and report your new readings. If compression rises valves not the issue.
 

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Discussion Starter · #12 ·
I'd already put a teaspoon of oil (a capful from a quart of oil) into each of the 4/5/6 cylinders. The piston faces weren't quite level, so the oil wasn't evenly distributed around the rings, but the indicated compression was higher with oil than without. That was the second use of a head gasket (not fired-up, though) as a test install. When I subsequently re-installed with a new gasket (2nd gasket this go-round) I got the same readings. The 1/2/3 bank of cylinders reads higher with the old L head in place. This is a well-used engine, by the way, ~150k miles, and it could stand the total overhaul that I haven't been organized enough to give it yet.

I didn't think the low compression indication lay with the head. I got even lower readings on 4/5 with the old L head, and only 30 on #6 due to a probable burned exhaust valve. But when I installed the S head the first time (yes, the only special thing about this head is its cam, but it's a different chunk of aluminum) and got ~180, it reminded me that I never checked these heads' clearances. The #5 intake was the only one out by a noteworthy amount. The other intakes were fine. I readjusted the exhaust valves that I thought were any off at all. But I wanted to understand what the intake issues were, and I think I do now. I just have to clear some working room, remove another block from the engine stand, pull the transmission/clutch that I'd put on this block and mount it on the stand, and start the process of opening up the bottom end. I have reworked S piston/sleeve/ring assemblies to install, new bearings and gaskets, and when that's done the engine will be fully S spec and ready to go. Just a day late and a dollar short, as usual. Gotta get the car back on the road soon for family use.
 

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I understand the issues. My concern with valve clearance relates to temperature. I understand the minimum clearance is specified to ensure the valve stays completely closed and sealed during the combustion event at the highest engine temperature expected. If you do not observe the minimum specified clearance there is a chance the valve will not be completely seated during combustion. If so, then a plasma plume could (and probably will) occur on every combustion event in that cylinder which will rapidly erode the edge of the valve where it is supposed to be seated.

Because this will occur at maximum operating temperatures this will not be revealed by any compression test as those will always occur at lower temperatures where there will be some clearance left.

Because even the manufacturer does not know exactly how much clearance will be absorbed by temperature expansion the minimum clearance has some tolerance. Are you a gambling man is the question.

As for using minimum clearance to effect maximum compliance with specified valve timing the manufacturer already allows for that in the clearance specification. So called zero clearance auto adjusting systems such as used on the 24 valve engine were invented to permit almost perfect valve timing.

I do not think tight clearances will adversely affect valve timing or lift. The risk is of experiencing zero clearance before the engine is at maximum possible temperatures. If you get there then the valve will leak at higher than that temperatures with expensive failure shortly thereafter.

I would correct this clearance myself before running the engine for this reason alone.
 
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