More oddities

[JayJay]

A couple of days ago I started a thread looking for advice on how I would have suddenly lost compression on #3 cylinder after a head gasket replacement. Turns out the cause is most assuredly a bent #3 intake valve. See the thread titled "Hmm, this is odd...".

Working on that issue, I measured the valve clearances on all the valves prior to messing more. I found the following:

#1 E - 0.014"
#1 I - 0.022"

#2 I - 0.024"
#2 E - 0.014"

#3 E - 0.015"
#3 I - 0.045"

#4 I - 0.027"
#4 E - 0.015"

A couple of things jump out at me.

• There is reasonable consistency between all the exhaust valves, and all the intakes except #3. That's the one that is bent, and allowing compression to blow out the carburetor.

• The clearances on the intakes, if you group them around say 0.024", are considerably wider than they should be (I believe the spec is 0.013-1.015"?).
• The valve clearance on the exhausts is close to Model A spec of 0.015".

The engine has been reconditioned at least twice, by my guess (it's overbore 0.080"), and I would also guess that somewhere along the line the cam was at least reground. But I have no idea to what spec. It has solid lifters, and I suppose that if the cam was reground and the lifters were not replaced that might explain the additional gap. But why would that not also be evident in the exhausts?

So, when I install the new valve to replace the bent #3 intake, do I set it to 0.015" (if there is enough length to the valve stem) or 0.024" to match the others?

FWIW, I plan to pull the engine and reseal it completely this winter, and I'll install adjustable lifters at that time. My plan at this point (see below) is to reset all the valves to factory recommended clearance.

A little bit of additional information: it has a 5.2 aftermarket head, and the compression is in the 80's to low 90's. It's 0.080" overbore. So I suspect the block and head have been decked a time or two. Maybe the builder was concerned about intake valves hitting the head and opened up the gap to compensate? I'll take some measurements on lift and see if I can come up with anything.

Thanks all.

JayJay

[J Franklin]

I helped a friend replace a head and he ended up with a bent valve also so we know it happens. no wedges or pries were used. Still don't know what caused itsince all the studs were in place so the head had to come straight up. He did what you are doing as a remedy. I would set the valves to spec.

[JayJay]

Originally Posted by J Franklin

I helped a friend replace a head and he ended up with a bent valve also so we know it happens. no wedges or pries were used. Still don't know what caused itsince all the studs were in place so the head had to come straight up. He did what you are doing as a remedy. I would set the valves to spec.

Same thing with me, all studs in place during removal and reinstallation. I'll make sure all valves are at least partially closed during re-reinstallation, I'm not sure if there is a piston position where all valves are closed.

[nkaminar]

Depending on the cam, the exhaust valves should be set at 0.013 and the intakes at 0.012. It looks like the mechanic set the intakes at 0.014 to 0.015 so go with that on all valves or maybe 0.016 on the exhaust valves. If the valves are noisy you can reduce the clearances by a couple of thousands later.

[JayJay]

Originally Posted by nkaminar

Depending on the cam, the exhaust valves should be set at 0.013 and the intakes at 0.012. It looks like the mechanic set the intakes at 0.014 to 0.015 so go with that on all valves or maybe 0.016 on the exhaust valves. If the valves are noisy you can reduce the clearances by a couple of thousands later.

Since the lifters are solid, I won't have the chance to change the settings until I put in adjustable lifters. My question was whether I should set the NEW intake valve to spec (if I can) or to match the other ones. It does have a valve clatter now which is explainable by the measured gaps.

[J Franklin]

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I would set it at a correct gap.

[Y-Blockhead]

I would set it to spec. With the others at such a large gap, makes me wonder if the cam lobes are excessively worn down.

[JayJay]

May be, but I'm still perplexed why the intakes are so out of whack with the exhaust. I'll figure it out when I pull the cam this winter.

[Bud]

One of our club members had a high compression head where the valves hit part of the combustion chamber upon lifting. From what I understand that head casting was made from using an original head as a pattern. The combustion chamber core shifted out of location. On an original head, the pattern accounts for the metal shrinkage that occurs when the metal cools (the pattern is larger than the part that comes out of the mold). Since an original part was used for the pattern, the shrinkage of the metal is not accounted for, so you end up with a smaller part than the original. Sometimes features shrink into areas where they were not meant to be. You can see the problem if you lay a head gasket over the head and compare how little the head covers the gasket. Then lay the same gasket over an original head. Look especially in the corners of the combustion chamber where the valves are.

[nkaminar]

When you get the new adjustable lifters the clearance as I suggested.

Yes, the large clearance on the intake valves does not make sense. As the valves and seats wear the clearances get smaller.

Bud had a good idea. You can use some modeling clay to check if the valves are hitting or coming close to the head. Put the head on without nuts and without the gasket to check. If the head lifts when the valves lift then that is a good clue.