Valve clearance becoming tighter over time

[Lazeum]

My engine is freshly rebuilt with new parts everywhere including cam, retainers, pads, springs & valves. It is a F54/P79 combo with flat tops & Rebello cam + surrounding components.

 

Lash is advised to be set at 0.005" (0.13mm) at cam cold. I'm doing the check at lash pads with clearance set at 0.005 x 1.5 = 0.0075" (0.20mm)

 

I'm checking valve clearance every 200-300 miles. I found some valve clearance being very small (almost non existent), below 0.05mm at valve whereas they were set around 0.20mm (everything done cold). Others remain within specs.

 

I'm doing the job with a torque wrench and the corresponding tools. lifters are clamped at 60N.m. I haven't found the torque specs in my 72' manual so I went with 280z manual.

 

 

I don't think it should act this way. It seems heat cycles make the lifters becoming somewhat loose & becoming higher (torque to unclamp them is still very high, it is still hard to do with a simple wrench)

 

Is there something wrongly done? Is there anything else I should check to make sure I'm ok...

Edited July 10, 2012 by Lazeum

[duragg]

In my experience it is pretty darn easy to get the adjustment just a little off.

Check and adjust all, then rotate engine a few times and recheck them all and the measurements are usually a bit different.

 

On a brand new engine if the valve is seating itself and receeding a bit wouldn't that tighten up the clearance?

Hydraulic lifters are a great invention in my book.

 

Just checked the valves on my L28 and they were all surprisingly about where I left them.

My Yak engine (9cyl radial) has 18 of them puppies with a 4 lobe radial cam and they are all over the place.

 

Tj

[Lazeum]

That's a good tip I haven't though about!!! I'll give it a shot next time I work on the car (next weekend)

 

 

[Leon]

On a brand new engine if the valve is seating itself and receeding a bit wouldn't that tighten up the clearance?

That's exactly what I was going to point out. As the valve wears into the valve seat, it will move up, thus decreasing clearance.

[Lazeum]

So basically, until valves are not matching perfectly the valve seat, would I have to check valve clearance?

Edited July 10, 2012 by Lazeum

[Leon]

So basically, until valves are not matching perfectly the valve seat, would I have to check valve clearance?

Yes, but if clearances keep rapidly getting smaller after break-in, you have issues elsewhere.

Edited July 10, 2012 by Leon

[rayaapp2]

I have a curiosity with the rockers in these engines.

 

I have at least 5 variations of the stock L series rockers and Im sure there are others.

I have rarely come across an L series head with a complete matching set of rockers.

With tolerances that tight I wonder if you find that the 'tight' valves correspond with non-matching rockers.

The theory being that a different casting may expand and contract differently causing issues with the valve lash causing tighter valves and resulting in erosion of the valve seats. I would think a simple hot vs cold lash reading might point to this. Ive had my own frustrations with mixed and matched rocker sets over the years.

 

As stated above they could just be seating still, but I am curious.

[Tony D]

"Valve Recession"--ideally your inspection/adjustment intervals would be at a point before there is zero clearance (from an engineering standpoint)... From a practical standpoint you want recession to be uniform on all cylinders and SLOOOOW!

 

The valves bang into the seat, and on a fresh engine can be quite profound. After the first 10K miles this should stop the radical changes and settle in to a normal recession range which means 0.002-0.003" per 25-30,000 miles (you convert to metric!)

 

If your valves become too tight, you get "hot valves" from not enough contact dwell time on the seat to transfer heat out of the valve, causing burning problems.

 

 

if it is uneven and continues unevenly after 10K miles...something is wrong. Maybe a valve stem is pulling, or a seat was not properly installed and is hammering out. It bears investigation.

 

Keep checking regularly every 500KM or so, until you see them even out and settle in to the 'long term' recession pattern.

 

Remember there was a 50,000 or so regular adjustment interval, that was for stock stock stock. Heavier springs and higher rpms may call for readjustment at 25 or 30,000 km instead of the original 50K

[Lazeum]

I haven't thought about this quite of phenomenon but it makes sense.

The adjusment is less severe that it was at first. I'm at the 3rd one, always cold with lash at 0.005" at valve (setup at 0.008 at lash pad).

The head was done with 5-angle chamfers on valve seats + new valves.

 

 

Unfortunately, I'm stopped in my break-in operation; my ignition stopped working (CDI Mallory 6AL box, Unilite Dizzy & Accel coil), so it will be root cause analysis enjoyment this weekend...

[HowlerMonkey]

I probably did 1000 valve adjustments at Z shop of miami and found it common on the early to mid S30s for the clearance to diminish because of the valve seat materials used when the car was manufactured.

 

If anyone lapped in the valves and could see that the "greying pattern" of the valve/seat where they meet was wide or narrow.

 

If it's too narrow, the psi goes up drastically and could cause rapid recession until the contact area is worn large enough to not promote more wear.

[Powerglide]

I grew up in Kendall about 3 miles from the Z Shop on US1. Dad bought a white 1977 2+2 new. I was 10 at the time. Chances are you worked on his car as he frequented the shop several times before trading the car in. The dealer was useless when it came to repair and maintenence. Small world.

[HowlerMonkey]

I started there in late 1989.

 

 

I used to walk out where the train tracks used to be and find a few spikes I could grind or cut into chisels and punches.