2.7 Weird Valve Lash

[DRACO A5OG]

Master Rebuilders,

I am posting this for one of our Pelicans that has a 76 Turbo Look Cabrio with a 2.7.

So last weekend, I was sharing with him how to do a valve adjustment and we pre-adjust measured all valves.

When we got to #6 lower valve, we found the lash to be literally at around 5.00MM gap loose. We verified this twice and then after we adjusted the elephant foot was nearly bottomed out, the nut was literally at the end of the stem. So I instructed him to turn the pulley again and we checked again then there was ZERO gap, so we re-adjusted it again to spec, then stem was higher over the nut but still compared to the rest of the valves, it was still turned it quite more than the rest.

I am suspecting, there may be some carbon build up or maybe the spring is broken or lost it's tension?

Once engine is back in, we are going to remove heat exchangers and check the exhaust port valve for carbon.

Have any of you every encountered this when adjusting the valves where the gap was super loose? Maybe carbon build up, bent Rocker Arm, Weak Spring???

History: a P-shop did the valve adjust 15-18K ago. I can not imagine they would leave such a wide gap.

TIA for Matt,

Jim

P.S. We also discovered #3 upper valve stem was hitting the valve cover, again bent rocker arm, Maybe? Gap was close to spec prior to adjustment.

[Tippy]

If the adjuster is bottomed, sounds like the lobe went flat. If so, possibly clogged spray bar.

[DRACO A5OG]

Hmm, good point, we will take a closer look, but the weird thing is 3rd checked revealed a vast change back towards spec but not much more but improved.

More importantly, upper valve was to spec, don't they share the same lobe?

[Tippy]

No, every rocker has its own lobe.

[mikedsilva]

Originally Posted by Tippy

No, every rocker has its own lobe.

That's what she said !!!

[DRACO A5OG]

Lol

I had a senior moment but again why would it get tighter?

[RedCoupe]

I'm not in my shop so I don't know whether there is room to measure the valve spring height with everything installed, but that would be one way to check if the valve is closing all the way. A leak down test would also tell you if the valve isn't fully closing

[prschmn]

in a perfect world you'd lose lash because the seat and face wear----but
I'd look first usually for a bent valve-quick leakdown test? But there certainly could be massive deposit buildup.
And course a cooked lobe-but you should be able to see that easily enough.
None of the possibilities are saying to me there's any reason to install it before you find out
what's going on though.

[DRACO A5OG]

Ah yes, leak down, that is a great idea.

[crummasel]

Not that i wisch it were the reason but consider also a loosened valve seat

[Walt Fricke]

A bore scope is a good tool to have - you could perhaps see if a seat had dropped.

If a spring (either inner or outer) is broken, you can depress the valve by hand (with some kind of tool to use to push on the retainer.

However, if only one spring is broken, the valves will still close just fine until you get up around 7,600 RPM - at least in the short term. So weak spring action cannot account for getting different lash.

Rockers don't bend. They are cast. Instead, they break. I suppose a rocker could crack, but you should be able to see that. And while that explains the large gap, it doesn't explain how the gap might get smaller.

This engine has obviously had a bad over rev. I'd suspect that this valve stem is bent a bit, making it sometimes not fully close, and other times close.

Leakdown should give you the bad news.

[DRACO A5OG]

Thank you Master Walt.

[Walt Fricke]

We all are awaiting the results of your further diagnosis. Did we get the right answer to the quiz, or not?

[DRACO A5OG]

Me too, it will be next week. I will post pictures and measurements.

Right now, we are rebuilding his 915 gear box, freakin Reverse Idler needle cage bearings fell apart on us. 1-4th synchros replaced, and sliders. Forks adjusted, properly.

[faapgar]

Could be a tight valve guide clearance.Fred

[DRACO A5OG]

Update:

Removed exchangers and rechecked the valve lash.

Strangely enough, it was tight again. We loosened the elephant feet jam nut considerably to observe the valve.

We turned the crank to TDC #6 but while observing all the valves movement, namely the closing of the valves, we noticed #6 exhaust valve was not fully closing at about 1.00 MM compared to all the rest of the valves that fully seated/closed.

I took out my video probe and found a huge piece of carbon that appear to be stuck at the lip but when we removed it, it made no difference, there were no other obstructions to be found.

Adjusted gap per spec, still no help. Valve did not close.

Anyone every experience this?

[DRACO A5OG]

Well, I fear it may be a weak spring. Can he use 3.2 valve springs in his 2.7? I will have a complete set after my pending valve swap.

[Walt Fricke]

You can use the 3.2 springs - all the same from day 1 through the 3.2s. Maybe through the 993s?

But it seems unlikely to me that a spring could, without both breaking, get so weak that it couldn't pull the valve that last millimeter closed. It takes just about no force at all to close a valve in a motor at rest.

You could test this theory by prying on the valve retainer - the hat-like thing on the top of the valve to see if you can move the tip up higher. You shouldn't be able to do so. And the bore scope should be able to tell you if the valve looks closed from the inside, as should an eyeball view with the header removed.

You could put the borescope in through the plug hole with its light on, and see if you can see light around the valve looking up through the port when all else is dark.

Me, I fear the valve stem is bent a bit, or (which amounts to about the same thing) the valve head is bent (cocked) from hitting the piston.

What were the leak down figures for #6? Pretty bad, I'd expect, if 1mm from being closed. I assume the bore scope pretty much ruled out a dropped valve seat?

[prschmn]

If the exhaust is off what does the valve stem look like? Enough grunge to make it hang?

[DRACO A5OG]

Thank you Gents!

No leak down, buddy did not have a compressor.

I will try the prying next round, because I am very concerned the valve is not seating properly.

With the HE's off, the valves looked remarkably clean. Owner reported no issues or back fires. Very strange. The engine has been out for about 8 months now.