2.7 Weird Valve Lash
 

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.

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

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?

No, every rocker has its own lobe.

That's what she said !!!

Lol

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

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

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.

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

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

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.

Thank you Master Walt.

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

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.

tight valve to guide clearance
 

Could be a tight valve guide clearance.Fred

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?

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.

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?

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

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.

Reviving this thread after over 7 years. Wow time flies fast! Jim (DRACO A5OG), posted this for me back in 2016. Jim, I hope you are doing well. I appreciate all the time you spent with me and giving me confidence to work on my 911. I hope we can get together soon.

After my life doing a near complete 180 since this topic started (in a good way), I am finally getting around to doing a 911 rebuild. The leakdown test revealed the following, in firing order:

Cylinder 1: 75% leakage from intake valve
Cylinder 6: 20% leakage from block crankcase breather port (CIS components off)
Cylinder 2: 20% leakage from block crankcase breather port (CIS components off)
Cylinder 4: 5% leakage from block crankcase breather port (CIS components off)
Cylinder 3: 5% leakage from block crankcase breather port (CIS components off)
Cylinder 5: 75% leakage from mainly the exhaust valve and small amount from intake valve. Don't have the heat exchangers off yet so can't inspect the valve.

Please note that this was done cold and with the engine sitting for at least a month without being run. Hence, cylinders #1 and 5 show the poorest results.

I anticipate that a rebuild, or at least a top end, is in order? I do not know the service history and the mileage is dubious as it has a replacement speedo. I know that I have driven it at least 70k with lots of more-than-frequent service over the years.

With those leak down results, especially from #1 and #5, you will be removing and rebuilding the heads at least.

The good news is you have an SC engine in it, and the aluminum cases are much more rigid and durable than the mag cases. Nevertheless, you are on the edge of the proverbial slippery slope. We could speculate on all kinds of work it might need, but start by pulling the engine and pulling off the heads, then tell us what you find.

If you don't have a good reason to split the case, avoid it. Does it leak oil from the case seams?

And how much of this work will you do yourself?
.

Welcome Back Brother!
 

Hey Matt,

Indeed, it has been a while!

Glad you are back to it.

+1, you may need to consider pulling the heads to see finally what is going on with those valves and cams.

Stay well brother and Break a Leg.

Jim

I've seen carbon chunks hold the exhaust valve open.
Generally you can dislodge the chunk/chucks by simply taps on the adjustment screw with a soft mallet or a hammer and a wooden dowel.
If you have compressed air, loosen the intake adjuster, loosen the exhaust adjuster and tap smartly on the screw to actuate the valve.
If you have air pressure, you will be able to hear if the valve starts to seat.
This may also dislodge other pieces of debris that has found it's way into the cylinder.

I recall we did remove debris the last time but still it would not seal up.

Only other thing I can imagine is the shaft of the valve stem having deposit that is not allowing it to seat all the way???

Thanks for the feedback. It does not leak from the case seams but I was thinking about inspecting it. Why avoid splitting the case?

A few questions I had:
1. The oil pressure was always high (4-5 bar) when cold. At operating temp, the pressure would never increase more than 3 bar even when revving high. I heard from a YouTube video that oil pressure is built in the connecting rod/crankshaft bearings. Should I replace these bearings?
2. See photo. After taking off the fiberglass engine cover, I noticed a lot of oil seepage on the #5 and #6 intake ports. In fact, #5 had a small pool of oil on top of the intake valve. I don't believe I overfilled the engine oil last time I changed it. Could this oil leak be from worn rocker shafts? I recall some of the exhaust rocker shafts were walking out when Jim and I checked them last time, so I'll probably need to replace with the RSR style shafts.
3. See photo. Cylinder #5 does not appear to have anything stamped onto the head. The other cylinders have a date stamp along with a serial number. Could #5 have been a replacement head?


I'm planning to do this rebuild (or as much of it as I can) myself.


http://forums.pelicanparts.com/uploa...1707863845.jpg
http://forums.pelicanparts.com/uploa...1707863925.jpg
http://forums.pelicanparts.com/uploa...1707863938.jpg

Good to hear that you plan to tackle it yourself.

Some preliminary questions:
What's your budget?
Street car? IF so, I assume you want to keep the CIS to pass CA emissions, correct?
Do you want to increase performance or keep it close to what you have?
How many miles on the engine? What kind of life did it have before you got it?
Does it have the oil fed tensioners?

Why avoid splitting the case? Because it multiplies the time and cost. The bottom ends of SC engines are very durable, so the usual finding when the case is opened for a rebuild is that the crank, main bearings, and rod bearings are all in good condition (unless there were other problems or symptoms).

Oil on the intake ports #5 and #6: The oil is not from loose rocker shafts. That would run down and leave oil along the bottom of the cam housing. If you have oil inside the intake port, it's probably from worn out intake valve seals and guides. On the outside of the port, it could be coming from a number of places. Don't worry about that right now, as you will rebuild the heads.

You mentioned that you were only getting to 3 bar oil pressure when warmed up. You should look into that further. You can unbolt and remove the #4 and #2 rods caps and inspect and measure or use plastigage to check the clearances. You might need to shim up the oil pressure spring.

Replacement head: Probably. Measure the diameter of the intake and exhaust ports to make sure they are the same as the other heads. There should be a part number on it somewhere.

But first things first: Start disassembly of the timing chain cases, cam housings, and heads. Take lots of pictures as you go to document anything out of normal. When you remove the timing chain covers, take a pic of the position of the chain tensioner. Then post pics here.

Pete,

Yes, this is a street car. Budget is fairly flexible (would like to keep it under $5-10k though). I wouldn't mind some performance enhancements if they're on the less expensive end (say, $1k more than stock replacements is the most I'm willing to spend). What do you recommend?

Yes, keeping CIS on is a must for passing smog. I am going to have Tony (boyt911sc) inspect and possibly rebuild some CIS components.

I do not know the life before I had it nor the true mileage. Records are pretty sparse. Yes, I installed the 3.2 Carrera chain tensioners on it around 2010.

"You mentioned that you were only getting to 3 bar oil pressure when warmed up. You should look into that further. You can unbolt and remove the #4 and #2 rods caps and inspect and measure or use plastigage to check the clearances. You might need to shim up the oil pressure spring."

Can you please elaborate on this further? Why #4 and #2?

I will keep going on the disassembly later this week once I'm back form a business trip and will keep you posted.

Those rods will show problems from lack of oil pressure first. If they are good, then the other rods and mains almost certainly are too. IF they are good, then you order 4 new rod bolts and put them back together and don't split the case. If they are not good, then you will split the case and inspect further.