2.7 Weird Valve Lash

[86 911]

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.

[PeteKz]

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?
.

[DRACO A5OG]

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

[Henry Schmidt]

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.

[DRACO A5OG]

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???

[86 911]

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.

[PeteKz]

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.

[86 911]

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.

[PeteKz]

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.