#2 Exh. Valve Guide Failure: Why rebuild?
 

My scenario. '78SC with 177k on the case, 44k on a top-end rebuild that was completed in 1994.

This will be my 6th year of ownership, I've put 15k on the car in that time.

Car has failed exhaust valve guide on cylinder 2, everything else leaks down great and the car has been a rolling restoration since I took ownership. I want to keep the car off the road for the shortest time possible and just resume driving/enjoying...now with my 2 sons.

I've priced out rebuilds, played with the idea of a 3.6 swap, considered purchasing a hot-rodded engine etc etc. The issue I'm coming across is I can't fathom spending the $$ required to do a full nut and bolt rebuild or swap for that matter. I can add onto and finish my dream garage for that money, buy a couple mustangs, a vette Z06 etc etc...

These engines break down into individualized/compartmentalized parts. My issue is very specific and the car was taken off the road as soon as I had professional opinion confirm my fears.

Why not take the #2 head off, have machine work completed and put it back together?

What say you Pelican engine builders?

If money's an issue do it yourself,if times an issue its not gonna take that much longer to do them all. It makes no sense at least to me to not do all valve guides.

When a race car breaks down, the owner fixes the problem, gets back on the road.
Labor will still be a big part, you have an R&R and disassembly
Head gasket, cam seals and other items are individually available.
A shop will do one head or all of them.
Bruce

Failed guide, or failed valve guide seal? You could replace the seal in the car.

Yes please help with the overall nomenclature.
You mentioned leak dwn values too.
Is it the guide to stem clearance? (that would be a guide failure)

A leak down test shows the ability of the cylinder chamber to hold pressure. I.E. the pistons/rings and valves. Bad leak down results indicate intake/exhaust valve and/or piston/ring leaks.....Although worn guides can certainly contribute to a valve not making good contact with the seat or wearing the seat, etc...the leak down test does not indicate valve guide wear directly. You would need to measure the guide to stem clearance to determine/verify that.

regards,
al

Good point Al.

If you can confirm it's just the number 2, then yes you could fixed just that head.

But, unfortunately it will never be that easy. Simply put, the second you open up the top end you'll probably find stuff that will be hard to ignore. Like loose valve guides, blown head gaskets, possibly cam and rockers looking sad. Sucks, but true.

Slippery slope.........
However I can do one or two valves for ya....
Send it over REAL clean with two cases Pranqster Ale
Also include two new guides and two new valves.
Pranqster | North Coast Brewing Co. | BeerAdvocate

You can't diagnose a valve guide issue based on a leak down. So why don't you post what info you have that lead to this conclusion (eg leakdown numbers + +). That way others may be able to provide more specific advice. If it is just a leak down number on #2, and others are good, it may be just carbon or crud stuck under valve lip, or bad valve adjustment etc. There are a few other avenues to go down before making that conclusion. And a bad guide is unlikely to lead to a bad leakdown unless it has totally destroyed itself.
Regards
Alan

You can check the valve to guide wear all installed in the engine.
If you have a some exp you can do this with valve in open position and a screwdriver.
If you have zero experience, don't do this as you might do more damage than good.
Also, you can use the "air in cylinder with a spring tool" and pull spring off valve, unplug air then check valve to guide wear.
Anything less than these procedures is an educated guess.( or less)

I share the info I was given by a highly respected (locally, nationally and on Pelican) shop that the #2 Guide had failed and was the reason I had 85-90% leak-down on #2. All other cylinders are 8% or less. Car is basically running on 5 cylinders.

Thank you for the confirmation Al.

VFR I hear you.

549, thank you for the info/ideas

Alan L, and everyone else, I hope the following helps a bit more,

About 5k miles ago the car started running a bit warmer than normal, went through all prescribed methods with T-Stat testing/replacement. Added late model Carrera cooler, did OPRV spring replacement, sump screen etc which dropped temps significantly, but was clearly a band-aid on the issue.

Realized it was potentially something significant in the engine when there was a direct parallel between engine temp and pushing the car. Run it around town going easy, it's get to about 220. Run on the highway 3-3200rpm, would climb a little more, stop and go or pushing the car 3500rpm or higher...250+ Especially compared to a friend's bone stock, 45k mi original car that would be doing the same thing and oil temps never rose above 180.

Had a leakdown done spring '14 with valve adj. #2 came back at 38%. Was told it could be carbon build-up etc, drive it. So I did, and fearfully so as every time I drove the thing it was like playing a game to keep the oil temp in a reasonable position.

Fall '14, bring it for an end of season ride, detect loud pinging 5k and higher, but more strangely a very intermittent ping at idle.

'15 season I literally chased the "pinging" for months, and it got progressively worse and the car ran hotter. CIS running great/goof AFR, new plugs, new cap/rotor, good fuel delivery/psi (new pump/accum/filter), timing dead nuts and advancing properly, newly built CDI box, new coil. Put BG44-K through the damn thing... Nothing changed, except the ping got louder and was now audible and rhythmic at idle and throughout rpm range..
Car got to the point were starting is hard and it runs like crap.

Since beginning of ownership, oil consumption through leaks had been minimized to nothing (yes, I achieved perfect dry-ness w/BP 20-50) but had increased from about 850mi/qt to about 500mi/qt.

Brought it to said good shop where it was diagnosed as described.

Thank you for the input thus far. I don't know what I don't know and am trying to learn as much as possible as fast as possible to make the overall right decision.

If it means saving my money for a couple years, so be it.

I have the ability and will likely remove engine from car and begin a very planned and organized tear-down regardless.
...now if I only had the scratch for the newly listed refreshed 930 engine for sale earlier this week...

That right there is a sweet offer.

I work for Great Ale !..LOL
I have too many helicopters to fix to get real involved with lots of other side lines.
But, this guy sounds like he could use a hand.

You got 85% leakage on #2? It does sound like something has failed. maybe a chunk off the valve even. I think you are going to end up tearing it down. The pinging may be a piece of something rattling around. If your mechanic had one of those tiny camera things he may be able to peek inside thru plug hole.
Regards
Alan

Either way, it has to come apart......its like hoping for a miracle and postponing the inevitable

I completely agree that it needs attention.

I think that the normal assumption is that although 'poor' leakdown results are usually due to a poor seal between the valve and the seat and that this is commonly caused by a poor guide having allowed the valve to move around causing excessive wear.



Does anyone have any good information on typical guide life on the exhaust side of a 911 engine?

You bet he could ;)

Funny thing. Mrs Saucy has very good listening ears and bought me one of these handy little cameras for Christmas!

With 2 little guys, one now 8mo and the other just over 2...Dad's broken fun car has been in storage since November and in last place on the priority list.

Maybe I'll take a run down this weekend and see what I can see. The 2yo loves the P-Car.

I think we are missing the question that was asked.... and are answering the question we want to answer.

The reason you cant just pop off head number to and fix it is because it is underneath a pile of other stuff.

Being overhead cam you have to take the cam tower off which bridges all three cylinders, remove the timing gear so the chain can come off, then the whole cam housing comes off that side of the engine.
Then if you wish you can just rebuild the head and put it all back together, this is a fair bit of work as the engine has to come out to do this.

I agree - sounds like has to come apart. The good thing is only one side probably has to be torn down. but depending on what has happened the other side may need checking out - guide clearance etc. There are a few threads on guide wear and there seem to be some types of guides that fail worse than others if I recall right. If a guide has destroyed itself, you would want to check the others and make a call as to replace them all.
Alan

Correct, all the other stuff was in my head (I picture it as one of those exploded parts diagrams) as items that must be removed to get to the head and engine drop is table stakes at this point. Just failed to communicate that.

I think the question I'm wanting answered but have failed to articulate is, "Is there any outstanding reason why it would be a bad thing to just do the single head and put it back together to drive?"

I'm feeling like the engine/top-end work done in the 135k mile range was crap because we've arrived here with serious mechanical failure inside 50k of general use.

Seems kinda screwy to do another top-end on an engine with 177k on the bottom-end, no? My gut tells me if I do the single head it's the cheap way out, if I do another top-end job, it's a more expensive band-aid. No?

I'm of the mindset, if it's going to get done, might as well do it right, once. But that $pend is killer.

The only reason the proposed plan is "bad" is that if something else is near the end of its service life and fails shortly after putting it back together, you'll kick yourself for not taking care of everything "while you're in there" and pay for 2x the labor.

I helped a buddy drop the engine on his SC so that we could replace one piston and cylinder that had broken from detonation. It was a "wham bam thank you maam" repair. Get in, get out, get it back on the road. We didn't even pull the CIS...just loosened the one side so that we could pull the one bank of heads to access the failed cylinder and piston.

https://asbury.smugmug.com/By-Land/C...DSC_4579-L.jpg

^^^This is exactly what I was envisioning.

I understand the risks, but I bet the cost was slim compared to doing everything...

ARE THOSE REUSED DILIVARS!? The humanity.....

This repair cost very little other than time, some gaskets and oil. My friend already had a set of good used P&Cs on the shelf to use as a spare.

AFAIK this car is still running and hasn't been apart since (the quick repair was done several years ago now).

On the up side, it sounds like the other heads amount to nothing more than "while you are in there" expenses.

On the down side, there are economies of scale in doing the job once rather than three times, (or six if you are talking about both banks)

To reconcile those two extremes, doing it three time in three month would be aggravating.
Doing it three time in ten years and delaying the other two time until more funds are available might not be so bad.

It is all just balancing risk

Risk = Impact + probability

It depends a bit on what you find in there. If you have a guide or valve that has suffered a catastrophic failure, yes, you can just remedy that one cylinder. But there remains the Q why the failure. If it turns out you had a suspect batch of guides, or a cheap brand of valve throughout the engine, or a guide that came loose, it doesn't make a lot of sense leaving them in there for them to fail one by one. There are some threads i am sure that discuss inferior makes of guides, and possibly valves. You may need to do some homewaork once you get #2 apart. Determining what has caused the issue will be important in terms of the decision you make.
Alan

^I was unaware there were potentially inferior brands of guides. Learning more about what I have will surely determine the direction I go once apart.

I was thinking possible bad machine work on the rebuild.

Well, just like Dilivar studs, some bits are inferior - but these things are only found out over time. Or you may have bad machine work and a guide come loose. In which case you would have to wonder about the rest. You will have a few decisions to make once you pull it open. if you have a handy engine builder (experienced in P engines) or you can post enough info here, the engine /machinist experts hopefully can put you straight as to best decisions. One you will need to make regards the dilivar studs if you have them in the case. There is a current thread in either the 930 or 911 engine build forum on this. Interesting reading.
Regards
Alan