#2 Exh. Valve Guide Failure: Why rebuild?

[Alan L]

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

[911SauCy]

Originally Posted by theiceman

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.

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.

[911SauCy]

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.

[jwasbury]

Originally Posted by 911SauCy

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?"

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.

[911SauCy]

^^^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.....

[jwasbury]

Originally Posted by 911SauCy

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

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).

[wayner]

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

[Alan L]

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

[911SauCy]

^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.

[Alan L]

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