About to strip the heads off a 911T motor with twin plug heads - any gotchas ?

[3barboost]

Hi All

Porsche Newbie here - have a 84 911T with a very modified motor in front of me
the turbos are off (twin kkk delivering 515whp at 1 bar), manifold / shroud etc etc

The heads have stripped threads on 5 of the 12 plugs - previous spanner swinger caused a bit of chaos here

I feel best choice is to remove heads and have the threads machined properly

Before I pull the heads off - is this the correct route ? and is there any special position that the motor / valves must be placed in prior to stripping heads off ?

[Spenny_b]

Originally Posted by 3barboost

Hi All
Before I pull the heads off - is this the correct route ? and is there any special position that the motor / valves must be placed in prior to stripping heads off ?

?

To get the heads off, you're going to have to do a full top-end strip down anyway....timing chains off, cam carriers off, etc, etc.....so at that point your valves will be all closed.

Not being funny, but probably best to read the relevant chapters in Waynes book (linked as a stickie at top of this forum) to see what's involved before diving in....it's a bloody good read, succinct and should tell you enough to understand the magnitude of what you're likely to be doing.

Cheers
Spencer.

Edited to say...welcome aboard mate....sounds like you've got a very interesting car!!

[earossi]

Not to seem trite about this, but if the only reason you are pulling the heads is to repair cross threaded sparkplug holes, have you thought though just helicoiling the holes. I've not done it to a Porsche, but did do it to several other of my cars I've had over the years where the plugs just galled themselves into the aluminum heads.

The process is pretty straight forward. The main issue is performing the work in a fashion that assures that all tapping debris is removed from the combustion chamber. There are ways to assure this. You'll have to pull the motor, which is not very difficult on a T and then have someone do the work who knows what they are doing.

Just a thought.

[Walt Fricke]

I think you can safely get going without Wayne's book if you can get the motor out of the car and (preferably) onto an engine stand. Pretty straight forward, only real decision is whether to remove transmission with engine or not. Me, I'd leave the transmission in for this unless you want to use the occasion to check and regrease the CVs, maybe clean up the transmission too.

I'd not try to fix so many stripped threads in situ. I'd pull the heads. You can't sensibly do that with the engine in the car. Pulling the heads is just a matter of removing all the stuff which is in the way - rockers, chain gear, cam. You can pull the heads off in blocks of three, but you will want to take bare separate heads to the machine shop, so I'd undo all those 13mm nuts (and the three barrel nuts per side) which hold the cam carrier to the heads.

Amazingly, considering I am cavilier about some things (like I never torque spark plugs with a torque wrench), in 45 years of working (sporadically, as need arose) on the aluminum heads of my air cooled, Porsche designed, motors, I've never had a plug seize. I do put anti-seize on them despite the warnings of some not to do that. So I don't have an opinion on whether a Helicoil or a Timecert or some other fix might be best. With all that power your plugs may see more stress than most. Machinist ought to have good ideas on that.

Were it just one plug I'd be more inclined to try to do it with everything in place, using air, vacuum, grease, something to keep the aluminum chips from getting into the combustion chamber. But, as you have no doubt noted, the plug is down at the bottom of a fairly deep hole. Not like the flathead Ford engines I first fiddled with.

Good luck

[3barboost]

the motor is out and partially stripped - i was hoping to do the threading via the plug hole with compressed air coming in the other plug hole and both valves closed - I will have a read through this book mentioned - appreciate all the tips and comments - what i was looking for was - put cylinder 1 on tdc and it makes things easier when stripping or something like that

[ajwans]

My heads are earlier vintage than yours but I think mine came helicoiled from the factory. If this is the case on your heads doing the job without stripping the entire engine should be more than feasible.

Depending on how bad the damage is there are some tools which you insert and then expand and unscrew through the threads to repair damaged threads. I forget the name of the tool.

andy

[3barboost]

the damage is bad on 3 of the 5 stripped ones - where those 3 wont tighten up a plug ie the plug keeps spinning - on the other 2 the plug threads are full of head material

I am inclined to do all of them once to prevent any further issues

[earossi]

Originally Posted by 3barboost

the motor is out and partially stripped - i was hoping to do the threading via the plug hole with compressed air coming in the other plug hole and both valves closed - I will have a read through this book mentioned - appreciate all the tips and comments - what i was looking for was - put cylinder 1 on tdc and it makes things easier when stripping or something like that

That should work fine. I would also resort to tricks like using lots of grease on the taps so that the chips have a tendency to get imbedded in the grease and then are pulled out with the tap.

You can also rotate the motor on the stand so that the spark plug holes you are tapping are on the bottom of the assembly. Doing it this way makes use of gravity to drop the shavings down towards the hole and not into the combustion chamber. Using compressed air in the other spark plug hole will also help tremendously and is key to being able to do do this little job.

I think that you should be able to do this well. Having more than one plug hole to do will also you to develop a learning curve while you are at it.

I agree with Walt on the use of anit-seize compound. You don't need to go overboard on the use of the compound, but it will help prevent further galling. If the issue is cross threading of spark plugs, then you need to be careful screwing them in by hand without the use of a ratchet or speeder wrench until you have them fully engaged by 4 or 5 full revolutions of each plug. Then you can hook up a convenience tool like a ratchet to finish driving the plugs into their homes.