ZG862

Sorry chaps - it's been a while but life gets in the way.

Last up I was struggling a bit with my nuts. The one's between manifold and catalyst naturally. The chap servicing my daily runner (who has a 993 Turbo it turns out) suggested that when the combination of heat and corrosion hardens them this much they really need to go in the pillar drill - and this clearly means the exhaust will have to come off. Those of you with long memories will remember that the original sin in this thread involved the poorly advised use of hardened steel stud extractors in the inner stud of No.1 cylinder's exhaust port resulting in a broken extractor wedged into the stud and an "oh well, let's refit the exhaust with 11 nuts and see what happens" approach. So I was reluctant to face the exhaust again.

"Let's give it a go and see if they move" I thought.
They did move. The ring spanner is perfect for all the nuts and a long socket with a cut down 8mm allen bar made short work of the rest. I needed to remove the primary silencer, the cabin air duct and right hand rear plastic capsule but hey presto, off came the manifolds! Looks like brass nuts and loads of coppaslip was a good idea.


The miracle? Take a look at this:



That's No.1 exhaust port. Cleaned up gingerly with a little bit of wire wool but otherwise unmolested. I looks like the combination of heat and vibration has shaken out the broken extractor and the original stud. Looks to me that I can see right into the end of the original drilling. The only bad bit appears to be that the original thread is well and truly gone.

So what next Rennlisters? My ancient Bruce Anderson Performance Handbook says Timesert not helicoil but do you think this can be attempted in situ? I recon I'd need to make up a guide from a bit of steel with holes at the correct centres bolted to the remaining stud but it seems feasible to clean up the hole and tap it for an insert without having to remove the head. Anyone got a recommendation of where to get Timeserts or know the spec I need?

Whilst we're there (groan) does anyone spot anything on the pic that I ought to be worried about? Here's a pic of 1 & 2 together:


Dare I reuse the gaskets or must they be replaced?

Finally, here's the reason I'm there. Let's see if they prove any easier out of the car:


Thanks for reading; any help with the myriad of questions gratefully received.

Z

ZG862

Anyone?

robt964

Given the environment it will be working in, I'd deffinately use a Timesert. From sat in my chair looking at your pictures :-) I can't see any obvious reason why it couldn't be done in situ.
As this is an area that will experience a large degree of thermal abuse, the tolerances of any drilling/taping required for the insert will be quite critical. Make sure you buy *exacty* the right sized drill they specify and of good quality. You will need to countersink the insert otherwise the flange will stand proud and the exhaust may not seal properly. This will be the tricky bit since you don't want to use a normal drill as it will cut the seat with an angle.

Edited to add: Other things you may need to consider: If you do need to drill the hole, is there sufficient material around it that won't cause you to break through the 'step' edge of the exhaust port. You'll probably be ok but in some of the pictures it looks close, as if the port is not central.

Also if the height of the timesert flange is less than the thickness of the compressed exhaust gasket, you may be able to get away without countersinking it. You'd also have to enlarge the through hole in the gasket to seat around instead of on-top of the flange.

ZG862

Thanks very much for your advice, Rob. Seems then like the next thing for me to do is get my hands on an M8 Timesert and take it from there. I guess I can measure up the spacing from another exhaust port to make up a drill guide so as to ensure the insert is truly perpendicular to the face of the cylinder head.
Still can't get my head around the vanishing stump though.

Z

robt964

As you only get one shot at this :-) putting in the extra effort to fabricate a kind of jig/drill guide would certainly be beneficial - You could then lend it out to other rennlisters afterwards :-)
A slow drilling speed is your friend here.

VR6-er

Is this the video you are looking for?

alexjc4

There is a thread regarding this sort of drilling guide jig on pelican i think there a couple of people that sell them.

Ken D

Here's one version of the jig, with a link to instructions. This can be done in situ.

http://www.stomskiracing.com/products.php?id=8

ZG862

Blimey. All quiet then a flood of REALLY useful information. Thanks very much everyone.

Glad I was sitting down when I followed the Stomski Racing link, Ken. That's exactly what I had sketched on my pad for a guide (though without the multitude of centering discs) but I think I may have a chat with my brother in law and see if he could ask one of the apprentices at his work to do "a little practice piece"... Rob - I'll be happy to lend once done. I'll never need it again, after all.

V6ER - that's exactly what I was looking for. That phrase has Star Wars overtones. ("These are not the droids we are looking for.")

Thanks again,

Z

VR6-er

Thats exactly what I had in mind when I posted the link ;-)

ZG862

Can anyone confirm the stud spec for me? 999 062 007 02 is described as "Stud BM 8 x 22" in the manual and 999 062 239 02 as "Stud BM 8 x 30". I assume my missing one is the 30mm variant but am I correct in assuming that I need the M8 x 1.25 spec thread?
Is this ( ) the kit I am looking for?

Z

robt964

To avoid guess work can you not check the thread on one of the existing studs? With a pair of calipers, measure the distance over 10 'peaks' of the the thread. Divide that value by 10 and you'll have the pitch.

ZG862

Thanks Rob. Alas I'm presently 5359.948 miles (approx) from my 964 at the moment so wondered if anyone knew? I'm reasonably sure that M8 x 1.25 is the standard metric thread but I reckon someone out there knows for sure whether this is the same as the exhaust studs.

Cheers,

Z

ZG862

Well I'm now 5359.948 miles closer to my 964 so work has slowly begun again.

The car hasn't fixed itself it would seem and again I really need your help...

Lots of little jobs on the go (I'll post some pictures below rather than type lots) but the killer today was when I tried to reconnect the rear brakes. Remember I had all the callipers stripped and repainted? Whilst they look beautiful, it would seem that the heating the guy did prior to blasting must have cooked the inter-half seals on the rears, as when I connected up the new lines it started raining brake fluid from the lower edge of the calliper. I checked the bleed screw and it is not coming from there; since they are the earlier 2 pot type there is no external pipe running between the cylinders.

So what do I do? Can the seals be replaced economically or should I throw them at a wall, weep and seek out some 4 potters?

Cheers,

Z
(Here's just a few pics of stuff I've been working on. No I didn't shear the bolts on the left hand engine tin - that must have been a dealer before my time. No fun trying to fix though.)

ZG862

Anyone got a suggestion on the callipers? I'm assuming that it basically a couple of O rings between the halves that have disintegrated.

If I "upgrade" to the 4 pot version am I right in thinking I will also need new discs and proportioning valve?

Cheers,
Z