aguk928

Hi all,

First I would love to congratulate everyone one here on such a great site.

Just browsing has helped me allot in deciding to take the plunge and get a 928. As has the enormous 928 enthusiast web sites. It’s nice to see such love for a car like this one.

I bought a 85 S2 Auto as a project and after getting it home have found that there was oil in coolant and water in oil. Hmmm Head Gasket? I guess so the Rad is pretty new. I did take this into consideration when buying.

So now I have stripped the top end down. Have taken the heads off, cleaned them had them skimmed, new exhaust guides fitted, all new valve seals, valves lapped.

So time to reassemble but first

Some questions!!
1) I have been advised to use a sealant such as Wellseal with the head gaskets, any comments? Or advice? If so how and where?

2) I am puzzled with the stud situation; my understanding is that there are two types black finish and gold finish. And the 85's should all be gold but I have both. The torque up on them is different as I understand. Anyone had similar? What should I do replace all studs or torque them all as 20nm +90 +90 ?

3) Although I have cleaned all the sludge I can out any advice on final flushing when assembled? As there is always some left in the Rad and Heating system. Use low suds dishwasher detergent, and vinegar?

4) What else to look for?

I am of course replacing all seals, gaskets and hoses etc. as I reassemble. Boy have I done allot of polishing and cleaning and yes I am looking forward to hearing that awesome rumble from that V8 once its all together again.


Advice would be appreaciated.

GlenL

1) Don't use sealant on the head gasket. I will break the rule if there is some deep pitting around coolant holes, but never around the cylinder bores.

2) Use whatever fits and torque to specs. The torque is fairly low so the studs don't have to be special.

3) Clear water or commercial radiator cleaning. If you have all of the coolant out, including block plugs, I'd skip this.

4) Do you think you've solved whatever prompted the head job? Also, I'd re-torque the heads a few times over a few days. Won't hurt and may prevent early failure of the gaskets.

aguk928

Thanks for such a speedy response.

Re answers:

1) The Porsche shop that recommended the Wellseal suggested that it helps reduce the occurence of gasket failure especially considering the problems with coolant and antifreeze erosion of the head. Any comments? I tend to agree with you and as I have had the heads skimmed I can't really see any advantage in using a sealant on the heads and yes definitely none on the bores.

2) Now the torque specs for both stud types are different, so should I replace to a consistent set or torque to the specs for the individual stud types. I also understand that the studs that are 20nm +90+90 can't and should not be re torqued once done. Comments?

3) Yep had plugs out the lot so a commercial Rad cleaner, god what is a good one in the UK as I have found things like the Holts brand are just a waste of time. Thats why I picked up on some previous posts to dishwasher liquid etc.

4) Well that is the $64K question. Looking at the gaskets when they came out the where not in a great state. The engine has done about 140K mi on these gaskets so may be it is to be expected. All else seems OK, the head pressure tested OK but as to the block short of fluxing it I can really tell it looks good but then don't they all. What other possibilities could it be?

Also I might add that I am doing the job with the block in car and if anyone wants to hear how I am managing or any experiences I will be glad to share. I have taken lots of photos on the way and must admit have not found it to daunting a task so far. Yes its tight in there but more than doable.

GlenL

On #2 I was confused on head studs versus exhaust manifold studs. My reposne was for the manifold studs. I believe all head gaskets can be re-torqued unless the studs are yielded as part of head installation. The studs on the 928 are not yielded so re-torquing can be done. (Other opinions?)

aguk928

Just looked up the tightening procedure on the head studs again and I see that there are three options

1) Old style head studs i.e. black/grey are torqued to 20nm/50nm/90nm as a 3 step process
2) New style head studs i.e. gold/yellow are torqued to 20nm then +90 +90 +90 degrees as a 4 step process
3) Head bolts are 20nm +90 +90.

Now looking at the head studs in my block it looks like I have both the gold and the black studs so I am bit lost what to do.

As to re-torquing I can see how to retorque torqued studs but not angle tightened studs any advice here?

So what to do any recomendations? Change all the head studs? or just angle tighten all those that I have the same. Or do the black one way and the gold another but that smells of head warpage to me any comments?

Now if changing all the head studs any recommendations as to studs or bolts?

UKKid35

I was under the impression that only the S3 had studs as standard. I also thought that studs precluded head removal in situ.

Look out for meets and other info on the 928.org.uk site and good luck with the rebuild.

bcdavis

I had my heads rebuild by a not-so-swift shop, that assumed that I needed it, because there was oil in the water, water in the oil, etc...

Well, guess what?

The oil cooler, and the radiator cooler, are often mounted inside the radiator itself.
So a leak in the oil cooler, will put oil in your coolant.
But your engine may be fine.

A better shop realized this and we replaced the radiator with a Devek unit,
and all was well. But I was not happy about the previous rebuild,
which was not needed.... Grrrrrrrrr...

So check out the radiator and oil cooler.

But since you already started on the heads, might as well freshen everything up...

aguk928

Well its good to hear from a fellow UK 928'r.

S3?? Which model year is that as straight after the S2 I thought they when to the S4 would be interested to know more.

Head studs according to what I have read were on all earlier models only later in 1986 they start to use bolts. Bolts can be retro fitted if wanted. So should I replace with bolts? Any advantage over studs? I can get the heads on and off with studs even with the engine in situ so that does not appear a problem to me. I know in racing studs are used and they are supposed to be more stable than bolts and take higher head pressures. Any comments anyone?

I have pressure checked the Rad and it does not appear to be at fault as the Oil and ATF cooler lines lines test OK. But the head gaskets where shot. So I am hoping that is all.

I have of course rebuilt the oil pump and fitted a new water pump, rebuilt the tensioner and fitted a new main tensioner roller. As for the idler pulley and the small tensioner roller I was quoted £110 and £35 respectively for these so I pressed new bearings in they feel perfect The bearings in both these pulleys are stock standard and its not difficult to have then pressed in. Total cost £20 So no excuse not to replace these.

As a side note the 928 I brought had wads of service history and documentation all done by Porsche main dealers or specialists. Although useful for knowing the cars history, I have found it does not guarantee the work to have been done well. I am amazed at some of the things I have found, and quick fixes. So it looks like either find a good specailist or do it yourself, my choice is to do it myself, although this is the first 928 I have worked on I am really getting a buzz working on this car, and its not as daunting as I expected. Especially with this list and its archives. Thanks guys!!

GlenL

I take it that you've got the 16 valve engine. The "conventional wisdom" is that the early 32 valve engine can't have the heads pulled with the engine in the car.

I'd stick with the studs that are in there.

The torque methods are for different gasket types and engine models. It is much easier to re-torque with the three-torque method as opposed to the "one torque and two angles" approach. Your engine gets the later method. I'd be tempted to back it off and repeat the whole thing. Who's done this?

aguk928

Thank Glen for you reply.

Yep it's the 16 valve engine.

With re-tightening the angle tightened head studs, are you suggesting to take the nuts back to 20nm torque on the studs and then re-angle tighten them. If so I would imagine that one would do the backing of in the reverse of the tightening sequence in 3 stages with the last one done so as to leave the correct torque on the stud nuts.

Any possible side effects to this and gasket crush etc? Would you recommend doing this on the engine that has just stood with the heads tightened unrun or run and over the few days that you mentioned before.

Many thanks again.

GlenL

I'd do it before running the engine. Let the engine stand for 12 to 24 hours between re-torques. If the coolant was filled, there could be leakage when loosened.

Yes. I'd take it back to 20nm and then do the steps. The idea is to crush the gaskets good while getting the right pre-load on the studs. This does work better with a pure torque approach.

aguk928

Thanks Glen,

I will give your suggestion a go unless anyone gives a good reason against it. Anyone?

I will do a leakdown test after each head tightening for comparison and also it should put a bit of pressure on the head and studs and just to be sure.

Well I know what I am doing tomorrow. Should be hearing that rummble pretty soon. Can't wait.

Any other tips while reassembling? My long term plans are that I get this top end rebuild done and fire her up then assess any other possible problems with the car and gradually restore her fully. I plan to try and bring it back upto showroom condition.

Ahh heres another question has anyone had experiance or advice on replacing the fixtures with Stainless Steal or titanium ones. Titanium might be just a bit to $$ also.

Thx

Thom1

I found fuel injector o-rings at Parts Plus local auto parts store for cheap, or the big 3 might have em. Do replace them now.

Any time is a good time to replace the fuel filter.

I'll PM you a document.

aguk928

Thanks Thom1,

Yes I noticed my O rings where lets say dead and now to be buried. Manage to find some here in the UK at a reasonable price.

I must admit if I had not pulled the top end fully apart cleaned and polished I may never have noticed the bad state they where in.

Again Thanks.

Thom1

Edited correction: I corrected the text below to refer to my other right side.

aguk928,

How did you get the heads off over the studs/studs still attached to the block? My USA model had interference on the left side with the brake booster. I loosened the motor mounts, and rolled the engine, finally put a lever under the left head to further roll the engine. (left side is as if seated in the driver's seat.)