3.2SS top end rebuild - compulsory newbie questions
 

I'm currently doing a top end rebuild of my 1978 SC based 3.2SS. This started out as a classic Max Moritz kit on otherwise stock engine. Since my purchase I've added EFI/ITB, 1 5/8 Headers and CDI+ignition (classic retrofit).

Car was running strong, no issues, no broken head studs.

I was going to clean up some minor oil leaks and wire work, so dropped the engine. I already knew the engine was "sweating" somewhat from the heads at the exhaust site. But when I took a closer look at it, I didn't even bother with a leak down:

http://forums.pelicanparts.com/uploa...1518462544.jpg
http://forums.pelicanparts.com/uploa...1518462544.jpg

It was pretty clear what I needed to do. So off with the heads :rolleyes:

http://forums.pelicanparts.com/uploa...1518462670.jpg

I must say, I'm amazed how easy the head bolts came off! I can't imagine these were torqued correct. Also, the previous builder didn't bother to change the lower studs - they are all Dilavar. None broken though.

What I also found was a wee bit of oil in the cylinders:

http://forums.pelicanparts.com/uploa...1518462670.jpg

I suspect this is from leaking (broken) piston rings and/or leaking valve guides no?

So, I'm taking the top apart. I'm not going to open the case at this point.

Just a few questions...please bear with me:

1. I will install new piston rings (working on finding some for my 98.00 Mahle - NOT EASY) - but how do I check valve guides? Is it mandatory to change them?

2. The Mahle kit does not use a head to cylinder gasket. Do you recommend grinding the mating surfaces?

3. I'm changing Dilavar to steel studs. But should I change the old steel studs as well?

4. Do I torque down the head to 32ft?

Oh and last: I'm installing DC20 cams. There seems to be some conflicting timing numbers on these. I keep reading 2.2-2.4, but Joh Dougherty states 1.8-2.0?!?! Anyone with experience?

Thanks!!!

In the Technical Specifications booklet you can find the wear limits for the valve guides:

https://i.imgur.com/0Kocyq4.jpg

To answer your questions, in general.

To accurately check your valve guides you should disassemble the heads, removing the valves. Then clean out all the carbon build up in the guide. There is more than one way to measure. The easiest is to install a new valve, dry, and measure how far it can be moved side to side. A dial indicator works. Your exhaust guides are more prone to wear. You can get an idea, just by using a screwdriver to see if the retainer can be moved with the valves and springs still installed. IMO, if they are not perfectly tight, replace them.

As long as the top of the cylinders and head sealing surface are not damaged and no sign of compression leakage, you should be good to go. No machining required.

Just replace the lower studs with steel. The uppers will still be good.

The torque is 24 FT LBS. 32 is newton meters.

no idea on the cams.

One shop I have used uses the dial indicator method. You set the dial against the tip of the valve stem and see how much lateral movement you get. They use 0.8mm as the max tolerance.
bear in mind only some of that will be the guide - the stem wears (tapered) too.
Gordon - do they do that test with the valve depressed at say 10mm, or closed?
Alan

The way I have seen it specified is to have the valve head 10mm off the seat. Use the dial indicator against the valve head.

One thing to keep in mind is the guide will wear more in one direction due to the forces of the rocker. The guide will have an oval hole.

Old timey mechanics will just put in a new valve, hold the head just off the seat, and give it a wiggle. Easy to tell if the guide is worn.

I called the local machine shop yesterday and asked for price incl cleaning, new valves and guides (with seat grinding if needed). Price = 1300$ auch!

So it would be nice to clean and check my self.

12 new valves/guides plus machine work. Thats a good price. Depends what sort of job you want out of it - long term.
Alan

If you're getting DC20 cams, I would throw in a new set of John's valve springs in there as well. Sounds like a great build

Part of the problem with the head sealing is the cylinders are Carrera requiring a different torque value.
Off my memory, the spec is 15 #ft, first torque. Second torque is 15#, then a 90 degree swing
Lube the threads.
Bruce

Yes, I have seen that technique described before. However, I do not understand the concept of "a 90 degree swing"?!

Can you elaborate please?

Oh you mean swing the engine!? Torque down one side in two goes, and then do the other side. Got it.

By the swing I mean a torque increase of 90 degrees on the torque wrench, not giving you an actual torque number but 15# + 90 degrees, +/- 2
Bruce

Interesting that Wayne in his book does not mention this?

How would you check or retorque after 1k miles using this spec?

The spec book contains this info.
Bruce

I don't see a mention of re-torquing the heads after break-in in the Spec Book.

So do you back each nut off. Then re-torque according to the book?

I’ve never had a problem with loose heads or nuts loosening on motors I ve built. I do test the torque several times before closing up. I have had motors come in that were loose on the nuts but they were not my builds.
I did have an 82 turbo with all 24 dilivars in place and needed a 4 ft breaker bar to break the nuts loose of the dilivars.
Bruce

Bruce - are you sure the 90 deg torque is correct for the head studs? Waynes book, and others I have all do a 2 step process, but to a final ft/lb value.
The angle torque is usually used for 'oncer' stretch bolts - eg rod bolts. I have not seen it used /recommended for head studs.
Regards
Alan

I'm pretty sure my leak was caused by loose bolts, but I also have Dilavar on the exhaust side.

The 90 degree swing must correspond to a second higher torque value, just like Wayne's recommendation.

Not exactly. Two different processes. Torqueing to ft/lb is just that - putting a defined load on the stud. Torqueing to an angle deflection is defining a certain amount of stretch. If the book says 23 ft/lb, then you torque to that load. there is no guarantee that a 90 deg deflection will give you that. It will have a ft/lb value - but that is not what you have torqued to - you don't know what the ft/lb value is. Not sure why you wouldn't use a ft/lb torque when that is the value specified.
Maybe I have been doing it wrong all these yrs. Just curious about Bruce's process.
He does more engines than me.
Alan

Butł
 

Yes I agree. The final torque value will be unknown - just like Bruce said. Apparently both methods work? But how about re-torque after break in?

Exactly. You can't torque another 90 deg, nor check. It is normally used for 'set and forget' bolts.
You basically would have to do ft/lb recheck - but you have no value to work with because you don't know the original value. So all you can do is make them even - 23 ft/lb? So why not in first case.
Alan

FWIW I have done engines/rebuilds and not re torqued them (my own engines/rebuilds). And had no issues. But ideally, it is advisable.
making me feel like I should go and re torque the latest rebuild.
Alan

Well FWIW, I'm an ENT surgeon. I have done many ears - but this is my first Porsche engine. I'm fascinated by the similarity between ear surgery and re-building these magnificent engines. There's plenty of literature, but it is also very much a apprenticeship - learning from those who have experience. What works, and what does not.

So when we find different solutions to the same basic problem, it must mean that we are operating within a significant safety margin. Which is why Bruce's method works and why Alan doesn't need to re-torque. The stuff you don't read, but learn from experience.

I really love this forum - thank you for your help guys!

ps: John Dougherty sorted my cam issue for me: 1.8-2.0 is the setting for low CR and 2.2-2.4 for higher, which is the advanced setting.

I don't mind tackling a 911 engine. But I would not do ENT - even with a manual.
Stick with this forum and you won't go wrong. Yes, more than one way to skin a cat. But these are great engines. just complex and time consuming. Take your time, get it right and you will be rewarded.
regards
Alan

Torque
 

Just because of age, I doubt myself at times. I ve built for a long time so the specs change with different motors, but they’re all 911.
Two things to discuss
I was correct on the head bolt torque angle for Carrera cylinders
When I first looked at the book there was torque angle on the rod bolts. I thought maybe i was wrong about the head nuts. I wasn’t.
New info on the rod bolts.
There is a new edition of factory bolts with 12.9 on the rod bolt head. This edition requires a second 90 degree torque angle.
Finally, you need to have a machinist that knows the work on the heads. I ve had the same man doing heads for the 17 years I’ve been in NC. Depend on their expertise as you have the motor apart and guides are no place to cut corners on reassembly.

Bruce
Photos taken from Carrera spec book.
http://forums.pelicanparts.com/uploa...1518638267.jpg
http://forums.pelicanparts.com/uploa...1518638328.jpg

Wow - thanks Bruce. Waynes book doesn't mention that.
So how do you get on for re torque after 1000 miles - or do you not bother?
Regards
Alan

It is interesting that Porsche snuck in the 15# + 90 on the Carreras and Wayne does not mention it.

The question I have is about re-torquing. Or as Wayne says in his book re-tighten at 500 miles.

So the real question is, do you back each nut off 1/4 turn and re-torque?

Or do you just put a torque wrench on each nut and if it doesn't move at 24 ft lbs, call it good?

Same with a Carrera?

If it a concern, I would go with the turbo spec @32#. Turbo spec may be less because the factory builds with 24 dilivars..but then Carrera builds with 12.
The last turbo, I used Supertec and followed Henry’s spec.
I wouldn’t back the nuts off because you’d be starting over again as build day
Bruce

Are you saying that for all steel studs 32 ft lbs is appropriate? Or is that just for the newer divilars?

No, I’m saying that the numbers are for factory new build specs. Dilivars on the turbo don’t expand further than the cylinders as the steel would.
We’re just swapping ideas, I only have my experiences and thoughts.
Bruce

I guess that the 90 degrees is more precis than x-amount of Nm.
You get the bolts snugged up with 20 Nm, then you add the desired amount of stretch with 1/4 of the thread pitch.

If I'm not mistaken the Carrera spec supersedes the older torque value for the earlier engines to?

I have another w/shop manual, - which also covers carrera - which I think also doesn't mention the 90 deg torque. I can't get to it for 2-3 days but will check.
Curious. I'm guessing there are an awful lot of Carreras torqued to 23 ft/lb. But it also suggests you can dispense with the re torque proceedure.
Makes you wonder why earlier 911s can be done to ft/lb and my 930 is ft/lb, but Carreras are different. Same studs I think?
Regards
Alan

it would be interesting to see what a 90 degree swing corresponds to in torque? Could it be that it is even more than 32ft?

It's quite typical for engineers to include a significant safety margin, which may be reason why you dont really need to re-torque?

Seems to me that Supertec paper work gave me 36 or 38 ft# for the turbo I’m doing.
Realize the 84 and later turbo used the same head seal as Carrera but used 24 dilivars studs so you don’t have the potential expansion as with steel.
Bruce

The Carrera head stud spec appears to apply only to the Carrera if you look at one tech bulletin in 1987 and does not apply the previous engines. But the 1986 bulletin says it does apply to the engines from 1978, due to an updated head nut. In other words, two separate reportings that conflict?

http://forums.pelicanparts.com/uploa...1518733822.jpg
http://forums.pelicanparts.com/uploa...1518733822.jpg

Note that Optimoly HT is basically antiseize paste for those who don't know this. It's nothing super high tech secret sauce.

Not sure why they would say the 90 degree application doesn't apply to the earlier engines like the SC 3.0L since the head studs and cylinders are basically the same. They also make a point of saying not to reuse the cylinder head nuts. I don't know if they state that because of the nut material or the potential that the nut's tooling hex can get damaged upon removal? But i've seen the head nuts reused on a number of occasions with no ill effects.

Since we covered rod bolts here too, here's the bulletin information on the change in the M9 rod bolts and how to torque them.

http://forums.pelicanparts.com/uploa...1518733822.jpg
http://forums.pelicanparts.com/uploa...1518733822.jpg

Well this discussion is rather timely as I was at the head torque stage in my assembly this week. Mine is an 86 and I previously used 24 ft lb (as per Wayne's book) with no issue.
So this time I did the 11 ft lbs then I used my trusty old deflection type torque wrench (it is reasonably accurate) to tighten an extra 90 degrees. Turns out, each one at a 90 degree turn equaled 30 ft lbs. Just to be sure, I verified that number with my calibrated click type torque wrench and it was the same. So there you have it, it was an extra 6 ft lbs more torque than the set rate of 24 lbs.
And I did reuse the cylinder head nuts and will again if I need to. Certainly, I can see not reusing rod bolts etc but head nuts, well I'm not getting it.

"Applies to the NEW CYLINDER HEAD NUTS".? What new cylinder head nuts?

It looks like, from above there is a new part number for the head nuts - yellow. Must be different stretch material. But they say even if using these new angle torque nuts, it is OK to use ft/lb torque on them on an SC. Seems weird.
I have just checked my other manual which covers Carerra from 84-87. No mention of angle torque. So I think it has come in since they changed the head nuts. Only thing that makes any sense.
So Bruce - even if the years are advancing, your memory is fine, and you are up to date. Unlike the rest of us (and my 2 manuals). Think I would prefer to use 'old' nuts. That way I can check and retorque after assembly/break in, if I got motivated enough.
Regards
Alan

Gordon,

If you wanted the final torque value when using the 90 degree method use a torque wrench with a dial indicator. Then you can see what the torque was at 90 degrees and use that value when re-checking the torque.

Good point. I just finished checking mine for the 1K mile service. All tight at 25 ft. lbs.

FWIW, I don't see how the nut makes any difference. It's the stud that stretches. How will the nut change that? Does anyone have one of the yellow nuts we can look at?

Where are all the engineers when you need them?