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Cylinder Head Studs Part number

What's the difference between...

993.101.170.51 ... and ....

993.101.170.53

Are both Dilivar? Are both fully threaded?

After all the pros/cons...what is the feeling today if we find rebuild receipts of a 3.2 done in 2000 ( and since driven 20k miles).... of a nice looking motor, showing all 24 of the suffix 51 ?
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Wil Ferch
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Old 09-27-2010, 07:17 PM
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In 2000 the cost of the 993 dilivars was about a dollar more than the original dilivars at the jobber level. I put 24 993 dilivars on my 76 turbo, replacing all the original dilivars that were there. At todays cost if the 993 dilivars, I would probably just install steel.
Bruce
Old 09-28-2010, 04:08 AM
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Wil, The 993.101.170.53 is the fully threaded dilivar, not sure about the 170.51 part #.
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Last edited by 356RS; 09-28-2010 at 09:14 AM..
Old 09-28-2010, 09:11 AM
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My point....we've gone from looking at dilivar as a God-send of a material that expands/contracts like the aluminum case....to being the Devil's own playground as to quick and sudden breakage.

If I'm looking to buy a stock 3.2....I got both....top row steel and bottom row Dilivar. However, I'm looking at a high-mileage car to possibly buy and notice the rebuild receipts show the "51" suffix Dilivar used at ALL 24 locations in the rebuild.

If this a disaster waiting to happen or is it seen as normal and OK risk?
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Wil Ferch
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Old 09-28-2010, 09:17 AM
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I see a little confusion in these part numbers. Looking at the Pelican part number for 993.101.170.53 it lists "fully threaded dilivar for 933 TTurbo" In the Porsche part number book I see the part # 993.101.170.51 for the M64.60 engine which is the TTurbo. BTW you don't want the one with steel on the top and dilivar on the bottom.
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Old 09-28-2010, 09:34 AM
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Quote..... "BTW you don't want the one with steel on the top and dilivar on the bottom..."

That's my question....why?....this is what you will get if you have an unmolested 3.2 as delivered from the factory, and what I've had good luck with in 3.2's that I know.

I've seen *some* people use ARP or Porsche-steel in ALL 24 locations on a rebuild process...because we've come not to trust the Dilivars...too unpredictable. That said....the most thermally-stressed engines of the bunch were the 930's...and they came from the factory with All-24 as Dilivar.

Shoulda been an easy question...apparently not.

So...356RS....you're saying the rebuild I'm looking at with all 24 locations using the 993-pattern ( threaded full length) Dilivar "51"....is viewed as superior to a good, stock 3.2 using steel top and older-style Dilivar bottom?
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Last edited by Wil Ferch; 09-28-2010 at 11:52 AM..
Old 09-28-2010, 11:50 AM
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Wil, From what I have read and with the small number of engines I have built my personal opinion would be to use either the 933 TT dilivar studs (24) or very good quality aftermarket steel head studs like Henry's Supertec head stud kit on all high compression engines. There are some good suggestions from well know engine builders that say, if you have a engine torn down and have the combination of steel studs on top and dilivars on the bottom now is the time to replace the bottoms with steel.
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Old 09-28-2010, 12:57 PM
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Well there ya go.....the engine I'm looking at (receipts) show an engine problem in 2000 that resulted in an ( overly-done, in my view) COMPLETE engine rebuild including new pistons, cylinders, oil pump, rockers, rocker shafts, valves, etc, etc....the parts list is fairly complete and the tab came to $11,000...parts and labor. Oddly...in the rebuild...they used 24 Dilivar studs as I mention. Done by a well-respected Porsche shop too !!! The question then....why all 24 Dilivar and why not all 24 steel ?

So for the used cars I'm looking at...I will encounter this nice-sounding engine (having done 20,000 miles since the year-2000 rebuild)... with all Dilivar....or ..other high-mileage stock 3.2's that have stock steel top and Dilivar bottom.

So I'm conflicted...the rebuild makes it essentially a 20k mile motor....and therefore desirable compared to high-miles motors....but I'm not sure if the ( odd use of) 24 Dilivars is another disaster ticking time-bomb?
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Old 09-28-2010, 01:06 PM
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Remember, it was the combination of the steel tops and the orignal dilivar (not fully threaded) studs that gave some problems. Having 24 fully threaded 933 TT studs is a good thing.
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Old 09-28-2010, 01:38 PM
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I did a quick search and found this. I trust Steve@Rennsport. The 51 suffix are good. And watch the spelling, there were cheap knockoffs made that spelled dilavar differently and caused a lot of concerns about the real ones.
964 - Repeat of Head Stud Woes
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Old 09-28-2010, 02:38 PM
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356RS....I don't know why this is....but with each exchange of ours, we seem to get off on tangents.

You say.." Remember, it was the combination of the steel tops and the orignal dilivar (not fully threaded) studs that gave some problems. Having 24 fully threaded 933 TT studs is a good thing.

Not necessarily. Why?...because for the engines with top-row-steel and bottom row Dilivar...it is almost ALWAYS that when you DO have a problem....it's with the bottom row Dilivars...and almost never on the top (steel) units. That's why I see the retrofit done by many to use all 24 steel...and ending up with ALL 24 Dilivar can make it worse than a top-steel/bottom dilivar of a stock engine...no? You now have 2x as many places for the goofy Dilivar to break ! ....

I think it was Bruce Anderson that showed the various permutations of Dilivar over time...bare, gold coating, black coating, non-threaded, threaded....the final analysis, it seems was to go to all steel on rebuilds. either Porsche brand or high quality aftermarket steel ( Raceware, ARP)....but I never heard of All-24 dilivar as being the solution. I also recall reports ( Anderson again?) that all-length-threaded Dilivar was also no good because of the many stress-risers on the v-groove of the threads...now exhibited along the entire length of the rod.

The reason the factory split this up the way they did....was the theory that the top row gets the proper cooling blast of fan cool air...so the expansion/contraction on the upper surface of the engine is not as much as the hotter-running lower row underneath.
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Old 09-28-2010, 05:44 PM
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Update and Edit.... E Sully..thanks for the link.

In that link, maestro Steve Weiner says--->

".... I'll offer another opinion here and express my strong preference for the latest 993TT dilavars,..

ARP studs, while quite strong and bulletproof, do NOT expand at the same rate as the cylinders and we've experienced everything from loosened head nuts to leakage at the junction of heads & cylinders from distortion when hot.

I'm a huge fan of ARP fasteners on other engines, but I'll only use their excellent rod bolts in 911's.

Small engines (2.4 & smaller) can safely use steel studs and mid-size (2.7-2.8) can use steel as long as Case-savers are installed and engine temperatures are well controlled. I really prefer the late 993 TT Dilavars for everything else. Porsche used these same items in all 3.8 RSR and GT-2 engines with no issues on these parts.

Just one man's opinion, of course so YMMV. ...."

Steve's reference later in that same thread identifies the 993TT stud as "51" I'm talking about.

356RS....I therefore stand corrected. Seems all 24 with the "51" part is indeed the way to go.
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Wil Ferch
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Old 09-28-2010, 05:53 PM
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It took 20 years for the original studs to become a problem and the black coated ones of the Carrera are doing better with 20 + years on them. What will be the concern at this point?
Drive it and enjoy it..
Bruce
Old 09-28-2010, 07:00 PM
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Will,
If cost is any area of concern, I would opt for aftermarket steel head studs. The 993TT head studs have gone through the roof in terms of cost over the past few years($35-$40 ea!). ARP's are half the cost of 993TT's.
I do have one (1) left over from my rebuild.....Hennesy Porsche sent me 25 by accident when I rebuilt mine back in '04, but they were only $19 ea back then. It's yours if you want it......now all you need is 23 more. Any volunteers?
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Old 09-28-2010, 07:01 PM
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Another tip from Steve @Rennsport....

Use the 964 Head nuts - 964.104.382.01 M64.01/02/03/05/07/08 & M30.69 engines

Cheers,
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Old 09-28-2010, 07:12 PM
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it seems this whole thread got way too complicated and WAY over everyone'e head. The original premise of my question was.-->

Baseline...factory engines used steel top and Dilivar bottom due to Dilivars matching the thermal expansion/contraction rated better than steel. The Factory obviously thought the risk to stay steel as being OK for the upper row,as it received the un-impeded cool air flow of the fan without first heating up.

Rebuilds.....first round...everyone thought "great"...Dilivars work well thermally and even the Turbos come with all 24 Dilivar..being the most thermally stressed...during a rebuild we'll be "extra careful" and use Dilivar everywhere?. Result?....sometimes a disaster as they were failing sometimes right in the workshop, with an unexpected "poing" happening overnight within the rebuild and no one knows what happened.

So..later...especially with the modern aluminum cased engines that weren't prone to pulled studs like the mag cased engines....rebuilders started to use "All-steel" again.

So it struck me odd that I find a car I'm looking at...that has ( in the receipts) a rebuild that uses all 24 dDlivar again. This is where I enter with my question. I ask "why"... isn't that asking for trouble for unexpected breakage?. Turns out from many here that the newest Dilivar....the 993TT/all-threaded versions....don't catastrophically break as easily as the earlier versions. This is a good answer but could have come out in discussion much earlier/easier than trying to re-ask so many times with side issues brought up.

So...fine...I'm OK with that. If its true. I'm not in the process of a rebuild....I'm looking at a few older cars each with different levels of new/rebuilt engines used...and I want to asses proper risk. That's where I am with the question.

Thanks.
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Last edited by Wil Ferch; 09-30-2010 at 11:25 AM..
Old 09-30-2010, 11:07 AM
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You answered the question yourself - the very nice Porsche engines in the NA cars use 12 dilivar studs and the premium engines (turbos) use 24 dilivars, 'nuf said.

24 dilivar studs, of the newest design and metallurgy, would be my choice.

Mark
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Old 09-30-2010, 03:44 PM
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Not necessarily.....yes....for thermal properties. If all 24 of the NEW dilivar have a habit of snapping easily and without warning like old....then, no...it would not be my first choice.

It appears that reports from a number of knowledgable people indicate this "51" suffix, newest Dilivar... is much better than the old in inadvertant breaking....this is a key finding. This implies good thermal AND mechanical characteristics.
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Old 09-30-2010, 04:23 PM
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