Here's a Heck of a Thing

1982911SCTarga · 03-18-2008, 04:34 PM

So I'm feeling all good about R&R'ing the engine on my cabriolet (including getting the word this morning from Bob at Anchor Atlantic that my heads had arrived OK). I decide as my dinner is warming in the microwave to go out and check on something that I've kept forgetting about.

The issue was the head studs. They looked pretty much all the same except the bottom row on both sides seemed newer (a little shinier, maybe). I figured they were installed at some point during a broken stud replacement episode (the history on the car is spotty at best but there was a supposed rebuild in the past) and thus appeared newer than their topside brethren.

Grabbing a magnet off the fridge, I began checking the top and bottom studs on both sides.

Gee, that's funny, the magnet does not stick to any of the bottom studs. They must be -- wait -- how can this be? -- gulp -- dilivar studs.

Yesiree, a bit of a Porsche punch in the gut.

Brian

Scott R · Scott R's Garage

Yea, thats an SC 3.0 alright, had two steel, and the rest dilivar. PO did a lousy job of putting it back together and it grenaded, all new steel and a profession rebuild later and I still wonder sometimes if they are all still OK.

Jeff Alton · 03-18-2008, 06:38 PM

NO big deal, the bottom row comes out pretty easy and new factory steel studs can be had pretty cheap.

Cheers

EarlyPorsche · 03-18-2008, 08:04 PM

Why didn't they use steel to begin with?

Jeff Alton · 03-18-2008, 08:19 PM

The thought at the time was that the dilivar expansion rate was more similar to that of the aluminum cylinder and they were suppossed to reduce problems with studs. Too bad it did not turn out that way in the long run.....

Cheers

1982911SCTarga · 03-19-2008, 04:20 AM

I never realized that dilivar studs looked so similar (yet still slightly different) compared to normal steel studs. I thought I was well clear of the stud issue on this one, but, alas, no dice.

Time to bond with my assistant crew chief as we remove 12 of these #$%@* gems.

Brian

Tim Hancock · 03-19-2008, 04:41 AM

Quote:

Originally Posted by 1982911SCTarga

I never realized that dilivar studs looked so similar (yet still slightly different) compared to normal steel studs. I thought I was well clear of the stud issue on this one, but, alas, no dice.

Time to bond with my assistant crew chief as we remove 12 of these #$%@* gems.

Brian

Brian, my SC came with 12 dilivar studs on the bottom also....it is normal. I replaced the 12 lowers with new stock steel ones.

Porsche_monkey · 03-19-2008, 04:49 AM

Contrarian opinion: If they are not rusty leave them in.

1982911SCTarga · 03-19-2008, 05:01 AM

Hey, Tim, I know dilivar lowers are normal as our cars left the factory, but my cab is a high-mileage car (140,000 miles or so). I figured the stud issue was corrected by whomever was last in this engine (yep, silly me for thinking that). I'm glad I checked this out with the magnet, so at least I know what I'm dealing with.

Quote:

Contrarian opinion: If they are not rusty leave them in.

I'm listening.

Brian

Porsche_monkey · 03-19-2008, 05:18 AM

A lot of what you read is just people repeating the mantra, dilivar is bad.

Why do they fail? From everything I've read they fail from corrosion. Every failure I've heard of was a rusty stud.

I researched this a fair bit when I rebuilt my 2.7 engine. I went with dilivar.

stevemfr · 03-19-2008, 05:34 AM

Dilavar is a cool material. Strength like steel and expansion rate like aluminum. Just very susceptible to corrosion. If you pick up the first edition of Bruce Anderson's "911 Performance Handbook", he makes a very strong case for Dilavar studs. If it weren't for the corrosion problems leading to breakage, Dilavar would be the optimal material for the studs as the threads in the case would in no way be unduly strained.

The bottom line is: how do you keep your heads attached to the motor for a long, trouble-free time? I tend to agree with PBH - although not for the aluminum case (and I do have to qualify this: my present knowledge comes from reading, not experience. Quit working on P's professionally 15 yrs ago). Here the likelihood is greater that a properly torqued Dilavar stud will snap rather than a steel pulling the threads out of the case. With a big bore on a mag case, I'd prob tend to go with good Dilavar studs on the hot (lower) side.

Either way, you shouldn't see it as a time-bomb in the back of your 911. Not a steel studs pull threads and not all Dilavar threads snap. You're talking about turning a relatively low risk to a very low-risk.

stevemfr · 03-19-2008, 05:37 AM

BTW, Anderson doesn't go back on his opinion in the new issue of the book - he kinda skirts the issue elegantly :-)

john walker's workshop · 03-19-2008, 05:38 AM

dilivars last longer now because the surface is protected with paint. any old unpainted dilivar needs to be replaced when the engine is torn down. they get a rust band where they are exposed, like in the gap between head and cylinder and cylinder and case. the rust penetrates and the stud snaps. they already lasted quite a long time, mostly, so too chancy to leave them in.

GaryR · GaryR's Garage

Quote:

Originally Posted by john walker's workshop

dilivars last longer now because the surface is protected with paint. any old unpainted dilivar needs to be replaced when the engine is torn down. they get a rust band where they are exposed, like in the gap between head and cylinder and cylinder and case. the rust penetrates and the stud snaps. they already lasted quite a long time, mostly, so too chancy to leave them in.

I agree with John (that's easy to do anyway...

). The picture shows some corrosion starting on the lower studs, I think it would be insane to leave them in with the engine dismantled.

1982911SCTarga · 03-19-2008, 06:02 AM

Quote:

The picture shows some corrosion starting on the lower studs, I think it would be insane to leave them in with the engine dismantled.

That's correct. As John says, there is corrosion on the exposed portions. I'll replace them. I just wasn't expecting to find them at all.

Brian

1982911SCTarga · 03-19-2008, 07:21 AM

Why didn't Porsche use Vibranium for the lower studs? That material works great for Captain America's shield.

Brian

88911coupe · 03-19-2008, 08:26 AM

do anything John says...

Tim Hancock · 03-19-2008, 11:47 AM

Quote:

Originally Posted by 1982911SCTarga

That's correct. As John says, there is corrosion on the exposed portions. I'll replace them. I just wasn't expecting to find them at all.

Brian

FWIW Brian, prior to taking my SC engine apart, I had zero broken Dilivars.....two of them snapped upon removal.

As others said above, replace them.

1982911SCTarga · 03-19-2008, 12:10 PM

Thanks, Tim, I'll approach the removal with caution.

Brian

Tim Hancock · 03-19-2008, 12:42 PM

Quote:

Originally Posted by 1982911SCTarga

Thanks, Tim, I'll approach the removal with caution.

Brian

Brian, I used heat to soften the loctite and remove the studs, but I was trying to make the point that they broke when I was removing the nuts on initial tear down.....

I would have been royally p!ssed if I had decided to re-use those lower studs had they not broken, only to hear a snap during re-assembly. Just to be clear on what I did....I simply replaced the lower dilivar studs with steel ones to match the upper studs (which I did not replace).