Rebuilding AHU - any tips for power or longevity?

[jtanguay]

I've heard that the ARP studs should be avoided on TDI's because the head lifts according to people on tdiclub.com

Stock studs work great. One dude's running stock studs and 258 bhp without any problems.

well if the heads lift, wouldn't that give a good hg leak?

Well that's why he should avoid them...

I have no personal experince of the studs on TDI engines, but that's what I've read on tdiclub.com. The stock ones seem to work well to so there's no idea changing them.

i don't get it... if the head is lifting, then there would be a hg leak.  if the head doesn't lift, then no hg leak right?  with the studs there would be no hg leak since the head wouldn't lift?

now if you're talking about some distortion (allowing the head to flex, etc but holding the pressures) and that the studs do not allow this distortion which could lead to head cracking, then that sort of makes sense.

[MikkiJayne]

I read a thread on here or TDIclub where a bunch of people running ARP studs were reporting improved mpg and were very pleased with them. The installation procedure is quite different for the studs compared to stock bolts - maybe people aren't torquing the studs properly?

I like the idea of reusable studs since I will be tinkering with this engine a lot when I get in to it. I also don't fancy paying stealership prices for bolts every time I take it apart! Two sets of bolts is more than one set of ARP studs  :shock:

Mikki x

[RabbitGTDguy]

I've heard that the ARP studs should be avoided on TDI's because the head lifts according to people on tdiclub.com

I'd be interested in reading that and also seeing how those people went through the installation procedure for the studs as well. Studs have been tested by time (not to mention the advances in metalugy and fastener technology) and are significantly better than stock. Studs actually by design would elmiinate head lift and prevent HG failure...especially under modified levels (such as more fuel, boost, etc.). Stock will do the opposite, as they are designed to stretch

Stock studs work great. One dude's running stock studs and 258 bhp without any problems.

Stock TDI motors...not a one that I can think of have "studs" as mentioned here. Stock TDI motors run head bolts...not studs. I might have to venture over to TDIclub and search out information on the above. Its weird...every motor that I have had with stock factory "stretch" bolts has eaten a headgasket...every time since I've had that happen (believe it was twice), I always build with studs now and have NEVER had a headgasket go.

Joe

[jtanguay]

good to hear some positives about studs... starting to make me question my decision of using studs  

[Bojje]

good to hear some positives about studs... starting to make me question my decision of using studs  

Well i guess the other ones are right, I'm probably wrong. I've mixed up something I think.

[Bojje]

"There was a discussion about head bolts (e.g. ARP, Raceware) at tdiclub.com and a handful of owners saw headgasket leaks after only tens of thousand KMs or miles. And many of these TDIs are not big-power ones either. It could be that they neglected to inspect & re-tighten the head bolts after every xxx km, but some of them are quite experienced TDI mechanics."

[MikkiJayne]

Mm I saw that too. Interesting that the two forums have completely differing opinions on this.

[RabbitGTDguy]

very interesting...

I can cite several good reference sources stating how much better studs are vs. bolts at "keeping things together" and preventing the "lift" that these TDIClub members are citing.

Once ref. I can think of off the top of my head...and I believe a pretty close to direct quote...lol...Corky Bells book on building/design of turbocharged system entitled "Maximum Boost".

"Studs are a engineers choice, bolts are an accountants..."

Or something very close to along those lines. Just count the number of people that have gone farther away from even just head bolts and installed not only head studs...but also studs for mains as well.
As much as their may be some "negative" opinions on TDIClub regarding studs...I can gurantee you that a good number of the people that I know on this and the other side of the pond...every one is using studs...and some have even gone the next step attacking the bottom end hardware (though...more so than head studs...there are some REALLY horrible stories about the use of aftermarket *ARP* and similar rod hardware in both the gasser and diesel world).

I'll stand by what I say...
my 1.6 IDI TD formerly in the GTD...very nicely built...well fueled, some may remember the homemade propane injection (boost sensitive).... NEVER replaced a head gasket with studs installed...

I had two head gaskets on plain old NA motors go with stock hardware... both were 12mm heads (12mm head either IDI or TDI use the same size head bolts). Thats no boost...mildly tweaked fueling on one...nothing but stock on the other.

Same goes on the mTDI now ...no issues.

Importance moves to making sure they are installed correctly and "retorqued" as per the instructions...
Of course one huge nice thing as well on TDI's is the use of the metal headgasket vs. the fiber headgasket on the 1.6's...though many choose the route of the 1.9 AAZ metal gasket to solve that problem as well.

I'll have to look around on TDIClub and see these comments... haven't visited much lately as there hasn't been much interesting going on there (waiting anxiously for the intake manifold shoot-out between PP's manifold, Kerma's (long or short...still to be decided?), and the stock PD and ALH manifolds)...

Joe

[RabbitGTDguy]

Just to update...

The particular thread "to head stud or not to head stud" over at TDIclub  at http://forums.tdiclub.com/showthread.php?t=194804 doesn't discuss how "head studs" cause gasket failure or "head lift"...

Rather...it suggests that it may be better to leave stock bolts in to PREVENT rod failure by ALLOWING head lift... i.e. the head gasket will go and save the rods. Supposedly, the lesser of 2 evils...

I could go on with that for a while...but I have class this morning, need to do some reading...

Joe