How to prep case threads for head studs?

[cowtown]

Just got my 24 new factory steel head studs from PP in the mail, and have been getting ready to put them in.

Now I'm wondering: what's the best thing to do about cleaning up the threads in the case? Should I chase them with a tap, just scrape them a btt, or not worrry about them?

Various threads recommend a "chasing" tap, no tap, and just compressed air, but I don't see any conclusions.

Thanks!

[yelcab1]

I chased mine, blew it off with compressed air, and then inserted the factory studs (which come with their own glue compound on the threads), and they stuck since.

It was explained to me later that an aluminum case such as a Porsche is probably drilled with a special rolled thread tap so that there is better grip holding on to the threads of the studs. If this is the case, you do not chase the threads with your regular Sears tap/die set. You just stick a brush down there, brush it off good, and blow it out. It is much harder to install the studs because the threads are not as clean.

However, mine has stuck since the rebuild, and no leaks or problems. I would think chasing it with a tap is probably a small price to pay, especially knowing that the factory studs come with their own Loctite compounds already on the studs. That stuff will lock the studs in really good and tight, chased or not.

[biggtbiggt]

I have a 1975 2.7 with the magnesium cases! All the head studs have been helicoiled. When I pulled the engine apart one bank of head nuts were loose. I was concerned that they had pulled from the case but they do not look pulled. the studs were loose in the helicoils so I tightened them up. They all seemed to tighten very good but I did not use loctight or any threadlock on them. Should I use something to hold them? I thought once they were torqued they would be fine!
thanks...Tracy

[Targa Dude]

Are you sure you installed Helicoils???and not Timeserts or Casesavers? I would be very worried if your relying on those Helicoils to hold the stress of that Mag 2.7
You should use Red Loctite and when installing them you don't torque them. For the reason being that when properly installed the Studs have to all be the same height. Hmmmmm


Jorge (Targa Dude)

[john walker's workshop]

definitely chase the threads to clean out any old loctite, then blow out with air.
the reason 2.7 engines loosen their heads after a "rebuild", is because all the seating surfaces are not on the same plane. the cylinder bases on the case must be machined to the same plane as the crank centerline, because the center one is generally low, the cylinder tops must be true, not worn down and beaten on, from running with loose heads, then reused, and the heads must be flycut so they mate evenly to the cylinders. properly done, they stay tight.

[cowtown]

Thanks everyone

JW and everyone: I'm (obviously) kind of new at this, and the tap I have is new and sharp. When I started chasing one hole, it started removing a bit of metal (!) within one turn. I backed off... what's wrong here?

I'm sure the pitch and size are correct. Are there different edges to taps? Are there types of taps?

I'm not trying that again until I get guidance from the higher powers. It's not supposed to remove ANY metal, right?

Thanks!
Colin

[Superman]

I'm confused about the what kind of case you're putting studs into, but I can report my experiences with the aluminum case. I used a regular Sears tap (GASP!) to chase the threads and I did not see any metal to speak of. The tap went in pretty smoothly. There was not a lot of drag there and no metal or very little.

Studs go in with red loctite, to a specific height. The factory studs I used from the dealership were not coated.

The fat washer gets coated with Optimoly (I just call 'em as I see 'em, from the Spec Book). This may be important, to get the proper torque when you install the heads.

[Zeke]

Colin, there are taps and there are thread chasers. From what I can, tell, the chasers are harder to find. They are not supposed to remove any metal. Try a machist's supply. I'm sure Snap On has them. I would also look at Napa.

[biggtbiggt]

Thanks for the info. I have looked at the time-serts web. I definately have helicoils installed. I have just purchased this car and took the engine apart to fix the leaks as some idiot put it together with blue silicone!! When I tightened the head studs with a pair of vice grips they all tightened to about the same height within about 2 mm. and I feel that they are tight at this point. Will the helicoils not hold at the proper torque? If not do you think time-serts will still be able to be installed or is the hole going to be too large allready?

any help would be appreciated!

Thanks...Tracy

[Wayne 962]

"When I tightened the head studs with a pair of vice grips..."

Noooo!!! No vice-grips, and no on the bottoming out of the studs in the hole! They need to be 135mm above the top mating surface.

See here, you need this: http://www.101projects.com/rebuild.htm

-Wayne

[dtw]

Tracy,
You've got to rethink a few things here, but don't sweat too much, you're still in a good position.

1. Helicoils gotta go. Period. Wayne would say replace with case savers, I'd say you can get away with time-serts. I'm a newbie, he's chummy with Walt at CE. Still, lots of wrenches have great luck with time-serts. The helicoils are a less robust insert than the time serts and case savers. I just had some non-critical holes re-worked from old helicoils to time serts, there were no hole sizing problems at all. Let a machine shop handle the procedure. This will cost you $175-300 depending on the shop. This is not an optional step!!!

2. Inspect your studs for any damage caused by the vicegrips. Replace as necessary, replace any dilavar studs with new steel ones anyway. Magnets will not stick to the dilavar, that's your telltale.

3. Check out proper installation procedure for the head studs- this is one of the most critical procedures in the assembly. Without studs at proper height, you have no chance of getting the heads torqued down correctly.

[Jim Sims]

Sears sells thread repair/chasing sets; they contain both the metric and English size tools. Jim

[cowtown]

Thanks everyone! The board comes through again. I'll get a "chasing" tap from Sears/Snapon/Napa.

BTW, it is the aluminum 3.0 930 case in my sig I'm working on...the 2.7 discussion about timecerts is someone else.

Thanks,
Colin

[rcwaldo]

AASE Bros' time certed my case for about $60... They do great work and very reasonable IMHO

Chris

[biggtbiggt]

Thanks Wayne for the info! I ordered that book last week and am waiting for it and a large order that I placed to arrive. I am just getting more scared as I am learning more. I originally took this engine apart to replace the silicone that was used on the oil return tubes and install the one piece tubes. I was planning on just cleaning up the pieces and installing new gaskets and replacing parts as needed! Now I have ordered bearings rings and other parts and now I see that I should replace my helicoils with case-savers. I am starting to lose interest as the more I read about this engine the more I think I should have looked for a different power plant! As I live in a remote part of Saskatchewan Canada it is hard to find a machine shop that has ever installed case-savers.

[David]

I notice people mentioning factory studs, is there any real concern about going back with factory studs on a street car. I'm asking since the Raceware studs are about twice as expensive.

Also, has anyone tried putting in timecert (or case savers) with the cases still bolted together? Of course I'm assuming the bore holes are taped over.

[Superman]

My engine now has 24 factory steel head studs. If I were to increase horsepower by seventy, I would leave those studs in there. If I were to turbocharge the engine for 200 additional horsepower, I would probably.....probably....change head studs.

The head stud threaded holes do not go through the case. I would feel okay about carefully drilling and tapping a case that is not split. Emphasis on carefully.

biggt, I'd split the case and send the halves out, if I were rebuilding your engine. I'd have the case savers or time certs put in, have it align bored, and have the deck height machined.

[rcwaldo]

biggt, I would definately split the case since it is mag. I say this because seven of the internal studs in mag cases have a tendancy to 'pull' especially the one near the 7th main bearing. I think its the 108mm one.

Chris

[john walker's workshop]

biggt, just bite the bullet and ship the cases to competition engineering in california, and let them align hone it, cut the cylinder bases and timesert all the studs. then your worries are over. 2.7s can be a good engine, but they have to be done right. might as well send them the heads too, for a flycut, and pro valve grind. then use wayne's book for assembly.

[Doug Zielke]

Originally posted by john walker's workshop
biggt, just bite the bullet and ship the cases to competition engineering in california......

Good advice as usual from JW.
If you go to: http://www.competitioneng.com/Welcome.htm
you'll find CE's price list for just about everything they do.