chaseing threads

outsider347 · 03-01-2017, 04:22 PM

My 3.0 is apart and in the cleaning process. I took all of the valve covers studs M8x1.25)out and started to chase the threaded bore out with a new plug tap. Really surprised to feel the tap starting to cut threads. Checked to be sure I was using the correct tap...which I was. Chased the 1 bore,

Are the factory stud bores machined slightly "off pitch" so the stud remains affixed in the bore.
Should I be using a different tap???
Have "chaser taps" don't seem to make a difference

Tks Gents
ed

Trackrash · Trackrash's Garage

Most standard taps will give a relatively loose fit of the threads. Not to get too complicated, but there are different classes of fits.

You could grind grooves in an old stud and use it to clean out the threads in the head.

The question is, why do you need to clean the threads for the valve cover studs? If you could remove the old studs why not just install new ones with lock-tite?

outsider347 · 06:12 PM

this is my first Porsche engine rebuild..... Every domestic engine that I have done, chasing the thread bores is SOP

Several of the studs that I removed came out hard...required a lot of working back & forth. None broke thankfully

I understand thread class fit
What is the class of fit for these studs?
Couldn't find any info on metric from my regular suppliers. MSC & McMaster
I guess that I'm not looking at the correct supplier.
Suggestions?
Tks
ed

Trackrash · Trackrash's Garage

Thread chasing tap.

JEGS Thread Chasing Tap Set | JEGS

Here is one I made from a head stud.

kevin930t · 03-01-2017, 06:19 PM

Who would of thought,thats really cool

Sent from my SM-N910T using Tapatalk

DRACO A5OG · DRACO A5OG's Garage

Nice Gordon!

Tippy · 03-02-2017, 04:44 AM

DON'T USE TAPS TO CHASE THREADS!!!

Most standard fare taps will over cut the hole resulting in less thread root.

That's bad for aluminum especially.

Must use a thread chaser.

outsider347 · 03-02-2017, 05:48 AM

Thanks guys
Gordons suggestion looks like a good plan for today
Thread chasers next
ed

KTL · 03-02-2017, 01:26 PM

The grooved bolt is a great trick to clean out the crud from threads and that's all you really need in this case. The threads in the housing should be in really good shape and all you're looking to do is remove the thread locking compound that was used to originally set the studs. Just be sure to use a fine file or something similar to clean your slotted threads before you put the tool to use. Because any little burrs left along the thread cut will booger up the threads in the housing.

As an aside, as long as you have the studs out of your cam housings, not a bad idea to have them surfaced/decked flat at a local machine shop. You'd be surprised how NOT flat the valve cover surfaces are on the cam housings. Same goes for the head sealing surface on bottom of the cam housing. Often you'll find these housings are a bit "twisted" because I don't think the part is all that dimensionally stable.

Here's what the exhaust side of a housing looked like after working it for ~20 minutes across some wet-sand paper on top of a slab of quartz. The gray areas on the gasket surface are the untouched areas. When I first started, the untouched area was huge and pretty much only the edges were being "machined." I've found that the four corners always seem to be the highest.

Walt Fricke · 03-04-2017, 10:10 AM

For routine rebuilds I think it is a bad idea to remove any studs at all. Why? You want the studs to stay put, and removing them isn't going to help with that. It is irritating to have valve cover studs come out hen you are taking the nuts off - just more work all the way around.

Now if you are having machining done, as in truing and shaving a case preparatory to getting the bores back to standard, or doing what Kevin did, then there is a reason. but I don't think it is routine, especially for us home builders, to go to all this extra work. You saw one issue - studs which are well and truly locked into place. With steel studs in aluminum you are asking for trouble. Of course, it can be done, but the various posts have noted how careful you must be about chasing the threads. Were it not for this forum I'd have had no idea a standard tap would cause looseness problems.

And you can fix a loose stud with a case saver insert or the like, but who wants to do that.

Maybe on some other engines - especially ones with bolts instead of studs for many of the joining jobs - there is a special value to removing studs routinely. But not, I think, on our engines - if machine work does not necessitate it. Valve cover gaskets compress for a reason.

Though I am impressed with Kevin's picture. Me, I have things apart often enough that I can live, with some cursing, with a little oil escaping. Less aggravation than the work of R&Ring all those valve cover studs, plus the problems it presents.

But in short why would you want to chase the stud threads? Having things tight down there is a positive virtue. If, in removing a stud, you found the thread coming out wrapped in aluminum, well that hole might be beyond chasing as it is. Head studs might be an exception, as they are often replaced with better ones, so careful chasing might be in order for ease of reinstallation to the proper height, and some thread locking fluid is commonly used.

Tippy · 03-04-2017, 10:27 AM

Agree Walt. There's really isn't a need to remove studs unless you need to true up the surface. As been commonly known, valve covers can be very potato-chipped and still seal.

I believe one chases threads of stud holes to remove thread locker.

Walt Fricke · 03-04-2017, 11:03 AM

Removing old thread locker makes some sense. Though the mechanic who first told me how to assemble these motors told me that the orange Loctite the factory specified for sealing the case halves and the cam carriers would loosen/dissolve when in contact with fresh stuff. Which suited me, as I omit a lot of tedious cleaning off of the old, very thin, layer from the se surfaces and just add new and reassemble. Others have questioned this, seeking to know where in the data sheets the Loctite folks stated this, or what chemicals would do it, etc.

But perhaps new thread locker softens old? Spark plug holes are about the only threaded holes I chase with any frequency. They kind of get gunked up with the anti-seize we are often told not to use but do anyway, having due regard for aluminum threads against steel.

Tippy · 03-04-2017, 11:31 AM

Plugs with nickel plating don't need antiseize.

Walt Fricke · 03-05-2017, 02:38 PM

So are all Bosh and NGK plugs nickel plated these days?

It is hard to teach an old VW guy new tricks.

I've never had a plug burn up, so my supposition is that anti-seize doesn't prevent so much heat transfer as to cause a problem.

Trackrash · Trackrash's Garage

A little anti-seize goes a long way. Nothing worse than having a plug come out hard the whole way.

Let's see. Anti-seize is zinc or copper with some oil? Why would this prevent heat transfer?

I was taught in college that the gasket is what transferred the heat from the plug to the head...

It's funny the way things change. I learned about anti-seize from a Caterpillar mechanic decades ago. Back then nobody at a FLAPS had heard of anti-seize. Now days when you buy plugs they suggest anti-seize.

strictly · 03-07-2017, 12:02 PM

Walt,

some great advice, thanks for the share

Tippy · 03-07-2017, 12:08 PM

Quote:

Originally Posted by Walt Fricke

So are all Bosh and NGK plugs nickel plated these days?

It is hard to teach an old VW guy new tricks.

I've never had a plug burn up, so my supposition is that anti-seize doesn't prevent so much heat transfer as to cause a problem.

I'm not sure. The ones with bright, silvery plating don't require antiseize and will result in over torque.

I believe NGK states this plus all other plug manufacturers.

KTL · 03-07-2017, 01:05 PM

I totally agree there's usually no compelling reason to remove all the studs in the cam housing. If you do remove them, it's not super critical to clean the threads. I don't know what the threadlocker goop is that Porsche used but it's non-hardening and kind of a pain to clean out of the threads. Just run the slotted bolt down in there a few times to clean out the bulk of the goop and call it good. Put a bit of blue loctite on the threads and you're all set. I see no reason at all to use permanent red loctite

Only reason I chose to do the "machining" to some of these cam housings is because they were abused and neglected by people. I tell you what, the cam housing has to be THE most mistreated part in the engine assembly. I've seen some nasty looking housings and i'm no pro who's seen a ton of these engines. I've seen them gouged, blasted, scraped, corroded, RTV'd........ Some pretty sloppy treatment to say the least.

So I figured i'd try to restore them to decent condition by touching up the surfaces on a flat surface. It started out as an exercise in seeing how much work it takes to manually surface the head sealing surfaces. Only reason I did it was because my racecar engine had some sketchy looking cam housings. So instead of reinstalling a leaker I had after a rebuild, I cleaned up a decent housing a local friend gave me. Then I toasted the engine (bearing debris damaged a lot of parts) and I went on a purchasing spree to acquire some decent replacement cam housings. Which ended up being a search to find decent condition cam housings that was harder than I ever would have guessed.......

But anyhow, it takes some work & patience. So you're certainly better off paying the minimal cost to have a machine shop do it if you're only working on the head sealing surfaces.

I totally agree that the valve cover surfaces are not ultra critical. Only do the lower/exhaust valve cover surfaces if you have some really annoying leaks. Between doing the exhaust side of the cam housing and the valve cover itself, you should be assured of being leak free. The upper valve covers rarely leak, even with twisted valve covers and uneven cam housing gasket surfaces.

One place I failed to mention is the camshaft bore gasket surface. I recommend surfacing this location to anybody doing service on the engine that gets into the removal of the cam housing. This location where the camshaft thrust plate seals both the chain box and the cam bore is often a challenge to get the paper gasket seated nicely w/out it getting pinched or a bit off-center. So surfacing this location goes a long way toward helping you avoid a leak right away (pinched gasket) or long term (uneven gasket contact) leak prevention. When i've surfaced this location, it's surprising how not flat it is. The thrust plate is not nearly as bad but it too is worth surfacing as well.

Take that for whatever its worth and sorry for the somewhat off topic tangent

Trackrash · Trackrash's Garage

A little off topic but below is what NGK says about anti-seize.

The issue I have is there is no reference to head material mentioned by NGK. I agree, iron heads probably don't need anit-seize. But aluminum heads? The only down side mentioned is possible over torquing.

From NGKs web page:
5 Things You Should Know About Spark Plugs

1. Anti-seize

NGK spark plugs feature what is known as trivalent plating. This silver-or-chrome colored finish on the threads is designed to provide corrosion resistance against moisture and chemicals. The coating also acts as a release agent during spark plug removal. NGK spark plugs are installed at the factory dry, without the use of anti-seize. NGK tech support has received a number of tech calls from installers who have over-tightened spark plugs because of the use of anti-seize. Anti-seize compound can act as a lubricant altering torque values up to 20 percent, increasing the risk of spark plug thread breakage.

Sorry for the rant. You may now return to the original thread.