Mazda MX-6 Forum banner

1 - 8 of 8 Posts

·
Banned
Joined
·
4,040 Posts
Discussion Starter #1
When you notice your boost gauge is not banging the needle as high as it used to, check under the hood for little sooty marks around the head, plugs, heat shield and rocker cover, usually accompanied by little putt-putt sounds.

If you see 'em, remove your heat shields and retorque the manifold.

However, sometimes that is not possible because of deterioration of the threads in the aluminum head. Threads can be destroyed by careless overtorquing or loosening due to vibration or by (as in my case) by someone having not bolted the turbo to the lower support bracket,

leaving the turbo unsupported except for the manifold studs.
Having that much weight unsupported that far away from the manifold studs (especially if your engine mounts are wheezy) will ultimately shake that manifold loose.

Once the threads are destroyed, you need not chuck the head out -- they can be repaired using helicoils.

This is how I did it.
 
  • Like
Reactions: crusty

·
Banned
Joined
·
4,040 Posts
Discussion Starter #2
Chapter deux

There are two different manufacturers that I know of: Heli-Coil (left) and Perma-Coil (right). Both come in a kit which includes a special tap, an insertion tool and a dozen coils.



The Helicoil insertion tool is plastic and seems not at all sturdy, the PermaCoil tool is steel but needs to be held in a tap wrench to enable it to be turned.
The coils, taps and insertion tools are interchangeable between those two manufacturers. For your exhaust manifold, you'll need M8-1.25 (8 mm diameter, 1.25 mm pitch) kit.

If you decide to go into the head repair business, you can buy extra coils separately, but the insertion tools and taps seem (in my experience) to be readily available only in the kits.
 

·
Banned
Joined
·
4,040 Posts
Discussion Starter #3
how'd i do that?

Some will recommend tapping out the head to 10 mm or to 3/8". While that is cheaper, it necessitates doing some serious clearancing of the bolt holes in the manifold. Different rates of expansion and different coefficients of thermal expansion mean you need a bunch of clearance around the manifold studs.

When you start removing material from exhaust manifold, you are compromising it's rigidity and ability to clamp and seal exhaust pressure. So I did it the right way, rather than the cheap way.


helicoils are coils of diamond-shaped wire



with a tang on one end used to insert in a specially threaded hole.
To use them, you must remove your exhaust manifold and turbo. I'm certain there is a how-to explaining that stuff. Even if there isn't, it's not all that tough.
 

·
Banned
Joined
·
4,040 Posts
Discussion Starter #4
That's not a stud and nut on the left, that's a bolt with the head broken off from the exhaust manifold on my engine.



I guess a previous tech/hack used bolts. I suspect a Mazda dealer, cuz the bolts had 12 mm heads, whereas most retail ones (and most hondas) use 13 mm heads on their 8 mm bolts. I purchased all new bolts and subsequently was told by 'Swat that Mazda originally built it using studs. Oh well. I was gonna build a new head anyway -- I'll put studs in that one (and this one when it comes off).
Sorry for the poor picture quality -- I was primarily using my Palm camera and it don't do a real great job in low light.


The bottom of the turbo was leaking oil from the oil return tube


so I fixed that with new gasket


upper cooling hose 2nd from left hardened and cracked (red arrow) and kinked (green arrow)



Previous repair used vacuum hose and omitted protective hose, causing roasted, brittle cooling hose.
While the turbo is off, it's a good time to check axial and radial play of the shaft.



All zeros for this guy. Amazing how good that dino stuff works when you change it once in a while.
 

·
Banned
Joined
·
4,040 Posts
Discussion Starter #5
drill & tap

For an M8-1.25 helicoil, you need to drill a 21/64" hole where the previous tapped hole was. Note that the drill is not included in either kit. To ensure I didn't drill too deep, I measured the depth of the existing tapped hole and transferred the depth to my drill bit, using a little teflon tape.



Use masking tape if you want, I just had the teflon tape around from doing some plumbing for my compressor.
Use a 6" combination square to ensure you're drilling straight into the old tapped hole (see photo below for alignment of tap). If you've got one of those drills with the bubble on the back to help you drill a horizontal hole, ignore the bubble. The engine is slanted back a few degrees, so a horizontal hole would be a bad idea.


Mark the tap at a point where there are sufficient full threads to allow the coil to be fully inserted.



Mount the tap in a tap handle -- trying to turn a tap with wrenches or pliers is idiocy.


start tap and check using a small combination square that it is perpendicular to the gasket surface (perpendicular in both directions)


once tap is straight and true, turn it clockwise one turn and then counterclockwise one half turn (to break chips). Repeat the back-and-forth until the tape marker is flush with the head surface.


After drilling and after tapping, give the hole a good squirt of compressed air. Cleanliness is next to boostliness!



Note the wadded paper towels jammed in the exhaust ports to keep the chips out of the ports. That orange thing in the right centre of the picture, for the benefit of our SoCal friends, is called a block heater.:D
 
  • Like
Reactions: el norm

·
Banned
Joined
·
4,040 Posts
Discussion Starter #6
insert coil, break & remove tang

Thread a helicoil onto the insertion tool (PermaCoil tool shown) until the tang on the helicoil contacts the spur on the end of the tool.


Then thread the coil into the tapped hole using the insertion tool (Helicoil tool shown)



Note how dirty the upper half of the manifold mating surface is from the leakage of exhaust past the gaskets due to tired threads being unable to clamp the manifold tight.

Once the helicoil is threaded into the tapped hole (at least 3/4 of a turn below flush) and the insertion tool removed, you must break off the tang. Some people recommend just cranking the insertion tool until it breaks, and helicoil says use a flat-nosed drift just slightly smaller than the coil I.D. but I prefer using a little screwdriver blade with a narrow slot ground into it.




I just slide it into the coil and when I feel it straddle the tang, twist it back and forth until the tang breaks off. On larger sizes, needlenose pliers can be used to break off the tank, but they need to be pretty small for an 8 mm coil. Don't forget to give the threaded hole another little blow job to get rid of the tang.
 
  • Like
Reactions: pjayb

·
Banned
Joined
·
4,040 Posts
Discussion Starter #7
New hoses mounted on the turbo ready for re-installation.



Note the outer protective hose that shields the upper coolant hose from the heat of the manifold (outlined in green). This is important.

Now replace your manifold, torque to spec, connect hoses and wires, reinstall rad and boost!
 
1 - 8 of 8 Posts
Top