Minimum intake manifold stud thread engagement question

[JFairman]

When installing CIS aluminum injector blocks with phenolic plastic heat insulators and extra gaskets needed the top of the 930 pancake intake manifold ends up about 10mm higher.

Is it OK to just thread the original intake manifold studs in about 9-10 mm less to keep sufficiant thread engagement for the manifold nuts?
Would there be enough thread engagement of those studs in the cylinder heads to still torque the intake manifold nuts on the studs to 18 foot pounds without ripping the threads out of the heads?
Or is standard procedure to buy approximately 10-12mm longer intake manifold studs?
If you need longer studs where do you get them?

Also, I'm guessing eliminating the 3 intake manifold gaskets needed to include the heat insulators would give you some stud length back and then using a sealant like hondabond 4 with no gaskets seems like it might work if the surfaces are flat and clean?

Lastly, not using the heat insulators at all would keep the same total thickness and hight as the stock injector blocks so thread engagement would be the same. I think I read going without the heat insulators when using aluminum injector blocks will transfer and heat soak the CIS injectors too much and vaporize the fuel in them after shut down or while driving, is this true? would it cause misfiring on hot startup and while driving?

thanks in advance for any answers...

[pete3799]

Just a heads up......my exhaust studs ( installed by the PO) were only threaded into the head 3/8 of an inch and two of them pulled the treads out of the head. Same 18 foot pound torque.

[jwasbury]

what aluminum injector blocks are you using? I bought a set from Turbokraft when I was doing my engine build. They came with heat insulators, but the stack height with the insulators was the same as the factory plastic blocks. I used OE gaskets only on the top and bottom of the stack, used a light coating of Loctite 574 between the aluminum block and the plastic heat insulator.

[philip j]

Get a length of threaded rod, and cut your own to desired length. If you have trouble finding metric ready rod, I could send you a piece. Philip

[JFairman]

I don't know who made them, there's no markings on them. They look a lot like the TK injector block casting but not exactly the same. They had a rough sand cast finish on the outside of them when I got them but I sanded them smooth and polished them shiny when i got them so they look really good.

They have 40mm holes and I've already ported the heads and intake manifold to match them. I bought them for around $250 used here on the forum around 6 years ago.

They are the same thickness top to bottom as the stock plastic 930 injector blocks but then when you add the 6.35mm plastic heat insulators I have and one of the approximately 2mm thick gaskets that came with them between the head and block it goes up to about 8.3 mm before installation.

I'd like to use one of those gaskets between the block and insulator and then it becomes about 10mm added on. These gaskets will squish down a little and how much is unknown until I do it.
I could probably just use the creamy consistancy hondabond 4 sealant I have between the insulator and the block with no gasket and then it would only be about 8 mm after installing them and squishing down the gasket in the process.
That'll probably work fine.

[TurboKraft]

Pic of aluminum block?

[JFairman]

Here's pic of an original plastic injector block and one of the aluminum 40mm ones I have side by side. You can see they are the same hight top to bottom.
Then a pic with one gasket and an insulator block under the aluminum one to show the hight increase and a pic of the gaskets and insulator blocks I plan to use if they work out.

[TurboKraft]

To the original question: Minimum intake manifold stud thread engagement question
As a rule of thumb, minimum safe depth is Diameter x 1.5.
An M8 fastener should thread in 12mm deep.

[TurboKraft]

Seeing that photo, I'd machine material off the bottom of the block.

The insulator's outer profile should allow it to drop through the fan shroud and sit atop the head gasket
Then the block sits atop it and the fan shroud, like the stock plastic block does.

You may have to cut a small notch in the insulator's bore, that's it.

[JFairman]

FWIW, I just snapped some more pics.

[TurboKraft]

Yes, I think machining off the base, notch the insulator:

[zcoker]

Hey Jim,

I used the aluminum injector blocks with just gaskets and everything is fine, no starting or heat soak issues, everything normal as can be. Studs had enough thread top and bottom like factory. Hope this helps.

[proffighter]

Using an insulator is highly recommended in my eyes. I shaved the bottom of my injector blocks for the amount of the insulators to get same height at the end

[T77911S]

Originally Posted by zcoker

Hey Jim,

I used the aluminum injector blocks with just gaskets and everything is fine, no starting or heat soak issues, everything normal as can be. Studs had enough thread top and bottom like factory. Hope this helps.

my mechanic friend said that is the way his are.


i would leave the studs threaded all the way in. mine are threaded to the top of the last thread on the studs. you dont want to pull a stud.