CrossfireTechSeriesIndex.htm

Install tips for Crossfire Manifolds

Gaskets:

I suggest FelPro brand gaskets because the block off is built into the side gaskets and the lid gasket has a nice elastomer bead in the center.

Do NOT use standard small block Chevy gaskets with the rear water ports open. They must be blocked of except for a small bleed hole, otherwise the water will simply run up the big water jacket under the crossfire manifold instead of thru the heads like it is supposed to. Crossfire heads get a bad rap as being 'prone to cracking', but I suspect the real story is people 'prone to using the wrong gaskets’, which will severely overhead the heads.

Do NOT use RTV everywhere. RTV is Room Temperature Vulcanizing (curing) synthetic rubber (silicone) . . . very good stuff for some applications. Use it on the ends of the manifold as instructed by the gasket manufacturer. I’m old school in a lot of things, but I find RTV is preferable to the old style rubber or cork end gaskets, but RTV is unforgiving of certain mistakes in its use.

NOTE: Head gaskets differ in thickness and rebuilt heads and blocks may have been re-surfaced. These things change the gap between the intake and the block at the front and rear sealing surfaces. It’s a good idea to set the manifold on the engine with the side gaskets in place just to test the fit and see what the gap is at the ends. With an idea of how big the gap is, you are in a good position to judge how big of an RTV bead to run around the ends. I’ve seen instructions that say as little as 1/16” . . . I would not try that! A ¼” to a max of 3/8” round bead seems about right. Just make sure it is slightly larger than the gap or you will have oil running down the bell housing.

Important: Clean the sealing surfaces with brake cleaner or lacquer thinner or acetone or Jack Daniels to get the oil off. RTV no sticky to oil.

You can use a little RTV around the water ports (on the metal, not on the gasket), but only if there is significant corrosion there that you feel may not seal with the dry gasket, or if the gasket manufacturer specifically instructs to use extra RTV sealant around the water ports. Modern gaskets like Felpro already have special sealant on the surface, often it is a ‘non-stick’ coating to keep the gaskets from welding themselves to the heads. Adding RTV to these can do more harm than good. Also keep in mind that when using RTV you need to assemble the parts within 5 minutes or so, so definitely do not spread it on a gasket and then set it to ‘dry’.

RTV is great for some applications, but for ‘helping’ a gasket to seal severe problem areas like around corroded water ports, I prefer a THIN layer of ‘sealant’ type material like Permatex non-hardening or their spray gasket adhesive if the sealing surfaces are in reasonable shape.

Simple gasket tip:

Don’t just spray gook all over your gaskets because Uncle Fred has been doing it that way for 100 years. Most quality modern gaskets are already coated, so install them dry unless you have some compelling reason not to.

Do NOT use Teflon tape on the Coolant temp sensor if you are using a stock one-wire sensor. That sensor grounds to the manifold and by using tape, you are possibly preventing the ground and the sensor will not work. Better yet, buy a new style two-wire sensor, which do not need a ground to the manifold. NAPA has the best sensor/pigtail combo.

Better yet, do not use Teflon tape at all, unless you are working on the kitchen sink. Also do not use RTV to seal the CTS. Do not use anti-seize (except on hot steel parts . . spark plugs, O2 sensor, etc) . . . but do make sure your new CTS is brass and not steel.

Simple thread sealant tip:

Use loctite white hi temp liquid pipe sealant on the CTS and all other treaded sensors (except O2) or threaded seals on the car, including head bolts.

Torque Tips:

There is no factory pattern or comprehensive or reliable torque spec that I ever found for the Crossfire lid. The factory manual has a torque spec shown for a couple of random bolts, but the high number is only appropriate for the two 3/8” bolts (in my opinion) and not for the smaller 5/16” bolts. The manual also has conflicting torque spec in the TB section (one TB bolt is also a cover bolt).

34 ft lbs is way too much for a 5/16” bolt in cast aluminum and the modern gaskets with the elastomer bead do not need or want this kind of crush anyway. My experience on actual Crossfire manifolds (and I’ve fooled with many) is that before you ever hit 34 ft lbs, the threads are coming out the hole.

My theory is that it is a misprint in the manual and the spec is for the manifold-to-head bolts (3/8” in cast iron, which is listed as a reasonable 30lbs in the chart on page 6A4-26) but was printed on picture of the lid instead of the manifold.

So my recommendation is based on engineering data for a 5/16” UNC bolt in cast aluminum.

First, a tiny discussion . . . why torque at all?

This demonstrated the essence of torquing parts together; place the heel of your hand on your desk with the fingers raised. Now roll your hand back down flat in the motion of a rocking chair.

Now put your hand down again with the fingers arched and the heel and finger tips touching the desk. Now press your hand down flat while keeping the fingertips on the surface.

You want the action of rolling one part onto the other, usually starting in the middle of the part, both to even out and reduce the stresses and to prevent damaging the gasket.

To investigate, put your Crossfire lid on the manifold with no gasket. Most of the lids have a warp to them and will be touching in two places and raised up elsewhere. You want to start torquing at the place where the top plate is touching and work out to the areas where it is not.

In my experience most are warped starting from the centerline of the car and curving upward toward the edges, so that's how you want to torque them down. Start with the centermost bolts front and rear and work your way out. When you get to the outer edge, do the middle bolts first and work from there to the corners.

Torque should be 15 to 18 lbs - no more. Do it in two passes 5ft-lbs (or just a little snug) and then final torque. It is best to use an in-lb torque wrench if you have one (216 in-lbs final), as ft-lb torque wrenches are not particularly accurate at these minimal settings. Overtorquing crushes the gasket and will cause leaks. Pay attention to the ‘feel’. The bolts should get progressively tighter up to the set torque. If the bolt is not getting tighter, but continues to turn, you are pulling the threads out of the hole. Stop, remove the bolt and get a longer one, or better yet, do the following tip before you start:

Preparation Tip

Crossfires are old beasts and a lot of stuff happens over the years, like people putting the wrong bolts in the wrong places, etc. Don’t assume that any bolt on the car is the correct one that came off the assembly line. I highly recommend buying an inexpensive hardware store tap (5/16” UNC) bottoming style and run it into each hole (if your manifold came from me, this has already been done for you). Two of the holes are 3/8”, but they rarely cause trouble. Pay attention to how deep the tap goes and make sure that the bolts you are using are long enough to reach nearly (say within ¼”) to the bottom (including the lid and gasket). Then run the bolts into the holes as far as they will go (by hand) and measure from the gasket surface to the underside of the bolt head. This must be LESS than the thickness of the top plate plus the gasket by at least say 1/8” or you risk bottoming out the bolt with no clamping force applied to the lid.

This seems like a lot of detail to go thru, but ultimately, this procedure is easier and less time consuming than fixing stripped threads or tracking down another infamous Crossfire leak.

For the manifold-to-head, just follow the factory pattern and spec, which is generally the same for all manifolds;

Put a drop of oil on the bolt threads (the bolts I included are for the inside of the plenum and already have enough oil on them.)

Torque the manifold to the heads with 30 - 35 lbs in a circular pattern starting from the middle.

Get the bolts all run down first, then go around and snug them a little. Pay special attention at this point because if you run down the bolts on one side with the other side loose, the manifold will rack over. Observe that it is sitting in a ‘V’. If you don’t get the manifold settled in nice and straight, you have a very good chance of leaks and a fair chance of cracking the manifold when you torque it (or later due to thermal cycling).

Once you have the manifold settled in and all of the bolts run down snug (‘snug’ is turning a ratchet with one hand from the center in the fashion of a screwdriver), then start torquing. First torque all to 15, then go back and torque final.

Once you get the manifold on you may find initial timing tips helpful. Look here:

http://www.thecubestudio.com/CrossfireTechTipsForSettingInitialTiming.htm

- Steve Simpson

If you find errors or have suggestions on how to improve these install tips, please let me know:

steve@thecubestudio.com