Hey Tom Nelson! Thoughts on cyl head sealing?

[rwhite692]

I read with interest the article about the 406 TT Small Block built by Tom Nelson ("F-Bomb") in the current Hot Rod.

Firstly, thanks and kudos to Tom, for openly discussing many of his build methods and philosophies in this article. Great stuff. Can't wait to see that engine in the car!

My question relates to cylinder head sealing methods.

It is obvious that, out of pure necessity, Tom has developed a very stout process for head-to-block sealing (as explained in the article, he is machining the deck and the head with grooves for ss wire sealing rings, and then utilizing an SCE Cu gasket, and sealant).

Given that Tom is attaining some phenomenal boost levels (nearly 30psi!!), the question is, for a home builder such as myself with a relatively mild TT setup, is a sealing method such as this necessary?

If one was to use the "next best" method, not requiring block/head machining(such as multilayered steel gaskets?), then, what method would be best, for an application where boost levels will not exceed about 14psi?

I am certainly willing to spend the additional $ for the additional machine work to ring the block, but, if this is pure overkill for my application, then I would like to just use a method which is well-suited to my (again, relatively mild) application.

Rob

[Blown353]

Very good luck with MLS gaskets here but your block and heads will need to have a very smooth surface finish, 32 RA or less for Cometics (the Fel Pros have a thicker coating and additional sealing beads around the coolant ports and will tolerate up to 55 RA or so they say.) Any halfway decent machine shop with equipment in good shape and a guy who knows what he is doing should have no difficulty achieving a finish that meets the criteria. After some tweaking at my friends shop we are getting surface finishes averaging in the 16 RA range using his Berco surfacer using a single point cutting head with a PCD insert.

I was previously running the Fel Pro "performance" gaskets with the pre-flattened SS fire rings and had no problems with them at 15psi but went to Fel Pro MLS gaskets this time around for some peace of mind. Also, the metal gaskets (copper and MLS) are more efficient at heat transfer between the head and the block and will help dissipate hot spots better than a standard composite gasket.

The other nice thing about MLS gaskets is being spring steel they have some give and when the head lifts a bit from excess cylinder pressure (i.e. detonation) they will resist blowing out.

[TOM NELSON]

if you don't want to run the o-ring receiver groove than my next step would be a cometic.I haven't tried the fel-pro, but would exspect good things from them.I've run the cometics at 1500+ hp levels and as long as the tune up is there you'll most likely get away with it.Caution if your carburated it's not going to work.I surface both my block and heads with a storm vulcan block master the ra is not that smooth what i've noticed is for the first couple of minutes of run time the gasket will seep very small amount of water once hot it will seal up and not give you anymore problems.So i would run cometic.Also remember if you go with a o-ring receiver groove and your tune up is not there neither will your piston be there so there is something to be said about that gasket being the fuse.Hope this helps

[rwhite692]

Hey Thanks Tom and Blown353 very much for the inputs. (my setup will definately be EFI, most likely using a BS3)

Tom you had said:

"...Also remember if you go with a o-ring receiver groove and your tune up is not there neither will your piston be there so there is something to be said about that gasket being the fuse..."

I'm guessing what you mean is that the "gasket-only" approach is "safer", in that the gasket will simply let go under these (bad tune) conditions, whereas if I have an o-ringed block, if I have a bad tune (ignition timing is way off, and/or I have detonation, etc) that the cylinder pressures can spike and damage the piston, etc., since the head seal won't let go?

A couple more questions:

If I were to just run cometic gaskets, is there any need for additional sealant on the mating surfaces (ie Permatex) (I would tend to think of the permatex as providing some compensation factor for surface roughness / extra insurance, no?)

Is any kind of specialized torque-down method needed for the cometic gaskets (such as the torque/hot air preheat/retorque sequence as shown in the article, for the o-ringed block and heads?)

Thanks again,
Rob

[Blown353]

No sealers required (or wanted) for any of the MLS gaskets except a little dab up at the thin corners near where the head gaskets poke into the valley but your block and deck need to meet the surface finish and flatness requirements if you want them to seal and not leak.

I have a set of Cometics sitting on the shelf in my garage because a couple spots on my block around a couple of the coolant passages were up around 40-42 RA; I decided to try the Fel Pro #1142 MLS gaskets instead and they work flawlessly. I actually prefer them a bit to the cometics because of the additional sealing beads of viton around the coolant passages make them a little bit more forgiving.

I have heard of guys with "questionable" surface finishes spraying MLS gaslets with aluminum or copper gasket maker or spray hylomar prior to installing and getting away with it but I would not recommend it, increased chance of a problem down the road. When installed properly they're pretty much bulletproof and a "install it and forget it" item.

No special torque down procedure needed for MLS gaskets but like with any performance engine you should have the block torqueplate honed using the same headgasket and fastener type (bolt or studs) you intend to run when you actually assemble the engine to simulate the actual in-service bore distortion.

[ProStreet R/T]

rwhite- What kind of power are you looking to make? And with what block/head combo?

In all honestly I would try to avoid using an O-ring setup on a car that sees primarilly street duty. And for the exact reason Tom stated, if something goes wrong it's going to take out the whole motor rather than just a head gasket.

Studs with an MLS gasket will hold 1khp so it shouldn't be a big problem for 95% of the cars out there. If you are using an 18 bolt head it's even stronger.

Not exactly the same, but I used regular ole copper gaskets (no o-rings) with arp studs and put 1380 to the wheels with no problems at all. This was in a 506ci V10 at 16psi and a pretty safe tune though, so cylinder pressures were probably less than on Toms 406.

[nitrorocket]

I am running 18 psi with MLS gaskets at the 1000 hp level and have had good luck. Just install them dry and torque them properly. Come back the next day and retorque, they will tighten a little more.

[Blown353]

Originally Posted by nitrorocket

Come back the next day and retorque, they will tighten a little more.

Good practice with any headgasket. What I usually do is after they sit a few hours come back and then in order back off the bolt about 1/4 turn and then retorque. I like to repeat this excersize about 5 times with a few hours "set time" between each cycle. Obvious issue to watch for is you need to use a non-hardening thread sealer otherwise you risk the chance of disturbing the seal.

In my experience MLS gaskets don't take a heat-set, so there is no need to retorque after the first heat cycle, but doing so is a very good idea with standard composition gaskets. If I were using new heads I would still retorque MLS gaskets as the aluminum will probably stress-relieve and move a little bit after the first couple heat cycles.

[TOM NELSON]

put them on dry re torquing i think is always a good idea we do three retq's on everymotor before it's run.I haven't used the heating deal on the cometics.it's very important that the head is straight there are some surfacing broach's that actually bend the head when it's clamped than cut it.I usually check this by putting a dial indicator on the mill head. clamp the head to the table and run it from front to back.Make sure that the mill is running true before this is done.But you might be really suprised at what you find i've seen a freshly surfaced head have as much as .006 dip in it.

[rwhite692]

Thanks to all for the info. It looks like I will be fine without o-ringing the block.

Originally Posted by ProStreet R/T

rwhite- What kind of power are you looking to make? And with what block/head combo?....

I would be quite happy to achieve 850 or so HP at around 13-14PSI on 91-octane.

And maybe, someday, work up the tune to 1,000HP

This is a motown block built as a 6" rod 406, with Brodix 11X cnc'd heads (227cc).