Cometic Head Gaskets $139.99

[SappySE107]

Please start a new thread.

[boscov6]

OEM GM graphite. At least to my knowledge...

FelPro does have some HD version out there, but I cant speak for their reliability... and I do not know if they fit a 3500. BUT in the end a 3400 head gasket should fit a 3500 fine since the 3500 MLS ones had a slightly smaller bore than a OEM GM 3400 gasket. IIRC Eric Brennan is using a set of GM 3400 graphite's on his 3500 motor.

My motor is a bored 0.030 3400 with a 3500 top so I really need 3500 gaskets that will take boost at 10 pounds. I think you are helping me with the stud issue as well. I have spent a shit load on the bottom and I really dont want the top to take a ride either. Whats your opinion on this gasket choice?

[3400-95-Modified]

OEM GM graphite. At least to my knowledge...

FelPro does have some HD version out there, but I cant speak for their reliability... and I do not know if they fit a 3500. BUT in the end a 3400 head gasket should fit a 3500 fine since the 3500 MLS ones had a slightly smaller bore than a OEM GM 3400 gasket. IIRC Eric Brennan is using a set of GM 3400 graphite's on his 3500 motor.

[boscov6]

What would be the BEST alternative for a 3500 head gasket that will be studded and 8-10 pounds of boost then?

[robertisaar]

Ask away, I am tired of being lied to and in return, lying to everyone else. I am ready to refund everyone at this point.

that does not sound good...

[SappySE107]

Ask away, I am tired of being lied to and in return, lying to everyone else. I am ready to refund everyone at this point.

[scott0999]

ok I'll ask Cometic directly then.

I think your overreacting a little.. asking for updates once a month isnt much.. especially when the ETA has changed twice already

people with money in it have the right to ask

[bszopi]

As Ben stated earlier in the thread (as well as almost everytime someone asks this question), they will be done when they are done. He has no control over a large corporation like this, especially when it is for this platform. Do you guys really think they are going to miss out on the dozen or so gaskets that have already been sold? I doubt it. They can take as long as they want, and anything Ben says (or asks about) probably doesn't mean anything to them. So stop asking the question. When they are ready (ie, when they are in Ben's posession), he will let everyone know.

[scott0999]

so whats up?

[SappySE107]

Shops use mill/fly cutter and I forget the type of bit but 50RA isn't difficult with good equipment. The block deck just needs to be cleaned, no sanding or anything.

[robertisaar]

flycutter and surface grinder would be my tools of choice here...

[chri0029]

I don't know what Cometic specifically calls for, but industry standard for surface roughness is Rz of 15 micrometers and Rmax of 20 micrometers. There is a maximum waviness spec, but it varies with the length of the wave. This is more used in the machining.

I really don't know how they do this in shops (maybe a mechanic can chime in here), but I guess Scotchbright pads are not recommended since the particles could find themselves in the oil system and eventually bearings. Sandpaper or steel wool might work after a razer blade to remove the old junk, but that doesn't address any scratches on the deck.

The viton coating on the outer CHG layer serves the purpose of microsealing around the beads. If you have some questionable areas on the head/block surface, you can possibly put grease or whatever on the CHG beads and put the CHG to the head/block to see where the beads lay. It's really the bead areas have to be especially clean and free of any deep scratches. The other areas don't really matter.

[scott0999]

speaking of that, I remember reading a "50 roughness average" is needed. whats the best way to achieve that.. I mean what do you use sandpaper?

[chri0029]

Good. Everybody has some extra time to polish the deck surfaces. These have to be a smooth as glass for MLS.

[SappySE107]

I was told a few more days, but have set the eta for the 14th because that is more reasonable for me to have the gaskets here. They compared them to the head and deck and it's good this time. Dies are done and they are finishing up the embossing.