head gasket thickness - Diesel Forum

smkndsl · 07-17-2008, 01:38 PM

Just wondering if anyone knows if the felpro headgaskets have a thicker crush height than the factory ones. My problem is I have a 94 idi turbo and when the head gaskets blew the fire rings dug grooves into the block,the machine shop is supposed to be decking it today or tommorow but he thinks it will need about .004 to 010 in machined off,I am concerned about high compression,valve clearance and fuel timing from the reduced combustion and prechamber volume,I could machine the top of the pistons off and have them reanodized but that leaves me with a weaker piston and still a smaller prechamber,I plan on putting the aurora 2000 turbo on it with an intercooler and i expect 18 pounds of boost so I want all the strength I can get out of the piston. if anyone has any suggestions or specs of crush height on the factory headgaskets please let me know. I am also putting in arp studs,there is not a specific 7.3 idi kit so I took measurments from the engine and they sent me some that will work-just wondering if anyone knows what I should torque them to-the factory bolts were 100 for non turbo and 110 for turbo.

icanfixall · 07-17-2008, 11:01 PM

Oh... Too many questions all at once. The felpro head gaskets are 10 thousands thicker than stock gaskets. They measure around 76 thousands thick. Your pistons can be milled a maxium amount of 15 thousands. Any more and the top ring will heat up way past the design specs. This info came directly from the Mahle engineers I talked with last year. Your ARP studs need to be torqued down and released 5 times. This is important. Otherwise the torque will be wrong. I felt this was foolish till I did it. My nuts made almost another full turn on the studs. Whats happening is the friction is breaking down and the true torque is found. The ARP part number for those studs is AR7.00-1LB. They are 7 inches long but. Be really careful. The studs will stick thru the nut so far that the socket interfers with the top threads. It will roll over the top two threads. Even a deep socket is built the same way. You can grind off about 1 /8 inch off the top fine threads and be done with this too. All the turbo and non turbo pistons have a dome thickness of around 570 to 580 thousands. They are plenty thick to take some milling. Decking the block can be done but. There is a measurement for how much can be milled off. The demension from the deck to the center line of the crank is 11.137 to 11.141. The pistons can be up out of the bore a maxium of 31 thousands. The head thickness is from 4.795 to 4.805. Intake valve set into the head 0.042 to 0.054. Exhaust is 0.051 to 0.063.. The precups can be up or down in the heads + 0.0025 or - 0.0025. You can use the 100 lb torque setting on the studs but only if you use the ARP moly lube. Use 30 weight oil and its 130 lbs. Big differance and I really don't want to be struggleing that hard at 130 lbs timea 68 nuts times 3 either. Careful what you ask for at the machins shop. Taking too much off the heads or block will kill things. Are you sleeving all 8 cylinders too???

smkndsl · 07-18-2008, 11:37 AM

Thanks for all the good info,I think the block needs less than .010 so if the felpro gasket has a crush height of .076 compared to the factory .060 I should have no issue. as far as sleeving goes i pulled all the frost plugs out of the block and inspected the cyls with a boroscope and found absolutely no signs of cavitation-I know there are no guarantees but im going to try it without sleeves. thanks again for the info

icanfixall · 07-18-2008, 10:50 PM

Now that the freeze plugs are out you will need the special 303d045 tool to install them properly. Otherwise your taking a big risk that they have not been properly set. Do use only the stainless steel set from Ford. I had a shop install brass plugs and one fell out at 2 miles. The next one blew out at 5400 miles and I burned up that new motor. Crappy work nets crappy results. The tool can be bought thru Rotunda tools. Phone number is 1800rotunda. Its around $180.00 but worth every cent. Also the sealant used on the freeze plugs is no longer made anywhere. I used Permatex Avaition sealant. Others have used Hylomar. Rolls and Merlin use it to seal the big piston engines in the spitfires and mustangs. It can be bought at better aircraft supply houses. They have a web site too. Don't intall them dry. I did and I even air tested the cooling system to 35 lbs without any leaks. But later on several started leaking. I fabricated an set of hydro plates to block off all the coolant areas of the block. I can even hydro the heads seperate of the motor.

smkndsl · 07-19-2008, 11:42 AM

cool, ill check and see if we have that tool at work-im a senior master mechanic at a ford dealer-but i started in 98 when the idi's were pretty much gone. the machine shop told me to jb weld the frost plugs in. what about the plugs that go in the blocks deck are they tricky also?

icanfixall · 07-20-2008, 10:35 PM

I'm not sure about the JB Weld idea. Are they telling you to use that instead of "setting" them with the tool? If so don't do it. I used it on my second set that was installed dry with the special tool. I applied it in 3 locations around the outside of the seated plug. As posted, they help 35 lbs of air pressure but later on they started to leak. Now maybe if I had used it to completely cover the seating ring around the circumfrance they might not have leaked or at least I would not have seen it. That still doesn't mean they would hold pressure for ever. I run a very good coolant and use only distilled water. I run about 40% distilled water and 60% coolant. Nothing cools better than waterbut it boils way too low. I may try the Evans waterless no pressure coolant. It seems like a better coolant for my needs. Its just so expensive but the better things usually are...No, the plugs in the deck are just the cup type plugs. They are not a problem but use a sealant on them anyway.