TBI small block intake gasket replacement (PIC HEAVY)

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someotherguy

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1994 TBI 5.7 intake gaskets

Written 02-10-2011

At 158K miles or so the intake gaskets on my 1994 C2500LD with the 5.7 TBI engine failed. Not an outright failure but obvious signs of seepage at the front of the driver's side head. Not wanting to let it go until the problem got worse, I tore into it for replacement...here's a write-up. It's not meant to be a literal step-by-step; it assumes you have some basic mechanical experience and tools and know your way around under the hood. DISCLAIMER: I wrote this in a hurry so if there's mistakes, don't sue me! But please email me and let me know. Thanks, and hope you find it useful!



Parts/supplies needed: gaskets - intake, TBI, EGR, thermostat, distributor; RTV silicone (I like Permatex black), new 195F thermostat (Stant or Robertshaw), fuel supply/return line O-rings, coolant, brake parts cleaner, PB Blaster, lots of paper towels, wide masking tape, scrap cardboard, oil and filter for changing oil after job is finished. Optional: spray paint and valve cover gaskets. This is also a great time to do cap & rotor, PCV valve, CTS, etc. if it's been a while!

I tried to take notes during the job for what all tools I used. This will be a mostly complete list: siphon hose, drain pan, pliers, #1/#2 flat screwdrivers, 3/8 flex handle ratchet, short & long extensions, deep sockets: 9/16; shallow sockets: 10mm, 1/2, 9/16, 5/8; combo wrenches: 10mm, 19mm, 5/8, 11/16, 13/16; 16mm flare wrench, small hammer, wood block, 7/32 nutdriver, 9/16 distributor wrench, gasket scraper, parts cleaning brush, timing light. A digital camera and notebook computer come in VERY handy for taking pictures along the way, and reviewing later during re-assembly.



I started by using a cheap siphon hose snaked all the way down the radiator tank to remove several gallons of coolant, to avoid making a big mess when I pull the intake. I was working inside and couldn't have any coolant puddles on the floor for my pets to get at. Next up are pics of everything as it comes apart, for reference when re-assembling. Everything is in the stock configuration except for the extra vacuum line T'd off the PCV connection for my vacuum gauge, and the brass fuel pressure test fitting at the rear of the TBI on the supply line.

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someotherguy

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Got as many angles as I could to show which bolts went where. You can see the poor condition of the sensor network grounds at the thermostat housing and next to it on the intake, as well as corrosion from the coolant leak from the driver's side front coolant passage. Four center bolts on the intake pooling oil due to no sealant.

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And more! In the final pic actual disassembly has begun; sensors disconnected, negative battery cable removed from intake, positive feed removed from alternator, pressure cycling switch on A/C manifold removed to help get harness out of the way, radiator hose removed. REMEMBER when removing the brace from the rear of the A/C compressor, do not turn the head of the bolt with any tool! Turn only the nut to remove it. The three bolts holding the A/C compressor on the bracket are kept in place by small tabs cast into the aluminum bracket; if you turn the bolt head you can easily damage or break the bracket!

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My "squeeze" method for breaking lines loose, in this case the hard line to the brake booster. Two wrenches, clock them just opposite of each other, hold the backup wrench so that it can't easily move - squeeze the two together in my fist to break the tube nut loose. Lots of PB Blaster was used prior to removal. Generally when working with lines I use flare wrenches but these came loose easily enough. Intake bolts are out, blue paper "shop towels" wadded up and placed in throttle bores and distributor hole.
Hint 1: use paper towels, not cloth, to fill holes. Paper towel debris is far less likely to damage engine internals if you get some inside.
Hint 2: removing distributor cap gives you more room to fish the distributor out of the engine compartment.
Hint 3: make two marks before removing distributor - rotor position, and body position in relation to the module connections. In this particular example mine was dead easy as the rotor was aiming directly at the firewall (12 o'clock) and the module connections ran square with the angle of the oil pressure sending unit behind the intake, so I didn't make marks. This isn't 100% necessary but goes a long way towards easy re-installation of the distributor.

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Intake removed...there will be some coolant still trapped inside it so bring it out as evenly as possible. Note the ports are filled with wadded paper towels - after the pic was taken I filled the coolant and EGR ports too; this is to keep any small parts, tools, or gasket crud from getting in the ports while working. More paper towels in the lifter valley to soak up small amounts of spilled coolant. Got a nice close-up of the failed gasket at the coolant port; both sides match. Note that it is not required to pull the valve covers to remove the intake. I chose to anyway, just to clean them up and re-seal with new gaskets.

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Cleaned up the intake as best I could with Super Clean and a small brush, and afterwards some brake cleaner and my fingernails (what was left of them; Super Clean is nasty!) You'll note I left the thermostat, CTS, and EGR on. I had just installed a new CTS, thermostat, and gasket less than a few thousand miles ago and didn't want to risk disturbing them. If yours are old, you should remove for replacement during re-assembly! I carefully masked off the throttle body mounting flange and other items then painted the intake with silver rattlecan. Back to cleanup, I've got scrap cardboard in the lifter valley to catch crud. Cleaned up the valve covers, masked the grommets, and sprayed semi-gloss black.

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After some careful gasket scraper and razor blade work, the cement-like old gaskets are long gone. Take care not to gouge up the metal on the heads and intake. Before removing the cardboard, I picked up most of the trash from it to reduce the risk of anything falling off it making clean-up harder. Again, you want to be extremely careful to not get any crud falling down into the lifter valley - you don't want anything in the lifter bores, oil return holes, or the distributor hole! Everything is wiped clean with lots of brake cleaner on paper towel so that no grease or coolant residue remains. I also sprayed the bolt holes clean and allowed them time to dry out. Applied a thin ring of RTV around each port on the head side of the gasket and laid it down carefully to tack up, using a few bolts to be sure I had it centered. Didn't get a pic but I use a healthy (but don't go crazy) bead of RTV at the front and rear rail instead of the worthless rubber strips some gaskets include, and also another thin ring of RTV around the ports on the intake side of the gaskets, before laying the intake down and starting the bolts. Four center bolts should get a dab of sealant on the threads, though I did all of them except the outer four corner bolts which are in blind holes anyway. Torque the bolts down in the correct sequence. Valve covers reinstalled, and a shot of some detailed/painted parts. The spare notebook PC comes into play for reviewing pictures to reassemble by. SEE BOTTOM OF ARTICLE FOR LINKS TO TORQUE PATTERN AND OTHER INFORMATION

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When reinstalling the distributor, remember the helical gear will turn the rotor as you push down, so turn the rotor counterclockwise slightly behind where you want it to end up. Remember the marks you made and line up the body of the distributor, too. Carefully insert the distributor and seat it; when it sits all the way down you'll know it's engaged the oil pump drive. If it won't seat don't force it; try lifting up and moving the rotor a tiny bit either way to see if that helps. If all else fails you can use a very long screwdriver to manually turn the oil pump drive to match what you need on the distributor shaft. Replace the fuel line O-rings! Once you're sure everything is buttoned back up and ready to go, be sure to disconnect the tan/black wire for the timing bypass, set base timing to zero degrees BTDC, snug distributor down, re-check, be sure distributor is tight (don't go crazy; you can crack the aluminum intake) and shut it down, reconnect the tan/black wire. Last engine shot is with all the freshly detailed parts back on, looking good!

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I finished up about 5AM, just in time to pull outside for a test drive as a bad storm came in. Backing down the ramps from the 8" dropoff in the dark, now you can see the "mess" I made by working carefully inside - just a couple small spots, easily cleaned up! You wouldn't have thought an intake gasket job just got done here.

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PAGES FROM GM FACTORY SERVICE MANUAL (1994) regarding intake manifold replacement. They may resize and scrunch up in your browser; choose to view them full size for best legibility, or print them out.

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Richard
 
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