the fuel inlet threads on a '69 'lark 350 4bbl rochester quadrajet (ran out of adjectives) are pretty much shot. the previous owner of the carb used some sort of epoxy to keep the fitting in place, but i want a better fix. i found a self-tapping threaded insert that is supposed to work, but it's advertised as a 1", so im wondering if that would thread fine into inlet, or is that the worng size? i tried measuring the inlet on the carb, and it looked to be ab out 7/8". or is there a better possible fix?? thanks for all the help guys!
I used one of those self-tapping fuel-inlet repair fittings... and it did a wonderful job of ruining the carburetor. I subsequently found an NOS version of that fitting from the 1960s and it worked MUCH better. The modern versions available today are cheap knocks-off that are not machined very well. They tend to strip the threads instead of cut new ones. In short, you'll be better off trying to get a proper carb repair shop to fix the threads with a heli-coil insert. Not cheap (around $100 was one quote I got).
The only effective repair is to install a heli-coil insert for the original fuel filter housing. Avoid any of the aftermarket self tapping or expanding fittings, they are not a permanent repair, and as mentioned, may ruin the casting. The oversize fittings tear up good material required for the heli-coil insert, and/or swell the front of the casting some, reducing the amount of sealing surface for the seal. We repair hundreds of 1971 and older castings every year that used the 7/8"-20 threads. The heli-coil insert is stronger than the original threads, it is a permanent repair. Unfortunately, I've had to be the bearer of bad news on many occassions that cheap attempts to repair the problem ruined the casting......Cliff
i've heard of those helicoiled inserts, but how do they work? machine out the threads, and insert the coil? and as an alternative fix, (cheap, since the heli-coil insert presumably would cost about 3x the cost of the carb) what do you think about removing the filter, permanently sealing the fitting into the carb, installing an inline filter, adn connecting the fuel lines together with a short piece of rubber line? i know this is a pretty 'ghetto' fix, but is this a viable option?
The heli-coil repair installation is reasonable, and permanent, we charge $45 plus the return shipping cost, 1-2 day turnaround. Few epoxies will hold the fuel filter housing into the casting permanently, they will deteriorate in the presence of fuel, and fuel leaks are nothing to mess around with in an engine compartment on the pressure side of the pump.....Cliff
The Heli coil is the way to go.Not expencive, not hard to do. most kits come with a tap, an insert tool and the heli coils. Tap the hole screw in the coil and reinsert your filter housing. Ive used them on everything from my sons skate board trucks to Spark plugs to head bolts on a motorcycle. Easy and cheap fix.
I bought the helicoil kit, was pricey but did the job: I also had to buy a 57/64" drill bit to bore out the stripped threads. :TU:
I also install heli-coils on both the 7/8" & 1" inlets Quadrajets. I just want to say that it is not hard to install the 7/8" heli-coil, BUT it must be perfectly straight otherwise the inlet fitting will LEAK. I built a fixture to mount the Q-Jet on my Bridgeport Milling machine in order to locate precisly and install the heli-coil concentric to the sealing flange. I would not recommend this fix for a DIYer with only hand tools. The 1" inlet heli-coil is even more difficult to do but I finally modified the tooling and procedure to make that a viable option.
Nice work, but just an FYI, thread sealer or teflon tape should not be used on inverted flare fittings. By design, the interface between the flare and seat does the work. If tape is used, you can't know if the seat is doing the job or if the tape is temporarily doing the job. Devon
lemmy-67 doesn't need anything to prevent corrosion from welding the fitting to the heli-coil in sunny Silicon Valley, but in RI my options are pretty much change the filter monthly or expect the fitting to get corroded in place. If teflon tape is inappropriate (including the yellow chemical-resistant stuff), what's recommended to prevent corrosion-welded threads? I mentioned anti-seize in another thread but that was poopooed too.
Wax or paraffin, believe it or not. It's used extensively for automotive inverted flare fittings mainly as a thread lubricant, but salt spray and galvanic corrosion testing shows that it helps protect the joint as well. Devon
