Hot Rods bolts that hold the fuel pump in place on small block chevy

Heres the deal. My 73 350 Chevy engine has a mechanical factory style fuel pump. It's weeping through the 2 small holes above the top and bottom flange. OK, usually means the diaphragm is leaking. Time for a new fuel pump. Match up the new pump, fittings in same place, good to go. Pull the old pump, use a long bolt at the front of the block to hold the plunger in place. Put in the new pump and THEN discover , the bolts I took out (look like small head socket, original factory style) are STRIPPED. 3/8th course thread bolts with about 1/2" of an inch of flattened out thread where it wont "BITE" and wont let it tighten up. Heres my question. Is the thread gone (worn out) in the block also? It appears that the bolt hole goes in about 2" or so. Is there thread the whole length of the bolt hole? Can it be threaded? I used a new 3/8th bolt and it's not grabbing. Now what? Bill

 

If a new bolt isn’t grabbing I’d assume the hole is stripped. I don’t see any reason why you can’t tap new threads but I’d be scared of all the resulting metal getting into the engine.

Hopefully someone’s got a better idea

 

new bolts not grabbing as not going into the hole or going into the hole but continues to spin?

 

Sounds like maybe the block threads came out on the bolt. Was it hard to remove? Or loose and easy?

Stick a pick in the hole and feel around. If it’s blind, maybe you can drill it oversize and tap it. Or a helicoil may work, but again you’re drilling and tapping and don’t want any of that getting in to the engine.




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Stick a pick into the block holes and see how deep they are. Maybe only the first short bit is stripped and some longer bolts will do the trick. Use a shop vac on the holes to get the loose bits out.

 

I like David's idea of a helicoil. I'd try that 1st...…..

 

Bill, the 3/8’s holes in a block I checked are only tapped to a depth of 7/8”, are you sure the holes in your block appear to be 2 inches in depth?
Regardless, if only a half inch of the bolts you took out is damaged there is probably almost 3/8” of thread left in the block. If you have a 3/8-16 tap I would carefully chase the damaged threads, that way you should be able to use longer bolts that will pick up the good threads.
I see no chance for any chips to get into the crankcase, those are blind holes but for your peace of mind you could tape off the opening in the block when you chase the threads.

 

Just put grease on tap and helicoil them. It's really not a big deal. Keep removing tap..clean chips...install new grease and proceed.

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^^^^^this

 

With the thickness of the fuel pump casting and 1/8” for the mounting plate I think you can use bolts that are just a touch less than 1 1/2” long. Dust a bit off the length of the bolts or even use a washer under the heads to effectively make them a little shorter and call it done.
Heli-Coils are great, but is this engine in a vehicle? How will you drill the holes for the H/C tap? Do you have adequate working room? Even more importantly, do you have a Heli-Coil kit available?

 

OK -- I'm working next to an exhaust manifold on the left hole, so my ability maneuver there is limited, right hole is easier to get at. I'm using a 3/8th 16 bolt hole. I'll check for the depth of the hole, again. First check, it appears (using a thin rod in the hole) to be a "blind hole" as in it does seem to go THROUGH any casting, it appears to END within the casting. This time I'll use some thing to see if there is thread, other than the 1st 1/2" or so. If there is meat there I may be able to run a tap into the hole and create more thread for the bolt. Also I can cut away part of the inner fender and be able to have a straight in access , both visually and for a tap.----Now, can you guys school me on helicoils. ---Does a 3/8 helicoil go into a 3/8 worn out thread hole or would you put in a 5/16th helicoil in there. How does a helicoil work? Does the hole have to be drilled out first? What kind of tool is needed to put a helicoil in? AND for that matter, where do you buy helicoils? NAPA? O'Reillys? Thank you guys for all the input. Bill

 

You will need the installation kit, Drill, Tap, plastic tool to screw the included helicoils in. You buy the correct kit by stating the size and thread of the bolt.

 

The intent of a heli-coil is to provide new threads of the same size as originally found in the hole in question. How that works is this...the stripped threaded hole is drilled oversize in accordance with the instructions. That new hole is then tapped with the heli-coil tap. A thread insert (looks like a short coil spring) is threaded into the hole. The outer diameter of the insert fits the newly tapped threads and the inner diameter of the insert is the same size as the original thread that was stripped out. So, the original size fastener is used to attach parts involved.

Ray

 

Yes, the hole has to be drilled with a 25/64 bit for the Heli-Coil tap. Next you need a H/C kit that includes the proprietary tap and that will be around $22-$25.
Chase the bad threads, those bad threads are only 1/2” deep as you said. Then you can use longer bolts in the remainder of the good threads already in the block.
No major clearance issues to contend with when doing the job and for sure cheaper than a Heli-Coil kit.

 

You may have reasonable results by drilling 21/64 and tapping with a 3/8-24 (fine) tap.

 

If the pump diaphragm is leaking, it also means it's likely pumping some fuel in to the crankcase. Might want to do an oil change before firing it up to test out the new pump.

 

Best tip yet.....

 

I'd use a 3-flute spiral "bottom" tap on them blind holes!!.…..

 

Still doing a Cha Cha---2 steps forward--3 steps back. Have found that there IS more thread than the current (bad) bolt has, as much as a 1/4 more thread. Have discovered my Access "hole" not big enough, and not quite in the right spot. I'll redo the "hole" and make it a removable panel. Then I'll see if a tap will run in. To be continued. Bill

 

done this trick many times in similar situations-grab a couple of bolts maybe an inch longer than you need,thread a nut on each one all the way down,now with the pump [[or whatever part you are working on] in place snug the bolts all the way down.now tighten the nuts down to secure the part.More or less what you've done is create a stud that uses all the available threads.if the look bothers you,cut the bolt head off.this trick has gotten me back on the race track many times when there wasn't time for a proper fix

 

Absolutely the best trick I learned today!! Ralphie

 

Or use a piece of All-Thread cut to the correct length. To make them easily removable, cut a slot across the end so you can engage a screwdriver to install/remove the "stud".

I've done this often on those older American made motorcycles that have aluminum engine cases. Seems like a lot of folks really beat up the threads that hold the inner primary to the left engine case. A section of all-thread allows total thread engagement, then top it off with a nut and safety wire.

 

Yea, as stated above, use a stud. Old motorcycle trick on aluminum cases. Use the whole hole then when you tighten the nut, you are just pulling on the threads of the stud. If the hole is too wallered out, weld the original size to a bigger threaded stud that will hold in the stripped hole.

 

WOW--The stud trick just might WORK!!! Had a conversation with a Hot Rod buddies who is a FOREVER mechanic. He explained HOW the pump housing threads probably got screwed up in the first place.---- If a guy forgets, or doesn't even know about the pump push rod, and the pump rod is down when you try to tighten the bolts. ----It can (1) bend the push rod or (2) gaul the bock threads or the bolt threads. Or any combination of them. If you try HARD to tighten it down, the misaligned pump plunger can REALLY play hell with all of the above.---- After I cut an opening in the inner fender well and had straight access to the pump block holes I found a longer bolt could catch about good thread at the end of the run and maybe a 1/4" at the beginning, the middle threads were gaulled out.---- I cut down 2 long bolts to pretty much exact length I needed and mounted the pump.-----Sort of. The right side bolt caught the rear good thread, But because of the exhaust manifold restricting my guiding fingers on the left, I cant catch the rear threads. I'll try again Sat. morning, maybe using a thin piece of metal under the bolt (behind the pump) to LIFT the bolt enough to "catch" the thread.-----If THAT doesn't work I"LL SURE AS HELL try the OldTom69 "stud" trick!!!!!!! Thanks again Guys---I'll give you an up date on Saturday. Bill

 

All-thread is a great invention, I've used it for various fixes over the years, the problem is, the stuff from the big box stores is not machined to a good tolerance, especially the major diameter which is usually somewhat undersize and will add to the problem here.
When I worked in the machine industry we could get a pretty good grade of threaded rod but not found locally for the most part.

 

Bill, since you indicate you have good access to the pump mounting area, I strongly encourage you to pursue the Heli-coil remedy. That is the one method that fully restores the thread integrity of the original holes in the block. Also, as I recall, you can get both standard length and longer thread inserts.

I do not have any connection to Heli-coil in any manner, my recommendation stems solely from the fact they are a widely recognized ‘standard’ for thread repair. While the alternative methods being suggested may work, and would be good options for a patch job to get home, they fall well short of restoring the integrity, and repeatability, of the original thread condition.

In some production applications, especially in aluminum products, Heli-coils are installed to prevent thread damage by providing a tougher thread than the parent metal for the fasteners to bear against. The softer parent metal has a stationery threaded insert to take the brunt of fastener thread loads.

Ray

 

..........Never really thought about this, but it sure makes good sense.

 

Or dip the studs in JB Weld and put some in the hole before you screw them into the block. Then leave them alone over night before mounting the pump.

 

Lots of good ideas here.See if you can find 3/8 x16 stud with allen/hex head in the end of it.use the allen wrench to give you a little extra length to get to hole. Just to be clear it does not have a head on it.Just a stud with a hex in the end of it .Good luck.

 

I found chevy fuel pumps a little harder to install using actual studs-your mileage may vary