How to Repair a Stripped Water Pump bolt hole

[webster]

Prob. is that the bottom (long) bolt that holds the water pump on has striped its threads. I've never replaced theards by heila coil (don't even know if the spelling is right) Anyway it's the long bolt on bottom of pump that bolts in to the timming chain cover. should I remove timming chain cover to repair or can it be done while it's installed? Is the wall thick enough to re- thread? Is there another way?
TIA
Webster

[jordan]

well this isnt going to be fun, but it would make it alot easier if the timing cover was off. if you use a heli coil you will have to drill and tap the next size up and it is about $30 for the kit to do one size, but the timing cover is aluminum so the stainless steel heli will start to eat away the aluminum (trust me it does, in a year is can do alot of damage) so your best bet is to drill and tap the next size up and use coarse thead it is alot stronger in castings.

[Travis]

Stainless and aluminum are quite close in the galvanic series and really shouldn't cause any corrosion issues.

-Travis

[jordan]

well not so on my snowmobile i put heli coils in the exhaust flange (aluminum) and the next winter the heli coil pretty much just sitting in "powdered" aluminum and the threads were gone.

[kwilford]

Standard practice is to reinforce critical threads in aluminum with Heli-Coils or other types of stainless inserts. I have bought kits (which consists of a special tap, an installation handle, and a few inserts) and re-fill packages for most of the metric sizes on the Opel. You also need a drill bit that is EXACTLY the correct diameter for the size of insert. They are much stronger than the original aluminum thread due to their larger thread diameter, and more resistant to stripping with repeated use since the insert is tougher that the native aluminum. And Travis is right, the difference in spontaneous potential between most stainless steels and aluminum is much less than between the steel bolt and aluminum. And many places that need to be repaired don't have enough "meat" to move up a bolt size.

Webster, the biggest problem with repairing the hole is getting access. The repair kits (which come by several names) are available from most auto supply stores, and are easy to use. Just make sure you get the correct size and thread pitch. Can you get at it, with the radiator and water pump removed, to drill it out? Once you have it drilled to the right "oversize", the Heli-Coli tap is fairly short, as is the insert installation tool.

HTH and good luck

[webster]

I went out and got the "OEM fix-a-thread repair system"
it says 1/4"-20 drill 6.7mm 17/6. but the thread on the tap looks a little more coarse do you guys suggest using the more coarse or try to stay with the finer thread? Also the thread on the bolt is about 1 inch long but the insert is only 1/4 inch should I look for a longer insert or is this one ok? can I put 2 inserts in?
TIA
Webster

[webster]

Oh yeah, one more thing the directions say to drill out damaged threads if necessary. WHAT does that mean. the bolt does grab but won't snug down to specs
TIA
Webster

[kwilford]

Are you using a metric thread insert? It sounds like you have a 1/4 inch by 20 SAE repair kit, which will require that you change to a SAE bolt. Inserts are available in metric, so it is better to stay metric through-out. Or else you will be branded as the %*^%*&% P.O. By the next owner who changes out the water pump. But the real issue is that the 1/4 inch insert may not be big enough to repair the stripped threads. The matching SAE size would be 5/16 inch.

My kit (which is a "Fix-A-Thread") says drilling out the old threads is optional in aluminum. It is NOT optional in steel or cast iron holes. As for thread pitch, I still maintain that you should stick with the standard metric (I believe those bolts are M8, which is a 1.25 (threads per mm) pitch. It says to use a 21/64" (or 8.3 mm) drill bit, which might be only part of a pretty good drill bit set. USe the next size DOWN (5/16") in your drill kit.

And it says that two or more inserts can be installed in longer holes. From my experience, that can be a bit tricky, since the top insert has to be JUST below the surface. And each insert's length is 1.5 times the diameter, which should be plenty of strength to snug up the water pump tight.

HTH

[RallyBob]

The timing cover/water pump bolts are an odd thread....they're 7mm x 1.00 pitch. You may have some trouble finding a Heli-coil kit locally for this. It'll probably be a special order.

Bob

[oldopelguy]

You might also try getting a long stud first. If you can get a stud that is the right pitch to go in past the "bad" threads and grab good metal, then all you need to do is put a nut on it and call it a day. The $2 for the stud and nut might be $ well spent if the problem can be fixed in 10 min vice 4-5 hours. Use a good quality thread locker/ sealant to make sure the stud doesn't move though.

You also might be able to get away with tapping the hole a slightly larger size until the motor gets pulled to install the helicoil. In this case, possibly a 5/16" tap would go down the hole and let you install a SAE replacement bolt for now. The overall tapped hole will still be smaller than the required hole for the helicoil and you might be on the road quicker. It won't be done "right" but it will be done. You might have to enlarge the bolt hole in the water pump slightly, so double check that before you try to reinstall it.

I highly recommend studs anywhere there is aluminum, then the wear is on the steel stud and not the aluminum case, and if there is a problem you just get a new stud.

Oh yeah, one more thing. Take your thread repair kit back and try to find one from Helicoil or Thread-zert. The "OEM" brand stuff is so cheap you usually end up with more damage than before and the thing still not working.

[kwilford]

Another case of me talking (typing) before I get off my butt and just look at my own engine. It's been a while since I changed an Opel water pump, but my engine is on the floor and just about to receive a new pump. And suddenly the wierdness of the water pump and timing chain bolts came back to me. Here's what I found.

Bob is right (as usual). The Opel water pump bolts are M7x1.00, which exists in my tap and die kit, but I have yet to see one in a bolt store. So even the bolts are probably special order, let alone the Heli-Coil kits. The 7 mm bolt is a bit bigger than a 1/4" bolt (0.278" versus 0.250") but that may be your only choice, unless you move up to an M8 (0.315") bolt. The closer SAE equivalent is the 1/4" x 24 NF, which is even a bit finer thread than the M7x1.00. So your choices, a I see them, are:

1) Find a M7x1.00 Heli-Coil (not likely) and install it in the block. But you will have to remove the chain case. BIG OUCH!
2) Use a SAE bolt of an equivalent length, and convert the hole (JUST in the block!) with an repair insert, either the NF (20 TPI) or NC (24 TPI). You still have to pull the chain case.
3) Drill out the water pump hole to allow you to use an M8x1.25 or a 5/16" NF or NC SAE bolt and insert. The timing chain case hole seems to be big enough to allow a 8 mm or 5/16" bolt through, but the water pump holes are not.

If it is one of the long bolts, they actually thread into the cast iron block, NOT the chain case. Only the short water pump bolts thread into the aluminum timing chain housing. So ignore the comments about not drilling the hole out, no matter which size you chose to use. And unless you have a VERY long tap for the new insert, you have to remove the entire timing chain case. Those long water pump bolts also secure the chain case to the block, so you are inviting a leak if you don't get a good thread for the bolt to grab.

I like oldopelguys suggestion. This is a PAIN to do with the engine in place. If you could find a longer M7 bolt or stud, you might be in business. Otherwise, do a makeshift repair now using a 5/16 NF inch tap, and just get enough thread into the block to get a grab with a SAE bolt. Then do it right (by removing the chain case) someday when you or the next owner next have the engine out.

JM2CW

[webster]

Thanks all,
Looks like I've got some more work ahead of me.
1 question I still have is if the bolt does go all the way into the block. It just doesn't seem to be long enough, and if it does how deep could the threads go into it. I like the Idea of trying a longer bolt to see if it will snug up.
Thanks again,
Webster