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Water pump Journey
http://forums.ctzcc.com/viewtopic.php?f=4&t=7523		 Page 1 of 1
Author:  porkbun [ Mon May 20, 2013 8:33 pm ]
Post subject:  Water pump Journey
BACKSTORY: When I was about to buy my new 240Z the previous owner said the water pump needed to be changed but I was running a little late and he had the time so he changed it himself. Everything had been fine until I noticed that in traffic my car would start to overheat. Upon further examination and guidance by Frank, I installed a missing thermostat and better flowing radiator from Zorro right before the fun run, but the temp gauge always showed that the car was running hot even after cruising at low RPMs in 5th in 50 degree weather.

ISSUE: A few minutes after bringing the car up to 6k during the fun run I noticed that the temp gauge was past the red but I assumed that the temp gauge/sender was acting up. A few minutes later the car started smoking and we pulled over

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Eventually realized that the car had been leaking coolant from the bottom of the water pump and the radiator was dry. Got it back home with the help of Zorro, a kind stranger, and RTV silicone. Took the water pump and found this:
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Blown gasket!
While taking the water pump off, I noticed that the lowest bolt for the water pump could spin freely and this is what the threads looked like:
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Realized that a bolt from my 260Z's water pump arm had the same threading but was a bit longer so I threw a ton of washers on it and began to tighten it. It was about to get as tight as the other bolts when I hear a snap and the bolt slackens :shock:. Pulling it out revealed this:
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The threads on the end are completely gone! I later noticed that the previous bolt had the same issue but on a smaller scale since it wasnt as long. Right now the car is running fine as it did before with a new gasket, but I am missing the lower bolt which opens the possibility of blowing another water pump gasket. MSA sells a water pump bolt kit, but I dont want to buy it if the threads on my lower bolt are just going to get eaten again. Any idea what could be causing this problem?
Author:  mikeatrpi [ Tue May 21, 2013 7:38 am ]
Post subject: 
Can you chase it with a tap or thread restore kit? Also, is the old bolt snapped off inside somehow or did it come out completely? You might have to remove the old pieces if they're stuck inside.
Author:  Frank T [ Tue May 21, 2013 10:00 am ]
Post subject: 
The remedies for deep-set broken bolts include drilling them out with increasing-size drill bits. I suspect the PO started to do that job, but quit before he actually removed the broken stub of the original bolt.

I *think* that shorter bolt is the original broken bolt. The end of it is probably still fully seated in the bolt hole, but now it has a 'cup' drilled into the center of it. It would be ragged around the edges, so trying to insert another (longer) bolt into the hole would chew up the end threads, just like you're showing on your second picture. Just a guess.

Step One would be to clean out that bolt hole and ensure you've removed the broken-off stub which I suspect is still in there.

If you mangle the threads along the inside of the bolt hole, you can try to dress them up (first) with a follow-up tap of the same thread count. If that works, you simply use a new bolt and gasket and your job is done.

If the threads are mangled beyond redemption, you simply drill them all out, re-size the hole and re-tap it with a larger thread diameter, then use the appropriate threaded bolt to replace the old one. Most of us use SAE bolts as replacements, since they're easier to find here. Your restriction would be the size of the hole in the pump housing itself ~ in other words, the bolt still has to be skinny enough to pass thru the pump housing, then screw into the engine. I've actually seen guys hone open the hole in the pump to allow them to use a fatter bolt.
Author:  padam07 [ Tue May 21, 2013 10:06 am ]
Post subject: 
Here is some good info if enlarging the hole and retapping larger isn't an option....

http://www.fjr1300.info/howto/helicoil.html

I feel though the hardest part is removing the broken bolt and not the thread repair.
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