Tap bolt hole for thermostat housing in intake manifold

[birdpiper]

1999 VP 4.3 GL 190HP

Last week I removed the thermostat housing and replaced the thermostat. As I was re-installing the thermostat housing I noticed that the hole for the starboard side bolt had become stripped (and possibly corroded), see yellow arrow on the attached diagram. A previous installer had used a thick washer in an effort to get a ?bite? on as many remaining useful threads. I was not as lucky, several tricks yielded few results. The hole is completely stripped out and I can not get the thermostat housing to seal with just the other (port side) bolt.

Has anyone had any luck ?tapping? out an existing hole in an intake manifold? It looks like it is a 5/8 size bolt and hole. Do I need to tap out to the next bigger size 3/4?

Any assistance or feedback is appreciated

 

[Bondo]

It looks like it is a 5/8 size bolt and hole. Do I need to tap out to the next bigger size 3/4?

Ayuh,..... I'd sooner think it's 3/8",..... 3/8"- 16 to be exact,....

A heli-coil could fix it,....

Drillin', 'n tappin' to 7/16" isn't a good idea,....

 

[Scott Danforth]

Helicoil it. available at your local FLAPS (Friendly Local Auto Parts Store)

its either 5/16" or 3/8"

if the head of the bolt is 1/2" hex, the threads are 5/16" if the head of the bolt is 9/16" hex, the threads are 3/8

 

[Jcris]

+1 above