Thermostat woes on '85

boblx2a · 04-29-04, 02:17 PM

I guess it has finally happened to me! I have read about this common Corvette malady many times on this board. My thermostat needed replacing so I began removing the bolts and that is where my problems started. I have an '85 C4 so the easiest bolt to reach is the rear bolt. Of couse it had become part of the manifold and would not move, of course I managed to twist off the head of the bolt, of course and easy out would not remove it, of course I wound up having to drill it out (well partially anyway).
Now I am faced with removing the plenum to make a straight drilling job of what is left of the bolt. My ulitmate plan (they have gone well so far.

) is to drill out the bolt and put a Helicoil in. Never having done this I could use lots of expert advise, which this board seem to excel in.
I have the bolts out of the plenum and of course it won't budge. Scattered around the board I have seen suggestions to hit it with a rubber hammer, use a 2X4 on it, etc.
Anyone having done this have any suggestions on raising the plenum high enough to finish drilling this bolt out?

Also, anyone had experience with using a Helicoil? Sounds like a good idea and everyone I have talked to has said it will work. Just wondring............ I really need to get my baby back on the road. It is my daily driver and I am currently driving my classic "55 Belair but would much rather be driving the Vette.

Thanks................Bob

86PACER · 05-01-04, 04:23 AM

You should have enough room and a straight shot by just removing the Throttle body off the plenum only.

boblx2a · 05-01-04, 11:40 AM

Thanks but that is not actually the case. I have removed the throttle body and almost everything else except the plenum. I have some extra long drills that extend above the plenum but still cannot actually get a straight shot at the hole where the bolt broke off. I need to get exactly above the hole in order to drill it out, retap it and use the Helicoil on it. They cautioned me to be certain the hole was straight. They suggested a milling machine but said I could probably get away with a hand drill if I were sure it was straight. Without removing the plenum I cannot get it straight in. Believe me I would do a lot of things to not have to remove that plenum if it were at all possible.

Thanks for your reply though I was beginning to think no one had ever tried this.

............Bob

LiteSleeper · 05-02-04, 11:05 AM

Quote:

Originally Posted by boblx2a

I guess it has finally happened to me! I have read about this common Corvette malady many times on this board. My thermostat needed replacing so I began removing the bolts and that is where my problems started. I have an '85 C4 so the easiest bolt to reach is the rear bolt. Of couse it had become part of the manifold and would not move, of course I managed to twist off the head of the bolt, of course and easy out would not remove it, of course I wound up having to drill it out (well partially anyway).
Now I am faced with removing the plenum to make a straight drilling job of what is left of the bolt. My ulitmate plan (they have gone well so far.

) is to drill out the bolt and put a Helicoil in. Never having done this I could use lots of expert advise, which this board seem to excel in.
I have the bolts out of the plenum and of course it won't budge. Scattered around the board I have seen suggestions to hit it with a rubber hammer, use a 2X4 on it, etc.
Anyone having done this have any suggestions on raising the plenum high enough to finish drilling this bolt out?

Also, anyone had experience with using a Helicoil? Sounds like a good idea and everyone I have talked to has said it will work. Just wondring............ I really need to get my baby back on the road. It is my daily driver and I am currently driving my classic "55 Belair but would much rather be driving the Vette.

Thanks................Bob

Same thing happened to me. I drilled it, ran a tap , then put a 3/8 stud . I don't want to go through that broken bolt B.S. again. good luck

boblx2a · 05-03-04, 12:08 PM

I finally did have to remove the plenum. I removed all of the bolts on the upper side and loosedned all of the bolts on the lower tubes. After removing the throttle body, cables, etc. I placed a 2" pipe under the front of the plenum from the left side of the engine and slowly raised the plenum. Be sure if you use this method to remove all of the bolts otherwise seomething is gonna give!

The rest of the job was pretty straigh forward, drill out the bolt re-tap the whole, etc. I finally have the 160 degree thermostat to go with the fan switch that I installed about 2 years ago.

Now maybe I will get my gas mileage back that I lost when my fans began running full time...................