exhaust leak on '89 5.0 in '70 coupe

my70stang · Aug 22, 2007

i tightened up all the header bolts because they had a bit of a leak and backed off since i ran the motor

but now when i put my hand to the rear end of the heads, theres a hole that exhaust is shooting out of

any idea of what these holes are for and if they have a thread what thread?

can i just plug them?

coupe5.0 · Aug 22, 2007

They are holes for the smog crossover tube. I bought some allen head plugs. Will be a pain to do in the car though.

65ShelbyClone · Aug 22, 2007

Those are holes for the air injection, also known as the Thermactor system. I have heard people say that a 14mm sparkplug will fit in the holes, but Trickflow has the thread size listed as 5/8-11. I would just as soon go get the correct plugs.

Rusty67 · Aug 22, 2007

Allen plugs.... I WISH I would have thought of that. My heads have a bigass bolt in the back of them. I just hope yours don't need to be cleaned out with a tap like mine did or you might have to drop the trans out to get the clearance (or pull the heads).

whatagearhead · Aug 22, 2007

Great input guys - I wish we had have known about this with the motor out of the car but oh well

The header bolts are certainly tight at this point

We will plug with allen plugs - any advice on thread sizes? Passenger side is bigger than driver side from what we can tell.

Thanks, Tom

Rusty67 · Aug 23, 2007

Both sides should be exactly the same size holes/thread pitch. If they aren't then I would guess that the holes need to be cleaned out with an appropriate sized tap. I don't remember what size it was being that it was like 4 or 5 years ago. Sorry.

You can try geting in there with a mirror to look and see if there is buildup causing the holes to appear different.

whatagearhead · Aug 23, 2007

Rusty67 said:
Both sides should be exactly the same size holes/thread pitch. If they aren't then I would guess that the holes need to be cleaned out with an appropriate sized tap. I don't remember what size it was being that it was like 4 or 5 years ago. Sorry.

You can try geting in there with a mirror to look and see if there is buildup causing the holes to appear different.

good tip - we'll try that

whatagearhead · Aug 23, 2007

Well, I looked at both sides with a mirror and can not see any threads. Looks like they need to be cleaned out. The bright side is there is a decent amount of room in front of the firewall to get behind the heads.

What a pain - I can't believe I didn't notice this with the heads off the block
Now I'll have to figure out how to clean them out

Rusty67 · Aug 23, 2007

you basically need to use a tap. You might be able to get a tap and cut a section off from the front of the tap that is short enough to fit into the head. Then grind 4 flats into it so you can fit a cressent wrench (grind it to an exact size if you have that kind of time) and then turn your new *short* tap with the cressent wrench. Not sure if that will work. You might gain some more room by pulling the drive shaft and yanking the trans cross member so you can tilt the trans/engine down. That might give you the room you need between the head and the firewall without pulling everything.

D.Hearne · Aug 23, 2007

Try spraying , spray carb cleaner in the holes first. That may get enough carbon out where you can start the allen plugs. It doesn't take much to plug these holes.

whatagearhead · Aug 24, 2007

D.Hearne said:
Try spraying , spray carb cleaner in the holes first. That may get enough carbon out where you can start the allen plugs. It doesn't take much to plug these holes.

I used a little PB Blaster and a plumbers wire brush to loosen things up some, then ran a "shortened" tap (per Jeff's suggestion) down the threads. Plugged the holes, cranked her up and she's leak free - man does she sound great with the new pipes and flowmaster delta flow 40s. The toughest part of this job was locating a 5/8 x 11 tap (Thanks Paul's ACE hardware - Tempe). Sears, Home Depot and Lowe's all suck for finding specialty tools any more.

We will attempt emmisions later today or tomorrow (not insuring as a classic so must smog all '67 and later vehicles in AZ).

Thanks guys!!!

Rusty67 · Aug 24, 2007

Glad you were able to get it pluged without too much extra work.

65ShelbyClone · Aug 24, 2007

Holy crap! You have to smog test that thing?! I thought CA was bad!

The main reason I got my '68 was to get away from that(sold my '89GT to do it). Here '74 and earlier model years are exempt. Before that was '65 and earlier.

allcarfan · Aug 24, 2007

just putty the holes up. JBweld will be too runny.

whatagearhead · Aug 24, 2007

65ShelbyClone said:
Holy crap! You have to smog test that thing?! I thought CA was bad!

The main reason I got my '68 was to get away from that(sold my '89GT to do it). Here '74 and earlier model years are exempt. Before that was '65 and earlier.

Yeah, that's my feeling as well. I even had to smog my '67 pickup. '67 or newer must have smog unless you do classic insurance - which has restrictions. My70Stang (my son) wants to drive this car.

Needless to say, I sailed through emmisions today. 10 degrees BTD center and stock (from factory) settings on the edelbrock 600CFM carb. Nothing like a little acetone in the fuel tank as well to keep things clean. I know folks that swear by it for performance and fuel milage as well. If you are interested do a web search and you will find plenty of reading material. The guys that did well in chemistry and engineers will love this stuff.

My70Stang went to his first cruise night with his Chevelle buddy (Alex) tonight. My wife took some pics. I'm sure he'll post 'em up in the coming days. They are out with their cars right now. Just sticking a few miles from home, but everything seems good so far.

Need to get that AC installed

68keyblr · Aug 26, 2007

whatagearhead said:
Needless to say, I sailed through emmisions today. 10 degrees BTD center and stock (from factory) settings on the edelbrock 600CFM carb. Nothing like a little acetone in the fuel tank as well to keep things clean. I know folks that swear by it for performance and fuel milage as well. If you are interested do a web search and you will find plenty of reading material. The guys that did well in chemistry and engineers will love this stuff.

I sail through AZ emissions every time since I put on the Edelbrock 600 carb. Haven't touched it since getting tuned 3 years ago

whatagearhead said:
Need to get that AC installed

What kit are you going with? I installed the Vintage Auto Air kit - works great, but I'm not crazy about the hose routing under the hood. The Classic Air kit is much cleaner under the hood.

whatagearhead · Aug 26, 2007

68keyblr said:
What kit are you going with? I installed the Vintage Auto Air kit - works great, but I'm not crazy about the hose routing under the hood. The Classic Air kit is much cleaner under the hood.

We have the Classic Auto Air kit.

I'm sure it work better in the car than sitting in the box

The condensor and compressor are mounted - just need to finalize the under dash unit and route all the hoses.

Here's a couple pics from the Town Center/East Valley cruize night (Arizona and Ocotillo). My70Stang is in the green shirt and his buddy Alex has the '72 Chevelle.

View attachment 367606

View attachment 367608

68keyblr · Aug 26, 2007

Lookin' good Is there a regular gathering there at Arizona/Ocotillo every week?

I'm up the road at Ocotillo/Ironwood

exhaust leak on '89 5.0 in '70 coupe

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