S_Mazza
Registered User
Hello, guys. I have recently learned some things that I think I should share. This post is pretty long. If you enjoy a tale of automotive woe and want to know more about Mustang cylinder heads, keep reading. There will be pics!
This past summer, I replaced the head gaskets on my 1990 SC. I wanted to upgrade the engine a little, so I ported a set of 1996-1998 Mustang heads, had a 3-angle valve job done, and installed those heads on the engine. As you probably know, the 96-98 Mustang heads are very similar to the SC heads. They have the same coolant passages. The main difference is that they use a smaller valve stem. Another important difference is that they use 2 fewer intake manifold bolts, and the bolts are 6mm instead of 8mm. I was somewhat concerned about this, but there was a lot of information floating around that suggested it would work fine.
So I went ahead using the Mustang heads. The installation went pretty smoothly. I only had to buy 6mm bolts (M6-1.0) and washers of the proper length. I used the regular SC gaskets. I did run into one problem, when I overtorqued one of the intake bolts and snapped it. The thing is, M6x1.0 bolts of grade 10.9 can only take 11 ft-lbs of torque (dry threads). But the M8 bolts we are used to can take 28 ft-lbs of torque (dry threads).
That was a pain, but I removed the manifold, put in another set of new gaskets, and got it together. As I had done the first time, I installed the gaskets dry, except for a thin film of blue silicone around the coolant ports. I carefully torqued the bolts and retorqued them after a day or so. Everything in the engine bay looked so nice and fresh.
I had some troubles immediately after the HG replacement, but they were not in fact related to the heads. I had a vacuum leak from the seal between the blower and inlet plenum. I sanded the plenum flat and solved that problem. I verified that there was no more vacuum leak. I thought things would be fine after that, but I had some part-throttle ping. I thought I might have a MAF problem, but I tested and ruled that out. Then I thought I might have a cam sensor timing problem, but I tested and ruled that out.
Finally, I narrowed it down to a vacuum leak. With carb cleaner, I found that the leak was somewhere around the rear of the blower. I was really annoyed, as I thought the same leak had opened up again. Well, I pulled off the blower and checked the seal to the inlet plenum. It was perfect. "Hmm." I pressurized the blower system from TB to upper IC tube and found a leaky hose and a small pinhole in a weld, and I fixed both leaks. Then I reinstalled everything and ... I still had a vacuum leak.
I checked with carb cleaner again, and I found that the leak was still near the rear of the blower. "Argh!" With the car running, I sprayed a little dab of shaving cream at the base of fuel injectors 5 and 6. It quickly disappeared. I thought it had been sucked past an injector o-ring, so I bought another set of o-rings. When a nice day came along, I went outside and took the blower off the engine.
When I was about to remove the fuel rail, I looked closely at the injectors that I thought were leaking. "Hmm, they look all right. Wait a second ... what is that?" Just below the injectors, I saw a strip of blue gasket material ... torn ... and protruding from the manifold. "Oh boy." After a "moment", I raced to the auto parts store 1/2 hour away to get a new set of gaskets before the store closed. (It was a holiday weekend, so the stores closed early. I tried the store 10 minutes away, but they told me it would be a 3-5 day wait to get the parts from the warehouse. No way.)
When I removed the manifold, I had a bit of a shock. The gasket on the driver's side had seriously stretched in the area where the Mustang heads omitted a bolt. The gasket walked up and right out from in between the manifold and head, and then tore over the top of the #5 intake port. I looked at the passenger side manifold, and although it was still intact, a witness mark showed that it had also moved about 3/32" and was just about to blow. It had moved the most in the area between ports #1 and #2, where the bolt had been omitted.
What I took away from this was that the missing bolts were actually pretty important. Now, when I looked at the rest of the gaskets, I got a couple
more surprises. The first surprise was that some of the bolt holes in the other parts of the gasket were elongated. It was clear that the gasket had stretched and moved upward in those areas, and the smaller M6 bolts had begun to cut into the bottom of the holes cut in the gasket. The last surprise was that the bolt holes were not elongated at the very ends of the gaskets. That may just be because of their position, but I think that the silicone I applied may also have had something to do with it.
Well, after seeing this, I was dead set against installing new gaskets with the same method. I saw no point in wasting my limited time doing something that would fail within months or even weeks. So I thought it over, hard, and decided that I needed to change some things. The first thing I needed was to add the missing bolts to the heads. Believe me, I had plenty of trepidation about this. Ruining a fresh, nicely machined set of heads was just about the worst thing I could do. But removing the heads and taking them to a machine shop was just impossible. So I got out the power drill and headed outside. I put the manifold back in place with gaskets to help me line up the holes and went to work. It was hard, and the results were not perfect, but I managed to drill and tap 2 new bolt holes within a few degrees of the correct plane.
I was still not sure if that would be enough to hold the gaskets in place. I mean, 14 bolts might possibly add up to 16.67% more holding power, but the previous gaskets had failed miserably. So I decided some sort of adhesive might provide extra insurance. I got a bottle of Indian Head Gasket Shellac and painted the head surface and the bottom side of each gasket. I left the top side of each gasket dry, except for a thin film of blue silicone around each coolant port, as I had done before.
I just finished the installation yesterday, and started the car for the first time this morning. The car is running well ... so far. I pray to God that these gaskets hold. Seriously.
I can't think of anything else that would help the situation, except for re-drilling every bolt hole to M8x1.25. That would not be easy, and I am hoping not to have to do it. But in my eyes, that would be the single biggest thing that could improve the sealing situation.
Post continued below...
This past summer, I replaced the head gaskets on my 1990 SC. I wanted to upgrade the engine a little, so I ported a set of 1996-1998 Mustang heads, had a 3-angle valve job done, and installed those heads on the engine. As you probably know, the 96-98 Mustang heads are very similar to the SC heads. They have the same coolant passages. The main difference is that they use a smaller valve stem. Another important difference is that they use 2 fewer intake manifold bolts, and the bolts are 6mm instead of 8mm. I was somewhat concerned about this, but there was a lot of information floating around that suggested it would work fine.
So I went ahead using the Mustang heads. The installation went pretty smoothly. I only had to buy 6mm bolts (M6-1.0) and washers of the proper length. I used the regular SC gaskets. I did run into one problem, when I overtorqued one of the intake bolts and snapped it. The thing is, M6x1.0 bolts of grade 10.9 can only take 11 ft-lbs of torque (dry threads). But the M8 bolts we are used to can take 28 ft-lbs of torque (dry threads).
That was a pain, but I removed the manifold, put in another set of new gaskets, and got it together. As I had done the first time, I installed the gaskets dry, except for a thin film of blue silicone around the coolant ports. I carefully torqued the bolts and retorqued them after a day or so. Everything in the engine bay looked so nice and fresh.
I had some troubles immediately after the HG replacement, but they were not in fact related to the heads. I had a vacuum leak from the seal between the blower and inlet plenum. I sanded the plenum flat and solved that problem. I verified that there was no more vacuum leak. I thought things would be fine after that, but I had some part-throttle ping. I thought I might have a MAF problem, but I tested and ruled that out. Then I thought I might have a cam sensor timing problem, but I tested and ruled that out.
Finally, I narrowed it down to a vacuum leak. With carb cleaner, I found that the leak was somewhere around the rear of the blower. I was really annoyed, as I thought the same leak had opened up again. Well, I pulled off the blower and checked the seal to the inlet plenum. It was perfect. "Hmm." I pressurized the blower system from TB to upper IC tube and found a leaky hose and a small pinhole in a weld, and I fixed both leaks. Then I reinstalled everything and ... I still had a vacuum leak.
I checked with carb cleaner again, and I found that the leak was still near the rear of the blower. "Argh!" With the car running, I sprayed a little dab of shaving cream at the base of fuel injectors 5 and 6. It quickly disappeared. I thought it had been sucked past an injector o-ring, so I bought another set of o-rings. When a nice day came along, I went outside and took the blower off the engine.
When I was about to remove the fuel rail, I looked closely at the injectors that I thought were leaking. "Hmm, they look all right. Wait a second ... what is that?" Just below the injectors, I saw a strip of blue gasket material ... torn ... and protruding from the manifold. "Oh boy." After a "moment", I raced to the auto parts store 1/2 hour away to get a new set of gaskets before the store closed. (It was a holiday weekend, so the stores closed early. I tried the store 10 minutes away, but they told me it would be a 3-5 day wait to get the parts from the warehouse. No way.)
When I removed the manifold, I had a bit of a shock. The gasket on the driver's side had seriously stretched in the area where the Mustang heads omitted a bolt. The gasket walked up and right out from in between the manifold and head, and then tore over the top of the #5 intake port. I looked at the passenger side manifold, and although it was still intact, a witness mark showed that it had also moved about 3/32" and was just about to blow. It had moved the most in the area between ports #1 and #2, where the bolt had been omitted.
What I took away from this was that the missing bolts were actually pretty important. Now, when I looked at the rest of the gaskets, I got a couple
more surprises. The first surprise was that some of the bolt holes in the other parts of the gasket were elongated. It was clear that the gasket had stretched and moved upward in those areas, and the smaller M6 bolts had begun to cut into the bottom of the holes cut in the gasket. The last surprise was that the bolt holes were not elongated at the very ends of the gaskets. That may just be because of their position, but I think that the silicone I applied may also have had something to do with it.
Well, after seeing this, I was dead set against installing new gaskets with the same method. I saw no point in wasting my limited time doing something that would fail within months or even weeks. So I thought it over, hard, and decided that I needed to change some things. The first thing I needed was to add the missing bolts to the heads. Believe me, I had plenty of trepidation about this. Ruining a fresh, nicely machined set of heads was just about the worst thing I could do. But removing the heads and taking them to a machine shop was just impossible. So I got out the power drill and headed outside. I put the manifold back in place with gaskets to help me line up the holes and went to work. It was hard, and the results were not perfect, but I managed to drill and tap 2 new bolt holes within a few degrees of the correct plane.
I was still not sure if that would be enough to hold the gaskets in place. I mean, 14 bolts might possibly add up to 16.67% more holding power, but the previous gaskets had failed miserably. So I decided some sort of adhesive might provide extra insurance. I got a bottle of Indian Head Gasket Shellac and painted the head surface and the bottom side of each gasket. I left the top side of each gasket dry, except for a thin film of blue silicone around each coolant port, as I had done before.
I just finished the installation yesterday, and started the car for the first time this morning. The car is running well ... so far. I pray to God that these gaskets hold. Seriously.
I can't think of anything else that would help the situation, except for re-drilling every bolt hole to M8x1.25. That would not be easy, and I am hoping not to have to do it. But in my eyes, that would be the single biggest thing that could improve the sealing situation.
Post continued below...