Keep Blowing Head Gasket, cylinder #5

[lobe50]

I just pulled my motor apart for the upcoming head and cam swap. And upon examining the head gaskets I saw that cylinder No. 5 has a blown spot at the top water jacket. This is the 3rd time this cylinder has blown. The 2nd time was a fuel pump failure (while on the n2O), so it could not be helped.

This time the motor really showed no symptoms at all, it is just a minor tear.

I think this may have to do with the N2O having the heads milled. This started after I had the heads milled .040. Maybe the milling does'nt agree w/ the N2O??

I think I also remember something about the No. 5 cylinder having a lean condition on the 5.0L's

I hope this does not happen w/ the new heads.

 

[txstang84]

Yes, 5.0's have a tendency to lean out on #'s 1, and 5 due to the runner shape. And yes milling the heads 0.040" probably has something to do with it. If you've blown it three times in the same place, there's a good chance either your block, your heads, or possibly both may be slightly distorted (read: warped). As long as your not taking off too much material from the heads or block, then you should be ok. But, running a power adder will only aggravate any shortcomings you may have.

Ck the block for warpage using a straight edge (metal ruler) and a feeler gage. I can't remember the acceptable limit, but 0.003" to 0.004" rings a bell for some reason.

 

[86bluecobra]

I agree odds are you have some warpage. I saw a magzine article a month or 2 ago about how a 1 nozzle system does not distribute the nitrous evenly through the upper intake. Perhaps if you have that kinda set up you want to take the upper intake off and shoot nitrous through it to see if you are getting even distribution. They were not and the did a few things to improve it. It maybe worth your time to have a look.

 

[lobe50]

86bluecobra, what did they do for changes?? Do ya remember? Or where was the article?? My system is a Nitrous Express system, it uses 2 jets (pills) 1 - for N2O, and 1 - for Fuel

Also txstang, So why is #5 a problem? How does the intake runner affect that cylinder running lean? You would think if it was a problem w/ the runner and air flow, that cyclinder would actually be rich??

 

[lobe50]

I was looking over the heads today, and noticed that the surface that was milled on the heads has slight "cut" lines in it from whatever they used to mill them. You can actually feel them w/ your fingernail. Is that normal, or should they have smoothed the surface off?? Was I supposed to sand them down or something??

Also an input on the gaskets?
I was just reading posts about the cometic gaskets, and was discouraged to hear about their "sealing" issues.
Is this still a problem, or are the Felpro 1133's better??
Thanx Again

 

[86bluecobra]

I found the article. Its in the december MMFFon page 122. Title,"The Street Racer's Special."
They hit the nitrous and actually no nitrous was coming out of 4 runners. They said they moved the vacuum log around and were able to get nitrous out of all 8 runners still not optimal but at least all were getting the hit. Whatever that means. I think it was where they mounted it they had to adjust. They were hidding the nitrous under the plenum. vconsealed nitrous system. The 5 lb bottle was mounted in the door.

 

[Modular2v]

i blew a head gasket on my c9 heads that were milled......i think the heads are the culprit here! Plus the groves that you are talking about should not be there! What heads did you get?

 

[lobe50]

The heads I am having the problem with are stock E7's milled .040
I am repalcing thm now w/ TW Track heats.
Thanx for the info.
The heads were most likely my problem, and I will check my fuel pressure again when it is put back together. Looks like from what I read it should be 40psi w/ vacuum off, correct.

 

[Maryland Stang]

Also txstang, So why is #5 a problem? How does the intake runner affect that cylinder running lean? You would think if it was a problem w/ the runner and air flow, that cyclinder would actually be rich??

My thoughts exactly. Since the number 1 and 5 intakes have that restrictive dogleg in them you'd think those cylinders would run fat. The EFI is still delivering as much fuel to those cylinders as the others, they just aren't getting as much air. Even with a carb or CPFI it still wouldn't cause it to run lean. It just wouldn't get as much of the A/F mix as the rest of the cylinders.

 

[Peties3]

The heads I am having the problem with are stock E7's milled .040
I am repalcing thm now w/ TW Track heats.
Thanx for the info.
The heads were most likely my problem, and I will check my fuel pressure again when it is put back together. Looks like from what I read it should be 40psi w/ vacuum off, correct.

Why run with the vacuum line off the reg.?

 

[greg251]

Your heads were milled on a broach head miller which leaves the lines you describe. They are known to leak n20 with that method. You need to have the heads milled on a CBN head miller for a nice flat surface. If that is not available then an old belt miller will do but it won't look as nice.

 

[lobe50]

greg, great info. I guess you know your machining
I was hoping that was the issue, I am now swapping those heads out w/ (most likely) TFS Track Heats, so I am hoping the problem will be gone.
Thanx

 

[TheUser]

Why run with the vacuum line off the reg.?

You don't run w/ the vacuum disconnected, you set your fuel pressure with the vac. disconnected from the Fuel Pressure Regulator because at WOT, you have almost no vacuum, so you're setting the fuel pressure you get at WOT. When you reconnect the vac. line to the fuel pressure regulator, you'll notice a drop; the drop is caused by the manifold vacuum present at idle.

 

[greg251]

One other thing I forgot to mention is the head bolts. Depending on what size shot of n20 you use it can actually lift the heads while spraying it. A good set of ARP head bolts will help to keep the lifting down. If you are spraying the heck out of it you might want to consider putting studs in the block instead of regular head bolts as they are much stronger.

 

[lobe50]

Yeah, I used ARP bolts on the stock heads, but maybe the grooves in the maching was an issue.
I really don't use the N2O that much, put it this way I just started my 2nd bottle in 800miles
I will use it some more at the track this spring with the new heads & cam setup
Thanx

 

[greg251]

Did you have the intake milled when the heads were milled? The reason I ask is when you take a lot off the heads it causes the intake to sit higher on the block and it won't seal as well against the heads and it could cause a intake leak thus causing a lean condition.

 

[lobe50]

Exactly what I did not do. The machinist took .040 off, and said the intakes should be ok.
BUT the lower did not sit right I take it because the rear of the lower started leaking oil pass the silicone of the rear of the lower intake.
This was actually why I started this project to begin with. I figured I would fix it, and it would be a good excuse to the wife as to why it was apart

I did not even think about the possibility of the lower beaing a head seal problem like you mentioned.
So maybe between that and the grooves in the head surface, it was causing my #5 to blow
And maybe I will still keep my N2O setup...
Thanx Again