All Small Six Checking for Air Leaks

This relates to all small sixes
StarDiero75

StarDiero75

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Howdy Guys,

So while the aussie head is being built, I'm still trying to make my car run decent. No matter what it seems like I can't get the vacuum leaks out of my motor. 100%, the leak is in the relative area around the 2V conversion on the E0 head. I finally used a combo of cork and rtv and it still leaks. So I start thinking, the guy I bought it from said he burned a hole in the piston with this head.... what if my intake has a crack in it somewhere??? I'm thinking when I had it mag'd he checked out the typical parts of the head, not the intake. How can I do a garage mag on the intake to check for cracks? (And yes I've checked the freeze plugs at the ends of the log).

Thanks,
Ryan
 
One area that these heads that can often crack is the center combustion chamber between the #3 and #4 Exhaust ports. If you make a plate out of 1/4 to 1 Inch material (note that if you made it out of thick enough material it could also double for use on the block when boring and honing) bolt on across the bottom of the head using a head gasket as the pattern (the Cylinder bores holes can be open to to be a bit lighter if you wanted) and a head gasket will also to seal it to head. This plate could used to test a short block too. Also Then you could make a small plate for the T State hole on the front of the head taped out to use with a standard garden hose connector and you can use water pressure to look for cracks going into the cooling system passages.

If you have from around 25 to 45 PSI of line pressure that should be more than enough to test with. You could also do this same method to pressurize the intakes and exhaust ports if you leave the valves installed. The intake Log would be the easiest one with a single plate bolted on the carb base mounting. You could of course also use compressed Air instead of water and then listen for the leaks. Best of luck
 
Another place to look at, the ridges below the carb. hole, it shares the roof of the 3=4 exhaust, it can crack there, that is one of the reasons I like the port divider, helps with extreme heat differential.
 
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I was actually just thinking of using compressed air to check the intake next. A fog machine was another idea.

So I don't believe the crack is into the exhaust at all b/c I've used brake cleaner and it definitely changes the idle/revs when sprayed around the carb area base. I'll see what contraption I can jerry rig to check this. Let me know if you all have any more ideas
 
Was your head was brazed for the 2V conversion it?
Brazing cast iron is a risky proposition.
It's a job for an experienced professional with a furnace not your local machine shop jockey with a torch.
I believe that the flat D7 head can be milled for the 2V conversion without brazing.
If the head is not cracked maybe try sealing the 2V adapter to the head with a couple of applications of JB Weld.
 
78_200_C4 said:
Was your head was brazed for the 2V conversion it?
Brazing cast iron is a risky proposition.
It's a job for an experienced professional with a furnace not your local machine shop jockey with a torch.
I believe that the flat D7 head can be milled for the 2V conversion without brazing.
If the head is not cracked maybe try sealing the 2V adapter to the head with a couple of applications of JB Weld.
Click to expand...
No it was milled flat and with a gasket. I would love to have it brazed or nickel tigged but I don't have the equipment for that yet, nor know how.

My E0 head has plenty of meat around the edges. Which is whats bothering me. The thinnest section is about 1/8". I'm considering JB weld but I want to 100% make sure there's no cracks in the area before I commit.

I just found a piece of plate I tapped and installed an air fitting into. I'm gonna drill the carb mounting holes, take the rockers off, and pressurize the inside. I figure 10psi should be good without popping the end caps off, right?
 
Well I figured it out. My custom 2V stuff has a very very minor leak, nothing like that the real leak is. Check out this video. The valve guide is likely fricked up. Which really ticks me off b/c this was all rebuilt 2 years ago, and I've been fighting this for the past 2 years. While the head is off, I will be epoxy sealing the 2V plate and EGR block off as well as having the guide and probably the seat replaced. I'll be having the shop check out the exhaust side too since I don't have a method to test that yet. Duct taping the air hose to the exhaust pipe? Haha.

 
Is a valve guide leaking or is the air pressure along with wiggling the valve unseating the valve causing it to leak?
Pulling a vacuum on the intake would pull the intake valves onto the seats instead of pushing them off the seats.
Your diagnosis could very well be right. I could tell you quite a few machine shop horror stories.
Take the valve spring off the leaky valve to see if a new guide was installed (if you paid for new guides).
 
Best to check to see if everything is good and within spec. Guides will leak especially when cold, when hot will tighten up. when running things work differently than still, you blew out the oil but when running the oil moves back and forth as the valve goes sealing some.
I think that the carb adapter would have been better if it was about an 1/2'' thicker or steel but who wants to work with that, aluminum is kind of a soft metal and expands more the cast iron. By the time you got the angle cut, it ended up maybe too thin.
 
78_200_C4 said:
Is a valve guide leaking or is the air pressure along with wiggling the valve unseating the valve causing it to leak?
Pulling a vacuum on the intake would pull the intake valves onto the seats instead of pushing them off the seats.
Your diagnosis could very well be right. I could tell you quite a few machine shop horror stories.
Take the valve spring off the leaky valve to see if a new guide was installed (if you paid for new guides).
Click to expand...
So, thats the only valve that leaks, the others dont. It was leaking the moment i put air on it before I touched it. And based on I could feel the air coming out, it's definitely not the valve seat and all guide. I do agree a vacuum would be much better but I don't have anything to do that. I definitely paid for guides. At this point, no matter what the head has to come off to have it replaced. It's likely it got a small valve and a large guide (tolerance wise) which stacked the gap too large. Or the guide is wrong lol.
 
drag-200stang said:
Best to check to see if everything is good and within spec. Guides will leak especially when cold, when hot will tighten up. when running things work differently than still, you blew out the oil but when running the oil moves back and forth as the valve goes sealing some.
I think that the carb adapter would have been better if it was about an 1/2'' thicker or steel but who wants to work with that, aluminum is kind of a soft metal and expands more the cast iron. By the time you got the angle cut, it ended up maybe too thin.
Click to expand...
But why is that the only one leaking? I ran my hands around the other ones and thats the only leaking guide. So you would be right, the car runs leaner and much worse when it's cold. Once warmed up its better. This would agree with that statement.
I completely agree with the adapter. I would have rathered not needing to run an additional 1" spacer with it to cut down on a gasket. I used remnant aluminum in our school machine shop to build it. And yeah it started off as .75" but after putting the angle on it, it definitely got too short on 1 side. I haven't had thr equipment to fix that but i got an aussie on the way so I'm just gonna get this guide fixed then drive this head till its ready to do the short block rebuild and roll in the aussie.
 
Good job on finding the problem.
I once checked an engine that had a dead cylinder at idle.
One intake guide was so loose that it created a vacuum leak so bad that cylinder would not fire at idle.
While working in one shop I saw new guides looser than the ones that were just replaced.
I found this out because we sent the heads out bare to get new guides then did the valve job in our shop.
Some machinists just grab a reamer off the wall and use it without miking it.
Once I asked a machinist how tight he could get the new guides on a (small log) head that I wanted to bring in.
He got nervous and his hand shook. He said "pretty tight".
I took the head without the springs to a machine shop that did the heads on a famous 460 Mach One that was featured in many car magazines.
The machinist honed the guides and was proud of what a good job he did. (I'm not sure if he honed the guides but i asked him about it before hand.) He had me check what I good job he did.
The last log head that I had rebuilt the machinist said that "people don't know what we do to a head. They don't even check it."
 
Back in the early 70's I could buy a new large head for 78 dollars and get new guides and seats, cheaper the messing with rebuild but had to re-port it, got better at it and improved.
 
Does this look like the valves are leaking?
 

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Set the head up level on your work bench then fill the Combustion Chambers with some gasoline if you see any fuel seeping into the intake log then you don't have a good valve seal. Good luck
 
When you get your engine back together start it with the valve cover off so you can check if the valve guides are being oiled properly.
I once had an intake valve stick on a rebuilt head that had an old model adjustable rocker on it. The rocker was getting plenty of oil but not dispersing it on top of the valve springs. I installed a later model non-adjustable rocker which solved the valve guide oiling problem.
 
Take the valve spring off the intake valve that you think has a leaky guide.
Give it the wiggle test,
Mount the rocker on the head then use a KD-915 to remove the spring.
KD-915 valve spring tool 2.JPG
Valve Spring Tool KD-915.JPG
 
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