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MG MGA - exhaust manifold studs
|I'm not sure I remember seeing this before and I'm a bit concerned. Last night I removed the intake/exhaust manifold studs from the head. When I did oil started to seep out of the stud holes. Is this normal or am I looking at a blown head gasket or worse?|
|Not normal! All 6 holes ? How much oil?|
I didn't think is was, but it's been 20 yrs since I last pulled the engine out of an "A". The oil came out as a fairly heavy steem for about a minute or so, enough to flow down the side and drip on the floor. The stud hole 2,3,4 and 5 (from front to back) were the only ones dripping and not all at the same rate. 3 and four seemed to drip a little more than the other two and th 1st and 6th had no evidence at all. I'm hoping its the head gasket although I didn't think the oil ports were on that side of the head. The worst caes would then be a cracked head :(. Unless there is another possibilty. I'm planning on pulling the head this weekend, so I guess I'll know soon enough.
|Norm, I just checked my head (MGB early). All the manifold stud holes are dead ended. So nothing should be coming out.|
|Art, Thats what I was afraid of. Hopefully its the head gasket, but I think that's wishful thinking. Thanks....Norm|
|Three wild guesses- |
1. Occasionally an over enthusiastic lad or lass will interpret "stud torque" as the torque applied to install the stud. The threads peter out (proper technical term for getting shallower due to tap lead) towards the bottom so forcing the stud in can cause spider cracks in the casting.
2. Maybe your head is an uncommon derivative? Didn't Datsun make a head that fits our cars?
3. The rebuilder filled the holes with oil prior to installing the stud knowing that the next person's discovery would have them flummoxed.
|Norm. Bill is correct and his number one is the most likely description of the problem. There is no way that any form of head gasket failure would cause oil to flow into the holes for the manifold studs, but not spray over the manifolds and engine. |
Now, the question is can the head still be used? I do not have a spare head to section, so all I can offer is a best guess. If the oil found in the stud holes was under pressure you would have had oil working its way out of the stud holes, onto the studs, the manifold gasket and the manifolds. Since it does not, from your description, seem to be doing so, the source of the oil must be non-pressurized, i.e. oil out of the rocker arm's pressurized system which drains back down to the sump through the push rod openings. If this were the case, it might be possible to install the manifold studs using some non-hardening Form A Gasket and run the current cylinder head for a number of years more.
It would be interesting to have the cylinder head crack inspected to see if the location of the crack(s) can be found.
|As far as I know, all models of Austin B-series engine heads have four of the six manifold stud holes going thorough to "T" into the head bolt holes. Oil can flow (slowly) down the head bolt from the threads and nut on top. It can then weep out (slowly) through threads on the manifold studs, resulting in smell and smoke as the oil drips onto the hot exhaust manifold. The solution is to apply a touch of thread sealant on the threads of those four manifold studs in the head.|
As a side note, on rare occasion someone may install incorrect manifold studs with too much thread length on the inboard end. These can then serve as set screws bearing against the side of the head studs, then making it impossible to remove the cylinder head until until the manifold studs might be removed.
|Barney, you are right. 4 of the holes are "dead ended" by the head studs. So, it would be wise to install the manifold studs after tightening the head, or loctite them in with clearance.|
On a related topic, the thermostat housing studs are drilled through to the water side, so I guess should be sealed ?
|I have had a similar description as Barneys from some other folks at another site confirming Barneys description. After removing the head and head studs it does appear that the middle manifold studs go through to the head bolts. What a relief, I was afraid my head was cracked. I'm going to have it checked as a process of the rebuild anyways but I feel a lot better knowing that it's in the design of the head. Thanks a bunch Barney and all for your input and assistance. |
This thread was discussed between 29/05/2009 and 31/05/2009
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