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MG MGB Technical - Leaking Head Bolts

I have a 72 B GT that recently blew a head gasket. I pulled the head, had it skimmed (it was warped) and pressure tested to check for cracks. Used a Payen head gasket and new standard studs and nuts from Brit-Tek. One item to mention - when I pulled the head, it was bolted in place with bolts - not studs and nuts. Not ordinary bolts, but obviously special bolts intended for the purpose - I've never seen anything like this before. Anyway - put everything back together, torqued in proper sequence to 47 Ft. Lb. and started and ran to temperature. The first three head bolts on the right side of the engine were leaking water! Re-torqued the head and ran again. Slightly less, but still leaking water from the head studs/nuts. What's going on?
Bob Lasater

Bob. If the head is nice and flat, as it should be after skimming, I think you need to look at the block for signs of unevenness. Did you countersink the threaded holes on the block? They may have been pulled up with the bolts previously used.

Tony
Tony Oliver

If you have coolant (or oil for that matter) coming up the bolt holes then either the gasket is leaking or there are cracks between the waterways in the head and the bolt-holes. If you get cylinder compression blowing coolant out then it is head gasket, or cracks extending down to the face of the head. If not then it is cracks inside the casting.
Paul Hunt

If the stud holes in the block are leaking water it's probably due to either corrosion or someone ran the bolts too far in and cracked the casting. In that case try using a sealant like Permatex on the stud threads. Unlike MG's lot's of American blocks were designed with through holes into the water jacket. The sealant on the threads was needed to avoid water leaks.

You still have to check the deck trueness and re-evaluate the head. Seems a crack as big as you see would show up on a pressure test of the head.
Robert McCoy

"someone ran the bolts too far in and cracked the casting"

Good point. Many think that the studs should be torqued into the block, but they definitely should not, just bottomed gently. Torqueing them in *will* crack the block, and that could also explain coolant coming through the holes in the head.
Paul Hunt

Bob, you could try backing of each stud nut a bit to relax the pressure on the head. Then remove the offending studs one at a time and put sealer on them. Then try retorquing and see if it leaks. If it works great, if not you haven't lost anything.

Good luck.
Robert McCoy

Guess I have a concern on the point you made on there being bolts in the head. My first question would by why whould bolts be used? Wonder if there was a leaking issue somewhere in the past and the bolts were someones fix?
Bruce-C

Bolts or studs make no difference. If the holes go into the water jacket you have to seal the male threads before you install the studs.

My guess is someone familiar with older American cars switched to bolts because that's what they thought you should use. NOT! Could be the studs were corroded or broke off and they went to bolts.

If sealing and retorquing the studs like I described doesn't work then he head has to come off. Then check the deck trueness and make sure the some of the threads from the block haven't migrated up into the sealing area. That's why you chase the threads with a blind tap and lightly counter-sink if needed.

AT that point you can inspect to see if the casting at the bottom or side of the hole has been cracked. One way would be to rig compressed air and see if it holds pressure or if you hear leaks. You could try filling the hole with antifreeze/water solution and see if it leaks down. Depending on the crack it may not leak out until under pressure.
Robert McCoy

Is there enough thread on the bolts now that the head has been skimmed?
Dave O'Neill 2

Bob-
The bolts were a DPO bodge. Robert is correct when they tell you that the threaded mounting holes in the block should be chamfered in order to prevent lifting of the area around the stud. Paul is also correct in advising you to not torque the studs down. Steel studs have a different coefficient of expansion than that of a cast iron engine block and preloading them will aggravate the effect of this factor by increasing stress on the engine block. Due to this different coefficient of expansion, if the steel studs are bottomed out against their shanks in the engine block, then the consequent preloading can cause the deck area around them to distort upwards as they expand more than the engine block, and that could lead to a blown cylinder head gasket, or even a cracked deck of the engine block. When the engine block cools, being a casting, it will tend to return to its original flat shape if it has not cracked. This, in turn, will drive you to despair when you try to figure out why your cylinder head gasket has been leaking. This becomes increasingly likely if material is removed from the deck of the engine block in order to significantly raise the compression ratio, thus decreasing its rigidity.

Chamfer and retap the threads in the engine block prior to installing the cylinder head studs. Should the cylinder head stud spin or wobble in its threads when installed dry, check to be sure that the studs are not undersize. Do not make the all-too-common mistake of attempting to torque the cylinder head studs down onto the engine block as this may lead to cracking of the mounting lugs inside of the engine block. Because the cylinder head studs extend into lugs that serve the secondary purpose of reinforcing the deck of the engine block from the interior of the coolant jacket, any cracking of the lugs will allow coolant to leak past the cylinder head studs and undermine the sealing of the gasket. It is always possible that a previous owner may have already made this mistake, so coat the bottom threads of each of the cylinder head studs with a flexible sealer such as Fel-Pro Gray Bolt Prep immediately prior to the torquing of the cylinder head. Torquing of the cylinder head stud nuts to their specified 45-50 Ft-lbs will accomplish the task of securing the studs in the engine block just fine. Never use a thread locking compound as it will result in damage to the threads whenever the studs are removed, thus rendering them useless. Coat both the upper threads and the smooth shanks of the cylinder head studs with copper antisieze compound or any other heat-resistant antisieze compound in order to prevent corrosion. This will make removal of the cylinder head in the future into an easier task.

Be aware that it is not unknown for suppliers to accidentally ship the wrong cylinder head studs. The eleven cylinder head studs of B Series engines are 3/8” (.375” / 9.525mm) in diameter with the upper sections of having 24 threads per inch and the lower sections having 16 threads per inch. Seven of these are 4 ½” (4.5” / 114.3mm) in length, while the remaining four are 6 ¼” (6.25” / 158.75mm) in length.
Steve S.

In emails with Chris Betson, who knows these engines as well as anyone, he specified that the studs should be little more than finger tight in the block. RAY
RAY

Thanks for the suggestions. When I installed the studs, I ran them in finger tight then about a quarter turn with a wrench. I'm going to remove the leaking studs one at a time, seal the threads with sealant as suggested and reinstall and torque. The stud holes in the block had been slightly counter-bored by a PO (maybe 1/32") so I didn't chamfer. If they still leak, I guess I'll pull the head back off and investigate further. The odd thing about the bolts that I removed was that the engine had performance work done on it previously - ported and polished head, mild cam and a few other items - so I don't think the bolts were makeshift - just really strange.
Bob Lasater

"I'm going to remove the leaking studs one at a time, seal the threads with sealant as suggested and reinstall and torque."

I hope you don't mean torque the studs in the block, which *definitely* should not be done. Even 1/4-turn with from finger-tight is too much. The only torqueing that should be done is on the nuts after the head has been fitted. The torque is there to clamp head and block together, not to secure the studs in the block.

Any sealant on the threads can only be a sticking-plaster/band-aid. Coolant can only leak past the stud nuts if the gasket is leaking or the head or block are cracked or warped.
Paul Hunt

Good luck Bob. Don't bottom the studs in the block as cautioned by Paul. For now I would seal them because we're assuming the block may be cracked internally and that's what we're trying to fix.

If the block is cracked I don't know what options you'd have except to seal the studs as described above. Like I said not a desirable situation but there are many cars designed with through stud or bolt holes.

I still don't know why bolts were used. Maybe they snapped studs off and decided to go with Grade 8 bolts figuring they would be stronger. There have been reports of improperly heat treated studs breaking off while torquing.

By the way the consensus seems to be to lightly oil the stud when torquing and not to use anti-sieze as you will stretch the studs using standard torque values due to the reduced friction.

If this doesn't work then it's teardown time again.
Robert McCoy

This thread was discussed between 21/11/2008 and 27/11/2008

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