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MGB-GT I have to replace the head on my '71 BGT

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Adam58

Adam58

Jedi Hopeful
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The cylinder head on my '71 MGB is leaking coolant onto the #2 sparkplug. I think it's cracked. My question are....

Does anyone have (good) head they want to sell? and

What should I look for when I take it off to determine the general condition of the bottom end? I don't hear any rod or low end noises and the car runs great but I don't want to invest the time and money into a head if the bottom end will come apart next week. ick!

Thanks!
 
Hi Adam, if the head is leaking you should not be running the engine.Hopefuly, if you drain the oil from the engine you may avoid any further damage.I might suggest that you drop the pan and have a look at the rod and main bearings if you find significant water in the oil.---FWIW---Keoke
 
Thanks Keoke, So far, I think the leak is external with coolant weeping down the side of the head. The oil still appears clean on the dipstick but I haven't pulled the valve cover to see if I have cottage cheese forming up there. Pulling the pan, however unpleasent is probably a good idea though! Adam

P.S. oh Jedi Knight... How the heck do I mark a forum, subject or thread on my homepage so I can check it when I log in?
 
There is a fellow on this forum named Basil he is just full of those kind of answers.If you want to waste some power just put the computer in standby-meaning I dunno!--Keoke /ubbthreads/images/graemlins/laugh.gif--- ps if the oil is clean you are safe! Oh! I think all you have to do is Book Mark it and add a shortcut to the desk top.
 
Speaking of heads on BGT's. As I am in a pickle with my motor, I wanted to ask this:

To my knowledge, when pulling an exhaust manifold bolt, oil should NOT be coming out of the bolt hole, correct? From what I understand this signals a broken oil jacket. Is it different on this head?

Thanks for everyones help in this!
 
Hi Zack, I think you are correct.However, most of the time a manifold is pulled I have not been required to pull the studs and have never experienced that problem.---Keoke
 
Adam, it's possible that you've just blown the head gasket, but you have to pull the head to find out. The only way to access the bottom end is either with a compression test, watching the oil pressure, checking the bores when you pull the head for wear and pulling the oil pan and checking the bearings. Good luck with your head and I hope it's not cracked. Keep us posted.

Howard, I'm not really sure how oil can come from a manifold stud. It's it a few drips or is it really running out?
 
its not spraying me in the face, but it does trickle out.

I think maybe someone broke a manifold bolt off in the head once, and drilled too far trying to get it out.

The motor had apparently been overhauled before. While pulling the bottom end out, we found all the studs holding the mains in had nasty plier marks on the middle, unthreaded part. And for an added bonus, the oil pump was missing a bolt! heh ::shakes head::

Brit-Tek will become my best friend now. :smile:
 
Zach,

That's possible. The oil pressure on the rocker assembly is not very high. And yes, during my engine rebuild, Bob at Brit Tek was the best. Good luck.
 
Eric,

Please email me at mgupnorth at yahoo dot com. I'm interested in you head. I live just north of Albany and could possibly pick it up locally as I will be in Plattsburg on the 28th.
 
Last night’s update: (I typed this all into the forum then but it crashed and lost everything so I’m trying again! $*T&$**%!)

I ran a compression test as part of my attempt to assess the general condition of the motor. At operating temperature, here are the results:

Cyl. No oil (psi) w/ Oil (psi)
#1 130 150
#2 145 150
#3 145 190
#4 125 175

I figure that this implies either unseated rings (optimistic) or worn rings (likely). Any comments from the pros?

I then removed the valve cover to inspect for cheesy stuff (emulsified oil.) I was surprised to find that it is bone clean up there! No cheese, no carbony build-up, nothing but clean oil! I lifted the valve-cover gasket above the #2 plug and I can see the crack, plain as day, across the clean mating surface so we know the head is toast.

Someone on the forum (who shall remain nameless unless he chooses to reveal himself) offered me a running engine (no smoke or leaks) from a ’77. The price is right and I could be back on the road quickly but with some uncertainty.

Eric (703MGB) has an early head core (mine is late) on Ebay that I might be able to use but shipping is $72 so I really have to make sure it’s the right thing.

Thanks for all the inputs!

Adam
 
I would suggest trying to find a later head, an early head has larger combustion chambers and combined with a low compression 18V engine really drop the compression rate.
 
My understanding is that he as a 71 engine. The 39cc head (smaller chamber) appeared with the introduction of the 18V engine for the 73 model year. Am I wrong?

I do not think the 77 engine will fit in your car. 77-80 engine bays were modified to accept 3.5 V8 and I think the repositioned the motor mounts on the engine. Check it out first.

Also budget wise a part from a core head you need to plan at a minimum valves and guides (150-160$) + head work (another 200$).
 
Ooops your right Eric. The smaller champer came about with the 18V. I was thinking about your car when I wrote that.
 
Adam 2 things.

Since you are in california I guess you need to retain all the smog equipment. The head that I have as no provision for the air pump.

Second thing cyl 3 190PSI that is way to much for a B!
 
Interesting stuff...

I'm aware of a '71 with an '80 motor so that s/b okay. You're right that I should check carefully.

CA smog ends at 1975 and earlier cars so that's okay but I would have traded the head at my local shop for a later one anyway. Better compression for me and maybe a rarer core for him. My airpump and smog stuff were long gone when I bought the car.

190 psi is high! It only did that w/ oil squirted in the cylinder though. (See table above.)

Thanks for the continuing knowledge!

Adam
 
You should not put a later head on an pre 18v engine.

If you do that your compression will be much to high. You will have to run very high octane gas. Later head is 39cc compared to earlier of 43cc. You will have some serious pining.
Early engine and late engine did not have the same piston design. To compensate for the smaller chamber of later engines the pistons have a greater dish.
 
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