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MG MGA - cylinder head needed

Hello,

My MGA project came with a later MGB head installed. After some discussion with my mechanic and reading some of the archives I have come to the conclusion that I would like to get a good 1600 head. My car is a 1960 1600 Mk 1. Anybody got a good head they can part with?

Thanks and...

Safety fast!

JMG
JM Greenlee

After further reading in the archives, I am more confused than ever.

It appears 1800 heads will work o.k., but need some skimming to raise compression ratio back to spec. O.K, I understand this. At what point do the 'eyebrow' machinings in the MGB block come into play?

Advice, people! Please!

Safety fast!

JMG
JM Greenlee

Get an early 1800 without the air injector ports. The head will look original and fit the same as a 1600 or 1500 head. You will have a hard time finding a 1600 head as they were only used on 1622 and most 1600 had 1500 heads. The early B head will have the larger intake port for better power.. The B head will be easy to find. check E-Bay
JEFF BECKER

Jeff,

Will the early 1800 head need to be milled down? When are the 'eyebrow' machinings an issue?

Safety fast!

JMG
JM Greenlee

JM. The "eyebrow" was first used on the early 18V engines. This was a five main bearing engine used from late 71 onwards. It has holes for the air injectors. If you follow Jeff's advice, you cannot go wrong. Les
Les Bengtson

Les,

Do I understand you correctly that using the early head precludes needing the eyebrows? Is that still true if the head is milled down to restore the appropriate compression ratio?

Safety fast! and even faster with the right head.

JMG
JM Greenlee

JM. It is my understanding that the early B cylinder head is identical to the cylinder head used on the MGA 1600. Thus, I do not know what you are writing about when you say "if the head is milled down to restore the approximate compression ratio". Everything I have been able to read and the people I have spoken with indicate that there is no need to mill the cylinder head unless it is warped. Then, you would mill it the minimum necessary to ensure it was straight. Where are you getting your information that the combusion chambers were larger on the MGB 18G cylinder head as opposed to the MGA 1600 cylinder head?

As to the "eyebrows", they were used with the 18V engine due to the size of the intake valves, which were larger than had ever been used before on the B series engine. Were you to use an 18V cylinder head having the larger intake valves, yes, you would have to modify your block. That is why all of us have recommended the earlier cylinder head which does not have the holes for the air rail. If you use one of them you should have no problems. Les
Les Bengtson

Les,

Thanks for your help. I have been digging around in the archives and speaking with my mechanic. My understanding is that starting with the 1622 engine they went from a dished piston to a flat top piston and increased the size of the combustion chambers. I have seen references to milling the head down to decrease the size of the combustion chambers back to the original size used on the 1500 and 1600 motors. I really have no first hand knowledge of my own, just trying to learn and make sense of what I have read, etc.

It sounds like the late MGB head (as supplied with my car) is not appropriate for the 1600 motor. I will continue to study as I seek a 1500 or early 1800 head.

All input is appreciated!

Safety fast!

JMG
JM Greenlee

Hey guys, I found this in the archives:

Posted 26 November 2003 at 03:20:53 UK time
I could be mistaken about aspects of the following, but this is my understanding: They will bolt right on. An MGB (1800) head has larger valves and ports than a 1500 or 1600, the same size as a 1622 (MGA Mk. II). Pre 18V heads have 43CC combustion chambers and 18Vs have 39cc (shallower chambers). 1500 and 1600 'As have 38cc combustion chambers. So if you put a pre-18V head on an otherwise standard 1500 or 1600 your compression will drop a bit; if you install an 18V head, you should more-or-less maintain your CR and benefit from the easier breathing HOWEVER you may have interference problems with valves and block-top. Check Barney Gaylord's site, mgaguru.com, as I believe he has a more detailed report on the matter.
I have a modified early 'B head (43cc)with larger intake valves on my bored 1500 and have no valve interference problems. I fitted flat-top pistons to offset reduction of compression ratio.
You could modify your current 1600 head but if i were you -- well, I just told you what I did.

I think the poster's name was Marvin Dupree?

So, what is the scoop?

Safety fast!

JMG
JM Greenlee

From Lindsay Porter's 'BMC and Leyland B-series Engine Data'

Capacity of Combustion Chamber:

MGA 1500 - 38.2 to 39.2 cc
MGA 1600 - 38.7 cc
MGA 1600mk2 - 43.0 cc
MGB 3 main 42.5 to 43.5 cc
John DeWolf

JM. After all these years, your chances of finding a stock cylinder head are slim. Most of them have been milled in the past to correct warpage. The depth to which the valves are sunk will also have an impact on the combustion chamber volumes. If the engine the cylinder head is being fitted to has been overbored, that will have an influence on the exact compression ratio. All of these are factors which need to be addressed with parts in hand. In theory, with a stock high compression engine, you will have a slightly lower compression ratio if you use an early MGB cylinder head. The combustion chambers are a nominal 10% larger than the MGA 1500/1600 cylinder head's combustion chambers.

However, if the block has been decked, that will raise the compression ratio. If the cylinder head has been skimmed, that will raise the compression ratio. If the pistons are oversized, that will raise the compression ratio. The math needs to be worked out to fit a specific example after you have measured the actual volume of the combustion chambers, volume of the dishes (if any) in the pistons, the area of the block above the top of the piston, thickness of the head gasket, etc. Then, you can do the math. As a practical thing, however, I know of people who have simply installed the early MGB cylinder head on their MGAs and are driving the car in that condition with no problems. Les
Les Bengtson

Jm,

Just to follow up with what Les said. You have a bit of an unknown quantity in terms of your head chamber volume at the moment. You will need to measure the chamber volume. I use a piece of clear perspex with two holes drilled in it and a cc calibrated burette, borrowed from the Science dept. at work. Stick the perspex on a chamber with grease and then fill the chamber up through one of the holes. Do this with each chamber.

As to the interference, again you will need to measure the valve lift as a product of camshaft and rocker ratio. Will that then hit the block at full lift?
This will also depend on size of the valves. Usually the block will need some relief cuts with a Mgb head. This will also unshroud the valves anyway.

Check out the MgaGuru site for how to do this with a router!! Frightening.

Chris.
Chris C

I thought I understood this issue of early B heads on 1600 or 1622 blocks but after reading the messages have become confused. Chris has said that if you put an early B head on an MGA block you will generally have to use eyebrows. I've put an MGB head skimmed for straightening on a 1622 block with dished pistons and had no trouble. At the time I did'nt even know about the problem. What know one has given a definitive answer to is JM's question about planing an MGB head sufficiently to restore the 8.3 to 1 compression ratio? Would eyebrows be needed then? It may be that the only answer is to assembly it all, tighten the head, wind the engine round and see if there is clearance. I believe this is the recommendation in a number of authoritive articles on the subject. But if your happy with a normal standard performance I don't think you have to put in eyebrows. You could always do the maths and see what compression ratio your going to get in advance.

John












































J H Cole

IMHO you will only need the cutouts if you fit the 18V head which has much wider and shallower chambers.

It is the exhaust valve (not the inlet as stated by Les) that needs the clearance.

In all cases where there is any doubt, I would cut the clearances anyway.
Chris at Octarine Services

Thanks all, you have been helpful.

It appears to me the thing to do is find an early B head, plane it down to make the combustion chambers nominally the same size as a 1500 head, and install it. I have some interest in cleaning up the breathing of the motor while I am at it, so maybe I'll get the special tuning books and set it all up at one time.

Safety fast!

JMG
JM Greenlee

This thread was discussed between 27/02/2005 and 01/03/2005

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