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Ehgine type and O/D questions

Posted by gord weflen

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Ehgine type and O/D questions #1
gord weflen	Posted: August 21, 2000 02:46AM

Hello gentlemen, here is question for the gurus of this board. Is there a difinitve way of figuring out what type of engine is installed in my 1970 MGB GT as the engine ID plate is missing. Can this be found out using parts connected, or by any other means? I know that I can request a copy of the original manufacturers cert. but I'd rather put the $50 into the engine right now. Secondly, what do I need to look for to see if I have an overdrive transmission?

TIA
Gord

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RE: Ehgine type and O/D questions #2
Paul Noble	Posted: August 21, 2000 07:39AM

I have the same problem with my 1970 roadster. It should have an 18GF engine, but the number plate is missing on mine, as well.

I don't think that there is any definitive way of telling from the external clues, which engine is installed. The only external clue that I can think of is that very early, three main engines have a fitting at the left rear of the block for a mechanical tachometer cable. The five main engines all used an electronic tach, and do not have the cable.

The problem is, that just about all of the external equipment, such as alternators, distributors and carburetors can be swapped from one engine to another, so your engine might be a hybrid of several years.

For example, mine has the correct AUD405 carbs, an alternator, but has a pre-68 cylinder head (no air holes), and a pre-68 distributor (screw-on vacumn fitting). The car has the correct, four synchro transmission and the correct starter, but it still could be a pre-68 engine block, if someone had switched the rear engine plate and flywheel.

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RE: Ehgine type and O/D questions #3
Paul Noble	Posted: August 21, 2000 07:45AM

Gord,

I forgot; the only truly reliable way to determine if your car has an overdrive is to crawl under it and look. THe OD is a rather large, barrel-shaped unit that attaches to the rear of the transmission, replacing the standard tailshaft housing. The standard housing is long and and tapers to the driveshaft end. The OD is about eight inches in diameter all the way back.

On US-spec MGB's, the OD switch (in 1970) was combined with the windshield wiper stalk. The up-down movement of the stalk controls the wipers; the fore-aft movement controls the OD. All cars were fitted with this switch, regardless of whether an OD was actually fitted.

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RE: Ehgine type and O/D questions #4
Gerry	Posted: August 21, 2000 08:13AM

All the pre 72 engines were originaly painted red and the ones after were painted black. You might be able to look at the head casting number to get an idea when it was made. Late cars with air injection had double grooved crank pullies. and an ear on the thermostat housing to mount the air pump. The fan was also changed several times. All of these could have been changed during the engines prior life so should be taken as hints only. If you ever remove the head, the 18V blocks have an extra cutout in the top of the cylinder for exaust valve clearence.

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RE: Ehgine type and O/D questions #5
Tom Bedenbaugh	Posted: August 21, 2000 08:22AM

As far as your first question about the ID of your engine. The answer is no. Spending the $50 want tell you anything either as all they will do is give you the engine ID #. What has happen is the block was hot vatted with the ID plate still attached and it desolved the aluminum ID plate. Like Paul said the only way you can for sure determan if you have an OD is look under the car.

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Paul - block manufacturing date #6
gord weflen	Posted: August 21, 2000 01:02PM

Refering to a reply post to "Various stamped #'s" on 8-15-2000, there should be a triangular cast stamp under the oilfilter housing. This number is the year your engine was cast, as per the author, I have not confirmed this.

Thanks for all the replies, guy's. I'll let you know what I find.

Gord

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Tom, how do I... #7
gord weflen	Posted: August 21, 2000 09:44PM

figure out what type of engine I have, then? All the literature that I have read makes me think I have an 18V, but others have made me think it is a 18GF, or does this even matter as far as tuning is concerned? Also, should I assume that it is a low compression engine?

As far as the previous posts, I have a doublr grove crank pulley, a vacuum on the distributer(WHY?), ears on the thermostate cover, air holes in the valve cover, and AUD405 carbs.
Didn't check for the O/D yet.

Thanks for your comments.

Gord

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RE: Tom, how do I... #8
Tony Barnhill	Posted: August 22, 2000 07:19AM

All the things you mentioned can be retroffited from any engine onto any engine...some guys blow an engine, pick up another from a junkyard & hang their ancilliaries on it...can't go by head as we all switch them about (my favorite is a '67 w/modified chambers), we all switch distributors, etc...if you figure out how to read the casting #, let me know...about the only way to tell what you have is to open it up & look at pistons..but, that's not certain either as some of us have favorite pistons we put back into any block we build....

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RE: Tom, how do I... #9
Paul Noble	Posted: August 22, 2000 07:55PM

For what it is worth, AUD405 carburetors are from a 1970 MGB. Of course, carbs are easy to move from one car to another and any HS-4 carb will fit the manifold from any car from '62 - at least '71. I'm not sure if the HIF-4 manifolds are different.

What type of distributor do you have? The early cars used a 25D, while later cars used a 45D. Once you have determined that, there is a part number that will tell you which sub-model you have. I don't think this can be read without removing the dizzy from the car. The model number is located on the distributor housing on near the base of the vacumn advance unit. The part number is stamped underneath the same location.

The part number will tell you what year(s) the distributor was used on. It will also tell you the advance curve, which differed for low and high compression engines.

None of these items, by itself, will tell you which engine you have. Any or all of them could have been replaced. However, we already know that your carbs are from a 1970 engine. The head could be a '70, since it has air injection ports. If you remove the valve cover and get the casting number, that will identify the head.

The vacumn unit on the carburetor is the vacumn advance. At high rpm's, there are spring-loaded weights inside the distributor that alter the spark timing. At lower rpm's, the high vacumn from the carburetor does the same thing. This allows the engine to change its operating characteristics in response to the current driving conditions. The advance at various rpm's, plotted on a graph, forms what is referred to as an advance curve. Reconfiguring the distributor to change the curve has a profound effect on the power produced and at what rpm it is produced. It also affects emissions. This is why it changed over the years, as MG struggled to meet the emission standards just coming into play.

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Paul... #10
gord weflen	Posted: August 22, 2000 10:15PM

Thanks for the response, I will check the distributer when I get to it. I assume then that the vacumm advance ports on the distributer and carb are not supposed to be connected to anything but just open to the atmosphere? Is this port on the carburator refered to as the Vacuum ignition take-off, or is that something different? As you may have guessed, this is my first time at this and there are lines and hoses running all over the engine compartment that are not connected to anything on one end. Very confusing! No offence to Robert Bentley, but the manual needs more pictures to refer to.

Gord

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RE: Gord #11
Jerry P	Posted: August 23, 2000 01:12AM

The vacuum advance uses engine vacuum, either from the carb or intake manifold, so the line from the distributor should be hooked up to one or the other.(Not just to atmosphere)

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