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MG MGB Technical - 1978 engine to fit 1971 car

hi will i have to make any changes to the 1978 engine out of rubber bumper car,when its fitted to my 1971 chrome bummper mgb roadster,any ideas .regards richard
r a pinfield

Basically they are interchangeable but depending on what you want from your car - you might want to keep the older engine (what's its number) with the head from the later 18V motor.

I made the change several years ago in a '67 GT from a '67 engine to '78.
There are several differences. I used the early pan and timing chain cover. The 3 synchro tranny has a different bolt pattern and the rear plate must be changed if you are going to use the 3 synchro tranny on the late model engine. The front engine damper/pulley is larger diameter on the late car. I used the early small crank pulley on the late engine. The motor mounts need to be used from the early car. I recall reading the block motor mount attachment is also different, however I don't recall any special issues in converting to the earlier mount. A different water pump is used. The mounting for the alternator is different. The crankcase ventilation is different.
The late model engines used a large dish piston with a small combustion chamber. The early engines used a small dish piston with the large combustion chamber. You can use the early small dish pistons with the late head to get a higher compression engine.

Basically, you will need to keep and use many of the external parts of your early engine to convert the late model engine.

Barry Parkinson

Richard. Roger is more correct here. There were significant differences between the Mark I cars and the Mark II and later cars. The Mark II and later cars, as you are discussing, have only one major difference between the various versions--the motor mounts and how they attach. The rubber bumper cars, at some point, switched to a round style motor mount rather than the rectangular mounts used before then. This required a different bracket for the motor mount to attach to the engine through. So, at the very least, this bracket will have to be used from the earlier engine. I do not know whether the engine front plate, on the 78 engine, will accept the brackets for the earlier style motor mounts. If not, you would have to swap engine front plates between the two engines.

If your current engine is actually an 18V, which were introduced in August 1971, the timing chain cover should have the timing marks on the right (as seated in the car) side rather than under the engine. The crankshaft pulley will also be of a different size (diameter) than the later 18V engine. If your current engine is an 18G series engine (my 68 has an 18GF engine) you will have the timing marks on the bottom of the engine and will find the side mounted timing marks of the newer engine a great improvement. All parts should, I believe, directly interchange between the two engines you are considering. But, you will want to check carefully before actually installing the engine. Make sure the engine will bolt up properly when you drop it in so that you will not have to remove it again. Les
Les Bengtson

I did this a few years back:

- I DID have to swap front engine plates. The old style brackets would not bolt to the front plate of the newer engine.

- I blindly transferred a shim behind the timing chain tensioner to the new engine, resulting in a very noisy clearance problem between the shim and the double-row chain. My guess is that that shim was either for the front plate off of the later engine, or for a single-row timing chain. For a late engine with (18V797) with an earlier front plate (18V673) with a double-row timing chain, you don't need the shim behind the the tensioner. I guess the bottom line is to pay attention to your configuration.

- The timing marks are in a different place. It doesn't bother me much: I use the vacuum method I learned on this site (get max vacuum then back off 1/2 PSI).

- I think I remember finding that the engine restraints were a little different, but this could be because my car was seriously munged up by a previous owner.

- If you're also going to use the later transmission, you'll need to match your speedometer to it. It seems that there was also a difference in the wiring to the seatbelt-warning-light stuff. I just bound these wires up in a Ty-Wrap or shrink-wrap to keep it out of the way.

- Though not a "difference", while you're doing the swap, I recommend the "Porter" mod to the rear engine support.

Hope this helps.
Larry Bailey

cheers for your advice.regards richard
r a pinfield

This thread was discussed between 18/08/2005 and 21/08/2005

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