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MGC Replacing 18 GB motor with 18V

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Marvin Gruber

Marvin Gruber

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I'm in the process of replacing a 18GB (MGB) motor with a later 18V motor. Going to reuse the early head. I've swapped out the front motor mount plate and using the 5" pulley instead of the later 6" dia. Anyone think of any other items I may need to swap out or troubles I may encounter?


Marv
 
Wait a minute. You're working on an MG and NOW you want to know about troubles you may encounter?
Good thing for my keyboard my mouth wasn't full. I'd be cleaning it for hours.
 
Combustion chamber different sizes from early head to a v series head. Later heads have a smaller combustion chamber with deeper dished pistons. Bob
 
Later engines have lower compression because of all the smog stuff . They are basically the same, the earlier distributor (25D) will fit into the 18V block. I prefer the SU carbs, but a good working Zenith is ok.
Jerry
 
I remember that specific issue...20 years ago?
Dished pistons, earlier large chamber head obtained by owner as his original was cracked beyond economical repair.
And the resulting power...sucked.

I remember looking into flat top pistons, but the cost was too much to do a full rebuild for what it was.
I don't recall the final outcome.
 
As I recall there were 2 different dish pistons in 18v engines. Early or deep dish on the later ones. I try not to mix and match early and 18v. It will bolt up but having the valves adjust in the center of their range and compression ratio would be my concerns. I wish I had more answers on this one. I hope it works out for you. Bob
 
Going to buy a couple of chrome bumper B's tomorrow. One has a 18GB motor that is still on the engine stand. PO said everything inside is new. Claims to has spent upwards of $2k on this motor. I'll check it out when I get it home. It may be the engine to use and same the 18v for later. Going to have a lot of B parts for sale soon. Alum hood, good fenders and OEM steering wheels.

Marv
 
Got the other MGB's today. PO's new rebuilt 18GF engine has a later head on it. I'm thinking seriously about swapping the heads and putting the later head on the 18v block. I'll probably ruin a new head gasket but I think its a better deal, both engines will have correct heads. Whats a general consensus about using the 6" crank pulley instead of the 5". It will turn the water pump and alternator a little faster. Should help right?

Marv
 
Marvin Gruber said:
Got the other MGB's today. Whats a general consensus about using the 6" crank pulley instead of the 5". It will turn the water pump and alternator a little faster. Should help right?

Marv
Click to expand...

Actually if you use the earlier smaller harmonic balancer, and the later RB MGB larger water pulley, you turn the water pump slower than any other MGB combinations, you get an exact 1 to 1 drive, this is what we do on the MGB race cars.
 
You don't want to run the water pump too fast, otherwise you could end up with the problem of the coolant not being in the radiator long enough to transfer enough heat and thus see the running temps rise. I don't know where the cutoff might be, with the same size pump pulley the 6 -v- 5 inch crank pully should result in about a 17% increase in pump speed which at highway engine speed might be too much.
 
I think that if you turn a water pump to fast it could cavitate and not work eficently. The British auto engineers designed the water pump to spin at a certain speed. Just an idea, I could be wrong.Barry
 
Picked up another 18 GB motor that has been rebuilt. Think I'm going to go with that. This car (MGA) is going to be a mixed bag of parts. It already had the 18GB and B sych trans installed. It spun a bearing before I got it. Going to try to fit an late model B overdrive in it when I go back with the engine. Going to use as much MGA engine parts as I can to make it look pretty original. It will have an alternator. If all goes well, it should be a nice driver. Car has a good paint job and interior.

Marv
 
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