MGB-GT 77 B to 73 BGT Interchangable

[LLAngus]

I have a 73 BGT and I have aquired a 77 B. I now know I will not have time to fix up the 77 and want to know if the engine and trans (OD) will interchange? Can I use the dual carb setup on the 77 motor (single SU)? How much trouble is putting the OD into the GT? If I do this I will have parts for a 77 if anyone needs. The other choice is to off the 77 to an interested party. Yes, I will get photos. Bought the wife a new digital for Christmas so I get the old one. No looking around to find a camera now.

Thanks. Bruce

 

[Steve_S]

Should bolt right in. Someone with more experience with later cars might advise you on drive shaft length and other minor potential issues.

 

[WA1KWA]

You will have to swap front plates on the engine. Chrome bumper & rubber bumper cars use different front plates. It's a straightforward swap. I did it years ago when I bought a good 1979 engine from Ted at T&S to replace the engine with a disintegrated piston. Swapped the original dual SU manifold back on the 79 engine, also. The 79 block is still in my 74.

I have no overdrive, so I'll defer on that question.

Colin

 

[Rick_Stevens]

Bruce, aren't you going to have problems come "smog" time using the dual carbs in the '77? The '73 is smog-exempt in CA, but the '77 isn't - and unless you have a shop up there that doesn't check the book, they're likely to gig you for a non-standard setup.

IIRC, anyway....

 

[Bugeye58]

He's going the other way, Rick. The '77 engine into the '73, with the earlier carbs.
Jeff

 

[Rick_Stevens]

Ah. Slinking back into the woodwork now.... /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

 

[davester]

I'd be a little wary of making the switch. Approximately that same switch was done to my '71 BGT way back when. Unfortunately, the later engine had lower compression pistons, hence less power and had other cheapened parts such as single row timing chain and gears rather than double row, etc. It made a huge difference when I later fixed those downgrades.

I'm not certain the '77 engine has those downgrades, but I'd guess that it does since it is one of the heavily smogged engines. Pray tell, why are you making the switch? If you're going to be yanking engines, wouldn't it be not much more work to fix whatever ails the original '73 engine rather than put in a probably inferior '77?

 

[Hap Waldrop]

Well here's one thought you could always switch the timing gear sets as well, the 77 will be a single row. There should be no difference in either 18V engine as far a compression ratio, they both have 38cc combustion chambers, and factory 8 to 1 compression ratio, however the 73 should have 12H2389 cylinder head which is the big intake valve head (1.625" intake). Both block will have the cutouts for the exhaust valves, which means the 12H2389 head will interchange on either block as well. So the moral would be, don't get rid of the 73 engine, or alteast the big intake valve head.

 

[LLAngus]

Two reasons I am thinking of the switch: 1) the OD transmission and 2)the 77 has a rebuilt motor in it. I am worried about who did the rebuild. I really want to put the OD in my GT if I can't sell the whole car. What are the problems in doing that? Do the drivelines interchange and can I put the 73 trans back in the 77?

 

[BOXoROCKS]

....yes but you will want to put your dist in the 77 engine, along with the other suggestions. The whole operation can be done in a weekend.

 

[davester]

Anything else we're forgetting? Is the cam the same? It's funny, but on the other thread I was advocating to NOT do a complete engine rebuild, but personally, if I had this one ripped apart far enough to be changing timing gears and the like, I'd just as soon complete the rebuild so I could keep the original engine...then there'd be two good engines and a more original car.

It's some effort, but not a massive effort to yank the cam, crank, pistons and cart them to the machine shop to check specs, recondition as needed and put back together with new bearings and rings (and you won't have to change out the timing gear and chain).

 

[Hap Waldrop]

The cam should work fine in the 77 engine, in fact swapping it to a dual row timing gear will advance it back to 73 specs, and that's a good thing.

 

[DrEntropy]

"...advance it back to 73 specs..."

I like that! "Advance to the rear!"

Single row chain. Another cost cutting cheapening of the B by Leylend... they were reducin' 'em down to 'rumph build quality. /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif