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MG MGA - 1800 3 main or 1622?

My '58 coupe came with a 1500 engine. I had planned to replace this with an 1800 3 main engine for more oomph, but have now been offered a 1622 engine.
Can anyone give me the pros and cons on these two choices? Thanks, Peter.
P.S Am fitting a Sierra/Merkur 5 speed gearbox and 3.9 diff also, so back plates are not an issue as 5th Gear provide it in their kit.
P. Tilbury

The only cons I can think ofis that the 18GA 3brg motor usually ends up with a cracked crank. They also always leak a bit out the rear main as they don't have a seal on the crank. If fitting the 1622 make sure you have the latertiming cover with an oil seal not felt jammed in a groove. I would look for an 18GB 5 main engine.
Garth Bagnall

Thanks Garth.
Reason for 1800 3 main is more torque and rev counter mechanical drive option. I was expecting cons on the 1622, if any.
I'll look for a later timing cover. Tks for the tip.
P. Tilbury

Depends what level of performance you are looking for. I believe the 1622 is a lot harder to find and may be more valuable but the 1800 has more power.
Kris Sorensen

3 main MGBs do NOT often end up with cracked cranks - in fact they are far more durable than 1500 cranks, and the engines are a plug in for an MGA. I'd go for one of those Peter, if you have one handy. That's what I run in my coupe.

Having said that, the 1622 crank is better than the 1500/1600 part, you just won't get the added torque an bit of power the 1800 offers.

Call me if you want details on how to fit the B motor.
Bill Spohn

Thanks Bill. Agree with your observations. Having difficulty finding an 1800 3 main at this time, hence considering the 1622 being offered to me. Power, however, is EVERYTHING!
Do you have comparative HP and torque figures for these 2 engines?
P. Tilbury

The power difference between a 1622 and 1796 motor are small. When overbored to 060, it's only marginally below the ccs of a 1796 anyway. Many internal parts are identical. The 1622 motor may be rarer in the USA, but it was a VERY widely used BMC engine, and blocks are plentiful and much easier to find than for example 1600 engine blocks (as that engine was ONLY used on the 1600 MGA).

A well tuned 1622 engine is an excellent alternative to the 1800. You can use B heads, water pumps, and con rods etc.
dominic clancy

Hi Peter, Accoring to the books I have - the 1600 Mk1 engine produced 79.5 bhp whereas the 1622 engine was 90 bhp. The 1800 3 bearing is quoted as 95 bhp.
Cam Cunningham

Peter - just sent you a link to a 3-main engine on Seattle Craigslist for $50; I think a couple cylinders need liners, but hard to beat that price!

Good luck!
Philip S Jones

This thread was discussed between 18/07/2008 and 21/07/2008

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