MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - 3 or 5 bearing engine

Hi All, Can you give me the pros and cons of the 3 and 5 bearing crank engines please. Thanks.
s page

Simon

I'm assuming you're talking race engines?

David Gathercole always used 3-bearing engines.
Dave O'Neill2

Pro 3 bearing free revving against con rods, availabilty, reliability.

Some race engine buiders mofify the 5 to a three main bearing.

Personally I would always use a 5 bearing engine.

Peter
Peter Burgess Tuning

If your going to put one in an MGA, the 3-bearing has the mechanical tach. drive; and you may not need to change the backing plate.
David Werblow

Hi Guys, Thanks, No Dave its for a medium fast road MGA.
s page

I found the first five main bearing engine I drove to be quite a delight--much smoother than the three main bearing engines I had been used to. For any non-race engine, I prefer the five main bearing engines. Better support of the crankshaft, parts are readily available, and with the proper cam and a modified cylinder head they are quite capable of keeping up on modern roads.

When we rebuilt the engine in my daughter's MGB, we used a Burgess econo-tune cylinder head and a slightly improved cam with .020" over pistons. It performs in quite similar manner to my younger daughter's Miata. A larger overbore, say .060", a hotter cam, and one of Peter's Fast Road cylinder heads would offer even greater performance improvements.

You need to define what you are looking for in a "medium fast road MGA", so you have some defined goals. But, I suspect that either of the engines will meet your defined specifications and the five main bearing engine, with its smoother operation, is my choice for my MGA.

Les
Les Bengtson

Simon.

If you want a 5 bearing engine then I've got a spare one and I'm after a 3 bearing engine for our Magnette.

Andrew
Andrew McGee

Not a great deal of difference, there is nothing wrong with a three bearing.

I love the three in my '64: fully balanced it revs far more sweetly than the two 5 bearings I tried in my MGB GT (which was a fair bit heavier car).

I used to know a man with a 1622 A who said it was faster than any road going B but I proved him wrong in my '64!

At Silverstone MG Live last year I was told that every car in the FIA MGB race used a five.

I was also told quite a while ago that the factory always used threes in the works cars - even after the 5 became available.

My bottom line advice would be use the "right" one for your car - a 3 before Aug '64, and a 5 for cars built after that. For an A that's obviously a 3.

John.
John Prewer

I have a new set of con rods for the 3 bearing if your interested.
Ken Harris

I also prefer the 3 main version, which is a much easier swap into an MGA, FWIW - pretty much just drop it in and drive away. Fitting a 5 main means screwing about with rear engine plates, transmission housings/front covers, tachometers, water pumps etc.

The 3 main runs more freely and looks like an MGA engine (see attached photo of one in my 62 coupe). I also prefer them for racing.



Bill Spohn

This thread was discussed between 27/02/2013 and 01/03/2013

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now