10 replies to this topic

[Maccmike8]

Hi folk.

 

What additional parts would I need to put a A plus 1275 in place of my A plus 998 with HS4 carb 1987 manual?

Have used the search function but keep coming across head swaps only.

Thanks Mike.

[Ethel]

What exactly do you have to put in?

 

There aren't many differences, fewer the more bits you have to swap.

 

You'd need a large bore primary gear to fit a 1275 on a 998 gearbox.

 

The water pump pulley & radiator bracket are different because the heads are different in that area.

 

The 1275 block is about 10mm taller, it doesn't often affect much, but depending on what exhaust you have it might.

 

Manifolds, distributor, carb can work, but might well be less than ideal.

[Icey]

Hi folk.

 

What additional parts would I need to put a A plus 1275 in place of my A plus 998 with HS4 carb 1987 manual?

Have used the search function but keep coming across head swaps only.

Thanks Mike.

Ethel has gone down route of swapping blocks, but are you doing that or swapping whole units (including gearbox)? Swapping whole units is a simple job just needing basic changes (thermostat housing and radiator bracket are the main ones I can remember).

[Ethel]

...it was my intention to cover both bases, but I did forget the thermostat housing

 

They're interchangeable, but different fitting angles & heights mean they don't line up with the hose.

[Maccmike8]

Complete engine and gearbox. 

No carb, no inlet, ex manifold.

Will I need new complete exhaust?

Thanks both.

[DeadSquare]

Complete engine and gearbox. 

No carb, no inlet, ex manifold.

Will I need new complete exhaust?

Thanks both.

 

You are trying to get 30% more gas out into the open so a bigger 'pipe' will be helpful..

 

A "long centre branch, 2 into 1" might be over the top, but allows for a hotter cam at a later date, but I'd aim for at least a 3 branch manifold.

[alex-95]

Make sure you use the correct starter for the 1275 as there are different  number of teeth on them and flywheels. also the stater solenoid may need some changing or some relays depending on the starter.

[Maccmike8]

Comes with the starter.

 

Make sure you use the correct starter for the 1275 as there are different  number of teeth on them and flywheels. also the stater solenoid may need some changing or some relays depending on the starter.

[Ethel]

Exhaust depends what you have again. A factory original pea shooter is restrictive on even a 998. Any aftermarket offering is likely to be at least serviceable. Most are aimed at the 1275 anyway, but one that's specifically for a small bore may lack clearance because the big engine is that little bit taller. 

 

If you're using the original carb it'll need setting up, but should be good enough to get it running as it is.

[Maccmike8]

This is the engine Im thinking of buying, any thoughts?

Ive bought from John Middlemoor before and have been satisfied.

[LD_Framework]

Sorry Guys, I make this alive again because I have an issue on my gearbox, and likely I need to put my hand on it. Now I have a cooper 1275 carb 1991 (code 12A2A), I have found a 1000cc engine (code 99HE20) reasonably cheap (much more than a new gearbox). Is the gear box (all) compatible? 
I would like to remove the gearbox in the 1000cc engine and assembly in my 1275cc. is it feasible? what change?
Any suggestion is very much appreciated!
 I need to make a decision quite fast so.... thanks a lot guys!

Edited by LD_Framework, 15 February 2025 - 09:38 AM.