differences between 1098's and smaller moggy engines.

Post by **aussiemike** » Sun Jan 25, 2009 1:21 pm

Hi just wondering if it basically the same blocks, just different bore or stroke??? any help appreciated, cheers, michael.

Post by **mike.perry** » Sun Jan 25, 2009 2:03 pm

The 803, 948 and 1098 engines have basically the same blocks with different combinations of bores and strokes and also other differences such as crankshaft bearing sizes, combustion chamber and valve sizes, probably different camshafts and in the case of the 803, a different oil filtration system.
Things get a little more complicated with the 1275 and A+ engines and there are numerous differences with the tranverse engines.

Post by **bmcecosse** » Sun Jan 25, 2009 2:37 pm

The 803 is different -forget it. 948 block has only one proper camshaft bearing (at the front) - and the 1098 block has all three cam bearings installed in white metal. It's the one to use! 948 crank can be fitted with Mini 998 pistons to give 998 capacity engine if you so wish. 1275 blocks are slightly longer and slightly taller - and have 2" main bearings - as do some of the later 1098 Spridget blocks.

Post by **mike.perry** » Sun Jan 25, 2009 4:39 pm

What is the difference with the 803 block apart from what I said earlier?
Just trying to learn something.

Post by **pauln** » Sun Jan 25, 2009 6:04 pm

As I understand it the oil flow in an 803 is different not all the oil goes through the filter wheras the later engines have full flow filtration. Crankshaft bearing sizes different as well. I did try to slip a dead 1089 crank into a dead 803 block but there just is'nt the room. Shame it would have been nice to make a 1098cc engined minor that looked 100% visually correct under the bonnet.

Post by **bmcecosse** » Sun Jan 25, 2009 7:36 pm

That's it - the bearings are tiny and the oil flow is 'bypass' rather than full flow. Differences around the water pump mount too - and the camshaft has ultra low lift -although obviously that can be changed! Obviously the bores are tiny - and I understand won't take any significant amount of reboring anyway!

Post by **aussiemike** » Mon Jan 26, 2009 12:40 pm

how hard would it be to turn a 948 into a 1098? what parts would be needed?
cheers, michael.

Post by **mike.perry** » Mon Jan 26, 2009 2:32 pm

It is not worth the money or effort.
Apart from the differences noted above, the bore and stroke are different, so new crank and pistons, compression and valves therefore new cyl. head etc. etc. If you can get hold of a 1098 engine, which you would need anyway for donor parts, you would be better of having it overhauled and dropping it in. You would however need a 1098 box with the larger clutch to take the extra power with better reliability.
If you are stuck with the 948 all is not lost as it is reckoned to be the smoothest running engine of the three and I am sure it could be tuned to deliver more power.

Post by **bmcecosse** » Tue Jan 27, 2009 12:33 pm

The 948 block would need boring by 65 thou - and you would still only have one cam bearing, which is ok provided you don't want to run a fancy cam or double (or even extra strong) valve springs Far far better to use a 1098 block - the later ones with the 2" mains are the best by far - especially is performance mods are intended!