1275 rebuild big end offset

[moggiegeek]

Just building up the engine now. Rings on pistons and pistons in block.
I remember there was a useful diagram re the offsets to match the crankshaft. It would be useful if someone could post it.
I've staggered the compression rings at 120 degree intervals but read recently that the gaps should be orientated opposite the thrust face - is this important?
Finally - just to reassure - is it actually possible to fit the big end bearing caps the wrong way round on their con rod?
Any further advice welcome

[philthehill]

So long as the ring gaps are not above one another you will be alright. 120 degrees will be alright. The manual says 90 degrees. With use the rings will move around the piston grooves so eventually the gaps could be anywhere.

Did you gap the rings in the bore before fitting them to the piston?

Look at the conrod where the cap meets the rod and there should be numbers on the cap and rod i.e. 1 to 1, 2 to 2, 3 to 3 & 4 to 4. Just match the numbers.

Also look at the rod - you should be able to see where the cut out for the tang of the cap bearing has allowed the oil to stain the rod. Match up the stain on the rod with the cut out of the and you will be ok.

So numbers and stain is the way to go.

Looking the BL workshop manual AKD7555 for the Marina/Ital 1275cc engine the off-set of the crankshaft bearings are No: 1 & No: 3 is to the rear of the engine and No:2 & No: 4 is to the front of the engine.

Marina/Ital crankshaft below:-

100_2546 (2).JPG (1.24 MiB) Viewed 1007 times

Marina/Ital conrods/pistons below:-

100_2548.JPG (1.59 MiB) Viewed 1007 times

Here is a link to a set of 1275cc con rods/pistons and you can see the off-set.

https://www.ebay.co.uk/itm/Classic-Mini ... Swlk1dOwBQ

[paul 300358]

The big end caps can be fitted the wrong way round but you wont turn it over, they are line bored, you need to fit the bearing position tangs together. See page A12 of the attached. https://issuu.com/morrisoxford/docs/morrisminor
I fitted my rings at 120 deg and it runs brilliant.


Sorry, Phil beat me to it.

[moggiegeek]

Yes I gapped the rings. Therefore with the big end bearing caps and con rod the numbers match on one side.
The bearing tangs are on one side albeit at opposite ends of the assembly.
Many thanks