mk1-forum.net

Hi,

Hope everyone's doing well.

I'm in the process of purchasing a MK2 Cooper S and the owner said he imported some 1380 pistons when rebuilding the motor in the 80's. There's no markings on top of the pistons and they're flat top. Now i know that here in South Africa, sadly it is quite common to use Mazda pistons, which also means the block needs to be decked etc. Quite sad, I know. Would anyone possibly be able to shed some light on these perhaps? I will hopefully be getting the car by month end and then i can strip the motor and check what pistons they are. Then wanted to find out, has anyone ever seen an inlet manifold for twin HS4 carbs like this before, or is it a custom one made possibly here in South Africa? As soon as i have the car, I will start my own thread on here of the build. It will just be slow, as I'm currently planning a wedding and studying and working. Fun, i know.

Good luck with the wedding etc. and hopefully leaves time in the garage?

Not familiar with the use of Mazda pistons, as far as I am aware the early 1380/1400's used pistons from a Triumph (6 cylinder I believe)

No idea on the merits of the Mazda pistons but the honing in the bores is visible and suggests that the rebuild is fresh. if the engine is out of the car would not take long to drop a piston and take a look, unless you are looking for extreme performance or something highly revving my gut feeling is that what you have, unless somebody knows different could well prove adequate and reliable.

Decking the block will not work for you as with the flat top pistons to possibly need to create volume within the combustion chamber, than reduce it, either by machining the tops of the pistons if viable and safe or using a spacer as are available.

I note that the pistons are inset a mm or so into the bores which could well have been intentional to prevent too high compression, before proceeding you need to measure the the volume of the head you intend to use together with that created by the thickness of the gasket and volume in the bore above the piston and determine the actual volume ans subsequent CR, from there you can decide which way to go depending on the CR you require.

Again regards performance, the cam and tuning stage of the head needs to be considered. With a half tidy head, and 286 cam with the twin HS4's with red spring and AAM needles you could well have 100+ BHP revving out at around 7500, which i can tell you makes for some very lively performance and satisfying driviing.

As long as the manifold is opened out to promote the flow and bored to match the carbs and head i think, as mine will prove to be more than adequate for road use.

The Mazda pistons are a popular large bore piston option in South Africa.

All looks pretty good to me, you do need to check your C/R though.