MX-5 MK2 cylinder head difference between 1.6 & 1.8

[R/M]

Howdy doo,

A lady friend of mine recently bought MK2 MX-5 with the 1.6 engine. It's smoking quite a fair bit on start up so it looks like the valve stem seals need doing.

Does anyone know if the 1.8 head is exactly the same as the 1.6? Because I can't find info online apart from the bore & stroke being different between the two engine sizes.

It would make sense if the cylinder heads were the same, but then as the bore is 5mm wider on the 1.8 then assumingly the combustion chamber in the head is going to be 5mm wider on the 1.8 too.

If any MX-5 techies are out there & can help me with this, it would be greatly appreciated!

Especially if head specs can be told, such as do they share the same lifters, stem seals, valves, guide sizes, cams etc?

Many thanks,

Rob

[Wallers]

Nope, it's longer as the bore spacing is wider. With MX5s just look up Miatas and you'll usually find the answer. I think the lifters are interchangeable. As for everything else you mentioned I don't know.

[R/M]

Thanks for the input, where did you read the stroke is longer?

[Wallers]

Miata.net. Although it is a B series engine they aren't interchangeable. Whereas with the 1.8 you can semi-easily swap to a later revision.

[R/M]

Hmm, can't get that Miata.net site to work?? I shall have a hunt around again elsewhere.

[Jonny]

Try forum.miata.net

Also - one of the korean companies bought the old engine designs, so valves, lifters, seals etc available from them at a lot less cost than mazda - I think it was Kia

[R/M]

Thanks for that, found out the info pretty quick by following a link posted on that forum.miata.net site.

Looks like it's a no go on using a 1.8, that's a bummer. Was hoping to find a second head & build that up so it could be a quick swap.

Lifted from " http://www.solomiata.com/Mx5Engine.html "

" Since the 1.8 is really just a stretched 1.6, most everything on the front and back of the motor will interchange between the them. This includes the cam angle sensor, coolant intake pipes, flywheel/clutch assembly, various covers and brackets, cam gears, water pump, and timing belt tensioner, etc. The intake manifold, exhaust manifold, motor mount brackets and camshafts do not interchange because of the bore spacing differences. The 1.8 ‘B’ motor has also seen duty in the 1991-1995 Ford Escort GT/LXE, 1990-99 Mazda Protege, 1991-95 Mercury Tracer LTS and Kia Sephia GS. (FYI, the 90-93 Escort GT and Tracer LTS 1.8 DOHC use the same throttlebody and flowmeter as the 1.6 Miata). There was also a SOHC 1.8 used for a short period in the 1990-93 Protege. "

The bit in bold says it's a no go on the B-engines (used in MK2/MK2.5 MX-5s from what I can gather) as the 1.8 has wider bore spacing, thus rendering the 1.6 intake & exhaust manifold + other internals useless.

Thanks for the help guys, lesson learnt...should have told her to buy a 1.8