Losing compression in 4th cylinder

[NRS]

I have a problem with the compression in one of the cylinders. Garage says it's probably burnt valves, which is a very expensive job here (near £1300 for the 4 valves and installing them!). Cars are also a lot more expensive here, so it doesn't write it off for that amount. I was wondering if there is any other likely explainations that would result in the loss?

If is the valves then is there any that you would recommend? And is there anything else that should be replaced when the top is off (timing belt, water pump etc)?

[MX-5 Lazza]

It'll probably be a lot cheaper to just replace the head than to fix up the one you have.

[snotrag]

Is this an early Mk2 we are talking about? (I might be confusing you with someone else).

If so just double check its the valves and not bottom end, as I think early (99,00) Mk2s can be susceptible to ring failure.

Otherwise, yes, by far the easiest thing to do is a 2nd hand head (or complete engine!?) and simply swapping bits out is well within realms of DIY.

Timing belt would need changing at same time yes.


Course, the crucial question is - WHY has it done this...

[NRS]

snotrag said:

Is this an early Mk2 we are talking about? (I might be confusing you with someone else).

If so just double check its the valves and not bottom end, as I think early (99,00) Mk2s can be susceptible to ring failure.

Otherwise, yes, by far the easiest thing to do is a 2nd hand head (or complete engine!?) and simply swapping bits out is well within realms of DIY.

Timing belt would need changing at same time yes.


Course, the crucial question is - WHY has it done this...

Yes, it is a '99 model, and has only done around 60 000 miles. This tends to suggest it's not the thrust bearing issue - although there seems to be some debate on this. However it is the 4th cyclinder with the problem... Might check this out as it would save buying a new head if it's messed up.

I had been wondering about changing the engine, and was wanting to do it to a 1.8 so I could supercharge it. However I'm not sure if this is possible (asked on here and Nutz and got no reply). There's lots about NA 1.6 to NB 1.8, but not from NB to NB. Also it involves at least a 6 day trip to somewhere where I could likely get an engine/ do it for a reasonable price. Might do that though, and get the supercharger etc done at the same time. I know the clutch doesn't fit between the two of them.

Thanks for the advice.

[ronime]

Premature oil control ring tension failure affects all Mazda engines. I have just rebuilt my '92 1.6 B6 engine for this reason.

Find a good garage/technician with leak-down test equipment. This will quickly tell you if the loss of compression is due to rings, valves or gaskets.