Further to a query about "tappet" (HLA = Hydraulic Lash Adjuster) noise yesterday, I found this on a 626/MX-6/Probe faq site. Most of it (and certainly the bits about HLA noise) is entirely relevant to MX-5's (except obviously the V6 aspects). The message is - change your oil - I have always recommended doing it twice as often as Mazda recommend! (And use a flush additive just before changing)

Quote
"The valvetrain is the wear issue if oil is not regularly changed and HLAs are allowed to remain noisy for 10,000s of miles. In designing the valvetrain Mazda had a difficult balance to achieve: hydraulic lash adjusters (HLAs) small enough to allow a 7500-7800rpm redline without succumbing to valve-float or resorting to solid tappets as Honda have to, yet HLAs large enough to resist collapse & dirty oil. Whilst the V6 with very minor changes is capable of over continuous 8900rpm from Ford testing in the US, dirty oil is known to clog the small oil-control ball valve of HLAs creating a characteristic tap-tap at idle if left untreated.

Initial HLA noise during cold engine startup is normal if only for a short period. During startup the 24 HLAs are in varying degrees of compression depending on where the 4 cams stopped at shutdown. Those HLAs experiencing the greatest compression from the cam lobe (against a 175lb/in spring) will take longer to pump up at a cold-start compared to their less compressed counterparts, compounded by the time between starts. HLA pump-up time is also to a lesser extent dependent on where the HLAs are on the oil path, with HLAs at the top left of the rear bank (cyl #1) taking slightly longer. The use of centre-oiled cams (as favoured by Porsche in race engines over spray-bar systems) helps to ensure fast targeted oiling in both cold start & high-rpm conditions. The actual mechanism of the noise from HLAs is a function of the degree of lash between the cam lobe and HLA surface: when HLAs are pumped up with clean oil & operating correctly they maintain this lash at zero for all rpm (and thus achieving the self-adjusting maintenance free operation of HLAs). "
End quote (6/00)

Don't think the brand matters - I've used various sorts, including Wynns and STP.

BTW - what it does is removes the coating of varnish which oil leaves on surfaces - especially hot ones. It's like your chip pan - if you clean it religiously every time you use it, you can keep it spick and span. If you let that varnish-like coating build up and bake on, you'll never get it clean. The inside of an engine is very similar to a chip pan! The critical areas in the HLA are the oil flow holes (which are very small), the ball valve and the sliding surfaces.

There was a service bulletin issued in the US in about 91, where people who complained about HLA noise could have ones with bigger holes fitted. Part of the instructions were something like "Tell people to change their oil on time". They didn't modify the ones fitted in production, though.

IMHO, the maximum long term regular oil change interval for any Mazda engine with HLA's is about 5000 miles. That's even if you use synthetic oil, and regardless of whether the specified service interval is 6000 or 9000 miles. The change to a longer interval was largely for commercial reasons - Mazda couldn't be seen recommending a much shorter service interval than was becoming fashionable. Thing is, it's fine if you buy a new car and keep it for ~50000 miles - you're never going to have a significant problem just sticking to the standard intervals. But if you're in the club that buys 50000 milers and runs them for 150000 more miles.......... It's interesting that Mazda have given up this particular struggle, at least with MX-5s.

Mk 2's don't have HLA's - they have solid tappets - presumably with shim adjustment? Changing oil regularly is a lot easier! All just my (often controversial) views, of course - comments welcome! (6/00)

(And use a flush additive just before changing)

Can you advise the best stuff to use, where to get it, and how to use it? My ignorance is total! (6/00)

Well, that's a valid subject for debate, and I have seen it argued that you shouldn't, because loosened debris might clog oil ways.

However, I don't go along with that. I think that these flushing additives are pretty mild, and don't do much dislodging of debris - rather they dissolve deposits. So yes - start flushing.

Years ago I bought a 626 (it was a SOHC engine with normal tappets). The guy who had it before me bought it with a warranty that required servicing at specified intervals ( I still have the book). He had done 22000 miles in a year, never had it serviced at all (and I could tell he hadn't touched it in that time), then sold it. Now that's one way to run a car!

Apart from the varnish deposits, it had thick encrustations of black carbon in the top of the cylinder head. I scraped at these, got them mostly clean, and flushing agents removed the varnish. Never had any problems in over 50000 miles, and sold it when I got waylaid by a DOHC 626 GT. Did over 90000 in that, including a head rebuild (compression was getting a bit iffy) at 160000 miles. The only head components needing replacement then were two HLA's and 8 exhaust valve guides. (It was a great car - used to surprise a lot of beemers. Not 540's, though ;-( ) I always flush! ;-) (6/00)

Engine flushing continued...

From my local Mazda dealer Cost 7 less 10% = 6.30 +vat

Run car until hot - cooling fan comes on (good check as well), Add to oil, run for 10 minutes, drain while hot (as you always should - I leave it as long as possible too - 1.5 hours minimum).

FORTE motor flush Forte, 22 Mopedi Rd, Sebenza, Edenvale, Rep of South Africa -

Cleans and frees piston rings - frees valves and hydraulic lifters - removes sludge and varnish - cleans internals of engine - removes harmful insolubles

Above is mostly pure marketing speak - you prove it!! (6/00)

Tappet noise on '5s is usually due to the HLA's being gummed up. A flush might shift it - if it's in for long enough (15 minutes at least). And make sure that 5W/40 or 5W/50 fully synthetic oil is used.

If that doesn't stop it, you could try adding half a litre of synthetic ATF (Automatic Transmission Fluid) to the engine for a day, drive 100 miles then change the oil. Unconventional, so at your own risk! ATF is very refined oil, and has a good flushing action. The source of this idea is Bob Hall - don't know where he got it from. I'll repeat what I've said in the past - I regard oil changes twice as often as Mazda recommend (ie 3000 - 4500 miles) as well worth while on Mazda engines which use HLA's with very tight tolerances.

A little bit of gum (which you get anyway with time, and more quickly with short journeys) makes the HLA's clatter. This applies even if you use synthetic oil. It doesn't apply necessarily to MK 2's which use solid tappets, but more frequent oil changes are a good thing anyway.

It is just possible that you've got one or more faulty ones, but it'll be a relatively expensive operation to get them out to check. (Involves removing the camshafts) (8/00)