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An annoying tick?

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An annoying tick?

Postby Skuzzle » Thu Oct 31, 2013 1:39 pm

Whats ticking ?

A very common mx5 problem is the development of a nasty ticking sound from the top end of the engine. Usually the first signs of this are when started from cold, but similarly the problem can be non-existent when cold, but appear after the engine has been given a good workout.

99% of the time the problem can be put down to the Hydraulic Lash Adjusters (HLA's) which are used in place of a more common solid lifter with shims (as found in the later mk2 cylinder heads).

The noise is not a real problem to the car, but can become a huge problem for the owner as it can make your pride and joy sound like an old wreck.

HLA Theory

The concept behind the HLA is to create a self adjusting valve lifter. Previously engines relied upon a lifter assembly that used shims. As things wear, regular maintenance was required to replace shims to take up the space between the camshaft lobe and the head of the valve.

The HLA should adjust itself automatically to take up the extra spaced caused by wear to the valve and camshaft. It works by sucking oil into the body of the HLA, past a valve to hydraulically expand the lifter assemble.

The Problem

The problem with the HLA is that they can become clogged very easily. Deposits from old, broken down oil can block the holes in the HLA stopping new oil getting in, and therefore not allowing the HLA to expand. This often happens when cold due to the oil being thicker when cold, but as it thins it can squeeze past the blockage and fill the HLA.

The other problem which appears when hot is that the oil becomes too thin. MX5 track cars tend to suffer from this. The oil gets so thin when raced around a track that it can squeeze back past the valve in the HLA, allowing it to compress and create a gap between valve and cam.

The Solution
There is no single solution to curing HLA clatter, but knowing why they are making a racket will give you a better chance of finding the solution. One simple solution is to change to a different oil viscosity, but this is not a great solution. It merely masks the problem and moves it somewhere else. i.e. if your HLA's are noisy when cold, a thinner oil will help, but it may cause them to be noisy when hot.

The real solution is to stick with the recommended 10w40 oil but to cure the source of the problem.

If they are noisy from cold, you have a blockage. The only solution is to clean them. This can be done by performing an engine flush, using a good quality flush followed by fresh oil. If they are really dirty, this can take several attempts. If it fails then they can be removed, dismantled, cleaned, reassembled and refitted, but this is a very labour intensive task, though may well be the only cure for some.

Now onto the noisy when warm.

Depending on the use of your MX5, there may be more than one solution. The ideal solution is to fit a thermostatic oil cooler. This is effectively a heat exchanger for your oil, usually in the form of a small radiator. The thermostat is in place to stop the oil flow to the radiator if the oil is not up to temperature (cold oil is as bad as overheated oil). This will help to maintain your oil at a lower temperature keeping it to the correct viscosity for the HLA's.

If your car is primarily a track car then the thermostat is not such a requirement, but also another solution may be to look at changing to a thicker oil. Personally I feel the oil cooler is a nicer solution though and should be top priority for anyone who uses their car under track conditions.

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