I’m looking for technical help or recommendations on: A very mild knock from the engine bay
I am getting a very mild knock (or sort off) from my engine bay, it can only be noticed around 1500 2000RPM (or 30mph in fourth gear). I have added the video where you can hear the sound when the engine is idling. It is very mild and you can notice it only if you are being very picky. The car has 112K miles on, I just did my filter & oil, and it was usually looked after during its life. On a quick inspection on the engine bay I found one of the idler pully to bit a bit wobbly, but I am not sure that is the cause of this. Also, it is not always this pronounced as it is in the video and sometimes it is really hard to hear it. Hence can’t tell if I am hallucinating.
Have a search on the forum, plenty of posts suggesting you check for worn type noises (squeaks/knocking) from the auxillary pulleys and/or tensioner pulley.
Removal of the auxiliary belt and start run the engine for a few seconds will give you the answer on that one, no change look elsewhere.
New auxiliary belt and associated pulleys job lot can be around £100+ if diying, if that it’s much cheaper than starting an engine strip/diagnosis.
If it’s not the valve tick you’re talking about, which can happen after oil changes because it lets all the oil ways clear, make sure your oil is brimmed to help stop that, then it sounds to me like a hollow noise can be heard. I’d make totally sure that nothing is rattling or knocking around inside the engine bay.
As Mick said, do some pulley removal if you think it’s a pulley. I think only the crank pulley on these cars has a vibration damper, so maybe that has started to fail, and given that it is only noticeable at lower revs, that is within the realms of possibility as at faster revs it will self-balance. You can unbolt the crank pulley to check that.
Honestly, to me, and I know it’s hard to tell with a mobile phone microphone picking up the sound, it sounds like some of the plastic from the air intake being knocked around or something. Sounds like a hollow plasticky knock, not an engine component. Check the cover on the top of the engine?
Take the oil filter apart. If you have a serious engine problem it will be in here glittering at you. A mild knock could be anything/nothing. Just keep on driving attentively.
Do this. Take off the aux belt, run engine (not too long as water pump wont be turning), this will tell you whether it is the tensioners, this is a common issue.
If not that, well hard to tell from the video. Normally you only get rod knock from low oil levels on these engines. The bearings are not the issue, the issue is oil usage and people don’t notice the level is low and that then causes the bearings to go. Fingers crossed its not that.
You will know pretty soon if its rod knock because it wont get better…7
Thanks for the suggestions, i have removed the aux belt and I can’t really tell any difference the way engine sounded. I briefly had it taken for a spin by MX-5 specialist here in Nuneaton and he couldn’t hear anything odd and told me ‘it sounds and runs as it should’. It has been more than year since I had this concern and I have clocked more than 8k miles since, touch wood the car is running fine. So I think maybe this is something which is simply there in my head and it is just a normal engine bay sound. However I didn’t know about the weak point of the NC engine though and I am sure there are no concerns of lubrication as I am tracking the oil level regularly and doing my rotinue oil changes
