Humming noise: Running on 3 cylinders? Alternator?

CARRisma · Post by **CARRisma** » Wed Jul 31, 2013 8:03 am

Last night a fitted a new seal / gasket set for the valve cover (http://www.ludegeneration.co.uk/viewtop ... f=5&t=8811). Started the car this morning and there's a humming noise coming from the engine bay. It's quite a low down basey sound. Very noticeable at idle and lower revs. Sounds a bit like a Hoover.

Any idea what's wrong here?

Here's some background… After carrying out the checking and adjusting valve clearances a few weeks ago, the valve cover was leaking so the seals / gaskets were replaced last night to sort that. Oil was even leaking into the spark plug holes, giving the HT leads a coating. Over last weekend while looking into the oil leakage issue, I removed the valve cover. To do so, it's required to disconnect the alternator as the cabling goes across the top of the valve cover. Foolishly, I didn't disconnect the battery first, a while later, there was lots of sparks and smoke coming from where the alternator's cable was making contact with the alternator's metal housing causing me to promptly disconnect the battery like I should have done in the first place. This caused a scare with the central looking when I thought I had friend something (http://www.ludegeneration.co.uk/electri ... t8817.html).

So, could the fault be spark plug related. Is the top of a spark plug / bottom of HT lead soaked in oil? Is the engine running of 3 cylinders? Or is it alternator related. Is it slightly cooked?

BMCC · Post by **BMCC** » Wed Jul 31, 2013 8:11 am

You'd need to get the car up and running to see what voltage the alternator is charging the battery at. Manual should tell you what the voltages are etc.

When doing the valve clearances did you change/clean the plugs and clean up the ht leads?

Ted · Post by **Ted** » Wed Jul 31, 2013 8:21 am

difficult to diagnose a noise from a description but i suspect the 2 are unrelated. noise probably from the alternator and you probably broke a lead or its soaked in oil and thats why its running on 3 cylinders. check your leads and disconnect the alternator belt and run it back up and see if the noise is gone.

CARRisma · Post by **CARRisma** » Wed Jul 31, 2013 8:23 am

BMCC wrote:You'd need to get the car up and running to see what voltage the alternator is charging the battery at. Manual should tell you what the voltages are etc.

When doing the valve clearances did you change/clean the plugs and clean up the ht leads?

I have only recently changed the spark plugs, twice! (http://www.ludegeneration.co.uk/honda-p ... t8227.html) And I did give the HT leads a quick wipe last night to satisfy my OCD tendancies. It was running lovely after the valve clearances and hasn't been driven since Saturday.

BMCC · Post by **BMCC** » Wed Jul 31, 2013 9:22 am

As Tramroad suggest you could remove the belt and see if the noise goes. You can also measure the resistance of the leads, can't remember the value but it is in the manual somewhere. Maybe before you start the car you could remove the plugs to see if they are oil soaked etc?

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Wed Jul 31, 2013 9:51 am

As you'd have removed the leads from the plug to remove/replace the rocker cover, that would be where I'd start?

Basic stuff first, check to see the terminals are ok on the end of the leads/wire not broken at that end (can happen on HT leads when you remove them, unfortunately) the terminal post on the top of the plugs are still screwed on tightly (the buggers can work loose when removing/refitting HT leads

) and the insulation around the ends of the HT leads are intact (no tracking across to earth down the spark plugs holes in the block)

Post by **vanzep** » Wed Jul 31, 2013 12:00 pm

you can check the output of your alternator - it should read 14 volts or more at idle.

Post by **Merlin** » Wed Jul 31, 2013 1:12 pm

Can you define the exact symptoms? Just a humming or is the car misfiring / running on 3 cylinders?

CARRisma · Post by **CARRisma** » Wed Jul 31, 2013 11:06 pm

My panic is over, sort of. I went out to look at the car at lunch time and saw oil splattered over the intake manifold chamber, indicating that the new gasket had become dislodged when I put the valve cover back on last night. I left work early to sort it out at home. Now, here's the worrying part... When I removed the valve cover, only 3 out of the 4 spark plug hole seals / O-rings were there. 1 is missing. There's 3 possibilities:

1) It fell off in the engine bay yesterday evening when re-fitting the valve cover and got lost on my way to work.
2) It fell off in the engine bay this afternoon when removing the valve cover and was hiding somewhere out of sight.
3) It fell into the top of the engine yesterday evening when re-fitting the valve cover and has been digested by the engine.

I spent a good 30 minutes with a torch carefully inspecting the cylinder head and engine bay and could not find it. I'm hoping it's down to one of the first two possibilities. I would imagine that if it did end up loose inside the engine, getting in the way of rockers arms, cam lobe and valve, the engine would have thrown some sort of tantrum whilst being driven today. What do people think? However, it has been running fine without any problems (apart from the earlier leak and Hoover sound).

I had no choice but to dig out one of the original spark plug hole seals / O-rings and reuse that along with a load of sealant. I'll pull the HT lead tomorrow evening to see if it's coated in oil indicating that it isn't up to the job.

Ted · Post by **Ted** » Thu Aug 01, 2013 12:58 am

And the noise ?