24 replies to this topic

[Teapot]

1981 Austin pick-up, MG Metro 1380 engine, high lift cam.

There is a rapid-fire, solid hammering noise coming from Huey's front end (possibly the nearside) when the engine is under load, for example if I accelerate at around 45mph in top gear. It stops if I lift off. Above 55-ish and accelerating, the wind and road noise are too loud to know if the hammering is still there, but I suspect not.

I first noticed this in the summer when I took all the soundproofing & carpets out. It has got slightly worse (more noticeable) in the last month.

The noise is NOT tinny or metallic. It is NOT a rattle or a rumble. There is no discernable vibration from anywhere. It's hard to tell if it speeds up with the revs, but I suppose it must do. Everything else is working fine.

The only suggestion I have had so far is that it doesn't seem to be in the engine or gearbox, but I should maybe look at the drive shafts or cv joints. Any suggestions about a specific possible cause? Or shall I just root around?

[Bungle]

is it a little old lady you ran over hitting your mini with her walking stick trying to get you to stop ?

[Teapot]

No, it's more like her zimmer frame is catching on a wheel spoke

[Paul Wiginton]

Sounds like no oil in the dashpot or the ignition is too advanced. Ive had this sound before

Paul

[Scotauto]

fan hitting the shroud? Maybe

[Ibexx]

Sounds like detonation (knocking), which is the exploding of fuel instead of the normal burning. This happens when the engine is under stress (low revs and foot down). Usualy caused by carbon in the cylinder area. Try something like V-power, see if that helps.

More info:
http://www.cartuning...t-is-detonation

[Teapot]

Thanks for your suggestions. I'm checking 'em out

Sounds like no oil in the dashpot or the ignition is too advanced. Ive had this sound before
Paul

Dashpot oil level is correct. Ignition recently retarded, so doubt if it's that.

fan hitting the shroud? Maybe

Checked. Nope, not that.

Sounds like detonation (knocking), which is the exploding of fuel instead of the normal burning. This happens when the engine is under stress (low revs and foot down). Usualy caused by carbon in the cylinder area. Try something like V-power, see if that helps.

More info:
http://www.cartuning...t-is-detonation

Running on V-power already. I know about "pinking" (the metallic noise of detonation) but didn't know it can also produce a banging noise. The engine's been running for six years so I suppose carbon build-up is to be expected. Thanks for the link. I'll try an additive as a first step.

(low revs and foot down)

Oo-er, I hope I've never committed that cardinal sin

[tnewson]

Could possibly be the valve clearances?


If there is too large of a gap it makes a loud tapping noise, if there is too small of a gap it will cause your engine to overheat.

[Teapot]

Could possibly be the valve clearances?
If there is too large of a gap it makes a loud tapping noise, if there is too small of a gap it will cause your engine to overheat.

My little brain is going to shut down in a minute ... why was the ignition retarded? I can't remember. The valve gap isn't likely to be too small since the engine has always run cool, what with a two-core rad. For five years it had a 74deg thermostat, then an 81 and a few days ago I changed it for an 88 due to the cold weather. The only time the needle really moves up towards red is after an hour in stop-start traffic. Does that imply something progressive?

Plus, the engine sometimes runs on. But not always.

The hammering noise I'm on about has remained more or less constant & predictable during all these changes though.

[rozzer1275]

[quote name='Teapot' date='Dec 10 2008, 03:51 PM' post='1250740']
1981 Austin pick-up, MG Metro 1380 engine, high lift cam.


High lift cam what type?, 286 say don't like load under 2,000rpm.

[Teapot]

[Blushes embarrassedly] Don't know. The power kicks in at 2.8k-ish and will go freely to 5k, although on the rolling road some years ago it was tested to just over 6k (with me hiding in the office)

Edited by Teapot, 11 December 2008 - 12:08 PM.

[998dave]

Dizzy advance curve? getting more advanced then it should at high revs, (high vacuum - throttle open), causing pre-ignition.

Head gasket? Big end shell?

What compression do you get?

coked up cylinder or running to rich at high revs? When was it set up?

If far to rich could be fuel int he exhaust downpipes? Would give black clouds when it bangs.

Dave

[Teapot]

OK, there will be a short* intermission while I go away and tinker. Dave, I will check out as much as I can of what you suggest. I'm sure the head gasket is ok and that the fuel isn't too rich.


*Oops, rather long I fear

Edited by Teapot, 07 May 2009 - 04:12 PM.

[Teapot]

Now then. The head's off and immediately we see the head gasket has been blowing between cylinders 2 & 3 So brownie points to 998dave.


The fact that three of the stud bolts were loose may have something to do with it. There is enough carbon on the pistons
and valves to ensure a good dose of running on and I'm surprised it hasn't been worse. Plus we have this little surprise



a not very round valve. The rest are ok and there are no bent stems so we'll just grind 'em in and replace the one.

Edited by Teapot, 07 May 2009 - 04:13 PM.

[Teapot]

ID markings are few and far between, and so far we have this



We can't be bothered to try and find out what the cam is since we know what it does (kicks in nicely at 2.8k).
Anyway I'm leaving the lads at the workshop to carry on while I swan off on holiday for a fortnight
I hope to return to a hammerless Huey minus his seats so I can start soundproofing.




If my tin of Sludge ever arrives, that is ...

Edited by Teapot, 07 May 2009 - 04:16 PM.