engine tapping noise

Side valve, 803, 948, 1098., 1275 and Vizard mods

engine tapping noise

Postby rswiper » Fri Aug 16, 2013 4:57 pm

I have noticed a tapping from the engine (pretty standard 1275 marina) recently and thought it sounded "tappety". Its a cyclical tap to the speed of the engine. Quickens with throttle and not detectable as the engine revs are bought high up but assume thats just because the engine noise overwhelms the tap noise.
With the rocker cover off and hovering an ear over each cylinder its much more noticeable over either 1 or 2 (can't tell which). Before checking clearances found no2 plug very sooted up, others fine. All tappet clearances 12thou apart from no2 inlet which was approx 20thou. Aha I thought! Adjusted back to 12thou but the lock nut won't quite lock. On removal the thread is damaged and only partial. Anyway it locks enough to keep the tappet at 12 to test it. But no joy on the tapping, still just as bad. I did a test with a stopwatch and although difficult to count that quickly I got around 40 taps in a 10 sec period both sure if that helps identity what it might be? Any help much appreciated.
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Postby chesney » Fri Aug 16, 2013 5:37 pm

Number 2 sooted up with what? Oil?
I'd suggest a compression test as a good guide to engine health, compare the results of 2 with 1, 3 and 4 and examine any variance.
Good luck!
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Postby rswiper » Fri Aug 16, 2013 7:15 pm

The plug wasn't wet. It was sooted, I.e black dry and powdery like its been running very rich. All other plugs are a nice healthy brown colour a-la the classic Haynes manual pics. I will have a word with the mechanic down the road (a mog enthusiast luckily) when I can get hold of him. Sure he will be able to do the test. Tks
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Postby DavidF2 » Sat Aug 17, 2013 7:46 am

Assuming you have one carb, one manifold and there are no air leaks it is not possible to supply No 2 with a different air/fuel ratio than the others. So it has to be that the air/fuel arriving is not being completely burnt hence the dry sooty deposits. This will be caused by a dodgy spark either plug or lead. It may well have been missing slightly under load for a long time and built up a thick layer of carbon on the piston crown which is now causing detonation. Or it may have only just started and the sound is the misfire. Change the plug straight away and see if anything changes. If possible shine a torch down the plug hole and see if you can take a look at the carbon build up. You may even be able to get a friendly garage to let you use their engine endoscope so you can look right inside.
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Postby rswiper » Sat Aug 17, 2013 10:49 pm

I was originally thinking something along the lines of the valve setting being wrong somehow causing the valve to be not completely closed and hence poor combustion on no2, but thinking about it, i guess, if anything it would just be shut for a fraction longer than reqd.
Its not running an unleaded head, as it doesnt do a lot of miles so guess it could be some valve seat damage causing poor compression & sooty deposits on just one chamber & misfire?... back to compression test i guess if its that.  
I will check the plug & lead and see if the spark looks as strong on all plugs first, tks.
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Postby DavidF2 » Mon Aug 19, 2013 8:00 am

Honestly, don't even look at the plugs, just change it. I have know many plugs that produce a perfectly good spark out of the engine, but fail under load. It may have nothing to do with the plug, but for the price of a plug it is worth eliminating this as a cause.
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Postby rswiper » Sat Sep 14, 2013 2:40 pm

Back from holds. Back to the mog. Compression test....
1 165
2 150
3 150
4 160

Removed fan belt to ensure it wasn't a physical "knock" on fan, alternator etc.

Replaced all spark plugs.

Using a listening stick (bit of copper CH radiator pipe) on rocker assy at each cylinder. Worst case tap from no2. Slightly less noisy no1. Almost nothing from nos 3&4.

Head off and take look? Or has anyone any more suggestion before that?
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Postby MM » Sat Sep 14, 2013 3:08 pm

Sounds like the head gasket may be failing between the middle two cylinders - a common A-series problem.

Does it use oil or water, and do you get any mayonnaise on the dipstick, etc.?

You could try checking the tightness of the cylinder head bolts, and ensure they're tightened to 40lbft.
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Postby rswiper » Sat Sep 14, 2013 5:10 pm

No mayo ever with this engine. Have checked torque on head bolts and they are all min 40. Am willing to accept head gasket on its way out but don't see how that would be to do with the tapping sound. Sounds like a moving part metallic sound. Think its gonna be head off first and then see if there's anything at the btm end.
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Postby chrisryder » Sat Sep 14, 2013 5:18 pm

You wouldn't get any mayo if it were blowing between bores. And you can have mayo without having a blown head gasket. Mayo is a very misleading thing, and can't be taken as a diagnosis!
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Postby MM » Sat Sep 14, 2013 5:27 pm

True, although often goes hand-in-hand with HG failure.

Try squirting an eggcup-full of oil down the middle two bores and see if it raises the compression...
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Postby rswiper » Sat Sep 14, 2013 5:37 pm

No mayo ever with this engine. Have checked torque on head bolts and they are all min 40. Am willing to accept head gasket on its way out but don't see how that would be to do with the tapping sound.
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Postby bmcecosse » Sat Sep 14, 2013 6:45 pm

With these comp readings - there is nothing wrong with the head gasket....leave it alone !  How about the exhaust manifold - is it tight to the head?
 









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Postby rswiper » Sat Sep 21, 2013 3:38 pm

Had a go on the exhaust manifold and all seems fine, couldnt do them any tighter. Its fitted with a a non-standard LCB manifold but seems to still be in good nick (i.e. no holes). I have included a shot of the new plugs i put in (LHS=1 RHS=4). Theyve been running maybe 20 mins and already black sooty deposits on no2. Its gotta be incomplete burn in no2 (plug may look wet under the flash but it isnt, its dry & powdery).
I am down to too much air or weak/badly timed spark, so maybe valves (doesnt make much sense with reasonable comp readings), or dizzy/HT leads.
Its had a new electronic ignition module, dizzy cap, HT leads in the last couple of months so I guess its less likely to be that (or maybe that makes it more likely!).
Any other ideas gratefully received before the head comes off for a poke about.

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Postby MM » Sat Sep 21, 2013 3:42 pm

Use a multimeter to measure the resistance of each HT lead; healthy ones should be in the region of around 7-8 kilohms, and certainly no more than 10 kilohms or so.

If in doubt, try another set of HT leads before removing the head.

It's unlikely to be any of the other ignition components, as all the other spark plugs look fine, but nevertheless, also try swapping the spark plugs around, in case you have a dodgy one.
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