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+--- Thread: Engine Knock (/showthread.php?tid=6776)
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Engine Knock - aharding - 24-10-2021
I am submitting this for a friend who has a problem concerning a 1928 Chummy which he has owned for many years.
It was running well until an ignition problem (almost certainly unconnected with the current issue) grounded it. While he was testing solutions to that,the engine suddenly developed an intermittent knock at around 1500 rpm plus which had never been evident before. The knock was not affected by pushing the clutch pedal – so probably it is not flywheel related. He then noticed that the engine was stiff on the handle at certain points of rotation. He has since removed the head and sump and found nothing amiss.
Any ideas please as to what this could be about ?
RE: Engine Knock - Duncan Grimmond - 24-10-2021
I thought I detected a "new" engine noise only to discover that I was wearing my hearing aids and hadn't "heard" it without them, durr.
I'm certainly not an Austin 7 expert but the most depressing thing I can think of that might cause a regular stiff point in the rotation by hand together with a knocking when running is the crankshaft showing early signs of a fracture?
RE: Engine Knock - Chris KC - 24-10-2021
Can we narrow down what type of engine it is e.g. 2-bearing? 3-bearing? etc.
RE: Engine Knock - Hedd_Jones - 24-10-2021
how much end float is in the crank? Does it belt the cam bearing?
RE: Engine Knock - Harry Hales - 24-10-2021
It could be that the piston pin is loose possibly a broken clamping bolt scaring the cylinder bore
RE: Engine Knock - Charles Levien - 25-10-2021
(24-10-2021, 11:19 AM)aharding Wrote: I am submitting this for a friend who has a problem concerning a 1928 Chummy which he has owned for many years.
It was running well until an ignition problem (almost certainly unconnected with the current issue) grounded it. While he was testing solutions to that,the engine suddenly developed an intermittent knock at around 1500 rpm plus which had never been evident before. The knock was not affected by pushing the clutch pedal – so probably it is not flywheel related. He then noticed that the engine was stiff on the handle at certain points of rotation. He has since removed the head and sump and found nothing amiss.
Any ideas please as to what this could be about ?
If it was me I’d take the engine out and have a proper look inside. As others have intimated, rough running at low revs [1500 rpm] is one indicator of a broken crank.
RE: Engine Knock - Chris KC - 25-10-2021
Are you quite sure it isn't too much advance? (Given that he's been tinkering with the ignition...)
RE: Engine Knock - David Stepney - 25-10-2021
It is difficult to diagnose an engine noise when you have not heard it. I would be inclined to remove the engine and strip it for careful examination. Sometimes the merest play in a component can give rise to the most horrendous noises. Some little time ago, my own car developed a sharp knocking noise, which eventually turned out to be the slightest of movement in one gudgeon pin. A new set of pistons cure the problem.
RE: Engine Knock - Ilmoro - 25-10-2021
I would definitely check ignition advance first. I nearly took my engine out, suspecting a broken crank: As a final test, I set the timing to TDC and the knocking completely disappeared.
RE: Engine Knock - Chris KC - 25-10-2021
(25-10-2021, 09:34 AM)Ilmoro Wrote: I would definitely check ignition advance first. I nearly took my engine out, suspecting a broken crank: As a final test, I set the timing to TDC and the knocking completely disappeared.
Indeed; but also because a basic principle of fault-finding is "what have you changed since it was last OK?"