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MG MGA - Sounds like marbles in my cylinder

When I accelerate through 2500 rpm to 3200 rpm there is a metallic gargling sound coming from the engine. It sound like what I imagine marbles or similarly size ball bearing might sound like if rattled in my cylinder. The sound can also occur if I abruptly let up on the gas pedal during those rpms and when the engine is very warmed up it can appear intermitantly during idle.

Thinking this might be preignition I have tried retarding the ignition, but there is no impact on the sound.

Does anybody have any thoughts. Its driving me mad!
T McCarthy

Hi, When was the engine last overhauled? Unlikely, but might possibly be a rod bearing on it's way out?, although I would think it would not make noise on deceleration, instead more under acceleration and load. Is it possible that long reach spark plugs were installed, and the pistons are hitting the plug electrodes? That is also probably unlikely. The metallic knock could perhaps be due to bad ignition timing (you already checked that) or perhaps even bad valve timing, if the timing chain somehow managed to jump a few teeth. Please let us know what you find. Glenn
Glenn

FIRST I WOULD DO A COMPRESSION CHECK. THEN OFF WITH THE HEAD. THERE IS A GOOD CHANCE THAT YOU HAVE BROKEN RINGS AND SOME HAVE COME UP OVER THE TOP OF THE PISTON.
THIS IS AFTER THEY HAVE CHEWED UP THE TOP RING LAND.
SANDY
Sandy Sanders

If the engine does this only on acceleration or under increased load, it is probably predetonation, caused either by the timing being too advanced or by the mixture being set too lean.

Predetonation causes serious damage so get it addressed.
Richen up the mixture a little, and retard the timing a smidgeon. Rinse and repeat till problem has disappeared.

My car suffers if I use 95 Octane (Superchargers can exacerbate the problem, a can skimmed heads and higher compression). On 98 Octane I run with an exhaust CO of 5% and timing 28 degrees BTDC at 3000 RPM. 1622 with 1800 head and Judson.
dominic clancy

This thread was discussed between 06/05/2007 and 07/05/2007

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