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MG MGB Technical - Knock on start up

I have a '79 B with a '72 engine. It has been bored out .002 with HC pistons and dual HS carbs. Recently it has developed a noticeable knock on startup. I assume this indicates a bearing needs replacing. Which one I'm not sure. Has anyone had any experience with Lucas Heavy Duty Oil Stabilizer as a stop gap measure? It supposedly clings better to metal to stop 'Dry Starts'.

Thanks in advance,

Jim
JMcHugh

I meant to add on the original post that the knock goes away relatively quickly as the car warms up and is not present if the car is started warm.

Jim
JMcHugh

Jim, More than likely you're hearing bearing rattle on start up when cold due to the draining back of the oil filter.This has been a topic of recent discussion. Mann and Wix (available at NAPA PT # 1068) have superior drain back valves and should cure your problem. The rattle is caused by the filter failing to hold the oil inside it while the engine cools down. When the engine is started the oil pump must first fill the filter before pressure reaches the bearings. RAY
RAY

Watch your oil pressure gauge, if it is still knocking after oil pressure starts to build you have a problem with a loose or spun bearing or piston slap. If it has to warm up before it quits knocking it is not due to lack of oil, but is very common with piston slap. Normal oil clings very well to engine parts so unless its been a year between starts it is unlikely to be the cause.
J Heisenfeldt

hi jim,
i have a 70 gt which does the same.when starting from cold i turn engine a few times on the starter without actually starting it (without choke),then when i do use choke no rattles,i think you will find ray right,oil circulation when cold.

BOB.
Bob Taylor

Jim,

Check out what RAY said. As for the Lucas oil additive, it is one of the few such products that I have demonstrated to myself some good results.

Back when it was known as Morely's Oil Stabilizer, part of a load I was hauling from Los Angeles to truck stops across the southwest was 8 skids of Morely’s. It was in the dead of summer and I was crossing the Mojave Desert when the oil pressure started falling below the double-the-RPM-rule for the Cummins engines of the era (i.e. minimum 40 psi at 2000 RPM). In addition, the lube oil temperature gauge was approaching the temperature at which I would have to shut it down or risk ruining the oil and the subsequently engine. The oil had just been changed before I left LA.

I stopped and drained out 2 gallons of motor oil and poured in 2 gallons of the Morley’s, which pushed it to the full 20 % mix ratio. Under the same desert conditions, the oil pressure came up. This I could have contributed to the oil simply being thicker. However, the lube oil temperature dropped significantly. Sorry, I can’t remember the numbers anymore as it was back in 1985.

If the filter doesn't fix it, I would give the Lucas a shot.

Charley
C R Huff

I'll get the better oil filter. Just to let people know, the Lucas Oil Stabilizer has quieted the knock on startup considerably. Ultimately how effective this will prove to be remains to be seen.

Jim
JMcHugh

This thread was discussed between 03/06/2008 and 07/06/2008

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