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Mystery rattle


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Hi guys

 

I am seeking help for a mystery rattle in my engine that has only covered 4000 miles since a total rebuild. The noise seems to be coming from the distributor side of the block and resonates out of the oil breather tube. The strange thing is that the noise has no relationship with engine revolutions. and the noise fades away as the engine temp rises to normal and is totally gone by time the temp reaches 60C. I have stripped the engine and checked every clearance and end float and replaced all the bearings only to have the noise still there. I have finally found that the noise has a direct relationship to oil pressure. If I reduce the oil pressure by using the pressure relief valve adjuster, the noise dissapears when the pressure gets down to 30psi and returns as the pressure is wound up again. The oil pump was fitted with a new rotor at the original rebuild and at the second strip down all the pump clearances were spot on. I have also replaced the distributor drive shaft and drive gear. I thought I would see if anyone else has had a similar problem before I rip the sump off and go to the expense of replacing the oil pump just in case it might be that. I was also wondering if the bush below the distributor drive gear could cause such a noise if worn. This is the first time I have ever come across a rattle that goes away when you reduce oil pressure. Apart from the mystery noise the car pulls like a steam train right up to 6,000 revs and runs as smoothly as a babies bum. Can anyone give me some ideas?

 

Thanks

 

Tony

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It maybe that you have a repro oil-pump drive shaft. There were a number made a while ago that were too short and rattled up and down in the drive. Take the dizzy and drive out and remove the oil pump drive shaft (don't drop the woodruff key!), you should be able to see a witness mark on the end that engages with the pump - check that it's not just the end couple of mm.

 

The one on my rebuilt engine was so short that it actually disengaged from the pump. Good job I was watching the gauge as it happened (I'd only just fired up the engine for the first time!) and was able to instantly switch everything off. :rolleyes:

 

Hope it's something as simple as that!

Adey

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Maybe what you are hearing is the spring loaded ball of the oil pressure releave valve : this valve is only opening when the oil is cold and thick. Maybe your valve is opening in a resonating way : opening and closing with the own frequency of the spring. To check this, you could turn in the adjusting screw : the noise should disappear sooner.

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When I replaced the drive shaft I checked the length of the new one against the old one as I thought that the old one might be too short. Both shafts were identical and there is a witness mark on the old one that shows that it was well and truely seating in the oil pump. I havent tried screwing the pressure adjuster screw in as she has plenty of oil pressure and I have been warned that if these engines run with too much pressure you can place too much strain on the shaft and shear off the woodruff key. I suppose that if I keep the motor at idle speed I wont run too much risk of a problem. If that doesnt work it looks like replacing the oil pump or the drive shaft bush.

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It's risky to turn in the adjuster screw permanently indeed.

A friend of mine tried this to have more oil pressure. When he started the engine the following morning,

the gasket of the oil filter failed and half a gallon of oil landed on the garage floor.

I still think that the rattle is caused by the ball of the oil pressure relieve valve.

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I will try tightening down the adjuster screw on the weekend. I will have to make sure I keep the engine at a slow idle(if that is possible with the cam I have in it).

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The oil filter has been changed a couple of times. I am running a modern filter conversion and I even tried removing that and going back to the old paper filter and that had no effect. I must admit that this has got me totally baffled.

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  • 14 years later...

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