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MG MGB Technical - Are the noises in my head?!?

Hi guys,

I have (well i think i have!) a problem with my 71 BGT. Basically i seem to get a noise which sounds like a rattle occure when i'm accelerating. This noise only seems to appear when the throttle is 3/4 down & at full thottle does not appear. I am pretty sure it's not pinking as i can put the engine under heavy load without the noise appearing.

The noise appears when i throttle upto 3/4 & disappears at full throttle. When i leave off the thottle as i slow down the noise will appear at 3/4 throttle but disappear once back past this point.

The engine was rebuilt by myself & is about 8,000 miles old & shows on oil pressure of 65 lb/sq in. running & 40 lb/sq in. idling. The noise does not appear if i rev the car while in neutral & stationary.

As it only happens when the car is moving along i am leaning towards the noise orignating from the drivetrain. I have recently renewed the UV joints and this has made no difference.

So i thought i would throw it open to you guys, any ideas however trival or serious (hopefully not!) would be appreciated.

Cheers

Scott
Scott Ralph

Scott:

First check your timing and is your vacuum advance working? On my B I cannot make it ping no matter how much I advance the timing. I’ve read other posters who have observed the same phenomenon. The only thing you will notice is that the engines seems to start running bad and sort of shaking. Real strange feeling. If you back off the timing everything smoothes out. With what you’re saying this occurring at 3/4 throttle this could be what’s going on. At this throttle opening you should be getting strong vacuum=maximum advance=engine rattle. Then at full throttle vacuum falls off=reduced advance=no rattle.

Well anyway, check it out.

Bryan
Bryan Prindle

Bryan,

i have checked my timing which, is currently at 8 degrees BTDC. I had thought about the vacuum advance unit & have obatined a new one. I will fit it this weekend & give the rest of the distibutor a good check & clean.

Any other ideas anyone?

Scott
Scott Ralph

Be sure to update us when you remedy the problem. I've had the same thing happen and never completely solved it.
Steve Simmons

Steve,

i will definately post again if i solve the problem or get it any better. How have you tried eliminatnig the noise so far, have you looked at the vacuum advance? It's annoying as the noise just appeared one day, just after i installed K&N's. I initially thought that the mixture was leaning out but have now installed richer needles & have tuned the car. I am planning to check as much as possible over the coming long weekend, hopefully i'll find the cause.

Cheers

Scott
Scott Ralph

Honestly it's been so long I can't remember, but I just started driving the car again and it's gotten very hot here in LA. Yesterday I caught hint of the problem again when it was really hot. I'll mess with it soon and see if I can figure something out.
Steve Simmons

This thread was discussed between 29/05/2002 and 30/05/2002

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