Triumph Repair: TR3 grinding noise when RPMs coming down, grinding gears, decel

Question
I know you don't profess TR3 expertise, but thought I'd try my luck anyways.  My 1960 TR3 recently started making a loud noise, a mix between grinding gears and a violent rattle, when I let off the accelerator and the RPMs come back down.  Doesn't happen when idling, and is unaffected by putting the clutch in or in gear.

I'm at a loss where to start...except to take it to a garage.  I'm fairly capable, so hopeful something I can tackle in my garage.

Thanks,
Cory

Answer
Hi Cory,
If you mean that you get the noise just by revving the engine and decelerating with the car setting still then it is in the engine. The first thing is to look at the oil pressure. If you have good oil pressure then it is not any bearings. (60+ PSI)

The next step is to do a cylinder kill test where you ground one spark plug at a time to see if the noise is changed a lot with any one cylinder killed.

Then get a mechanic's stethoscope and try to ID the noise to a smaller location. A loose timing chain can make a noise on decel.

I did do a lot of TR-3 work in dealerships but a decel noise was not a common problem with them. so you need to isolate the noise to a smaller location to find it.

Howard