MG Car Repair: 77 mg roadster, compression test results, piston slap

Question
I've had a 77 mg in the shop for a little over 2 weeks and and it has a real loud rattle coming out of the motor almost sounding like a wristpin going bad. It also needed the thevalves adjusted so we got em all to a .13 and im just lost with the issue and need some more info on this

Answer
Hi John,
To narrow the noise down to a small area I found that first look at oil pressure. If you have 30 to 40 PSI at idle (warm oil) and 50 + at 2000 RPM up, it is not likely a rod or main bearing noise.

A wrist pin is possible but unlikely. Piston slap can sound like it is up high and sound like a wrist pin but usually if that were so, you should see other indications like excess oil burning, poor wet compression test results and signs of excess carbon in the combustion chambers.

Excess carbon can usually be seen in the plug hole and we have successfully removed carbon by removing the CAT and setting the RPM up high and allow water to enter the intake and keep the RPM up high and controlled the RPM by the amount of water. It usually only took one Coke bottle of water to completely clean the combustion chambers. (The CAT must be removed as the carbon will clog up a CAT.)

You should also run a cylinder kill test to see if it is associated to one cylinder.

A very heavy knock on a light rev up could be loose flywheel bolts or even a broken crank shaft. The loose flywheel bolts would only be if someone had been in the engine that was not an MG wrench as they normally use a lock tab on the bolts.

In the dealership I have run into a few broken cranks that brake in such a angle as to still turn and run but had a heavy knock like a main bearing.

Howard