Pinking or shell damage?

[jonathan49bat]

The 3.2l engine has covered 55,000 miles since 1977, at start up and until upto temperature the engine is quiet and responsive, thereafter it rattles at around 3500rpm.

The head was overhauled a couple of years ago and stem seals replaced but the head was not converted to unleaded fuel. Compression readings are consistent at 10 bar.

Would this indicate that it is a case of pinking? and would a lead additive cure the problem?

 

[x_atlas0]

Have you replaced the timing chain tensioner and performed a valve adjustment? That could help quiet things down a bit.

 

[Malc]

You do not have to replace valve seats to run on unleaded fuel - the head can cope. Additives you don't need
if you get a "tinkling" sound at higher revs then it could be pinking, though this is more apparent if you say have the car in top gear and put your foot to the floor from about 30 miles an hour.
you need to retard the timing to get rid of it.

Other rattling sources could be as suggested the timing chain
It might be piston slap - worn rings and little end bearings and gudeon pins
Is it eating any oil?

 

[Bill Riblett]

Another possibility is that there is something in the engine compartment or under the front of the car that rattles at a 3500 rpm.

 

[MichaelP]

I'm with Bill. At 3500 rpm, the motor is on cam and pre-ignition or TDC detonation would be pretty hard to detect. Motor bottom end issues (broken rings or bent rods) would also reveal themselves at low revs. Does it rattle after 3500 rpm as well? Is it carbureted or injected?

In any case, you should probably be running the highest octane fuel available.

 

[jonathan49bat]

pinking or what?

Thanks for all the thoughts - I carried out a compression test and they are all very close to 10bar. It does use some oil but not I think excessive for this engine maybe a pint in 750 miles of 20/50 grade.

I did change the chain tensioner about 1500 miles ago and the head was overhauled with new valve stem oil seals, when the head was off there did not seem to be any bore wear and the pistons were not loose in the bores which I think the compression test bears out.