To change big end bearings or not? I’m tracing down engine noise

[The_Doc]

Hi All,

I am trying to track down a knocking noise that is mostly evident when the rev are low and reducing (on over run(?)). Using my stethoscope, it sounds like the knocking is coming from the back of the engine block closer to the crankshaft then the cylinder head.

I checked all the obvious stuff and now am onto the big end bearings. I have pulled the piston 4 big end bearing just to have a look and it doesn’t appear that bad. There also doesn’t appear to be any issues with the crankshaft, so I highly doubt this is what’s causing the knocking sound.

my question is, from the picture, would you advice while I’m here to go ahead and change all the big end bearings or just put this one back in and revisit in 10,000 miles? 

Thank you,

Adam

 

Edited October 3, 2023 by The_Doc

[Motorsport Mickey]

Those bearings look fine. That noise could well be a loose crankshaft dog bolt. Have you had the front pulley off in the recent past ? or it may have not been tightened enough by a previous owner.

If the bolt isn't tightened to 120 lb ft minimum and comes loose the front pulley moves against the crankshaft woodruff key which positions against the woodruff channel, I've had 6 pulleys on rebuilding engines with damage to the woodruff channel, the worst was a 6mm side slot cut into the woodruff channel.  When it's loose it makes a dreadful clacking noise which sometimes disappears as the torque reverses on the crankshaft.

Loosen off the crankshaft belt and put a large Stilson onto the crankshaft pulley nose and see if by leaning hard or reversing the stilson and pulling up you can see or feel any movement in the pulley upon the crankshaft. It may not be much but if you suspect it is loose removing the radiator and tightening the dogbolt with a 1 1/8" AF single hex drive socket and torque wrench to 120 lb ft is necessary. The original torque setting is shown as 140 lb ft but in deference to 50 year old material I reduce it to 120, I've never had a pulley come loose at that. The bolt is shown as having a stripping force of 150 lb ft and the crankshaft material will stand more. Car in 4th gear with a bricks in front of the tyres and your wife or friend standing on the footbrake will stop the car moving.

Mick Richards

[The_Doc]

Thank you, Mick!

On the top bearing on the right hand side there is a little bit of the copper showing through so it might warrant a change as a precaution but thanks for confirming that it isn’t badly worn.

I haven’t had the front pulley off at any point, but I will give it a check. The previous owner of the car runs very reputable TR restoration business so I have been working on the assumption that everything on this car has been done properly and to be honest, I have found no evidence to the contrary. 
 

Can you think of any other parts of the internal engine that could be easily checked? I haven’t noticed a huge drop on oil pressure and I sent the oil from the sump away for an analysis; it came back with slightly high, but not alarming, levels of iron (50 ppm) so this could point to crankshaft or even camshaft wear.

 

TIA,

Adam