Changing Main Bearing

[morris63]

After running the engine with no oil! (oops)I think I need to change the Big Ends and the Main Bearing. I know I can change the big ends with the engine in place, but can I change the mains? I seem to remember doing this a long time ago by pushing the mains out and then pushing new ones in, or am I very much mistaken? Thanks

[philthehill]

You can do the centre main bearings but to do the rear and front main bearings you need to remove the engine.
The cap of the front main bearing is retained not only by the two main cap bolts but also by the two 1/4" UNF bolts holding the front engine plate in place against the front main bearing cap which means removing the timing gears to access the two bolts. Invariably the front engine plate gasket tears which means taking off the front engine plate to replace the gasket.
The rear main cap is masked by the rear engine plate which does not allow the rear main cap to be removed without removing the flywheel and rear engine plate.
Therefore to cut to the quick - the engine has to be removed to replace all of the main bearings.

[oliver90owner]

What were the circumstances of the ‘no oil’ drama? What do you really mean by ‘no oil’?

[Bill_qaz]

Is it knocking?
What is the oil pressure?
How long did it run with no oil?
Do you really mean no oil or low oil?

[morris63]

Thanks for all you replys. The engine was rebuilt but we did not change the timing chain. After running it we decided that the chain did need changing. So we pulled the engine out and drained the oil to change it after around 500 miles. Fitted a new chain put the engine back in and then started it. Forget to put any oil in. Ran for a while but the oil light did not go out. We then remembered the oil! The engine still runs but the oil light comes on on tickover. I don't have access to an engine crane at the moment so I am looking and changing the bearings without removing it again if possible. Thanks

[morris63]

I don't have an oil pressure gauge.

[Bill_qaz]

Remove the centre main and big ends with engine inplace and inspect the bearings for damage. Make the decision on you findings.I would of thought running for a few minutes under no load is unlikely to have caused major damage.
Good luck

[oliver90owner]

”Ran for a while”

Not exactly a definitive response.

How long? What engine speed/load?

Oil pumps also require lubrication.

[morris63]

So, we started the engine on tick over, probably for less than a minute, then gave it a short rev to see if the oil light would go out. Which it did not. Then realised we had not put the oil back in. There was a brief knocking noise. Overall, probably around a minute maybe slightly longer
The engine runs fine now but the oil light comes on on tick over when warmed up. Compression is also good at around 170.

[morris63]

Remove the centre main and big ends with engine inplace and inspect the bearings for damage. Make the decision on you findings.I would of thought running for a few minutes under no load is unlikely to have caused major damage.
Good luck

Yes, good idea I will do that.

[oliver90owner]

If the rebuild included a crank regrind, the knocking may not have been too serious.

If the crank was worn, when the engine was ‘rebuilt’ it was likely time for a regrind.