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MG MGB Technical - Big end knock

oil change a thread on about taking the sump of my 1973 MGB. I think i must have killed an Albatross as i am having a nightmare with my cars. This one has an Ivor Searle engine fitted at a cost of over
A Basham

At the very least I would drop the pan and look and the bearings. Be wary that if the mains ran out of oil, most likely the rods did too.
Kimberly

As it wasn't under load, the chances are good that a new set of shells will be all that is needed.
Chris at Octarine Services

Kimberly, I think its a big end knock, Main bearings normally make a rumbling sound and its the big end's that make the knocking sound. I can look at three of the main bearing shells with the sump off but i cannot change them. The big ends shells i can change if it is that the journals on the crank are not damaged. I did have a Volvo 240 that upon kicking it down on the auto box, the big ends went and i lost oil pressure within seconds, and it sounded terrible all the time. This engine doesn't knock on start up and is holding good oil pressure cold or hot, so i have got a bit of hope that i may not have damaged the journals, many thanks for the advice regards Tony
A Basham

As said by others, you can certainly drop the pan for a look, but let's face it, you've got a nice, 7000 mile engine there so you might as well do it properly. Pull the engine and hopefully you'll get away with a new set of bearings, as Chris said, and maybe a bit of polishing of the journals. Let's face it, if a garage was responsible for the oil loss, you'd probably be insisting that they do the same.

Good luck.
Derek Nicholson

If you've got a crane, lift the engine out, it's about 3 hours DIY, and putting the sump back on lying underneath aint fun.
c cummins

You can change all five mains with the sump off - and it is a LOT less work than pulling the engine.
Chris at Octarine Services

Got to love the differing opinions!
Myself, I'm not big on lying on my back with oil dripping in my face so I would just pull the motor and replace the bearings on the bench. For the price I wouldn't check them, just replace them, and check the oil pump, clutch, etc while I had it apart.

Good luck!

Rich
Rich McKIe

For general info, here is the reply to Tony from my own BBS, he asked how to replace all bearings while the engine is in the car:

It helps to drain the oil overnight so the maximum amount of oil is removed to avoid too many drips while working underneath!

Remove sump and oil pump (this will cause quite a lot of oil to come out of the drillings above the pump, so go and have a cuppa while this drips out).

Take the spark plugs out.

Note: keep the caps in order when removed to be sure they go back in the same place! Also, the caps fit so that the shell locating tabs sit on the same side of the crank.

Turn the crank so two of the big ends are down and undo the caps, push the rods up clear of the crank and turn the crank 90 degrees and pull the rods down to change the shells.

Push the rods up, rotate the crank back and pull the rods down, change the shells in the caps and refit - torque the nuts up to 35/40 ftlbs.

Repeat for other two rods.

Undo the 10 main cap bolts.

Pull off caps 2 and 4.

Insert a cap bolt into the threaded centre hole on the centre cap and use a claw hammer and a suitable block of wood to lever under the head of the bolt to draw down the cap.

Repeat on the rear cap - more force needed here to break the seal with the back plate and because the cap is a tight fit in the block - use the hammer as a lever with different sizes of wood to pull the cap right out.

Undo the two 1/4 bolts at the bottom of the timing chain cover and repeat the process to remove the front cap.

Use a thin bladed screwdriver gently to tap the edge of the shells in the block on the side WITHOUT the locating tab until they rotate enough to lever against the tab and use the screwdriver on the back of the emerging shell to lever it out.

Slide the new main shells round the crank and push them round till the tab locates in the recess, fit new shells to the caps and refit them (with the thrust washers located on the centre cap, bearing surface outwards).

Use Hylomar to coat the back of the rear cap and front of the front cap and re glue the cork strips if they have come adrift. Refit the two bolts in the timing chain cover and torque the cap bolts up to 70 ft lbs.

Refit the pump and sump (after cleaning out any bits of shell!) with a new gasket.


Chris at Octarine Services

Chris,
I'm guessing that you've got a proper inspection ramp in your workshop....
Neil :-)
Neil Lock

Yup - a two post lift!!
Chris at Octarine Services

This thread was discussed between 04/03/2007 and 07/03/2007

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