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MG MGB Technical - Refreshing bearings

67 BGT with 98,000 miles. Very tiny amount of gray smoke on startup. Uses about 1 qt of oil every 500 miles, some of that from slight leaks. (tappet cover, timing cover, etc).

Oil pressure at 70 all day long. Head redone at 92,000 and at that time, I found the pistons are stock size and the cylinder had nearly no upper edge ridge.

Compression is 135 to 140

Only item I notice is when it starts with the choke on colder mornings and runs up the revs quickly, I note what I call bearing noise for that quick split second until oil pressure jumps up.

So, It looks like I have to pull the transmission this winter to evaluate why shifting into 3rd and 4th is getting stiffer. While I have the engine out, I am thinking of refreshing all bearings. I know on way to check wear is to plastiguage the current setup to see what the clearance is. After taking the caps off, I assume I also have to Mic the crank to see what size (oversize) bearings are needed.

Without any obvious damage, any reason to do anything else to the crank or cam?

Next is the issue do I replace rings? Can I just add a set of new rings, go with the next size over? or just leave the pistons in and not touch this area? If I change them, just do a cylinder hone to rough up the walls?

This is one of those, do I do a full short block rebuild or just a few items such as bearings?
Bruce Cunha

Bruce I did a freshen up on a friends B last year at the same milage as yours. We found the pistons and bore good and the crankshaft dead standard. Fitted new standard rings, bigend and main bearings. The engine came up "sweet as". I did get the cam ground and new lifters plus head work. Its not usual to go oversize with rings unless you bore. I did run the hone down the bore to allow the new rings to bed in with a little oil retension. Denis
Denis4

If the bearings look good (no copper) and there is no taper on the journals (plastigage in 3 spots, middle and both sides to see) then just fitting new shells should work just fine.

Make sure to measure the ring grooves with a new ring in there to make sure there isn't excessive wear and too much clearance with the new rings which could lead to broken compression rings.
Bill Spohn

The start up noise, that you are hearing, might simply be the oil pump priming itself. My '67 did this for years until I installed an inverted oil filter, from a later B engine. After that, the noise disappeared. RAY
rjm RAY

Bruce,

Your oil consumption is a wee bit high and the compressions a wee bit low unless of course you have a low compression engine. I'd be inclined to run a hone through the bores and then fit a new set of standard size rings as you only fit oversize after a rebore. Now bearing noise is not completely unusual until you see the oil pressure rise but at 70 psi yours is very good. Have a look at the bearings and see what like they are and look on the back of them to get the size I assume they are stamped STD. Mic the shaft by all means but I doubt if you will find any significant wear. It should be sufficioent just to replace the shells. Now I'd be inclined to check the oil pump clearances and perhaps even replace it just to make sure also check the spring length on the pressure relief valve to make sure it is within spec
Iain MacKintosh

Thanks All. Probably have the B in the shop for the winter sometime towards the end of October. I will update the post once I get things out of the car.


On the issue of oil pumps. Probably not a bad idea to replace it at that time. Can anyone educate me on the difference between the Moss 4 main standard and the 5 main upgraded oil pump?( other than around $30)
Bruce Cunha

That obviously should be the Moss 5 main standard and the 5 main upgrade.
Bruce Cunha

Bruce-
The Moss "Upgraded" oil pump incororates the modifications used by the factory race team. On a street engine, it's a waste of money.
Stephen Strange

Hi Bruce,

For what its worth I have freshened many cars, with rings and bearings, but not a B.
At over 200,000km, when they started using oil, I pulled them apart, eyeballed to make sure no obvious defects, cut the lip at the top of the bore and fitted new rings and bearings. Still going strong 100,000km later, when I got rid of the car.

Probably make a mechanic turn in his grave, but it worked.

Herb
Herb Adler

Herb. If done prior to serious wear, that really is all that may be needed. You are only replacing the parts that wear. If the cylinder is not severely oversize, that should be good for a number of miles.

Used to drop the pan and replace bearings in the 1950'/60's cars of my youth as a routine practice when buying a used car.
Bruce Cunha

This thread was discussed between 18/09/2012 and 23/09/2012

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