Main Bearings rumbling

Post by **Stewart_Boik** » Tue Aug 01, 2006 9:18 am

My 1965 1098cc car has run the main bearings after just 6000 miles. They were originally replaced at about 38,000 then again at 80,000 miles. This seemed a reasonable interval and on the second occasional the shaft was ground to 10 thou. and a new oil pump fitted. But now after just another 6000 miles the bearings are rumbling again. Admittedly this was 10 years ago, as the car gets very little use. I have checked the oil pressure and it looks OK. 65 Lbs/sq" on cold idle, dropping to 25 (idle) when hot. It sits around 45 when running at normal temp. Any one got any ideas what I should look for this time when I strip it down? I heard or read somewhere that the early 1098cc motor may have had problems with the bottom end. Anyone know anything about this?

Regards
Stewart - Durban SA

Post by **bmcecosse** » Tue Aug 01, 2006 10:18 am

They should last a very loing time - provided they are not starved of oil. I suspect your car may stand for long periods - the oil in the pump will slowly drain away - and then when you start it there is no oil circulating for the critical first few seconds - maybe even minutes. Could also be general low oil level - but I'm assuming you keep it well topped up! The oil pressure you report is low - no option but another regrind and new shells all round - and yes - another new oil pump ! Also check the elief valve - but it looks like it is working ok from what you report. In future - if it can't be started and run regularly - it would be better to take the plugs out and spin the engine up on the starter motor till oil pressure shows - then replace the plugs and start it up.

Post by **brixtonmorris** » Tue Aug 01, 2006 3:13 pm

did you have the big ends reground at the same time?

Post by **Stewart_Boik** » Tue Aug 01, 2006 3:32 pm

Yes, complete engine rebuild, re-bore full shaft grind, although thinking about it, I did not do the camshaft. Any chance those bearings could be rumbling?

Post by **bmcecosse** » Tue Aug 01, 2006 7:18 pm

Highly unlikely! They only get damaged if the engine is run into the ground - with no oil in the sump for example.

Post by **brixtonmorris** » Tue Aug 01, 2006 11:31 pm

i second that

Ratbag · Post by **Ratbag** » Wed Aug 02, 2006 8:53 am

Stewart_Boik wrote:My 1965 1098cc car has run the main bearings after just 6000 miles. They were originally replaced at about 38,000 then again at 80,000 miles. This seemed a reasonable interval and on the second occasional the shaft was ground to 10 thou. and a new oil pump fitted. But now after just another 6000 miles the bearings are rumbling again. Admittedly this was 10 years ago, as the car gets very little use. I have checked the oil pressure and it looks OK. 65 Lbs/sq" on cold idle, dropping to 25 (idle) when hot. It sits around 45 when running at normal temp. Any one got any ideas what I should look for this time when I strip it down? I heard or read somewhere that the early 1098cc motor may have had problems with the bottom end. Anyone know anything about this?

Regards
Stewart - Durban SA

What kind of running-in procedure did you follow? Easily forgotten in an age when new cars don't have one....

Post by **Stewart_Boik** » Thu Aug 03, 2006 8:58 am

Hmm, it was ten years ago, I am sure I would have gone easy on it. I see no-one has commented on the early 1098 motor's small centre bearing which they upgraded on later 1098s.....

Post by **bmcecosse** » Thu Aug 03, 2006 1:24 pm

Only the later Spridget engine got 2" main bearings - and it was all 3, not just the centre one. This was to give them a 'competition' engine - effectively a Cooper S engine for north-south use. Yes they are much stronger - never fitted standard to Minor or A40.
Your mains (if you are sure that's what it is making the noise) will go on for long and weary with reasonable driving. Just don't labour the engine - better to change down - and use 20W50 oil.

Post by **brixtonmorris** » Thu Aug 03, 2006 11:18 pm

where is your timing at?

Post by **Onne** » Fri Aug 04, 2006 12:21 am

1964...

Post by **Stewart_Boik** » Fri Aug 04, 2006 8:20 am

Timing is fine, car performs very well. Thanks everyone for your comments. I will post a comment when I eventually strip it down and see what I find. Probably a few more hundred miles taking it easy in the meantime.

Regards, Stewart, Durban SA.

Post by **bmcecosse** » Sun Aug 06, 2006 10:12 pm

The Marina 1275 engine was said to suffer from mains rumble - dunno why it would be any different to other 1275 engines - anyway, they 'cured' it by fitting a dizzy with NO vacuum advance !! Exactly what this was supposed to do (aside from spoiling the fuel consumption) is not clear. Obviously it stopped the ignition over-advancing in high vacuum conditions (closed throttle) and presumably this somehow stopped the mains from rumbling ?!?!

Post by **bigginger** » Sun Aug 06, 2006 10:32 pm

Never heard that before, even during my ownwrship of 8 of the things

Post by **Packedup** » Sun Aug 06, 2006 11:30 pm

bigginger wrote:Never heard that before, even during my ownwrship of 8 of the things

I have - Might have been in the Vizard bible, and probably mentioned on the Austin Rover resource site. Though it was referred to as crank case rumble IIRC, never saw any description of what caused the rumbling, only that removing the vacuum advance cured it!

Post by **bigginger** » Sun Aug 06, 2006 11:32 pm

Beeeeeeeeeezarre!

Morris Minor Owners Club

Main Bearings rumbling

Main Bearings rumbling

Re: Main Bearings rumbling