Morris Minor Owners Club

Right. Symptoms:

• Uneven but regular 'rattle', sounds like it's coming from the back of the engine. Continuous through clutch usage and rev range - gradually getting worse.
  
  Today it started a quiet but regular knocking...
  
  Idle is becoming more and more uneven.
  
  Momentary loss of power while driving (bucking)

I'm going to put an oil pressure gauge on tonight to check if the pressure is up but it sounds like the big end bearings are going? Would anything else fit the symptoms? Maybe I'm just being paranoid...

The problem is, this is a brand new 1275 engine! I bought it reconditioned (but second hand, never used) and put it in about 2-3 months ago. I'll have to get in contact with the builder but I suspect the warranty on certain parts doesn't include the big-ends.

I don't understand how they could have gone so early! And if they have, what does it mean for the rest of the engine? If there is some problem with oil flow or something that caused it, would it even be salvageable?

It's a big job, but is it going to be economical to take the sump off and re-grind the crank (which I assume needs doing) and put in oversized bearings in? I've never gone so deep into an engine, so it's completely out of my depth. Would I have to take the engine out of the car?

I assume there is oil in it!

Blown headgasket is a lot more common and can sound like a big end if it's gone between cylinders.
Check the compression first.

Certainly check the oil pressure - an oil gauge is ESSENTIAL on an A series... But your problem may be elsewhere - head gasket is certainly a possibility - even just a burned valve maybe (check valve gaps)...Or something come loose in the clutch?? If the big end bearings have failed - it's engine out to regrind the crank - it has to come out of the block.......

Someone has suggested the thrust bearing may be loose, for some reason I didn't think of the head gasket duh - I'll pop by halfords (urgh) and get a compression tester.

I set the valve gaps to 12 thou a few days ago, some were a little bit wide but not excessive. There was no mayonnaise!

OK, results on compression test are... Interesting.
front to back:

1=175 after a few seconds idle
2=100ish, goes to 150 with a bit of throttle
3=60, 130 after throttle
4=100 to 110 after throttle

It was knocking, or "clacking" a lot on the last two.

With throttle?? The comp test is done on a hot engine, all 4 plugs out and the throttle held open with a brick on the pedal....... Your results go down progressively - is it possible the battery was going flat as you did the test? Although poor - they don't show a blown headgasket.

I'll do it that way, battery is fine. Oil pressure 60

bmcecosse wrote:With throttle?? The comp test is done on a hot engine, all 4 plugs out and the throttle held open with a brick on the pedal....... Your results go down progressively - is it possible the battery was going flat as you did the test? Although poor - they don't show a blown headgasket.

Doing the test properly (thank you!) Gives a much better:

1=210
2=200
3=205
4=215

Oil pressure and compression fine... Maybe it is a problem with the clutch?

My problems with the "blip" of loosing power for a fraction could be unrelated.

These are exceptional pressure readings! Nothing wrong there - and the oil pressure (assuming that's the hot pressure after a good 10 mile run..) is fine too. You know I advise 15 thou gap for the exhaust valves.....

bmcecosse wrote:These are exceptional pressure readings! Nothing wrong there - and the oil pressure (assuming that's the hot pressure after a good 10 mile run..) is fine too. You know I advise 15 thou gap for the exhaust valves.....

Yeah, I set them to 12 to see if that was the rattling, but I don't think its regular enough to be that (and isn't proportional to revs)

Oil pressure reading wasn't after a run, that was pretty much straight away, wasn't cold but not warm. I'll run it for a bit and see if it changes.

The rattle/knocking may be loose flywheel........... You could remove the rubber bungs and try to check if there is any movement with a tyre lever - engine NOT running, obviously - I think.. Is it a Marina engine - with a 1098 flywheel grafted on ?

isn't proportional to revs

What does make a difference?

bmcecosse wrote:The rattle/knocking may be loose flywheel........... You could remove the rubber bungs and try to check if there is any movement with a tyre lever - engine NOT running, obviously - I think.. Is it a Marina engine - with a 1098 flywheel grafted on ?

It is a marina block yes, and modified 1098 flywheel. I'll give it a poke, wasn't aware of the rubber bungs (on the bellhousing I assume?)

MarkyB wrote:

isn't proportional to revs

What does make a difference?

Not much, it's fairly continous if uneven. I drive fast, or slow and it's still pretty much the same. Clutch up/down, in gear/not - nothing really affects it.

It doesn't seem to increase in frequency much with the revs of the engine, though it feels like it lulls at certain revs - might just be it being uneven though.

The engine is running a lot better now, found a missing bolt on the alternator that might have been causing the knocking! Feels smoother and less lumpy, but there is still the rattle. Fingers crossed that that's it...

Thanks for the help.

Hope that's done the trick, it does sound like something loose, big ends would change with engine revs.

You sure the rattle isn't pinking?

bmcecosse wrote:You sure the rattle isn't pinking?

Yeah, this was my first idea of what it was! It's exactly how it was described - high pitched "tinkly" like a stone in a can kind of rattle (though this one does sound a little 'kalcky' when you are standing in front of the engine rather than in the car).

But I retarded the ignition to the point where it was noticeably underpowered and it didn't change the noise at all, this led me to believe it wasn't pinking. Also, it's present at idle, I thought pinking only really happened under load? It sounds the same going uphill at speed.

Maybe I left something in the bell housing and it's rattling around :S

I'm pretty sure the knocking was the alternator though. I've gone for a drive and it's not nearly so lumpy, and there was no low pitched knocking like before. Yey

The bolt was completely missing, never noticed it loose, wonder if it snapped or just worked itself loose.