Morris Minor Owners Club

Michiel wrote: ↑Fri May 20, 2022 6:19 pm But stationairy there is no rumble at any revs.

This could be significant. Can you get it to rumble under load in third gear (ie climbing a hill), and if so does it happen at the same approx revs as in top gear? If "yes" this helps to narrow it down to engine. If "no" , then the rumble could be coming from another source altogether.

At 3000-4000 rpm throttle closed and then opening slightly it is loudest and gradually disappears at full throttle. Third and fourth gear.

Not on a moggie but investigating a similar crank rumble the block was cracked up the thread where the main bearing bolted, this caused the cap to move under load, although torqued correctly. The tell tail was fretting marks on the contact faces of cap and block.

Thanks Bill. I'll keep that in mind. Phil also mentioned main bearings. But the mains measured correct. Was it an A-series engine, that crack?

No it was a truck engine but similar that crank and bearings had been checked but had a bottom end rumble but oil pressure ok This was likely caused by main bearing bolt being fitted with oil in the drilling, which hydraulics when assembled and creates extreme pressure, fracturing the casting.

What are your mounts and torque restrictor like, if the ground out under load (or you have new overly hard bushes) you get the engine harsh noise transmitted through the body which sou ds a bit like a bottom end rumble, you could as an experiment even remove the torque restrictor and see if t makes any difference.

Mounts are new and rock hard. I'll remove the steady bar. If that's the cure I will post it here. But it really really sounds like bottom e d rumble.
When I was twenty I had a A55 Cambridge that I drove much to 'agitated'. It rumbled for a long time untill we went uphill full throttle and within seconds the noise was really loud ending in a bang. I found a big end cap behind the battery...

Mounts are new and rock hard.

Then this could be the problem. New stock mounts seem to be pretty much without exception far too hard.
I suggest that you see if you can find some new old stock ones or failing that some good used old ones.

Don

I'll have a search for nos ones. AHA5484Z..OK a lot of them out there, no nos.

Not tried it myself but apparently drilling holes through the rubber softens them up a bit

If you are patient yo should be able to find some NOS rubber mounts, I eventually got some after a couple of months looking on ebay.

Phil P

As Mr Panky says, modern hard rubber mounts can cause roughness in the 30-40 mph range that I cured in my installation by drilling holes through the rubber; see here viewtopic.php?p=606467#p606467 Alas, the photos in these old posts seem to have been lost but I did 3 holes 6mm dia across the front engine mounts at about their centre.
I hope you find your fault soon, MikeN.

what was the spiggot bush like ,could be the shaft clattering before full take up of power,or would that not be the case once fully out clutch,wear in the spigot bush on ford transits(I've had many over the years) causes loads of vibration and clatter.

I renewed the spigot bush when I reassembled the engine. Further I really doubt it is hard engine support rubbers. It really sounds like bottom end rumble and, like Phil said, main bearings. I’m now just driving my dear Morris until there will damage visible when I take the engine apart. Again… A lot of motor way driving at the national maximum daylight speed of 62 Mph. And the rumble slowly gets worse.

I'm also thinking of an unlikely cause that are the bearing locating collars of the main bearing caps. When I took the block to the reconditioner it was necessary the remove all the collars. The block has to be flat to enable it being mounted on a machine. It was difficult to remove three off these without damaging, so I bought some new ones. What if these new collars are a fraction to high? They could be torqued up all right. And it takes no more than a thousandth.

That's an interesting possibility, you could test with plastiguage to check if the main bearing caps are clamping up correctly.

It could well be resonance of the stainless exhaust as Jowettjavelin suggested, combined with stiff short rubber exhaust straps. Will let you know.

Did you ever find the cause of the rumble now this post has resurfaced.

No, I resurfaced with an assumption. I'll follow that and will report back. It all takes a while