Engine vibration.

[michaelsmorris]

I've just fitted a rebuilt engine from Charles Ware's. The engine is going well but at tickover I have a vibration that wasn't there with the old, knackered engine. I also fitted a new clutch.
I have an electronic distributor. The vibration was really harsh to start with but Ian Allen at Witchford said that retarding the timing to 10btdc would help. This did make a real difference, but there is still some remaining vibration. I know it's an A-series and won't be silky smooth, but I think it should be better than it is.
The plugs, leads, cap, coil and rotor are all fairly new and were on the previous engine. The colour of the plugs suggests the carb is setup correctly. The engine pulls well and isn't any harsher than I'd expect whilst driving.
The engine mounts aren't the hard, almost solid ones, and I've adjusted the tie-bar so that it's doing its job but not pulling or pushing the engine to one side.
The tick over is, if anything, slightly high so it's not just lumpy.
Now I'm out of ideas!
Any suggestions welcome.

[panky]

It may be running a bit lean, is the vacuum pipe to the dizzy OK? have you tried the lift pin test? Try turning the jet nut out a couple of flats and see if it improves things.

[bmcecosse]

10 degrees before is FAR too much static advance - swing the dizzy to get the smoothest idle. And have you checked and reset the valve gaps?

[liammonty]

If you fitted new engine mounts, these will likely be the cause of more vibration, as the new ones are awful. Caught me out when I rebuilt my engine...

[michaelsmorris]

Thanks for the input so far.
I have now advanced the ignition timing a little, but this has not altered the vibration.
The vacuum pipe appears okay, it doesn't leak.
The colour of the plugs suggest the mixture is okay and it did as it should on the lift test.
I have talked to Tim Brennan at Charles Ware's and he suggested it might need a damped front pulley. He also said to check the gearbox is sitting correctly, that went in as a unit with the engine but I will check it.
Work keeps getting in the way of life, so it may be a few days before I get back to the Moggy.
Engine mounts are about four years old but were on the previous engine, which didn't vibrate.
Tappets are fine.

[bmcecosse]

What a load of cr@p - damped pulley.. I've never heard such nonsense. And more rubbish about the gearbox maybe not sitting correctly.... Good old Wares - again. Yes - the damped pulley is a good thing to preserve the engine at high revs - nothing to do with idling. Why do you keep advancing the ignition timing when it is already FAR too far advanced at 10 btdc ?? It needs to be RETARDED - the correct setting will be somewhere around 3 degrees. I suggest an urgent compression test to check the engine condition...the head gasket may be blown... Really basic check - Are you sure the spark plug leads are on correct order - 1342 anticlock round the dizzy cap..... ??? Have you actually checked the valve gaps - or are you assuming Wares ( ) have set them correctly ??

[michaelsmorris]

Sorry, meant retarded. It's now about 6 btdc and seems to have smoothed out a bit. Only a drive will confirm it fully but run out of time again.
I've checked tappets twice, using rule of 9 process, set at 12 thou. Checked compressions not exactly matched, but not much more than 10 psi between them. More miles will help to free things up, so far only a hundred on this engine.

[michaelsmorris]

I've come back to this post after almost two years. I've done almost a 1000 miles now and still haven't solved the problem. A recap and update.
Recon engine. Same mounts as previous engine. A harshness/vibration can be felt at tick-over and whilst driving. (Since day one with this engine).
Ian Allen, a highly-regarded Minor restorer has tuned the engine as close to perfection as a Minor engine is going to get.
The cylinder compressions were 155, 155, 180, 180. After much thought I decided to take the head off and have a look. There appeared to be nothing wrong. Once the head was cleaned up I check it and it's totally flat across the surface. I poured white spirit into the combustion chambers and left it overnight. Fluid still there in the morning.
I took the rest of the engine out wondering if the rings had been damaged on pistons 1 & 2. Nope, they're fine.
So, that's top end looks okay and now bottom end. That leaves the gasket. The faces of both the block and the head appear fine. The gasket appeared to be okay when the head was lifted. It was torqued down after the engine had been run a while and again after 500 miles.
A friend has an A35 with the same engine. We had both cars running side-by-side. putting a hand on each car, on his you could tell the engine was running, but it was smooth. On mine you could feel the vibration through the body. He's an engineer and wondered if the crank could be bent. I would hope that would have shown up at the recon stage. (Ivor Searle job). I thought it was more likely to be the difference in compressions, but can't find out what's caused that. As the vibration is there from stone cold I don't think it's a crack in the head.
So, over to the wider world of the MMOC messageboard community. Suggestions please.

[martin418]

is the flywheel on in the correct position ? . the bmc workshop manual shows the correct orientation of the flywheel to the crankshaft , also are the engine mounting towers on the right way round ie o/s on n/s etc

[philthehill]

I doubt that the problem lies with the flywheel as the flywheel was not balanced as part of the individual engine build but was balanced as part of the manufacturing process. That is why it is possible to replace the flywheel with another and the engine still run perfectly.
The reason that the flywheel is fitted as it is as shown in the wksp manual is because of the 1/4 marking on the rim of the flywheel which indicate TDC for No: 1 & No: 4 pistons.
The flywheel can be moved around on the end of the crankshaft and was and still is a useful way of overcoming a worn starter ring gear.
Check that your starter ring gear is running true and fully fitted.
The Minor crankshaft is quite strong and it would have to have had a hell of a bang to bend it.
If the crankshaft has been re-ground the re-grind process may have been faulty but I doubt that has happened.
Therefore I think that you need to look elsewhere for your vibration.

[Nickol]

Is it possible that it is periodically missing? i.e something on the HT System is not right. A friend of mine had similar Problems with his MG (actually worse , the Motor would sometimes cut out ) which was eventually traced to a cracked Distributor cap.

I have read that you are reusing the old System and in line with "it's never the coil" , perhaps something else is past ist sell-by date.

[michaelsmorris]

Thanks for the suggestions so far. What I should mention is that the engine runs fairly well. It accelerates as quickly as can be hoped for and cruises at 55. Much more than that and the vibration becomes a distraction.
I'm going to put it back together and refit it and see what happens. The only thing left is that although it looked okay, maybe the gasket was faulty. I've got a copper one to fit, but that was what was on it before. I wonder if a composite one might be better?
As a matter of interest I weighed the piston/conrods and they came in the same, so that's not the problem.

[martin418]

sorry if i got it wrong with the flywheel idea it was just a thought

[philthehill]

Martin
No need to be sorry - your suggestion has not been disproved - input to this forum comes in all shapes & sizes and from all directions and sometimes the most improbable ideas are the right ones.
Phil

[kennatt]

have you considered the clutch, unbalanced cover maybe. although you probably used same cover as before so maybe not, spigot bush ok, does the vibration go when you depress clutch.

[edd_barker]

Checked the gearbox mounts? Mine has a vibration that kicks in around 55mph when everything resonates together and makes a hell of a racket!

I would imagine if it were crank you would have noticed on assembly, when I built mine I could spin the crank with all main caps torqued down, it would rotate freely and had a pleasing inertia to its rotation. Any imbalance should have been apparent at this stage.

If it vibrates with the clutch depressed at idle I would second Phil and check ring gear. I have had two deform and sit incorrectly.

Gearbox steady overtightened maybe?

[michaelsmorris]

The gearbox and engine mounts are the same ones fitted to previous engine. The flywheel is the same and just to be on the safe side it is fitted with the 1/4 mark at ther top on TDC. The complete clutch was changed but the original cover is back on because it was one thing I did suspect. But it wasn't that and the vibration remained. There wasn't a gearbox restraint fitted when I had the previous engine in but I've now fitted one and Ian Allen checked the tension on it and said it's fine.
I've fitted new plugs, it's got good leads and the coil is fine.
I'm sure the vibration is down to the difference in compressions, it's just that I can't find a reason for the difference.
I've just finished reassembling the engine but won't have time to fit it until later in the month. A twelve hour working day leaves me to too little time or inclination to get out in the garage!
I'm hoping that somewhere along the line I will have sorted the problem. I'll post the result when it's back in action.

[oliver90owner]

I would expect running compression to be very much more even with a properly rebuilt engine after sufficient miles on the clock. 5%, or better, difference in compression pressure would be the norm, I would guess.

Obscure reasons for differences might be compression rings fitted upside down on the two offending pots. Even pistons fitted the wrong way round. Even different bore diameters or surface finish could be something to suspect.

As they are adjacent cylinders, I would be suspecting something on the inlet manifold side may be responsible - but surprising as it occuring at the cranking speed for the compression test. I might even question the camshaft, if a replacement was fitted, for instance - so I might be carefully checking opening/closing points and durations - and possibly lift on each pot - with a dial gauge and timing disc.

Further head checks could include crack testing for a fault between those two chambers, or combustion chamber volumes due to more valve recession on the two front pots.

Strange. The above would be unusual for a properly reconditioned engine, but something is causing those pressure differences and it would not be tolerated in a race engine, for instance! All the above might seem like 'clutching at straws' but there will be a simple reason for the difference, if those compression test results are confirmed.

RAB

[dalebrignall]

do the compression test with a few drops of oil down the bores if the results increace and are all uniform then you know the rings have had it worth a go

[kennatt]

there is of course rebuilt engines and REBUILT engines ,if you are convinced that the rings,valves and head are ok,your comp differences have to be down to cylinder bore ,I would try to find out if the block had a rebore and what size pistons were fitted.I have seen some cr.......p engine rebuilds,over the years, from supposedly reputable establishments, The only safe way is to do it yourself then you known what has been done.