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MG Midget and Sprite Technical - Rattling Tappets - Does this look right?

All you engine gurus out there, my newly rebuilt (not by me) 1275cc engine has very noisy tappets. I have set the clearances several times using the "Rule of 9" and have made no difference. The car has driven about 900 miles since reassembly.

Looking under the rocker cover today I noticed that several of the rocker arms are well off-centre in relation to the valve stems. See photo. Is this OK? Five of the eight are like this.

The engine runs well, but doesn't half tap. All components were renewed including camshaft (Kent Fast Road), cam followers, rocker shaft and rockers, valves and springs.

Mike


Mike Howlett

It is normal for the rockers to be offset on a 1275.

As long as the whole of the valve stem is covered, it is fine.

The 1275 rockers have wider pads than earlier versions, as the valve spacing is different for the bigger valves, but the pedestals are in the same place.
Dave O'Neill2

Mike, you say you've adjusted the rockers several times. Did they NEED adjusting each of those times? If so, I would worry about lifter or cam lobe wear, sometimes a result of improper break-in. But 900 miles isn't much. Might want to measure the lift of each pushrod.

Peter C
Peter Caldwell

What state are the rocker pads in? They can wear quite a bit and get pockets in the face which makes correct adjustment troublesome and if the cam has been changed resulting in extra lift can put extra loads on the valves.
David Billington

Thanks for your comments. The whole valve rocker assembly is new so the pads are perfect. I shouldn't have said I keep adjusting them, but rather checking them. The gap isn't changing. If the offset is alright, and the components are new and set to the recommended gap of 12 thou, why does it tap so loudly? From inside the cockpit the only thing louder than the tapping engine is the whining gearbox. Disappointing in a rebuilt car.

While I'm here, what is the most likely cause of the whining gearbox? I bought the car dismantled but with most parts already rebuilt. The gearbox was smart and clean inside and out so I didn't dismantle it. Now I wish I had. It is a 1966 vintage 1098 ribcase box and it shifts gears beautifully with strong synchro on 2, 3 and 4. But it is only quiet in fourth. I expected some noise in first, but the racket in second and third seems excessive to me. My logic tells me that the layshaft is the likely culprit since it isn't carrying the load in fourth. Would it be end-float or roller bearings? Or something else? How tricky is a home rebuild on this 'box?



Mike Howlett

Mike, I would suspect layshaft roller bearings as well but if you're going in there, you might as well change all the bearings.

If the rockers are all new they shouldn't tap that much. I know its messy but have you tried putting a feeler in when its running to see if it's one or all that's causing the problem? If you're up this was you can borrow a used set to try.

Best of....
MGmike
M McAndrew

Waiting for the shouts, but only from those that have never tried this method

Set the tappets with the engine warm and running, yes running.

You do need a plan, have the tools at hand and some rags to collect the oil, and yes a pair of latex gloves stop the burns, first set tappets cold with the rule of 9, then run engine to temp and adjust again, slide the feeler under the rocker and you'll feel it go tight and then loose, after a few times your get the feel, that lightly trapped feel of the gauge, this method removes all the working tolerance that give you the noisy tappet after static adjustment. Once this method has been mastered your never set tappets any other way.

Shout away lol
Al Charles

Mike

Sometimes the cam is ground with the base circle significantly off-centre compared with the journals - it shouldn't be, it's unusual but it can happen. A thou or two of this "base circle run-out" is not of much consequence, but I have seen up to 6 or 7.

The a result of the base circle not being concentric with the camshaft is that the tappet clearance varies as the cam rotates. If the variation is too much, then the valve train take-up point is off the end of the opening ramp (aka quietening ramp) even if the tappets are set correctly on the back of the cam.

This condition is easy to check for: Insert you 12 thou feeler with the rocker adjusted to provide just enough gentle pressure to nip it in place but no more. Then turn the engine over in the forwards direction slowly by hand. If base circle run-out is present, the blade will come loose at some point before the valve starts to open. If this happens, try to find where the extra clearance is greatest and measure the gap. If it doesn't happen, then repeat in the backwards direction to see if it comes loose that way.

It will be necessary to check at least 4 lobes before ruling this out as a possible cause. (Either all inlets, or all exhausts)

If the blade does come loose, then try to find the point where the extra clearance is greatest, and measure it. Similarly it is useful to know what the minimum point and clearance is (a bit more difficult as there is the beginning of the opening ramp to confuse things) Obviously this analysis would be much simpler with a dial gauge, but for initial diagnosis to see if there is a problem or not the feeler blade is quicker.

If significant run-out is present, the ultimate fix is to replace the camshaft. However, in the meantime, a good move would be to set the 12 thou at the point where the clearance is greatest. That way at least you are not hammering the valve train. The downside is that the valve stays off the seat a few thou for a bit longer, but in practice the negative effects of this usually aren't that marked.
Paul Walbran

Is .012 correct for that cam?
Did you check valves at full lift for sufficient over-travel available, no spring bind etc?
Correct retainers for double springs?
Not hitting the guide tops?
Pushrod cups not hitting the rocker bottoms?

FRM
FR Millmore

Well thanks again for everybody's advice. Had another good look at it this morning and checked that there is no spring binding, the correct retainers are fitted, they don't get near the guide tops, and the pushrod cups are clear of the rockers. I put the cover on loosely and ran the engine to warm it up, then removed the cover again.

With the engine idling and using Mike McAndrew's tip I sacrificed a 0.3 mm feeler and slid it in each of the gaps in turn. When it went in numbers one and three the noise quitened right down. Stopped the engine and very carefully adjusted those two gaps back to 12 thou - they were about 16 thou. Bingo! Peace resumes! The engine now sounds like it should - like a well oiled sewing machine, as someone once said. I don't know how I managed to set them wide, but I obviously did.

Thanks all. Now for the gearbox. Not quite such a simple fix.
Mike Howlett

Mike, A quick check on the Kent web site indicates all their A series cams should be set at .016 You might want to open yours up a little and I guess they'll run noisy! Hope you can live with that, if not add some more under bonnet sound proofing ;0)

Best of...
MGmike
M McAndrew

Mike, glad you're getting it sorted. Another way to check clearances, easier for me, anyhow, is the go-no-go way. If you want .012 use a .013 that wont fit, and a .011 that will.

Peter C
Peter Caldwell

Id becareful getting rid of valve noise

As trevor says.. noisey valves are happy valves

Im a fan of both go-no-go valve adjustment

and using a feeler gauge on a warm running engine..after all the valve are going to be tapping at normal operting temp range not cold engine tick over temp

Just depends how oily you want to get



Btw....is the valve cover and its gasket stock ???

On my aftermarket the valve spring was just touching the side wall of the VC and made alot of tapping noise till i ground out the side of the VC for extra clearance

Prop
Prop and the Blackhole Midget

Mike: If someone put in straight cut "racing" gears instead of the usual, that would make 2nd and 3rd sound just like first gear, which is always straight cut.

keith
keith anderson

I had also thought about straight-cut gears.

I once bought a midget 'project' and the seller told me he thought it had a straight-cut 'box because of the noise it made. It hadn't, it was just knackered!
Dave O'Neill2

me too but I discounted this as Mike had said it looked clean "inside and out" and I'm sure he would have noticed straight-cut gears.

Mike, I've not had one of these boxes apart but it should be pretty much the same as others..... be methodical and watch the spring loaded balls in the syncro hubs as they will fly at speed if unchecked. Put a cloth over the hubs and work by touch as you remove them.

Best of.....

MGmike
M McAndrew

<<Put a cloth over the hubs and work by touch as you remove them>>

Another method is to put them inside a clear plastic bag.
Dave O'Neill2

It doesn't have straight cut gears (a) because I had a look inside before I assembled the car, and (b) because the synchromesh is strong on 2, 3 and 4. But it was a good thought. I can see another dismantling project looming. Bah! When will I get the time to build my Elan which is lying in pieces in the garage, shed and attic?

Regarding rebuilding the 'box, I don't envisage having to dismantle the mainshaft assembly as gear swapping works so well, so really the only bit I will need to be careful over will be the end-float on the laygear. Is that right?
Mike Howlett

Mike

Straight-cut gears use the same synchronisers and synchro rings as the helical gears, unless it's a more recent 'dog' box.
Dave O'Neill2

OK Dave, but they were definitely helical gears I saw in the box. I was out in the car last night (freezing cold weather, but a lovely heater with the hardtop - cosy) and the gearbox noise seems less somehow, so I suspect I'll leave it for now and see what happens over the next few months. Maybe I'm just getting used to it, or maybe the ZX1 treatment I poured in the 'box has helped.
Mike Howlett

Yepp... Oil treatment cures all

When i still had my ribby, i used lucas oil treatment, and it made a big differance in both performace and quitiness, but apperatly its not good for the transmission... I sqy if its broke, then go for it anyway
Prop and the Blackhole Midget

Mike

I have exactly the same problem with exactly the same cam. Still noisy - well to me anyways, after adjustment to 12 thou, but as the other Mike says, should be 16 thou - and noisier still! Loathe to decrease gap further because of that...

Engine pulls well enough - better loose than tight I suppose...


Mark O

Thanks for that Mark. I have mine set at 12 thou now and it is much better. I didn't realise it should be 16 thou until Mike McAndrew pointed it out to me. I shall leave them at 12 for now. The car is running well and I intend to put some miles on her so that I can have a go at sprinting and/or hillclimbing next season. I've even managed to stop the rain getting in, and since she is achieving 44 mpg at the moment on the HIF44 carb, she is in my good books. I'm one of those people who don't stop using my old cars in the winter. My wife takes out the modern car, so if I don't use an MG I'm stranded.

As secretary of the Caledonian Centre of the MG Car Club (http://www.mgcaledonian.com/), I note that neither you nor Mike McAndrew are members.... Let me know if you want a form for the original and best MG club. ;-) (tongue firmly in cheek)
Mike Howlett

This thread was discussed between 24/10/2012 and 29/10/2012

MG Midget and Sprite Technical index

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