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MG Midget and Sprite Technical - Engine rattle and compression

I have a 1275 69 midget that has done about 20K on a plus 30 rebore engine now totalling 87K. Their is a top end rattle that from a stethascope, sounds as if it is at the front rockers. I have set the gaps cold to 12 thou. However I wanted to check out the rest of the top end and did a compression test on a warm engine the readings are 1 152 psi, 2 150 psi, 3 145 psi. 4 155 psi. With a little oil in 3 compression went up to 150 psi. Question can I take off just the rockers which will release torque on those head studs and then retorque OK, or should I take the head off. What do you think of the compression readings, I!m feeling that perhaps it could do with a valve inspection and re grind. The head is standard not converted to unleaded the PO and I have used valvemaster additive. Other than above, the car pulls and drives well. Although I haven't contributed to comment on this forum I do enjoy readingit and thank you all for the entertainment.
G.E Verney

Compression seems fine as all readings are pretty uniform. Usually one at least is way off if there are problems. Not sure why you would wish to remove the rocker assembly in particular - unless you also wished to remove the head of course. Rattle - if tappets - is not necessarily bad news. Far better loose than tight, but I would redo the clearances. TPI on the adjuster nut is very course and it does not take much to be out by a few thou. Not timing chain is it?

Valves - well unless you are smoking badly - possible valve stem oil seals - the mantra is if it ain't broke then don't fix it, which seems to be the case if you say the car runs well. However, if you have a burning desire for preventative maintenance, then the head is reasonably easy to remove, and new valves and springs are cheap-ish...don't forget to lap them in though, and a new Payen head gasket is the way to go.

Unleaded heads are no issue provided you don't thrash it, keep using the additive - though personally I am not wholly convinced - and use a decent fuel.
Mark O

My 40 over 1275 rattles at tick over and up to about 2500 RPM. Always has. I tried adjusting the valves, I've done a valve job, everything I could think of. Finally, I just accepted it since it runs well all day long. It's probably just one of those things.
Martin Washington

These are not modern cars, and even when new they where already outdated by 15 plus years

Its sort of like leaking fluids... its an mg, its to be expected ... rattling is sorta okay, clanking is another story

Is your exhaust system tight and secure... it dosnt take much to get those dancing, and when they start to party, it sounds like the fun is inside the engine

Prop
Prop and the Blackhole Midget

If the rattling is definitely from the rocker gear and resetting clearances doesn't help one possibility is wear in the rocker bushes and/or rockershaft.
The stethoscope would help here - it's not easy to identify positively because a **little** wear can make a fairly loud rattle.

I'm with Prop up to a point that rattles are to be expected and not necessarily to worry about unduly.

I wonder if the rocker bush wear scenario is the root of your rattle, Martin. It certainly is on mine. Calming down over 2500 rpm might just be related to the rise in oil pressure and flow to the rocker gear. Just a thought.
Greybeard

####Calming down over 2500 rpm might just be related to the rise in oil pressure and flow to the rocker gear. Just a thought.####

Just a shot in the dark test idea... does the rattle occure right off the key ... thats when oil pressure is at its highest, esp when its chilly weather... my thinking if the same rattle does not exist at start up, then that would give Greys thought alot of .... ( gravitas ) ... if his idea proves to have merit, your ( fix the symptom not the problem soluution ) could be as simple as getting an adjustable oil presurre valve kit and raising the oil pressure a few extra psi

Come on grey... you can swim with me a little deeper on rattles... the water is fine... haha

Prop... ( to a point )
Prop and the Blackhole Midget

Thanks for the comments, I should add the the oil pressure is 60 when cold but when warm it drops to around 25 at tick over but increases to around 50 when driving at reasonable speed. The oil is comma 20/50. There is a general low level rattle from the rockers as to be expected but a louder sharper tap from the front of the rockers area and is there from cold. I know the rocker pads are quite warn with indentations in them, and as suggested perhaps one rocker bearing is warn. Do you think it too much of risk for the head gasket if I just remove the rocker assembly and re torque it down after.
G.E Verney

I have removed the rocker shaft pedestal nuts before now, with no adverse effect on the other head stud and HG. With an iron head it isn't going to warp. Assuming this is all done on a cold engine.


If there is wear in the rockers you may find that it is largely in the shaft. Although good workshop practice would advise renewal of rocker shaft and all the bushes at the same time I have satisfactorily just replaced the shaft which is easy and cheap to do.

One side effect of worn rocker shaft and/or bushes can be excessive oil discharge onto the top of the head, which lowers the running oil pressure, especially at lower revs. It can also cause the valve guide tops to become inundated and result in excessive oil getting down the guides with resultant BLUE SMOKE!
Guy W

Hmmm. Sorry - I doubt it Prop. You'd have to increase the output of the pump in some way. Like fitting a high-volume pump if such a thing is available.

I like your thinking, but I'm not sure about the idea of listening for an absence of rattles at cold start up. There's next to no oil up there until the pump gets into it's stride. But if it's significantly quieter in the rockerbox with very cold oil than with warm oil then you have a point. Don't forget to allow for the clearances being looser on a cold engine though; that would tend to mask the effect.

Much easier to identify if there is wear by finding out if there is any movement between the bush and the shaft, other than rotational.

I've learned to live with it for the time being, but at least I know where the racket is coming from. One day soon I'll actually fix it tho'!

BTW my engine is a T*****h so has no bushes, but IIRC the A series does have them. In which case I would guess they would wear more than the shaft, being softer. I had to listen to mine with a very sensitive deaf-o-scope while a glamorous assistant pulled up and pushed down on the rockers with closed valves before I was sure. I had backed off the adjusters to prevent the rockers contacting the valves or pushrods but they produced a distinct click. Then if I slid a rocker across to an unworn section of the shaft and tried again the click went away, leading me to conclude the wear in my engine is mostly in the under surface of the shaft, where I can feel a slight ridge.

The same tests can be done on A engines easily as it is possible to slide the rocker sideways against the spring; (No.1 and No.4 exhaust rockers excepted, obviously).

To my mind any detectable movement at all between rocker and shaft is going to make a rattle that no amount of adjustment will get rid of. Does that sound reasonable to you?

All that woffle aside I'm with Mark about the compression and not pulling the head without a pressing reason. I'd defo recheck the clearances as a first step, then the rocker bushes. If they get bad enough it will compromise the oil supply to the top end, which is why I'm going to have to spend some money on mine.

Edit: Sorry Guy - crossed in the post!
Greybeard

If the rockers are worn, i.e. concave, it can be tricky to set the clearances accurately with a feeler gauge and you can easily end up with excessive clearances and noisy rockers. If you have access to a dial gauge, that can be used to set the clearances accurately.

Peter
Peter Blockley

Grey ... that sure makes scence to me, luckly I hav e not had to explore that road


Prop
Prop and the Blackhole Midget

Greybeard,

The A series is known for rocker shaft wear as the standard shaft is quite soft, the bushes don't wear so much. You can get, or could, hardened shafts which I think are well worth it, I fitted one to mine and rebushed the rockers and all good after about 65k miles.
David Billington

Back in the day when there were more experienced garage mechanics well used to these engines, it was common practice to set the tappets on a running engine just by listening to the noise each one made as it was adjusted. It was actually the recommended method on some vauxhall engines, 'though still using a feeler gauge not just listening. Doing it by sound got around the problem of wear of the rocker pad, - IF the mechanic was experienced enough, but it is all too easy to end up with too little clearance which is a BAD THING

If you do have a single tapetty tappet, then running the engine and slipping a feeler under each one in turn will quickly identify which one is making the noise. Just beware the amount of oil that splashes around. Best to stick the cork gasket to the head with some grease first.
Guy W

Greybeard,

Good point about the rocker bush wear. I haven't checked that but when the weather warms up, I'll give a good looking at. It is an old shaft so you are probably right. That could also explain why my oil pressure drops lower than I'd like it to be, especially when warm.
Martin Washington

Peter B That's a very wise and apposite comment. Thank you. I routinely use a DTI.

David I didn't know that about the shafts and I'm grateful for your correction. Another bit of free knowledge! It was a guess on my part as I said.

Guy - excellent post. I have (in desperation) done the same thing myself and got away with it, on my old Triumph 2000. I didn't think of damming the top of the head with the gasket though, so I made a mess. That's a good spot.

It used to be that I simply accepted that older engines were noisy, but in the case of rockergear wear I'm now a bit more alert. Mainly because of the compromised oil delivery. My T*****h engine's top end oiling is crude enough by design without letting it get any worse!

BTW I hear it's possible to renew the shaft and/or rockers in situ without pulling the head or pedestal bolts. As I recall you have to remove the radiator, undo the engine mounts and ease the engine up a bit on a jack and the shaft can come out forwards. Is that true? It sure looks possible on the 1500.
Greybeard

####BTW I hear it's possible to renew the shaft and/or rockers in situ without pulling the head or pedestal bolts. As I recall you have to remove the radiator, undo the engine mounts and ease the engine up a bit on a jack and the shaft can come out forwards. Is that true? It sure looks possible on the 1500.####

I dont know about the 1500, but id think it could be done on the 1275... but ive never built a house starting with the roof then the foundation then the walls last

I think it would be alot of work compared to just whipping the rocker gear and if need be a HG replacement
Prop and the Blackhole Midget

I reckon you're right Prop. When I do the the rockergear I'd be inclined to do whole top end at the same time. It's not hard. So agreed; I was just curious.

I just found out that Moss offer a complete kit for the 1500 with BUSHED rockers. Also for the 6 cylinder Triumph and I have matey's GT6 to do before spring. Interesting.

BTW Martin my hot idle oil pressure is less than I'd like and I agree that the worn rockergear is a contributor to the problem. We shall see.........
Greybeard

There's a lot of M & M here!
On the 1500 the pedestal bolts for the rocker assembly only fasten into the head and there is no reason at all not to just undo the 4 and lift the whole caboodle off. No one in their right mind would consider removing the rad and disassembling the rocker set by sliding the shaft out forwards!

On an A series you might, because the pedestal bolts double up as head studs. But its probably easier anyway to just take the head off. Or several engines I have just removed the 4 pedestal nuts leaving the head clamped down by the other 5 head studs. Done on a cold engine the CI head won't warp and it shouldn't release pressure on the HG. I probably wouldn't be turning the engine with the plugs in though.

The myth about removing the rad may possibly be related to changing out a camshaft with the engine in situ, rather than the rocker shaft. Though this probably cannot be done on a 1275 without the removable tappet covers. Though even then, there are rumours this can be achieved with the use of magnets to lift the tappets as the camshaft is withdrawn.
Guy W

Guy/chaps

Interesting about the rocker shaft. I have been chasing my tail somewhat in setting clearances correctly. One reason why I have not chosen other methods of setting is my worry that I will set them too tight, and besides, the car seems to go pretty well anyways.

However, I would like to try and quieten it down, and judging by the rocker pads, it may also follow that the shaft is worn. Therefore, is this a simple bolt off/on job, and where do you recommend for the parts? In addition, what say you to replacing the rockers themselves whilst I am at it? If the bushes are not prohibitively pricey, I may go for them also.
Mark O

Mark, its a quick job to check the rocker shaft for wear. The wear occurs on the underside. Slacken off one (or more) of the tappet adjusters sufficient to disengage the rocker from the pushrod. Then press the rocker to one side, against the alignment springs on the shaft and feel for wear ridges on the underside of the shaft with your finger nail.

As you will be, I am restricted to online and mail order for supplies so any of the main outlets should have the part you need. I rather favour Sussex Classic Car spares as I like the photos on their web site and they are always helpful and it feels like one is dealing with an individual
http://www.sussexclassiccar.co.uk
Guy W

Are you running it with an alloy rocker cover? Are you sure your rockers aren't hitting it if you are. In my experience alloy rocker covers transmit a lot more noise than the steel ones.
J White

I had an annoying click in a B engine that turned out to be a loose rocker shaft. It had worn severely at the tower were it is supposed to be locked and must have been occluding the oil passage hole during certain angles of its movement.

The rocker bushings were fine so replacing the shaft and locking it down tightly at the tower solved the problem.

I am accustomed to the A engine sound and this was loud enough for me to disregard the "Oh Bs are just noisy engines" comments.
Glenn Mallory

I've got a quite loud 'knock' in the Midget(1275) engine. Worse when cold.

I can't tie it down. It sounds louder in the car than out, and weirdley, sounds as if it comes from the rear left of the car when sitting in the driver's seat. Hence I've had the exhaust off and on again looking for a leak, that may be emulating an engine noise.

It increases frequency with revs, and best guess, is it's one in four. I'm thinking piston slap. Hence when I pull the engine next week, I'm going to pull the pistons and see which one it is.

It's a drag actually. The engine has good compression hot and cold, and it goes perfectly well, 38mpg avg and doesn't use anymore oil than it should.

If I wasn't selling the car, I wouldn't bother. But I have no doubt that this noise will put off most, if not all potential buyers, even more than the paint. :(.
Lawrence Slater

This thread was discussed between 08/01/2016 and 16/01/2016

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