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MG MGA - Noisy tappets

I wonder if anyone can throw any light on this problem. When adjusting the tappets, after I finish setting one tappet to the specified gap, I turn the engine over to adjust the next one. I then measure the gap on the tappet already adjusted and find it about 1 or 2 thou larger than my setting. Exactly the same is happening to all other tappets. Mystery to me.
The following parts were replaced with new ones less that 2000 miles ago:- Camshaft, followers, pushrods, rockershaft, rockers bushes and the valves and their seatings were machined by an engineering firm.
With the engine running the tappets are noisier than they should be, and, short of reducing the gaps considerably, I don't know the answer to this problem. Any suggestions what might be wrong, and possibly a solution.

Frank
F Camilleri

Hi Frank

A couple of things

How do you know that the tappets are noisier than they should be?

Tappets adjusted to within 1 thou are very good I would suggest.

Anyway back to your observation

When a tappet is set using the rule of 9 then the gap is measured when the cam follower is at the rear (opposite the full lift) of the lobe. This actual low point is actually around probably half the rotation of the cam lobe and is the base circle of the cam lobe. I suspect that this appears to be out by about 1 or 2 thou which quite frankly is nothing IMO

If you are concerned then set the tappets 1 or 2 thou finer to take this into consideration.

Closing the gap by 1 or 2 thou will have almost no affect on noise and again I would ask what are you comparing this engine to?
Bob Turbo Midget England

Frank,this may be due to your method of adjustment since it seems to happen with all tappets. Are you using the workshop manual method of 1+8=9 with no 8 valve fully open? etc.
a while ago this topic came up and advice given to me on the subject of noisy tappets especially when the noisy tappet could not be identified was to insert the feeler gauge whilst the engine was ticking over. This should identify the especially noisy tappet(s) that you can then screw down a touch but not too much.
J H Cole

The tappets are excessively noisy when their gaps are adjusted to 17 with the engine cold. If I reduce the gaps to 16 with the engine cold, the ticking becomes acceptable. We all know that the book says adjust tappets to 17 hot, which in effect is 18 with a cold engine. That's a difference of 2 thou. So, is a gap setting of 16 cold acceptable? What are the consequencies if any? That said, I am very curious as to what exactly is causing the deviation in gap settings. Surely, if the adjustments are being done with the valve fully closed, i.e., using the rule of nine, then the gaps must remain as set and only get smaller when the valve begins to open but never larger than initially adjusted. Apart from the camshaft being defective, the one thing that comes to mind would be worn camshaft bearings???
Bob after having adjusted valves on various BMC engines in the past, my ears have been accustomed to listen to quieter idling sound. Not sure if I'm right here, but my next door neighbour's MGB engine runs much quieter compared to my MGA.

Frank
F Camilleri

This might help.

John Twist Video.

http://www.youtube.com/watch?v=fezXUwVfH7U

Cheers.

Larry
Lmazoway

Frank, is your assessment of noise being made when the engine is running cold? If you haven't already done so get the engine temp up to 190 plus and see if there's an improvement. B series engines cold are like a bag of nails. I would be comfortable at 15 thou if it solves your problem. Is your timing chain and tensioner in good condition?
J H Cole

Frank I am not sure you have undersood my point

Imagine the camshaft like so

It is a shaft running in bearings. On that shaft are a number of circles ground "concentric" with the shaft. These are the base circles for the cam lobes. Imagine fore a moment if these base circles did not have a lobe on them and simply a cam follower and tappet were adjusted to it. Naturally you would not see any lift and any gap you were to set would be constant. Say 17 thou. However now imagine that this base circle was actually ground slighly of "concentric". This time in one part of the rotation the gap would close slightly yet a little further around this would change to slightly wider perhaps.

This is possibly what you are seeing from the base circle which sounds like it has be ground slightly off centre. (not unusual with reground cams)

If you adjust the tappets to 15 thou and you believe the noise is far better then I would do that. I personally set mine at 15 as an absolute maximum without problems.
Robert (Bob) Midget Turbo

Frank I have always set my A at 15 and check with engine idling. This quickley tells if one is loose or tight. The engine is quiet even with the pressed metal tappet cover. After the 5000 mls they are still ok. I had to change the gasket a little while ago and checked them running , all between 16 and 17, and still quiet, so I left them. Sean
S Sherry

Frank,
You do not say if your engine is 1500 or 1600/1622. For the latter, the gap specified in the Workshop Manual is 15 thou with engine running, i.e. hot.
Maybe 15 thou is what you should aim for.
Peter.
P. Tilbury

Peter my engine is a 1500 with std bore(sleeved).
OK, since you all seem to have had no problems with the tappets set at 15 thou I think I'll go for that figure. Hot or cold engine??
Bob, I fully understand what you mean. What I can't understand is how can a brand new camshaft be ground slightly off centre. This is a new cam which I had installed myself not so long ago. Well I do believe that I may have bought a badly grounded cam. I shall have to reduce the tappets gaps to 15 and live with it as it is.
John Cole... My timing chain & sprockets have only just been renewed, and the tensioner has been in use for only a short space of time, so I have excluded those.

Frank
F Camilleri

If I remember rightly, my MG Magnette (similar 'B' series 1500 engine) called for 15 thou hot normal and 12 thou hot for quiet running. You could try 17 on the exhausts and 15 on the inlets if you are at all concerned about burning an exhaust valve.
Lindsay Sampford

Interesting paragraph in a B-Series and XPAG engine specialist's guidance notes I am reading:

"The biggest problem in the block is usually the condition of the cam follower holes. You cannot have quiet valve gears if the cam followers are rocking from side to side in oval holes. This is the principal cause of noise in the XPAG valve gear, but is also a problem on the B-Series. Oversize followers are available for the XPAG but many blocks are already at this value and worn.

The only solution is to sleeve them back. This is potentially expensive and must be done properly......."


I must admit to not having heard of this problem before.

Steve
Steve Gyles

Lindsay, does reducing the setting to 15 thou across the board have any effect on the engine performance? And, is the adjustment best done with the engine hot or cold?

Frank
F Camilleri

Frank, I don't know if reducing the valve clearances decreases performance, but I have read somewhere that if you are going to drive your car hard, then wider clearances are advisable. Incidently, my valves clatter a bit, so it could be the norm for an MGA.
Lindsay Sampford

Frank, what are the rockers like underneath? They may be worn, so giving an inaccuarete gap. So they may need refacing?

Colin
Colin Parkinson

Reducing the valve clearance makes it open sooner, close later, and lift higher (slightly). In essence this is leaning slightly in the direction of a higher performance camshaft. Reducing clearance by .002"-.003" may make just enough difference in performance that you may be able to notice it, if you were very attentive (1 or 2 hp at best).

There is substantial tolerance for adjustment or wear in the valve train. If you miss the adjustment by a couple thou one way or the other, no harm done. If you intentionally reduce valve clearance, then you need to keep an eye on it, check it a little more often to be sure it doesn't get too small.

I drive my car hard a LOT, somewhat more than a quarter million miles on MGA so far including lots of autocross and more than 100,000 miles of trailer towing. I have never heard any recommendation for increasing valve clearance above the standard spec (except with a special high performance cam).
Barney Gaylord

Barney, I can't remember where I read it, but it could have been in the Magnette literature (which I let go with the car), or even the MKII midget (again, the literature went with the car, help me out here Bob!). It was words to the effect, normal (or hard) driving 15 thou or quiet running 12 thou. Definitely read it somewhere!
Lindsay Sampford

That sounds like the 12 thou is the exception to the standard 15 thou setting. It is probably acceptable, but do inspect it periodically. By my own experience, prolonged hard driving can cause valve recession that may close up the valve clearance a lot quicker than you might expect.
Barney Gaylord

Frank,
Somewhere on this board. Someone had a link to a Youtube video about engine noise. This may give you some idea how loud the engine tappets should be. Seems most in agreement the engine sounds were normal.

Ray
Ray Ammeter

When I was putting my BGT engine together with a custom cam, I also noticed that the clearance was greater when the high point of the cam lobe was not opposite of the cam follower. I called the cam grinder and was told that this was normal and had to do with lobe ramping, and that I should do the adjustment with the high point of the lobe opposite of the cam follower.

Charley
C R Huff

Hi Charley,

That's a very interesting point. I just want to ask you for a small clarification. When you say, "...the adjustment should be done with the high point of the lobe opposite of the cam follower," do I understand you correctly, the valve being adjusted has to have the base circle resting on the cam follower with the highest point of the lobe away from the follower, i.e., pointing downwards?

Frank
F Camilleri

Frank, this probably wont help you but the 1950cc 3 bearing MGB engine in my MGA has really noisy tappets too.

I have adjusted them a few times and reduced the clearance by 1 thou to see if this helps but they still create the most mechanical noise on the car.

You may recall my friends comment when I first took him for a drive in my car. When I started the engine he grinned and said "Wow, I havent heard that sound for years and years!"
When I said "What noise?", he said "Tappets!"

So I think it is just a design feature of the B series engine

I have just got hold of an SPQR tappet adjuster to see if I can get a more accurate adjustment with it but its a bit too cold out there to do anything to the car just yet.

If it makes any difference I will let you all know.

Colyn
Colyn Firth

Frank, it may depend on how you are locking the screws. Normal procedure is to hold the adjusting screw with a flat screwdriver whilst tightening the locknut. There is a possibility of the screw moving when you do this, esp. if there is some slop in the screw slot. But you are probably too careful to let this happen.
Art Pearse

Colyn, I know these BMC A & B series engines are quite noisy at the top end. I have had about 5 or 6 BMC cars in the past, like Morris Minor 1000, Austin 1100, Mini 1000, and one or two others. Yep they do clatter a bit, but normally when wear sets in all over the place. Engines with low mileage are fairly quiet. In my case there should be no worn parts anywhere inside the engine, as everything has been replaced with new parts. It is quite natural for tappets to be heard ticking away, but for me there is an acceptable tappet noise, and an unacceptable tappets clatter. If my camshaft is badly ground, as I strongly suspect, then there is no way of getting rid of the loud clatter completely by reducing the gaps, but it would quieten it considerably. I shall go for 15 thou on all tappets and see(hear) how it sounds. As long as the performance of the engine is not badly affected, I will be too happy to leave it at that.

Art, I can assure you that my tappets are adjusted correctly, and the screws are locked in the proper manner all round. I do all settings and adjustments on my engine myself, and I am very precise.

Frank
F Camilleri

Hi Charley

Now that sounds interesting

Did you ask them to explain the mechanics of that suggestion? Seems like a cop out to me.

If that were the case then the people adjusting the tappets with the engine running would get the wrong results for your cam grinders wouldn't they?

Frank I note you suggest you are comparing the B Seies tappet noise with that of A Series engined cars.

I too have both and my A Series engines are far quieter than the B Series. I admit I adjust my A Seires engines to 12 thou cold which possibly makes a difference but the B Series has always been noisier.

Also in aid of Lindsay

Why would closing the gap reduce performance Frank? So long as the valve is closed at some point then it should be fine

Reducing the gap on a pretty much standard cam simply increases the lift slightly and as noted by Barney will slightly increase the duration neither of which should cause any problems apart from giiving you more power. Naturally the valve has to close otherwise performance will suffer as will burnt out valves occur but a couple of thou less ain't gonna worry too much

You might ask what is the purpose of the gap and how is it calculated?

Well it ensures the valve closes correctly and allows for heat expansion. It also allows for wear? the manufacturer has to allow an excess on the gap so that if something happens wear wise to reduce the gap in service then there is some free play built into the system

From our point of view I am not sure we push our cars so hard as to never serice them or whatever. Reducing this free play slightly can only IMO be of benefit.
Robert (Bob) Midget Turbo

Going back to the beginning, Frank was complaining that after he adjusted the tappets to the correct gap on re-check they would be out be 1-2 thou.

A suggestion, you might not be comparing like with like. When making the adjustment you are pushing down with the screwdriver on the adjuster screw head. On re-check if you are just pushing the feeler gauge into the gap this force has gone. This might be enough to account for the discrepancy. 1-2 thou is not much and you are dealing with three contact points (cam to tappet, tappet to push rod and push rod to rocker) each with an oil film.
Malcolm Asquith

You are correct Malcolm, but that should make the gap smaller not larger! Of course you also have rocker to shaft!

Neil McGurk

More out of possible interest than relevance to MGA tappet clearance. Two motorcycles I have owned call for nil tappet clearance. The first is a Panther 650cc single cylinder with a cast iron head and barrel, the second is a 350cc Royal Enfied with aluminium head and cast iron barrel. The pushrod length is adjusted until it will spin freely with no up and down movement, engine cold. Contrast this with the BSA A10 650cc twin cylinder, iron head and barrel with 8 thou inlet and 10 thou exhaust adjusted cold. It begs the question, why the difference?
Lindsay Sampford

Yes, Frank. I think you are restating it correctly. In other words, if the cam follower and push rod were pointing straight up, the high point of the cam would be pointing straight down.

Robert (Bob), no I didn't ask for any more explanation about the extra clearance for the lobe ramp. It did occur to me that they might be giving me a snow job, but they essentially said that was the way it was done, and I didn't know enough about cams to argue the point. Also, I had finally gotten around to putting the engine together and didn't feel like taking it apart again.

I agree that adjusting it running would defeat the purpose unless the valve lash specification takes into account any extra clearance at the ramp. I adjust my 46 Chev 2-ton running because an old mechanic friend said that was the way to do it. I don't know if it was factory recommended, but truck was only 30 years old when he told me that.

Charley
C R Huff

Motorcycles - air cooled cylinder runs hotter than the external ? pushrods so compensates for the valve growth - possible explanation.
Art Pearse

For what it's worth my memory from the early fifties when I was an apprentice on the A and B series models the tappets were not noisy when new. Getting rattly after ,say ,10000 miles , an adjustment to factory specs shut them up again. Can we ever bring back a 50/60 year old engine to its youth , I don't think so... Sean
S Sherry

Sean, I suspect that with enough attention to detail, an engine can be brought back to it's youth, and perhaps even better. In the States, the term would be "blueprinting" an engine.

Charley
C R Huff

Malcolm, the gaps always remain at exactly the same setting when set using the rule of 9. I can check the gaps as many times as I want, again using the rule of 9 method, and the gaps are found spot on. It is when I turn the engine and the valve which was fully open for setting its corresponding valve is more than half way closed, then, I find that the gap on the valve just set has increased by 1 or 2 thou. The way the cam lobe is ground has to have its lowest point at the very centre of the base circle, and anywhere else that lowest point remains constant until it comes to the point where it starts to lift the valve. To sum up, when the gaps are set correctly, there cab be no increase of the gap anywhere else, the gaps can only get smaller when the lobe starts on its peak until eventually they close completely with the peak right up. That is my understanding of the workings of the valve train.

Frank
F Camilleri

New cam followers have very slightly convex crowns. This is to encourage the follower to rotate in the bore. Combine this with the bores having been worn oval over the years and you have the ingredients for the minor variations you are talking about.

Steve
Steve Gyles

Neil,

You are quite right, I got it backwards.

Frank,

The lowest point is, as you say, at the centre of the base circle but it depends on how the grinder is set up as to whether or not that point is actually opposite the cam peak. As Charley pointed out, cams are often ground effectively slightly off centre to help the opening/closing action. However, I don't think any of this would cause the effect you have seen.

There is a video of a cam grinder in use at:

http://www.youtube.com/watch?v=mzscFuggl5Q

You can see how the cam profile is set by the templates at the end of the grinder. I suspect this is quite an old machine and modern grinders use some sort of CNC wizardry but it shows the principle of a grinder well.

Malcolm

Malcolm Asquith

Frank

I know that you have replaced the wheels and timing chain and you say you have discounted them as a problem. However, did you check and shim the wheels for correct alignment before fitting the chain? Mis-alignment is another source of noise.

Steve
Steve Gyles

Yes Sir Mr. Giles, I most certainly did. In fact I had to remove one of the existing shims to get both sprockets aligned perfectly. Thanks for your observation.

Frank
F Camilleri

My apologies Steve, re-spelling your name: GYLES. Late night typing and I'm nodding away happily. Good night all.

Frank
F Camilleri

This thread was discussed between 05/01/2011 and 09/01/2011

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