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MG MG Y Type - Time to do the tappets...

I was at classic car night at the Ace Cafe in North London (www.ace-cafe-london.com) a few weeks ago with the Y (the proof of this is on page 80 of the October issue of Classic Cars magazine!) and parked near a very nice TF. I couldn't help noticing how quietly the TF's engine ran, with very little tappet noise, and I realised that the time has come to adjust mine.

Now, I need the collected wisdom of this august community on this topic: it's a long time since I did the job. While we all know that the brass plaque on the side of the XPAG rocker cover enjoins us to set the tappets at 0.019" hot -
1) this produces an almighty racket from the top end. Something nearer 0.012-0.014" from memory used to work well.
2) it's almost impossible to do all the tappets anything like hot - once you've got the aircleaner and the rocker cover off even a hot engine has cooled a long way.

So: hot or cold adjustment? And to what clearance would you work? I don't want burned valves, but the engine should run quieter than it currently does, particularly when warming up. Any thoughts?
Tim Griggs

I wish that I were technical enough to comment, however, somewhere, I've got a couple of interesting articles about this subject.
One is about adjusting tappets cold, but the more interesting one suggests adjusting by the amount of rotation of the adjusting screw related to the thread pitch. This should overcome the dishing of the tappet where the push-rod hits it, which probably increases the actual gap because the feeler gauge bridges the dish.
I could dig these out if you want them.
Can any experts out there comment?
Michael Nicholson

A lot of the 'tappet' noise in the XPAG is not the actual gap between the moving parts, the 'valve clearance'. That is either 12 or 19 thou. The noise is as a result of side play in the cam followers, ( they wear oval and can really set up a racket when well worn.) Such wear is harmless, but annoying. They can be opened up 10 thou and oversize followers fitted. Most Gold and Silver Seal replacement engines have already got 10 thou over-size cam followers. The other culprit is wear on the rocker shaft. This get very under-cut on its underside, making valve clearance setting a bit of a lottery. You can check for this by rocking the rockers 'sideways'. Removing the shaft and fitting a new one will kill fifty percent of any noise. Often, the rocker bushes are hardly worn. The cause is running the engine for very shost periods, so oil never gets to the top of the engine. Then there are push rods with loose end fittings, again noisy but harmless, in fact all the above clatter is harmless, just annoying.

Where it becomes less harmless is when the cam lobes are worn. This sets up a loud clatter as the cam follower literally 'takes off' and leaves the cam lobe profile and crashes back down again. Looking at the valve rockes will show this up, as less movements than the others, ( most often on an inlet for some unknown reason.) The cause is failure to change the oil regularly, and the thin 'case-hardening' of the camshaft wears through. Once into the softer centre, the lobes wear away quickly. The cure is a new cam shaft. Also, old engines suffer from cam followers that have concaved bases, where they are beginning to break up. Removing the followers will confirm their condition. This bit that rides on the cam lobe is the most highly stressed bit of the engine. The cause is poor quality oil, and/or lack of oil changes.

The 'later' 12 thou cam has silencing ramps on it. That means you MUST set up the gap on the very back of the cam. These 'ramps' are hard to see, but close up the gap more slowly than the older 19 thou cam.

More in the booklet on the XPAG from Harry Crutchley, Octagon CC.

Neil.
Neil Cairns

Nearly forgot, if you renew your rocker shaft, note that there are two different lengths. Measure yours acurately to get the right one, and take note of where all the bits go on dis-assembly.

Neil.
Neil Cairns

Thanks Neil and Mike: the engine on my car is effectively "new" (15000 miles, anyway) and had new rocker shaft and tappets at rebuild, so I think I'm addressing the rocker clearances question here: certainly the noise is from the top end only. With respect to Neil's point about wear from cold use, and to the previous thread on lubricant quality, I don't expect to be dealing with significant wear yet: nearly all the car's use is longer runs fully warmed up.

My thought at this point is: what are the risks if I set things to a closer tolerance than recommended? Does anyone have experience of doing this/dire warnings/guidance etc?
Tim Griggs

Neil,
Have you seen the article about adjusting in relation to the screw thread pitch? If not can I send you a copy and ask you to comment?
Michael Nicholson

There was a tool sold for valve adjustment based on the thread pitch, it was a good idea as it did not rely upon a feeler gauge. It is easy to have worn rocker ends and valve stem top, so tightening up until there is NO clearance, then backing off seems OK.

It is NOT a good idea to close up any clearances that the manufacturer reccommends. This leads to burnt out exhaust valves. The clearance is not just for expansion, it is to ensure the valve closes long enough to dissipate the heat into its seating. So if it is a 19 thou, or a 12 thou cam, that is the gap to use. I find the sound of tappets quite nice.

The danger is when you cannot hear them. This is a sign the valves are receding into the head, closing up the gap. That means your valve seats are being burnt away by unleaded fuel.

Remember, your engine is turning an upwards force through 180 degrees a few thousand times a minute. It has every right to make a noise. The cure today would be to fit self-adjusting hydraulic cam followers. That is why a modern engine is so quiet. Old engines are noisy, they leak and clatter away quite happily. When you get over 50mph there is so much clattering going on it seems to smooth out. It is not really, the noises are just joining up together and our human hearing system cannot differentiate the piston slap from the worn cam follower from the distributor cam from the valve clatter.

Live with it.

Neil.
Neil Cairns

Nicely put Neil!

Cheers,
Saul.
Saul

Neil:

Isn't it more like you, (we), can't live without it?

Safety Fast
Paul
Paul

The valve adjustment tool Neil refers to is still available from Frost Equipment, (www.frost.co.uk). At £30 it's a bit expensive, but it gets round the problem of accurate tappet adjustment on a worn engine. It also speeds up the job, and you only need 2 hands not 3!

Cheers,

Bill.
Bill Bennett

If you go to http://www.triumphstag.net/start/phorum/read.php?f=1&i=7979&t=7976 and http://mgaguru.com/mgtech/tools/ts080.htm there are discussion pages on this tool (the Clickadjust) which makes it sound difficult for mechanical idiots like me.
The article which I referred to futher up this thread is from Australia,and looks much easier. Just screw down the adjuster until the gap is closed, then back off half a turn to give a 20 thou clearance when cold, which is supposed to equate to 19 thou hot.
Apart from the worry that adjusting cold is not what MG recommended,does any one know how much the gap will close up when the lock-nut is tightened?
I have sent the article to Neil but if anyone else wants it, ask.
Should you be desperate to buy one, the tool is also supplied (? made) by Gunsons, www.gunson.co.uk who will tell you where your nearest supplier of their products is. Their part number is G4094.
michael nicholson

This thread was discussed between 20/09/2005 and 27/09/2005

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