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MG MG Y Type - Valve clearances - the right setting

While the brass plate on the XPAG rocker cover sternly advises us to set the tappet clearances at 0.019" hot, I have two problems with this:
1) By the time you've got the engine warm and then removed all the aircleaner, ducting and rocker cover bits, the engine isn't fully warm any more so you can't get the right setting;
2) 0.019" has always seemed an enormous clearance, even compared to other pushrod engines of the period, and produces an unholy racket even at running temperature which can't be healthy for all those tappets, pushrods and rockers.

OK, I know, those pipe-smoking designers at Morris must have known what they were doing, right? My thought is that with modern lubricants (better film strength, better cling, more stable viscosity) they might have gone for smaller clearances and a quieter life.

So my question is - what's the current rule of thumb people are using in modern conditions to set the tappets cold, or are you all sticking to regulations? One of the charms of the XPAG is its friendly clatter from the top end, but is there a way to keep this to a minimum without damaging the valve train?

By comparison and for interest's sake, I found out from a Riley RM-owning friend that the comparable setting on the 1.5 litre engine is 0.003-004". Of course, the valve train is very different - high cams, much shorter pushrods, etc - but five or six times that clearance for the MG engine seems excessive.
Tim Griggs

Hi Tim

You can go a little tighter (a couple of thou') on the tappet clearances as your engine will probably by now have wear in both the tappet cam buckets, the ends of the push rods and slack in the rocker arm, but dont over tighten too much as this can lead to a lack of compression on the engine with valves remaining open, oil getting into the combusion chamber and you burning away oil, or (worst case) the pistons hitting the valves!

Paul
Paul Barrow

Hi Tim,

Do you know which camshaft you have? If the engine was reconditioned, chances are that the camshaft was uprated, too. If you have a later (TD?) camshaft yoou can use 0.012". Other "modern" profiles use 0.015", so that should be a save minimum.

In Neil Cairns' book about MG-engines is a describtion about how to identify the profile of your camshaft.

Willem
Willem van der Veer

The 19 thou setting is to do with the cam profile and the cam's ramp, nothing to do with the lubricant. Later engines had sine-wave cam lobes and the gap wasreduced to 12 thou. Do not run the engine with less than 19 thou or you will eventually burn out the exhaust valve seats.

Reducing gaps seems to be a modern thing to do, do not muck about with old engineering, there was a reason for it all.

If you run a 19 thou cam at 12 thou, you will loose power; if you run a 12 thou at 19 thou you will sound like a diesel.

NC.
Neil Cairns

<<do not muck about with old engineering, there was a reason for it all>>

(walking backwards, bowing respectfully): Yes, Mr. Cairns, of course Mr. Cairns, sorry Mr. Cairns, it won't happen again Mr. Cairns. ;-)

Tim, so all you have to do is to determine which camshaft you have and follow Neils'advice!

In the factory XPAG special tuning booklet, for maximum power, an even larger gap was recommended.... strangly nothing was written about optional earplug specifications.
Willem van der Veer

Next time you will get lines and I shal write to your parents...

NC.
Neil Cairns

Whilst I remember...

Virtually all the camshafts used by Morris Engines had the 19 thou gap, due to their design, ( which was pretty ancient.) This applied to the sv as well as ohv 'bread and butter' engines. The SA/WA was 15 thou, and the later eaqual overlap XPAG one 12 thou. ohc engines were ofcourse much less, 8 to 10 thou.

NC.
Neil Cairns

Some techy stuff to keep Willem happy....


XPAG Camshaft Checking.

This is the most important part of the engine in terms of performance and drive-ability, though good cylinder head design does help. As years pass, people modify their cars, or fit replacement items that have been improved by the manufacturer. One problem that often occurs is trying to decide which camshaft your XPAG has fitted, without stripping it down. Many cars have the 0.012" clearance camshaft, but some still have the older 0.019" clearance version. By far the best method I have seen was in the MGCC Safety Fast magazine, sent in by David Clark of Westminster, Vermont, USA. It relies on the fact that only the later cars had 5;45;45;5 cam timing, known as equal-overlap, or split-overlap if you speak American. That is both inlet and exhaust cam have the same timing, but in 'mirror' fashion. The earlier 'T' types had 11;57;52;24, very un-equal. The first pair of numbers read as inlet opens BTDC, closes ABDC, then exhaust opens BBDC and closes ATDC. The XPAG is not a quiet engine anyway, and one to worry about is one with no tappet clatter, as it is better to hear it than not. In today’s lead-free petrol age, no noise means the valves are pocketing, ie eating away the seats, and closing up the clearance.

If David Clark's check is carried out, and you decide you have a 12 thou cam, but performance is awful, you actually have one of the mid-way 5;45;45;5 1140cc timed and ground camshafts, but with an 8mm lift at the valve for the M.G. 1250cc XPAG. See modification list. This cam still has a 0.019" tappet clearance. Conversely, running a 0.012" cam at the 0.019" clearances sounds almost like a diesel engine.

" I would like to share with you a cheap and cheerful method for making an accurate determination of high verses low camshaft with your feeler gauge, a screwdriver, and a five-sixthteenth’s BSF spanner.
Because of the equal overlap of the valve timing, of the 0.012" clearance XPAG 5;45;45;5, they are split evenly about top-dead-centre ( TDC ) and bottom-dead-centre ( BDC ). This is called split-overlap.
Now, to check the valve timing, adjust the valves to the recommended valve clearance, in this case 0.012". Turn the engine on the starting handle until the fan belt pulley on the engine indicates TDC for number one cylinder, with the valves ROCKING. This means we are at the end of the exhaust stroke and beginning of the inlet stroke, with both valves partially open. At this TDC loosen the locknuts and turn the tappet adjusting screws all the way up and then down again until there is exactly no clearance at the valve. The valve will now be shut, and the adjusting screw just touching it. Now turn the engine one more crankshaft revolution ONLY, ( till you are now at the top of the compression stroke,) turn until the TDC marks on the pulley once again align exactly. Using your feeler gauges measure the resulting valve clearance. If the clearances match, you have a split-overlap camshaft, possibly with 0.012" design. If you are out five to ten thou, with the differences being from keyway tolerances, etc, it is still a split-overlap cam. If it is an earlier, or fast cam, the clearances will differ a lot."

Camshaft lobe design is a very precise art, and the shape is very important. Morris & M.G. strove to get the best with silence, but a compromise was the result. The .012" gap was it. The gap is part of the camshafts design and has to do with the 'ramp' and its acceleration of the valve lifting gear. Stick to the clearances given.

Model Cam Timings Lift Part No, ( if known.) .
SA 2 ltr Saloon, 11;59;56;24 8mm
VA 1 1/2ltr Saloon, 11;59;56;24 8.4mm (later 11;57;52;24)
WA 2.6 ltr Saloon, 11;59;56;24 8mm
1147cc 10hp engine 5;45;45;5 6.5mm
TA Midget, 11;59;56;24 8mm X24084, MG862/171, AAA5776.
TB & TC Midget, 11;57;52;24 8mm MG862/171, X24084, AAA5576.
TD Midget & YT 11;57;52;24 8mm MG862/171,168552, AAA3096.
TD after TD2/24116 5;45;45;5 8.3mm AAA3096, 168553.
YA 1 1/4ltr Saloon 11;57;52;24 6.5mm MG900/106.
YA after SC/16831 5;45;45;5 8.3mm AAA3096, 168553.
YB 1 1/4 ltr Saloon 5;45;45;5 8.3mm AAA3096, 168553.
TF 1250 & 1500 5;45;45;5 8.3mm MG862/171, AAA3096, 168553.
Wolseley 4/44 5;45;45;5 8.3mm AAA3096, 168553.
half-race; 13;59;50;22-8.3mm, AEG122, full race; 32;58;60;30-8.3mm AAA3095 .

NC.
Neil Cairns

Neil thank you for a most informative essay but I think the point is that it is simple to adjust the valve clearances to 19 and if it makes a din adjust down to 12 unless it is a new camshaft from B&G. The real point is that the standard Y type camshaft 6.5mm lift is useless and should be replaced for 8mm lift TC-TF,YT type. One can get another 3-4 HP by raising the compression to 8.6:1 but in the end there is much to be gained with the camshaft. In my opinion MG should not have fitted the 6.5 cam anyway which presumably prevented the Y type outpacing the TC, [the Y type will really start rolling with an extra 4HP]. However I wonder how many Y type owners were frustrated to see Lancia Aprilia's walk away from them let alone Ford Consul's!
Bryan

It was for a more 'saloon car' type engine, quieter and more docile. The better cam did go into the YT. I suspect they had lots of Morris Ten cams left over, and they were used up in the Y.

NC.
Neil Cairns

This thread was discussed between 14/06/2008 and 27/06/2008

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