|
We often get asked questions on technical matters relating to basic specification data on the MG Y Type, so it seems sensible to make available a printed sheet with all the usual data on it.
Source: Maintenance Manual and Instruction Book for the MG One and a Quarter Litre (Series 'Y') - available as a reprint in full from the MG Octagon Car Club - see Links page. While every effort has been made to carefully copy and reproduce the data shown accurately, your attention is drawn to our DISCLAIMER.
NB This data is correct for the MG YA and YT - not the MG YB! Download this sheet as a PDF file here.
MG Y (YA) and MG YT only
ENGINE: |
Type: XPAG/SC. Four cylinders, water cooled, with overhead valves, push-rod operated, with detachable head. |
Bore |
66.5 mm |
Stroke |
90 mm |
Capacity |
1250 c.c. |
Bore/stroke ratio |
1.353 to 1 |
Compression ratio |
7.2/7.4. |
Depth of head |
45.5 c.c. |
Cylinder head gasket |
.045 in (1.14mm.) thick copper and asbestos |
CONNECTING ROD: |
Type |
Steel |
Length |
178 mm with loose steel shell white-metal bearings. |
Bore at big-end |
48.658 mm — 48.671 mm |
Bore at small end |
18 mm. +.03 mm —.01 mm |
Width at big-end |
27.865 mm — 27.890 mm |
Width at small end |
19 mm |
Gudgeon pin |
Type: Clamp. Dia.: 18 mm. — .015mm Length 58.5mm — .010mm |
CRANKSHAFT: |
Diameter |
Width |
Radius |
Main journal (front) |
52 mm — .035 mm. — .015 mm. |
38 mm. |
2.5 mm.±.15 mm |
Intermediate journal |
52 mm — .035 mm. — .015 mm. |
38 mm — .02 mm. — .01 mm. |
2.5 mm.±.15 mm |
Main journal (rear) |
52 mm — .035 mm. — .015 mm. |
40 mm. |
2.5 mm.±.15 mm |
Crankpin journal |
45 mm — .035 mm. — .015 mm. |
28 mm — .015 mm. — .010 mm. |
2.5 mm.±.15 mm |
MAIN BEARINGS: |
|
|
|
Bore size of crankcase for main bearings |
|
56.34 mm. ± .02mm. |
|
Diameter |
Width |
|
Main bearing (front) |
52.020 mm 52.005 mm |
35.12 mm. 34.88 mm. |
|
Main bearing (inter.) |
52.020 mm 52.005 mm |
37.955 mm. 37.925 mm. |
Radius 2.75 mm. U/cut .25 mm. |
Main bearing (rear) |
52.020 mm 52.005 mm |
35.12 mm. 34.88 mm. |
|
Main bearing clearance on crankshaft diameter |
.020 mm .055 mm. |
Main bearing (inter.) end-float on crankshaft |
.035 mm. .095 mm. |
BIG-END BEARING: |
Diameter |
Width |
Thickness |
|
45 mm. |
22.46 mm. 22.21 mm. |
1.825 mm. 1.831 mm |
Big-end clearance on crankshaft diameter |
|
.011 mm. .056 mm. |
CRANKSHAFT REGRIND |
Bearing and crankshaft dia. undersize |
Reference |
Crankshaft main journal std. and regrind sizes |
Crankpin journal std. and regrind sizes |
Main bearings std. and regrind sizes |
Standard |
Standard |
52 mm. |
45 mm. |
52.020 mm 52.005 mm |
.5 mm (.020 in.) |
R.2 |
51.5 mm. |
44.5 mm. |
51.520 mm. 51.505 mm. |
1.00 mm. (.040 in.) |
R.4 |
51.00 mm. |
44.00 mm. |
51.020 mm. 51.005 mm. |
CAMSHAFT DRIVING CHAIN: |
Renold chain number 114036 (duplex) Type: Roller 3⁄8 in. pitch. 60 pitches endless. |
CAMSHAFT BEARINGS: |
|
Front Bearing: White metal. Outside diameter 43.61 mm. Press fit in cylinder block. Inside diameter to be reamed in position in cylinder block to 41 mm.+.05 mm/+.08 mm. |
Centre and rear bearings: Zinc alloy |
Outside diameter 43.5 mm.+.00 mm. — .02 mm. Inside diameter 23 mm. +.015 mm. — .005 mm. |
Bore of cylinder block for bearings |
43.5 mm. +.02 mm. — .01 mm. |
CAMSHAFT: |
|
End-float: .005 in. — .013 in. (.125 mm. — .325 mm.). |
Diameter of shaft for bearing: |
Front: 41 mm. +.01 mm. — .02 mm. Centre and rear: 23 mm. +.05 mm. — .08 mm. |
Cam lift |
4.334 mm. = 6.5 mm. at valve. |
Cam lift (after Engine No. XPAG/SC/16831) |
5.334 mm. = 8 mm. at valve. |
VALVES AND GUIDES |
|
Valve port throat diameter |
Inlet: 30 mm. Exhaust: 26 mm. |
Valve head diameter |
Inlet: 33 mm. Exhaust: 31 mm. |
Valve stem diameter |
8 mm.±.01 mm. |
Valve seat angle |
30˚. |
Valve guides |
Bore: 8.06/8.08 mm. Outside diameter: 14 mm. +.02 mm. +.04 mm. |
Valve guide length |
Inlet: 59 mm. Exhaust: 54 mm. |
Valve spring pressure |
Inner |
Outer |
Shut |
31 lb. (14.1 kg) |
62 lb (28.1 kg) |
Open |
43 lb (19.5 kg) |
82 lb (37.2 kg) |
Valve lift |
6.5 mm. |
|
Valve timing
|
|
Commencing Engine No. XPAG/SC/16831 |
Exhaust opens |
52˚ B.B.D.C. |
45˚ B.B.D.C. |
Exhaust shuts |
24˚ A.T.D.C. |
5˚ A.T.D.C. |
Inlet opens |
11˚ B.T.D.C. |
5˚ B.T.D.C. |
Inlet shuts |
57˚ A.B.D.C. |
45˚ A.B.D.C. |
Valve clearance (engine hot) |
.019 in. (.48 mm.). |
|
LUBRICATION: |
|
Oil pump speed |
Half engine speed, gear type. |
Oil pressure |
70 lb./sq. in. to 40 lb./sq. in. (5.0 kg./cm.2 to 2.8 kg./cm.2). |
Oil pump by-pass |
60 lb./sq. in. (4.2 kg./cm.2). |
Oil sump capacity |
9 Pints (5.1 litres). |
Oil filter |
Full-flow type. |
IGNITION: |
|
Ignition timing |
T.D.C. |
Order of firing |
1, 3, 4, 2. |
Sparking plugs |
Champion L.10.S 14 mm. |
Sparking plug gap |
.020 in. to .022 in. (.51 mm. to .56 mm.). |
PISTONS: |
|
|
Type: Aluminium alloy, tin coated, controlled expansion. |
|
|
Width |
Diameter |
Compression ring groove |
.0886 in. (2.250 mm.) .0087 in. (2.253 mm.) |
2.381 in. (60.477 mm.). 2.385 in. (60.579 mm.). |
Oil control ring groove |
.1576 in. (4.003 mm.) .1577 in. (4.006 mm.) |
2.389 in. (60.680 mm.). 2.393 in. (60.782 mm.). |
Side clearance of rings in grooves |
.001 in. (.025 mm.). .002 in. (.050 mm.). |
|
|
Width |
Radial thickness |
2 off. Compression rings |
.0885 in. (2.248 mm) |
.109 in. (2.768 mm.). .101 in (2.565 mm.). |
1 off Slotted oil control ring (8 slot) |
.1575 in. ( 4.0 mm.) |
.105 in. (2.667 mm.). .097 in. (2.464 mm.). |
Piston ring gap |
.006 in. to .010 in. (.15 mm. to .25 mm.). |
|
Gudgeon pin bore |
18 mm. — .0001 in (.0025 mm.). — .0003 in. (.0076 mm.). |
PISTON AND CYLINDER BORE SIZES (XPAG Engines)
REPLACEMENT CYLINDER BLOCKS (Normal Standard and Oversize Bores)
Cylinder bore oversize in thousandths of an inch |
Cylinder bore size in mm. |
Cylinder bore size in inches |
Piston size reference |
Standard |
66.50 |
2.6181 |
A...OK |
19.7 |
67.00 |
2.6378 |
C...OK |
39.4 |
67.5 |
2.6575 |
E...OK |
Note: After oversize "E" the cylinder bores are relined to standard. Bore sizes will be found stamped on the top front left-hand side of the cylinder block.
STANDARD AND OVERSIZE RANGES When fitting new pistons selective assemble is necessary, and to facilitate this the pistons are marked on their crowns with an indication of their bore size. Note particularly that the pistons markings indicate the correct size cylinder bore for which they are suitable, the correct working clearance having been allowed in the grading operation. The piston size should therefore correspond with the marking on top of the face of the cylinder block on the right-hand side, which indicates the actual size of each cylinder bore. The bores and pistons are graded in four sizes: — Bores of normal size ±.000 in. to +.00049 in.—marked "STD" Bores of normal size ±.0005 in. to +.00099 in.—marked +.0005. Bores of normal size ±.0010 in. to +.00149 in.—marked +.0010. Bores of normal size ±.0015 in. to +.00199 in.—marked +.0015.
The piston clearance is .0021 in. minimum to .0029 in. maximum (.056 mm. to .073 mm), measured at the top of the skirt, immediately below the oil control ring, and across the thrust faces, i.e. at 90˚ to the gudeon pin axis. This is important as the piston skirt is tapered and oval, and the extreme edge of the skirt and clearance can only be measured in this one position. There is .005 in. (.127 mm.) ovality at the extreme bottom edge of the skirt and the clearance measures at 90˚ to the gudeon pin centre line at the bottom of the skirt should be .00125 in. (.0317 mm.) less than that at the top. To facilitate correct measurement of the bores and pistons, the actual sizes of the various gradings are given at the top of page v (sic see below). The markings on the top face of the
cylinder block will indicate these sizes clearly. Oversize bores on reconditioned engines supplied under the M.G. reconditioned engine scheme are limited to two oversizes: — +.020 in. graded in 4 sizes as the standard settings +.040 in. graded in 4 sizes as the standard settings The actual sizes of these pistons and bores are provided in the tables on the following page (sic see below).
STANDARD PISTON SIZES Production engines with bores .002 in. oversize or over are made into +.010 in. bores and graded in the same steps are the standard bore engines
Piston size (across thrust faces below oil rings) |
Piston marking |
Suitable for bore size
|
in. |
mm. |
in. |
mm. |
2.6156 2.6160 |
(66.436) (66.446) |
To suit "STD" bore |
2.6181 2.6185 |
(66.500) (66.510) |
2.6161 2.6165 |
(66.449) (66.459) |
To suit +.0005 bore |
2.6186 2.6190 |
(66.513) (66.523) |
2.6166 2.6170 |
(66.462) (66.472) |
To suit +0010 bore |
2.6191 2.6195 |
(66.525) (66.535) |
2.6171 2.6175 |
(66.474) (66.484) |
To suit +0015 bore |
2.6196 2.6200 |
(66.538) (66.548) |
OVERSIZE PISTON SIZES (+.020 in. RANGE)
Piston size (across thrust faces below oil rings) |
Piston marking |
Suitable fore bore size
|
in. |
mm. |
in. |
mm. |
2.6356 2.6360 |
(66.944) (66.954) |
To suit +0200 bore |
2.6381 2.6385 |
(67.008) (67.018) |
2.6361 2.6365 |
(66.957) (66.967) |
To suit +.0205 bore |
2.6386 2.6390 |
(67.021) (67.031) |
2.6366 2.6370 |
(66.970) (66.980) |
To suit +0210 bore |
2.6391 2.6395 |
(67.033) (67.043) |
2.6371 2.6375 |
(66.982) (66.992) |
To suit +0215 bore |
2.6396 2.6400 |
(67.046) (67.056) |
OVERSIZE PISTON SIZES (+.040 in. RANGE)
Piston size (across thrust faces below oil rings) |
Piston marking |
Suitable fore bore size
|
in. |
mm. |
in. |
mm. |
2.6556 2.6560 |
(67.453) (67.463) |
To suit +0400 bore |
2.6581 2.6585 |
(67.516) (67.526) |
2.6561 2.6565 |
(67.465) (67.475) |
To suit +.0405 bore |
2.6586 2.6590 |
(67.529) (67.539) |
2.6566 2.6570 |
(67.478) (67.488) |
To suit +0410 bore |
2.6591 2.6595 |
(67.541) (67.551) |
2.6571 2.6575 |
(67.490) (67.500) |
To suit +0415 bore |
2.6596 2.6600 |
(67.554) (67.564) |
PROPELLER SHAFT: |
|
Type |
Hardy Spicer needle bearing (balanced). |
Length |
Face to face 46 ¾ in. (1.187 m.). |
Tubular shaft |
2½ in. diameter (6.35 cm.). |
Joint size |
KR—1111. GB 22/1118—GB 65. |
CLUTCH: |
|
Commencing Engine No. XPAG/SC/16916 |
Type |
Single dry plate—Borg & Beck |
Diameter |
7¼ in. (18.4 cm.). |
8 in. (20.3 cm.). |
Facings |
Fabric |
RYZ |
Thrust springs |
132 to 143 lb./in. Colour "Red" (23.6 to 25.5 kg./cm.). |
150 to 160 lb./in. (26.8 to 28.6 kg./cm.). Colour "Brown" |
Clutch plate damper springs |
3 off (Blue on "drive"). 3 off (Black on "overrun"). |
6 off (Black/Green) |
GEARBOX: |
|
|
|
Four speed, synchromesh second, third, and fourth gears |
|
Oil capacity |
|
|
1¼ pints (0.7 litre) |
Gearbox ratios |
Overall ratios |
|
|
Top |
1 to 1 |
5.143 to 1 |
|
Third |
1.385 to 1 |
7.121 to 1 |
|
Second |
2.07 to 1 |
10.646 to 1 |
|
First |
3.50 to 1 |
18.000 to 1 |
|
Reverse |
350 to 1 |
18.000 to 1 |
|
INSTRUMENTS: |
|
Speedometer |
British Jaeger Model 58597. Type SC.52 |
Reduction gear for speedometer |
6/15 ratio |
HYDRAULIC DAMPERS: |
|
Girling piston type front and rear |
|
Type: Front Rear |
Luvax Girling PR5X/2, No. S.87/30. Luvax Girling PPR5/7 L.H., No. S.87/31Y. Luvax Girling PPR5/8 R.H., No. S.87/31X |
COOLING SYSTEM: |
|
Cooling by radiator, pump and fan with thermostat
control |
Total capacity of system |
13½ pints (7.7 litres). |
Capacity of radiator |
7½ pints (4.3 litres). |
Circulation |
By pump fitted in front of cylinder block. |
Drain taps |
1. Bottom of radiator 1. Front end of cylinder block below exhaust manifold |
|