Ariel SQ4 Engine & Gearbox Tolerances

Parameter
Transverse = parallel to crankshaft axis
Longitudinal = parallel to motorcycle axis
Dim’n
Wear
Data Source
Position
Cylinder number 1-4
Bearing 1 = TS Front; Bearing 2 = TS Rear; Bearing 3 = DS Rear; Bearing 4 = DS Front;
Number 1
Number 2
Number 3
Number 4
Cylinder Bore upper transverse
2.579”
0.008”
Waller (2.559” +0.020” overbore
2.582”
2.582”
2.582”
2.582”
Cylinder Bore upper longitudinal (A)
2.582”
2.582”
2.582”
2.582”
Cylinder Bore middle transverse
1 ½” down from gasket face
2.580”
2.580”
2.580”
2.580”
Cylinder Bore middle longitudinal (B)
2.582”
2.582”
2.582”
2.582”
Cylinder Bore lower transverse

2.578”
2.578”
2.578”
2.578”
Cylinder Bore lower longitudinal (C)

2.578”
2.578”
2.578”
2.578”
Piston (ring land area longitudinal) (A1)



2.568”
2.568”
2.567”
2.568”
Piston (ring land area clearance) (A-A1)

0.023”
0.020”
Waller
0.014”
0.014”
0.015”
0.014”
Piston (below rings longitudinal) (B1)



2.575”
2.575”
2.575”
2.576”
Piston (below rings clearance) (B-B1)

0.005”
0.003”
Waller
0.007”
0.007”
0.007”
0.006”
Piston (Extreme Skirt longitudinal) (C1)



2.577”
2.569”
2.576”
2.576”
Piston (Extreme Skirt clearance) (C-C1)

0.003”
0.001”
Waller
0.001”
0.009”
0.002”
0.002”
Piston Ring Gap (Compression)

0.017”
0.012”
Waller
>0.060”
>0.060”
>0.060”
>0.060”
Piston Ring Gap (Oil Control)

0.020”
0.015”
Waller
>0.060”
>0.060”
>0.060”
>0.060”
Piston Ring Groove Clearance (Upper Compression)

0.002”
0.0015”
Irving: Tuning for Speed




Piston Ring Groove Clearance (Lower Compression)

0.002”
0.0015”
Irving: Tuning for Speed




Piston Ring Groove Clearance (Oil Control)

0.004”
0.003”
Irving: Tuning for Speed




Piston Weight







Gudgeon Pin
0.6865”
0.6862”


0.6865”
0.6865”
0.6865”
0.6865”
Gudgeon Pin Weight







Piston & Gudgeon Pin Weight







Inlet valve stem
0.312”
0.311”






Exhaust valve stem
0.310”
0.309”






Inlet valve guide bore
0.314”
0.313”






Exhaust valve guide bore
0.314”
0.313”






Rocker Shaft
0.499”
0.498”






Rocker bush
0.5005”
0.4995”






Small End bush
0.6868”
0.6863”
0.003”

0.689”[1]


0.689”1
Crankshaft Big end journal
1.3745”
1.375”


1.373”
1.3725”


1.374”
Con Rod Big end eye

0.004”
0.003”

1.384”
0.009”[2]


1.383”
0.008”
Camshaft lobes



Samples show 0.003” – 0.005” wear
Camshaft (bush end)
0.8735”
0.873”

Waller 4G


0.871”
0.869”

Camshaft bush in crankcase
0.875-0.874”

Waller 4G


0.874”
0.872”[3]

Timing side crankshaft main bearing journal
1.252”
1.2515”
0.005-0.004”

1.247”[4]
1.248”4
1.2475”


Timing side crankshaft main bearing bush
1.250-1.2495”
0.005-0.004”

1.2545”[5]
1.252”
1.2525”5
1.2505”


Crankshaft End Float
0.004”
0.002”

’52 Owners Guide p.23
>0.015”
>0.015”


Oil pump drive block



0.561” – 0.563”
Oil pump drive block clearance to camshaft nut
0.005”



Oil pump feed plunger block gap



0.573”
Oil pump return plunger block gap



0.570”
Oil pump feed plunger (D)


0.1870-0.1875”
Waller; Singles
0.436” – 0.4365”
Oil pump feed bore (D1)


0.1875-0.1880”
Waller; Singles
0.437” – 0.438”
Oil Pump Feed Clearance (D-D1)


0.001”
0.000”
0.002”
0.0005”
Oil pump return plunger (E)


0.3745-0.3750”
Waller; Singles
0.4995” – 0.499”
Oil pump return bore (E1)


0.3750-0.3755”
Waller; Singles
0.499” – 0.500”
Oil Pump Return Clearance (E-E1)


0.001”
0.000”
0.001”
0.000”


Parameter
Dim’n
Wear
Data Source
Drive Side
Kickstart Side
Sleeve Gear Bush



0.939”
0.939”

Mainshaft at sleeve gear


Waller
0.932”
0.932”

Mainshaft clearance at sleeve gear
0.002”
0.0015”
0.007”
0.006”
Waller
0.007”
0.007”

Mainshaft bending
0.005”

Waller



Mainshaft end float
1/32”
1/64”





Layshaft Bush



0.658”
0.6585”

Layshaft Bush clearance

0.007”
0.005”
Waller
0.007”
0.0045”

Layshaft


None
0.651”
0.654”

Layshaft bending
0.005”

Waller



Camshaft Bush



0.502”


Camshaft


None
0.496”


Camshaft Bush clearance

0.007”
0.005”
Waller
0.006”


Camshaft end float
0.002”
0.001”





Layshaft 1st Bush




1.212”

Layshaft 1st Pinion




1.215”

Layshaft 1st clearance




0.003”

Layshaft 2nd Bush



1.2095”


Layshaft 2nd Pinion



1.214”


Layshaft 2nd clearance



0.0045”


Roller Bearings




Play present





[1] Little end bush at top end of acceptable tolerance. Replace.
[2] Little end bush oil hole misaligned.
[3] Camshaft journal is in poor condition, needing a light regrind. Bush diameter must be finish bored to provide factory clearance (0.0005 – 0.002”).
[4] Journals are at bottom of acceptable tolerance. Bush diameter must be finish bored to provide factory clearance (0.0015 – 0.0025”).
[5] Clearances acceptable but white metal flaking from both front & rear bushes. Bushes to be replaced.

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