Bottom End

For gasket sets click here; individual gaskets click here; pistons click here; for oil, oil pipes and unions click here; timing sprocket extractors click here; for ball bearings click here; for gear case information click here.

Crankshaft

All single cylinder engines have a built up crankshaft, which means that the big end, flywheels and mainshafts are separate components that are pressed together and retained by nuts. The big end should be free to rotate without any tight spots and there should be no detectable movement of the con-rod in the vertical plane, however do not confuse this with movement from side to side. A fair amount of side play is acceptable, however figures for it are hard to come by and it is also expensive to cure. The only other problem likely to be encountered with the crankshaft is wear on the shafts where the bearings run; they should be a light drive fit, this problem can be cured by industrial hard chromium plating the shafts and grinding to size. All cranks from 1931 onwards are fitted with a patented sludge trap, make sure that it is removed and the oil ways are clean before assembly! The original method of shimming the crankshaft to limit end float to between .008″ to .012″ was to swap one size of shim for another, they were originally available in sizes from .012″ to .104″.

Our big-end assemblies are manufactured in the UK by a specialist company with over 60 years of experience in the manufacture of big-ends. The standard big-end assembly with a tapered crank pin was fitted to many models under different numbers, the variation being the position of the oil hole, our pin fits all but the locating peg may have to be fitted in a different hole. In 1935 the VH, but not the VG, was fitted with a parallel crank pin measuring 15/16″ diameter, which was increased to 1″ in 1937; the VG was finally graced with this pin in 1949. It is advisable to check the big end eye for ovality and to have it honed out to true it up before fitting the outer race. Assembling and truing of the crank shaft assembly is a specialist task and not suitable for the home mechanic, I know some of you are clever enough to do it but it is beyond most of us normal people. Crankpin and flywheel nuts should be done up tight, no torque figures were ever published but 60 lbs/ft is adequate and is considered the maximum for cast iron flywheels.

Shock Absorber

The later type absorber assembly with a wider face cam that was fitted after 1945 can be fitted to 1930 and later models. Overall gearing was altered by changing the engine sprocket; see section 20 for alternative clutch sprockets and the owner’s guide for the original sprocket recommendations.

Timing Gear

Prices of camshafts and followers are for exchange only, THIS MEANS THAT WE WANT YOUR OLD ONE FIRST. If the follower or lobes of the cam are badly worn there will be an extra charge to cover the cost of building them up, price per lobe is part number 1750-91 (single lobe cam, 1750-51 = 2 lobes) price per cam follower is 1750-94. The 1800-31F followers always need to be built up, so their price already includes this. Additionally if the camshaft is worn where it runs in a bush or bearing there will be an extra charge for reclaiming it by industrial hard chrome plating it back to size, price is given by part number RES-14. This guarantees that you get a good cam. The profiles we use are close but not necessarily exact copies of the originals. We can recondition any cams not listed.

The cam pinion will always show slight wear on about one third of the teeth, according to an Ariel Service Bulletin, this is perfectly normal and does not warrant replacement of the said item. The original application of camshafts is shown but almost any cam will fit any engine providing the relevant followers and push rods are used.

Other Parts

Although Ariel listed shims for the cams and followers they do not appear to have listed what the end float should be; however, as the clearances will only increase as the engine warms up, they can be reduced to a minimum.

Timing Case

An oil pressure regulator, part no. 2150C-30, was fitted in the front of the gear case from 1930 until engine number BH 13,716 sometime during 1941. This regulator was not intended to limit the maximum oil pressure within the system but to control the pressure reading on the gauge at a reasonable figure! The regulator was replaced by a valve consisting of a ball, spring and retaining plug inserted between the big end oil feed quill and the rear of the oil pump. Part numbers are: – S9-1, 2154A-41, and 2150-41 respectively, the side valve models used a different plug and spring, 2150A-41 and 2154A-30 respectively; the plug has a groove down the side to allow the oil pressure gauge to return to zero. When the rocker oil feed was altered to be supplied by the return to the oil tank instead of at pump pressure in 1952, these valves were deleted. In 1956 an oil pump spring (2220-29) was fitted in the return line along with a S9-1A ball bearing, without a plug. 1957 saw the reintroduction of the plug, ball and spring arrangement in the feed to the big end as used earlier, the only difference being that the part number of the plug had changed to 2150-57. So in conclusion (parts listed in order of assembly):-
1941-51 ohv,  Feed = Spring 2154A-41, Ball S9-1, Plug 2150-41; Return = Nothing
1941-51 sv,  Feed = Spring 2154-30, Ball S9-1, Plug 2150A-41; Return = Nothing
1952-55 all models, Nothing at all
1956 All models, Feed = Nothing; Return = Ball S9-1A, Spring 2220-29
1957-58 All models, Feed = Spring 2154A-41, Ball S9-1, Plug 2150-57; Return = Ball S9-1A, Spring 2220-29

Any of the above, behind the pump mechanisms, can be fitted to the 1952-55 models which normally do not have anything; the case will have to be modified. It should however be pointed out that they are not oil pressure regulators but a back up valve in case of the failure of the valves in the oil pump.

We receive a lot of enquiries for magneto oil seals to prevent oil from entering the magneto on single cylinder models, unfortunately one does not exist. Whilst a small amount of oil will do no harm, a large amount will, and where this happens it is usually due to excess crankcase pressure caused by a worn cylinder bore or piston and rings. The sealing washer listed, part no. 2090-53, will prevent oil escaping from between the timing case and magneto but it does not prevent oil from entering the magneto.

All big end assemblies include the crank pin, outer race, nuts, locating pin, rollers and cage (where fitted).

For gear case information click here.