Engine Autopsy
Inside the Jowett Bradford’s neat sidevalve engine.
Mention the Yorkshire marque Jowett and people think of the daring flat-four
overhead-valve Javelin and Jupiter. However, Jowett’s first prototype in 1906 was powered by a sidevalve flat-twin. A production version arrived in 1910. The capacity rose from 800cc to 907cc in 1921. It was ‘modernised’ in 1930, then expanded to 946cc in 1937. It grew again in 1946 to the 1005cc unit we see here.
The Bradford was essentially a vintage-style light commercial that could be bought with seats and windows, in which form it was known as the Utility. The Javelin re-invented Jowett, but it also lost money. The profitable Bradford outsold it 4:3, offering a sturdy combination of reliability, durability and plodding indifference to hills. ‘The little engine with the big pull’, as the slogan went, described it perfectly.
[A] TIMING GEARS The larger camshaft wheel and the smaller crankshaft wheel are positioned at either end of the timing chain. On either side are the tensioner components. The bolt locates in the top of the piece under it, which mounts in the front of the crankcase and supports the gear to the left. Adjust the length of the bolt to alter the chain tension.
[B] DAMPER BRACKETS These rubber bumpstops bolt to the bottom of the cylinder barrels and bear on the chassis below, stopping the engine twisting too far under torque.
[C] DISTRIBUTOR AND SHAFT The distributor fits diagonally into the top nearside of the crankcase and is turned by the engagement of the gear on its shaft with a scroll gear on the camshaft, visible on the opposite page.
[D] CYLINDERHEADS AND BARRELS The water-cooled cast iron barrels fix on to the crankcase over four studs. The exhaust ports are facing us. The sturdy copper head gaskets seal the simple lid-type cylinderheads.
[E] INLET MANIFOLD This aluminium casting straddles the engine, fixing to the cylinder barrels over the four studs on the top (or right side, as viewed here). The carburettor to the right of the manifold mounts on the hole next to it. The thermostat housing above mounts on the other hole. The small brass item by the manifold is the oil pressure relief valve, which fixes to the holes visible on the sump.
[F] CRANKCASE It’s cast in one piece, rather than two halves. This is possible because it doesn’t have to sandwich a centre main crankshaft bearing, as it would in a flat-four. It’s stiffer and stronger as a result. There’s no detachable sump, however, so everything has to be assembled through the hole in the rear. The tube emerging diagonally is the oil filler.
[G] BACK PLATE AND COVER The back plate carries the rear main bearing and fastens on to the rear of the crankcase on the six studs, clearly visible. The main bearings are below the the crankshaft on the opposite page. Beneath the back plate is the pressed-steel timing cover. The hole would usually contain an oil seal and allow the nose of the crankshaft to emerge, mounting the dynamo drive pulley.
[H] OIL PUMP AND DRIVE The oil pump nestles in the sump and is driven by the long shaft above it. The shaft's other end engages with the short shaft on the opposite page.