Engine number

[TedAllen]

Collected an engine from JCS in Bradford yesterday evening. It's part of the ' Oxford hoard '. It turns over nicely and has all it's outside bits apart from a starter motor and gearbox, but that's ok, I have spares. It's going to need a fair amount of cleaning with paraffin before I have a look inside. My query is the engine number. It's stamped, in the usual place, R4957. I assume the R is for reconditioned but others I've come across were all stamped RO. Anyone know about this number ?

[johnairey]

I believe you are correct 'R' is for reconditioned 'O' is fitted with an oval crank and 'N' is for nitride treated crank bearing surfaces.

[TedAllen]

Thanks for the reply. I certainly hope it's got an oval web shaft. I don't suppose many, if any, were reconditioned with a square web....but who knows. Will get the sump off later in the week and see.

[ian Howell]

Ted: =

Back in the early 1970s when I was running a Javelin as everyday transport, I managed over 120,000 miles on a flat web crankshaft.

Whilst I realise that oval webs are better, I believe that as long as you don't want to go racing, a flat web will serve pretty well = as long as a previous owner has not gone rac . . .

[David Morris]

Hi Ted,

I am sure John is right. I don't think the factory started using oval web cranks until at least 1955 or maybe later. Certainly no production cars had them fitted from new. The last square web cranks were known as 'black sided' and can run for ages without problems, provided they haven't been 'thrashed'. Jowett's must have experimented with several different types of crankshaft before the development work on the oval web. We have about five different examples in the spares shed. Oval webs were also not immune from breaking! Engine endurance for the Jupiter/Javelin engines does seem down to a heavy dash of luck and the degree of speed demanded by the driver!

Supposedly identical engines can either be real 'wrong-uns' and suffer all kinds of problems or they can be sweet as a nut and are a dream. I think a lot must be down to balancing? I know that the engine in my Javelin, once well warmed and perhaps having run a hundred miles on a run, sounds and behaves completely differently to when it is cold. Obviously that's not down to balancing, but it helps to feed the soul and reminds you why we love the marque!

There are lots of design areas in the engine that are open to potential problems. It is a long stroke engine with high piston velocities which means the potential for high piston wear. The three bearing crank needs attention to being balanced with the heavy flywheel and clutch. The valve train is awkward and the camshaft sits high in the crankcase, inviting noise. The choice of an aluminium crankcase was probably driven by steel shortages at the time, but has been a problem for corrosion and the potential for oil leaks throughout the engine is high. The engines run hot and you can burn your fingers on the dip stick! So, cooling is marginal and an efficient radiator is a must! But it was the early 1940's when it was designed and nobody else was so advanced! Did the development work by Jowett's influence later marques, like the Alfasud and Subaru?

Look for the last development by Jowett's on the Javelin engine that was in the Coventry Motor Museum, with the twin overhead camshafts!

All the best,

David

[TedAllen]

I ran a square web many years ago with no problems so wasn't too bothered. I spent today cleaning the engine exterior then turned it over and took the sump off. The front timing cover had the dynamo bracket broken off so that came off too. It's fitted with an oval crank and the journals and bearings look pretty good. That's good, I didn't want to split the engine to mess about with the crank . The big end cap bolts have internal Star washers....maybe some indication of when the crank was fitted. I don't know when they came out but it's not too many decades ago, I think. Had it hung in the garage with the rear hose outlets blanked off and filled it with water. No leaks over a couple of days. Removed the clutch and the n/s manifold which has both rear lugs broken off. The sump is badly knocked about so I'll replace that as well.

While on the subject of engine numbers I seem to go from one extreme to the other. I had a very clean, uncorroded early set which I let Drummond have as it was a hydraulic tappet one. Ive just looked at another spare set which is numbered E4 PE. I hadn't realised they still cast engines in1954.

[Nick Webster]

With a spot of luck your oval web crank will be stamped with an "N" denoting it is suitable for nitriding. The only early "soft" oval web I personally have come across was in a factory reconditioned engine using a series 2 crankcase.

Nick