Javelin back to life - first drive since 1980

[RandalColman]

The recent JCCA national rally in Tasmania saw two Javelins emerge from hibernation, one of them being mine (E1-PC-18562). Last driven in 1980, I am told, the car has undergone a protracted rebuild in the years I have owned it but until now the engine has not received any attention. After all, I had receipts for extensive engine work in 1974 so it should be fairly fresh, shouldn't it? Well, not really, as our webmaster will attest, having endured a ride in it for part of the rally.

The car struggled through the weekend, consuming some 50 litres of fuel, 5 litres of oil and 6 litres of water. Plenty of noise and vibration but not much torque. So it was time to open up the engine and have a look inside. At first things looked surprisingly good – reasonable compression (128 to 135 psi) and valves and heads in good condition. It appears that most of the lost water had simply leaked rather than being consumed internally. More good news when I removed the clutch and found one reason for the general vibration - lodged in the central recess of the flywheel, in front of the clutch plate, was a clutch fork pivot pin! A mass of 38 grams at about 35% of the flywheel radius, equivalent to 13g at the rim. The mechanical equivalent of those surgeons who leave their instruments behind when they sew up their hapless patients.

There are of course other problems with the engine, but I am hoping to avoid a full rebuild. The camshaft is very badly worn, the lowest lobes being 1.4mm below the highest, which represents a loss of a quarter of the valve lift. So the followers are obviously shot as well. Removing them was no easy matter. A Google search reveals a type of slide hammer used for this function but it appears to rely on an internal circlip groove which is not on offer in the Jowett engine. I managed to take out two of them with nothing more sophisticated than a finger, but for the others I had to resort to separating the crankcase. Someone will probably tell me now there is a simple way that I hadn't thought of. Anyway, they're out now, and although I couldn't help getting a glimpse of the condition of the main bearings I decided to bolt it all together again rather than dwell on them. I will find out after the Easter break whether the followers can be refaced. There seems to be about 5mm of thickness in the base so I would imagine that it can be reduced by perhaps half in order to get past the pitting?

Assuming I can pick up a second-hand camshaft and the various gaskets and oil seals, I would hope to have the car running again in the next few weeks. And if anyone wants to buy it, I'll be aiming to sell it soon after that.

[Forumadmin]

You have been hard at work. I would not have diagnosed those problems from the many miles we traveled in the car!

You live and learn every day with Jowetts!

[ian Howell]

With regard to refacing the camshaft followers, I have been warned that, with regard to my 1930 long Four, (but the problem may be the same) the face onto the camshaft should be slightly domed so that the followers rotate themselves. Also I would think that taking 2.5mm off the face would also remove any hardening that may have been there?

Others will comment I am sure.

Good to 'hear' that another Jowett is about to be doing what it was built for!

[RandalColman]

I have just come across Jowett service bulletin no. 49 of May 1951 (http://jowett.net/Parts/TechNotes-Part24-ServBul.htm) which described how to make your own tappet extractor - but, like the modern ones, for hydraulic tappets only. For solid tappets it says "a firm hold can be obtained on the conical end of the tappet insert. A special puller is therefore not necessary in this case."

It didn't work for me. In fact, the only tappets I managed to withdraw were the ones where the bronze insert fell out and I could reach into the barrel of the tappet. I suppose the factory couldn't conceive of cam followers as totally munted as mine were.

[TimKelly]

I have refaced the cam followers (flat) on many Javelin engines if not fitting new ones. Have not had a problem to date.
Kind regards
Tim Kelly

[Forumadmin]

Flat cam followers would result in them not turning on the camshaft resulting in excessive wear. I have seen followers with a depresssion worn into them because they were not turning.
Worth looking on an engine with flat grind and seeing if they have been turning. Happy to be prooved wrong! It is possible the friction of the rotating cam turns the follower if it is off centre.

The definitive statement is here.

Flat based tappets are usually allowed to rotate in their guides; indeed they are encouraged to do so since this reduces the rubbing speed between cam and tappet and spreads the wear over the whole of the tappet base. Rotation of the tappet is encouraged by offsetting the tappet from the centre-line of the cam or by grinding the cams with a very slight taper (about 1 deg) in which case the foot of the tappet is ground very slightly convex, forming part of a sphere of large radius

Proper flat tappet should always be convexed, but that is predicated on the cam lobe also being off parallel by a .001" or so to match the convex. The two work together to assure rotation of the tappet.
You can have the machine shop grind the tappet flat and finish the convex quite easily on an oil stone by hand.

The convex will result no matter how careful you are to try and keep it flat against the stone if you work it in a rotational figure 8 pattern across the stone, no matter how hard you try to keep it flat it will by nature of the process generate
a convex face.

That is why one needs three surface plates to hand lap and get a perfectly flat surface if you only use two plates one will end up convex and the other concave. This is the one time that a problem in lapping is used to your advantage.

and more on the topic here

[RandalColman]

It seems to me that there are two distinct ways of inducing tappet rotation. The more obvious method is to offset the cam lobe from the tappet axis so that the contact patch is biased to one side of the tappet (towards the front or back of the engine). In the Jowett engine the cam lobes are 12mm wide and are offset 1.7mm from the tappet centrelines, so the contact patch is a narrow rectangle with 7.7mm tending to follow the cam and 4.3mm rotating against the friction force. If the tappet is domed appreciably, the contact patch becomes an ellipse centred on the tappet and offset from the centre of the lobe. Tappet rotation is inhibited.

An alternative approach is to recognise that the cam lobe and the tappet face are not always perfectly parallel, and that any misalignment will move the centre of pressure towards one end of the contact patch, producing an undesirable peak at one edge of the lobe and possibly at the edge of the tappet. If it is biased towards the “short” end of the contact patch, rotation is inhibited. So rather than leave it to chance, we grind a deliberate taper into the cam and then dome the tappet so that the centre of pressure is a predictable amount offset from the tappet axis. Although the contact patch is smaller, it is a more favourable shape and avoids high stress near the edge of the lobes where the shear strains are more damaging. This is probably the design favoured in recent decades, though I understand from what I have read that roller tappets have now virtually taken over from plain sliding tappets.

It can be argued that a small amount of convexity is desirable in all tappet faces to avoid high edge stresses due to misalignment, but this can also be avoided by relieving the edges of the cam lobes when they are ground. According to the Repco Engine Service Manual, a cam grinding wheel is not moved axially while grinding and consequently it wears more in the middle, thus making the cam slightly convex. My guess is that the Jowett camshafts were ground in this way, and were therefore compatible with perfectly flat tappets. I certainly can't recall any mention in the Jowett technical notes of a need to dome the tappet faces.

What this boils down to is that if we are using a reground camshaft we should probably follow the advice of the camshaft grinder in selecting or refacing the tappets, but if we just have a secondhand camshaft it will have worn into a slightly convex lobe profile (corresponding to the dished face of worn tappets) and will therefore function well with flat tappets, as Tim has found.