Camshafts

[k. rogers]

Could anyone tell me if the '8' camshaft is the same as that used in the Bradford? I realise that the prewar cams are interchangeable, but I am hoping to use a Bradford one in my 7 although I have discovered I'm not able to use Bradford cam followers as originally intended - the cam won't rotate with them fitted, so I just wanted to make doubly sure that the cam will be ok!
(Message for Paul Beaumont: I will let you have your follower back next time I see you!)

[george garside]

I have fitted Bradford camshafts to pre war 8's with worthwhile improvement in torque so if 7 & 8 are interchangeable then a bradford one should fit a 7?

george

[k. rogers]

Thank you for those words of encouragement, George, in fact I've been able to shine a torch from where the cylinders will go in the crankcase and I am able to see the followers make contact with the cam lobes almost perfectly central on the follower - a big improvement on the original 7 cam which although had wider lobes were each worn on one side which begs the question why did they not design it more like the Bradford one which makes contact with the followers bang on? Any ideas as to why the cam won't turn with the Bradford followers?

[Tony Fearn]

Hello Ken and George.

Mrs. F's away on a jolly for a few days, with a couple of friends, so Liverpool:- look out!! I've just come back from an evening with mates (enough said, but you might just be able to smell the fumes!).

I've used a CB camshaft in 'Sarah Jane' the 1933 'Flying Fox' on the advice of our late-lamented friend Roy Braddock, and it does seem to have upped the 'power-band' such as it is.

Timing is supposed to be done with a 12 thou tappet gap with running gap at 6 thou. I took it to a well-known Jowetteer who has a garage in Keighley (W.Yorks) who 'laid his hands on it', but I'll never know just how many thous finished up between tappet and valve nut, although it didn't seem to be what the instruction book said.

Nevertheless, she runs a treat, so I don't care.

Three of the tappets are pre-war and one is a Bradford type, but it doesn't seem to be detrimental that they aren't all the same. I had an awful knock on the engine which proved to be, after much consultation with the Yorkshire gang,(I.P., M.K., P.R.,), and taking her over to them to listen to the engine, a wrong-sized split pin in the camshaft end nut which allowed the shaft to unwind a fraction resulting in an end-float of a couple of thou. You wouldn't believe what a din it made.

Ken's observation vizwhich begs the question why did they not design it more like the Bradford one which makes contact with the followers bang on? might just be evolution and improvement.

Perhaps you'll need to suss-out the rear bearing for a different camshaft, as I have a few in stock and they aren't all the same diameter, but at the end of the day Ken, what are you expecting to gain? A couple of mph in top gear?

Regards to all,

Tony.

[k. rogers]

Very useful information, Tony, I will need to examine further the compatibility of the Bradford followers in the 7 crankcase - should be easy enough using the torch method I've mentioned! It isn't really a problem because I have a set of pre-war followers but there are advantages if the Bradford one can be used. I'm intrigued with your experiences with end float on your cam in Sarah-Jane. I have felt for some time that 7s suffer with knocking which could be due to end float on the cam and for your car to have knocked so badly just because of the slight movement caused by the wrong split pin almost confirms this. I had a shim made up - courtesy of Geoff Wills - to produce the allowable clearance of 1 - 4.5 thou and an intersting observation by Geoff was that out of all the pre-war engines he has ever stripped, none of the cams were shimmed. Is it possible that the cams were paired up with suitable front bearings in the factory to enable the correct tolerances? I would be interested to know other members' experiences on this.

[k. rogers]

Further to my last post, I can now confirm much to my delight that the Bradford followers do in fact fit in the 7 crankcase and the reason previously the cam wouldn't rotate must have been because the follower wasn't positioned correctly in its guide and jamming between lobe and guide. The only advantage with using the Bradford followers is the newer design which makes for a quieter tappet, however, if I can get a few more mph on top gear by using the cam, Tony, I'll be a happy man, after all, that makes all the difference when driving a 7! The only problem now is that I will need a pair of the square block washers which secure the guides in the crankcase.

[PJGD]

It is a while since I have had a Jowett twin engine apart so I can't remember what the tappet looks like; I assume that it is a typical mushroom-headed type.

Anyway, the reason that the cam lobe normally does not address the tappet bang-on center is that it is intended to be off center so that the friction between cam and tappet will cause the latter to rotate and thus spread the wear evenly over the tappet face instead of wearing a single track across the face of a non-rotating tappet.

Philip

[Forumadmin]

Cam followers should also be dome shaped and not ground flat.

[Keith Andrews]

Are there any unused cams still around?
Has anyone had the profiles mapped?
I do have the bradford profile here, its basically a square cam and relies on overlap and duration in the tappet gap...Thisa is real good for the old british pool fuel between the late 30s and about 1956, but is bloody useless on pre british pool and modern fuels since aroud 1956.
Along with the cam I believe they also increased compression...combine the CR and the cam that amounts to a big difference in what is realy important, the Dynmaic compression ratio.
Now this raises the question of history as Jowett stopped production at the same time the pool fuel was scraped.
They changed cams when the fuel changed, did they redesign the cams for post pool fuel but never used ????
If they did, and the profiles still exist, we should be using these or a small step up from that
Did they have plans to increase CDR? by a new design of both cam and CR?

Running on these old cams profiles and CRs and timing cent curves, there is no way we can get these old cars running as well in torque or HP, as much power in the rpm range or even have the same rpm range (as small as it is) as they used to.

Which brings the ultimate questions
Should we be updating these profiles so they can run with as much power as when they where made?
or
Should we stick to the old combination for obsolete fuels and have slower low power cars than produce at the factory?

[Keith Clements]

Over the years we have tried various cam profiles on Javs and Jups at least just to get a bit more lift and to open slightly earlier for the racing speeds. Did it make much difference? It really is hard to tell unles you keep everything else the same and then tune on the dyno. But heh, it feels as though it was better!

[Keith Andrews]

least just to get a bit more lift

I hope that the valve springs where replaced to match.
That sort of technology and line of thought was was more or less obsolete 30+ yrs ago
Hence the expression "gee that sounds lumpy"
lumpy by just increasing the lift generally means too much lift has meen added
Its all in the duration and over lap and lift rates...increase these gives a 'lumpy' idle to...only because the rpm range is out of spec for idle and the engine runs ineffient
The term used for a good cam with duration etc modded is 'loppy' and such an engine has a sound far 'stronger' and 'solid' than just a crap lumpy sound.
Boy racer technology of the 50s 60s and even 70s remains just that ..boy racer...but the old wives tails just hang on in there.