valve clearance

[MarkRado]

Hi all,
I want to check and if necessary adjust the valve clearance on a 4.2 engine from a late 420G (1970). Engine number is 7D60135-8. Both cams are the later 4bolt and have the code P31818A cast in. Actual clearance measured on a few valves showed 009 on inlet and exhaust. Afaik the cam profile was generally changed around 1968 enabling bigger valve clearance. But the original chassis plate on this 420G shows 004 / 006 in/ex clearance. Is this a stamping error? What is the correct clearance for this engine?

Thank you

[abowie]

The Jaguar manual says clearances of 4/6 thou for the 420G, but I think that the P31818A cam is the C35556 cam for the S2 E type and also used in the XJ6. So your cams have either been changed at some stage or Jaguar fitted the quieter cams to later 420s.

[mgcjag]

Hi Mark...does this help...it shows how to identify camshafts......Steve http://www.georgiajag.com/Documents/Camshafts.html

[christopher storey]

AFAIK all the cams were changed to the parabolic type in c 1968. This is why the earlier 420G information ( which dated from late 1966 ) referred to by Andrew is for the old cams. If you have 4 bolt cams, then they are definitely parabolic and require the .012" - .014" clearances

[MarkRado]

Andrew, Steve and Christopher,
thank you vey much for your input.
I was puzzled, because a) the comissioning plate says 004 / 006 rather than 012-014 and b) the interim parts list of 1969 still only lists the early camshafts. So either it is a very late engine and nobody bothered using the appropriate comissioning plate, or the camshafts were changed during its life (although unlikely- a car with 30 kmiles, current owner since 1974).
Anyway. I'll adjust the clearance to 012-014 inlet and exhaust.

Thank you

[christopher storey]

Mark : something which might interest you ( particularly when it comes to a bottom end overhaul ) is that there were some intriguing differences between the Mark 10 / 420G engines and any other XK engine . This resulted from the fact that the bodyshell was found to have a resonant frequency close to and/or the same frequency as that of the engine, and Jaguar went to a lot of trouble to deal with the resultant Noise/Vibration issues . IIRC the fix which they eventually used was to grind the crank journals with a predetermined degree of ovality which altered the resonant frequency . Thus measuring a mark 10 /420G crank can produce interesting results !

The ovality is not required if the engine is now used in an E type

[Gfhug]

Christopher, FYI for E Type engines (don't know about the 420) Clausager shows the change to the parabolic 12/14 thou camshafts was in November 1969, engine numbers from 7R8688/7R38855

Regards

Geoff

[MarkRado]

Wow, thats really some special information. The indepth knowledge of this forum is impressive and invaluable, thank you very much

[PeterCrespin]

Just remember to go by the cams and forget everything else when it comes to setting clearances. Cams are easily changed between engines - sometimes in the mistaken belief that ‘E-type cams’ are better. All 4-bolt clearances should be in the 12–14 thou range on every valve.

[johnetype]

Christopher, FYI for E Type engines (don't know about the 420) Clausager shows the change to the parabolic 12/14 thou camshafts was in November 1969, engine numbers from 7R8688/7R38855

Regards

Geoff

My August '69 car has 2 bolt cams and 4/6 thou clearances.

[mgcjag]

Just be aware that the 2 hole camshaft with the grove around the front flange is also 12-14 gap....as in the link i posted above....Steve

[Gfhug]

Steve (mgcjag) did a post from you in this thread get deleted? I thought one or two posts on this and elsewhere I had read now don’t seem to be showing?

Geoff

[mgcjag]

Hi Geoff...yes i deleted a post that i posted here in error.....only others iv delete recently were spam....Steve

[phoenix]

Sorry but I am confused about the valve clearance on my S1 4.2 E type. It has engine number 7E 2165-9 with 2 bolt type camshaft. They seem to be set at they wider of the two types of settings at the moment. Thanks for your help.

[phoenix]

I have just checked the cams and they have 4 holes but only two are used . Does this mean I have a later camshaft in an earlier engine and what clearances do I use ?

[mgcjag]

Follow the link to the Georgia Jag site I put up in a post above...it explains camshaft variants and gaps....Steve

[rfs1957]

Sad to come across references to dear Christopher Storey.

However, his rapier brain would have required that we test some of his hypotheses, and I’m going to query the wisdom of his #6 post, above, where he refers to oval journals being used to combat resonant frequencies.

Having some clue how hydrodynamic lubrication works, and in an earlier life having been expected to justify it mathematically, I do not believe this for one second.

Beyond the physics, show me the machine that would have been capable of producing this result on the cranks when they were manufactured, and then where Joe Garage would have gone to get his regrinds.

It sounds to me a like a mis-interpretation of some other remark regarding perhaps a degree of deliberate imbalance.

Legends like these grow wings, and need to be either shot down or substantiated - I would be delighted to find out Christopher was right, but this will require more than heresay.