Difference between XJ6 and Eytpe engines

[chiney_dolly]

hey everyone,
im new to the forum and have a few questions.
i had inherited a few jaguars etypes and xj6s

im currently in the process of selling one of the etypes
and the person interested is having difficulty finding the engine number
and is also claiming the engine to be from a xj6.

could you guys assist me with the differences in engines if we are unable to find the engine numbers.

its a 1970 etype.

thanks much,
natasha

[PeterCrespin]

could you guys assist me with the differences in engines if we are unable to find the engine numbers.

its a 1970 etype.

thanks much,
natasha

The XJ6 engines for any given year will be broadly the same as the E-type engine of the same year. If it is a later engine (after about 1979) it will have several useful upgrades internally and is really no disadvantage unless he want a perfect numbers-matching car for some reason.

They stopped stamping the engine number of the front of the head on E-types around the time the XJ6 came out, so you do have to look on the block for the number. If it is not on the horizontal block surface just above the oil filter housing, it should be on the edge of the flange where the bell housing attaches. This is at the rear on the left hand side. The engine number will tell you whether it started as an E-type or XJ engine. A 1979 n E-type will start 7R. An XJ from the same time will probably start 7L or later ones 8L....

[chiney_dolly]

thanks much,
will check the engine numbers again.

when you mean "broadly" the same.
all parts are the same? compression etc
what the guy is saying is that he CANNOT find the engine number.
so i am curious as to how he is identifying it as a XJ6 engine.

thanks again

[christopher storey]

There is essentially no difference between E type engines and those from an XJ6, except that the later XJ6, from say 1973 to 1979 used 7.8 to 1 pistons instead of 8 or 9 to 1 , and after 1979 it used 8.7 pistons . The cylinder heads are identical . The only functional difference was carburation , and if your car has 3 carburetters that difference is eliminated . The effect on performance is absolutely minimal, and indeed my FHC which has a 7.8 to 1 XJ6 engine is a good bit quicker than my 9:1 OTS . What may be confusing your buyer is that a 1970 E type engine will have 5 core plugs, unlike the earlier ones which had only 3 . It sounds to me like someone who thinks he knows a good deal about the subject, but is in fact less knowledgeable than he thinks!

[chiney_dolly]

ok...
thanks much.
will speak back to him and im sure will have more questions soon.

[christopher storey]

The only other distinguishing feature which definitely marks the engine as XJ6 is if it is an 8L engine from a series 3 XJ6. These are distinguished by ribs running vertically up the block each side of each core plug

[skiday]

Whilst discussing the difference between the two models, I would be curious to know why the E-type has a support on the top of the bell housing just where it meets the engine, but the XJ6 does not?

[christopher storey]

It is NOT a support ! It is a stabiliser bar and bush . The number of mechanics who manage to lift the engine up above its normal position us ing this is amazing and the effects a. on refinement , and b. on breakage of the weld to the bulkhead , are considerable . The correct technique for setting it is, with the engine and box installed, to screw the lower " nut" up until it meets the bush, and then to screw the upper part downwards until it reaches the bulkhead fitting, and go no further

[skiday]

OK, it's not a support, it's a stabiliser. So why does the E need a stabiliser and the XJ6 not?

[christopher storey]

Andrew, I presume you meant XJ6 as in your original post . I imagine that the reason for the stabiliser on the E is to eliminate torque reaction which would affect the "solid" throttle linkage adversely . Also, the clearance between the throttle linkage and the frames is very limited, particularly on 4.2 cars, and if you get excessive torque reaction, there is a danger of jamming the throttles wide open against the frame , which might prove too exciting for many of us!

The clearance, or lack of it, on 4.2 cars is such that if the spacer which fits in the right hand engine mounting is omitted, the carburetters regularly touch the frames

[PeterCrespin]

In the XJ6 and many other saloons the XK engine is bolted to a front suspension subframe via brackets halfway along the crankcase, not fixed to the very front of the block like on E-types.

The engine stabiliser on E-types is constructed to control vertical movement primarily, rather than rotational. As with all levers, the length of the arc travelled for a given angular rotation increases the further you are from the pivot point. Think wheelbarrows etc. By the same token, the force required to move the lever is less the further you are from the pivot point due to the longer lever.

If you regard the XK engine/gearbox as a lever pivoted around the front engine mounts (like a wheelbarrow is pivoted around the wheel axis) you can think of the E-type having a longer lever (distance between front mounts and rear mount) compared to the same measurement on an XJ.

On the XJ the front and rear mounts are closer together, so for a given force tending to bounce the engine up and down (road shocks etc) the back of the engine is going to jump less around the front pivot than the back of the E-type engine supported by the same style vertical spring rear mount.

The vertical movement has to be controlled to keep the propshaft in line and stop the bell housing or gearbox etc fouling the transmission tunnel but the control of the reduced movement on an XJ is easier than on a 'longer lever' E-type. It is accomplished without a restraint, using triple-sandwich metal/rubber front mounts of larger area. These give good cumulative isolation but are stronger overall. The V12 uses a similar design as the XJ but even larger mounts IIRC. Plus, as Christopher mentions, there is more clearance around ancillaries (XJs have a cable throttle) and even bonnet line.

Pete

[PeterCrespin]

Someone asked me off list why E-types used engine mounts that seemingly offered less secure location of the engine? I forgot to mention that the reason the E-types mounts are further forward is I think because the engine loads are thereby fed into the main suspension uprights, rather than the long tubing, as would be needed with mounts halfway along the block.

My OTS V8 lump carried engine mounts halfway along the tubes and they had massive and ugly steel plate reinforcements to carry the load. The E-type's chrome-moly thin wall engine frames are triangulated to carry loads primarily in tension/compression rather than bending.

Pete