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Compression test on 4.2 XK engine

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bmurphy7369

bmurphy7369

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I just purchased a decent compression tester kit to diagnose the XJ6's internals. This may be a dumb question, but is it truly necessary to do all of the "Professional Testing Procedures" such as grounding the HT Lead, etc. I always just thought plugging the guage in each spark plug hole one by one would give a compression reading. I know many of the steps are meant for modern cars with F.I. and lots of ignition components that the 1975 XJ6 doesn't really have, but the car does have an electronic ignition (OPUS type). I'm a bit hesitant now to just do the plug and read method, just wondering if I should follow the instructions completely or if I can verify compression by simply doing the one plug hole and crank/read method? Thanks for any advice,
Brian
 
Why not follow the instructions? If you don't ground the HT lead, there is a chance of causing a high voltage insulation breakdown, or damage to the ignition system.

Doing one plug hole will tell you nothing about the engine overall condition.
D
 
Its OK Dave, he is going to check all the holes one hole at a time. However, To use this method require remo9val of all the spark plugs, the distributor cap and No ignition circuit on while a remote starter switch is used to operate the starter direct from the battery.--Fwiw--Keoke-?
 
Hey Dave and Keoke,
Thanks for the replies. I don't think I have an HT lead due to the Crane module, but I should probably disconnect the Crane module (the Crane eliminates all wires from distributor to the coil). I guess I don't know how to make a remote starter, my kit didn't come with one. I guess there is a way to make one with a wire? You wouldn't know I have ever turned a wrench with all of these questions on a common procedure, but I haven't ever done one. It'll be interesting.
So.......

All plugs out at once.
Crane module disconnected from the distributor.
Remote start from battery.
Missing anything??
Thanks guys, big help to me.

Brian
 
Hi Brian. you can buy a remote starting switch at most auto parts stores they are simple and can be had very little cost.--Fwiw--Keoke
 
Thanks Keoke, think I'm on track now.

Brian
 
That sounds great, I'll have to check the SII repair CD-rom to see if the '75 has one. The part sounds familiar, but the Heritage Repair/Parts CD covers SI and SII XJ6. I may have seen an older version somewhere. Thanks for the tip Exotexs.
Brian
 
Hello all,

I think that this function was lost many years ago. What it was, (I think on the MK 2 and possibly the 60's 'S' type\MK10)the solenoid itself had a rubber cover on the bottom and you pressed the armature to activate the solenoid manually as it were. This will only be possible on cars with an inertia drive rather than the modern pre-engaged.
I installed a similar feature on my Triumph by fitting a push button switch and altered the wiring. It certainly is invaluable especially with bigger engined cars.

Alec
 
Hello Alec,
I think I have poured over too many manuals and catalogs. Terry's Jaguar covers the "Saloons" of that era, and now that you mention it, I believe this is where I have seen the part mentioned or listed, probably elsewhere as an add-on. Thanks for the information. Sounds like I'll be picking one up locally for this compression test.

Best Regards,
Brian
 
yes piman, what it comes down to is that the Starter Solenoid is mounted separately from the Starter itself, unlike modern Starters which have the Solenoid mounted on the Starter, (the "hump" seen in modern starters). The Starter Solenoid in my '65 'S' type is mounted on the firewall, all the wiring is there, and a Cable goes down to the Starter pole. The Solenoid is always "live" and it has a push-button that when pressed, turns/cranks the starter whether the ignition switch is on or not. The idea to install a push-button like you did does the same thing.

I think the "old" arrangement is superior, because when the Starter Solenoid fails in a modern Starter, the entire Starter has to be removed from the car!

Brian, I see these old Jaguar Solenoids everywere, eBay and online vendors, they are not expensive at all. however, I don't know it they will work in your '75 without rewiring.

check this UK site, but you can get them here in the US too:

https://www.classic-car-accessories.co.uk/acatalog/Classic_car_parts_SWITCHES_6.html

Ex
 

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Exotexs said:
Brian, I see these old Jaguar Solenoids everywere, eBay and online vendors, they are not expensive at all. however, I don't know it they will work in your '75 without rewiring.
Click to expand...

Well, Exotexs, I think I'm already into it deep in the rewiring department... sounds like a great idea to just go the extra step while I'm doing the rest of the ignition harness... Thank you for the link also.

Brian
 
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