Purchasing and fitting nonstandard gauges

[Fingolfin]

Basically, what should I beware about shopping for some nice Smiths gauges for Mog? Particularly, will these fit?
http://cgi.ebay.com/ebaymotors/Jaguar-X ... mainQ5f100

http://cgi.ebay.com/VINTAGE-SMITHS-TACH ... 3cb782bd71

http://cgi.ebay.com/ebaymotors/Jaguar-X ... mainQ5f100

I don't want to spend good money and have them not fit properly.
This being my first car, and not knowing exactly how the engine is supposed to sound and when, I'd like some insurance in the form of gauges...so I don't blow up the engine or anything.

[Neil MG]

The oil pressure gauge may work if you buy the jaguar sender unit, however it is recommended to buy them in pairs for accurate calibration. The MGB tachometer (doesn't look like a 68-71 MGB gauge) should work and is negative earth. The temperature gauge should also be ok, but probably with a Jaguar sender unit.

Just my opinion, but I would save your time and money and keep the dashboard as it is. You can hear the engine revs and you will most likely hear and smell if it overheats and there is already an oil warning light. As you drive more you will learn to listen and feel whether the car is running sweetly or not, in the same way as you would learn to trust the gauges (and then ignore them!).

[Fingolfin]

Well, I certainly may go without. But I'm given to understand that the oil pressure warning light only comes on at extraordinarily low pressures, ~5lbs., by which point the engine would already have eaten itself. And I'd rather it didn't get to the point of actually overheating! I wouldn't cut into the dash; instead I would make a plate and hang the gauges under the dash.

What would you say about an ammeter?

About the tacho -- I want that because I want to see how much power I can get out of the engine at what revs. It's a 948, but has a (properly-skimmed) 1275 head, so I want to test and see how mighty the little thing is.

[bmcecosse]

An oil pressure gauge is an essential - and an ammeter is handy. No need to count the revs - and as already indicated - you soon know if it's overheating. But get a mechanical gauge - not an electric one. And - the 1275 head should NOT be skimmed for use with a 948 engine....... the CR will already be quite high without any 'skimming', and with a skimmed head it will be even more difficult to avoid the valves bashing the block........
Edited to correct 'pistons' to 'block'

[rayofleamington]

the CR will already be quite high without any 'skimming', and with a skimmed head it will be even more difficult to avoid the valves bashing the pistons........

They'll bash the block, not the pistons.

I've never had any benefit from an oil pressure guage. On a hot day after very hard driving, an average minor will be down to 20 or 15psi at tickover - at around 10psi you may see the oil light flicker, but only at tickover. A freshly rebuilt engine should be down to about ~30psi in hot weather after hard driving.

The light tells you the engine has poor oil pressure and you'll see it at tickover, but when reved up the pump volume increases and the pressure rises so it's fine to run, albeit not as good as it should be.
If the oil light comes on solid at tickover as soon as it's warm then you have BAD oil pressure and the engine will need work at some point in the future.

If the oil light comes on when driving, then stop the engine immediately. An oil pressure guage won't tell you much else.

[Fingolfin]

Oh, my mistake, not 1275 head. MG1100. We went through that before: http://www.mmoc.org.uk/viewtopic.php?f=6&t=33844
Okay...so the general mood is somewhat anti-gauge, though there's disagreement about which gauges are useless.

[bmcecosse]

Yes - silly me - it is of course the block the valves will hit - not the pistons . but the 295 head (suitably skimmed) is fine, although not nearly as good as the 940 head! An oil pressure gauge will warn you to stop the engine BEFORE serious damage is done - the oil light tells you the damage has already been done.......