Newfound tapping on 948 head...water temp?

[Fingolfin]

I've been reading around avidly about water temperature gauges, because I want one. But I'd excluded the possibility as wishful thinking, because I have a 948cc engine, and they don't have tappings for the sender units, right?

But look...[frame][/frame]
And that's the tapping for the temperature sender, isn't it?

I'm absolutely positive it's a 948 engine (it has a big '950' stamped on the block in the right spot). So there are two possibilities: 1) someone has put a 1098 head on my 948 or 2) there was an anomalous 948 manufactured.

Having a 1098 head would tend to strangle the (very meager) power of the 948 block, wouldn't it?

[PSL184]

Get the casting number off the head (beneath the rocker cover) and we'll know for sure. No harm in a 1098 head on a 948 block - It's a good improvement but you could have a mini head, minor head, MG head etc.....

[bmcecosse]

As above - take the rocker cover off and read the casting number. If 12G 202 then = 1098 head. If 12G 295 = MG 1100 head. Bigger valves and better porting - but both would need skimming to use on a 948 - but will up the power!

[katy]

And that's the tapping for the temperature sender, isn't it?

Yes, it is.

[Fingolfin]

[frame][/frame]
12G 295, if I read it right. So it's from a Morris 1100! How interesting! There won't be any problems with the 1100 head on the 948 block, will there be? BMC mentions 'skimming'.

[bmcecosse]

No - it's the very desirable head from an MG1100 - or a Spridget 1098. Well done ! Yes - it's needs at least 60 thou skimming off to be much use on a 948 (or a 1098). So - next move - measure the thickness of the head to determine if it has been skimmed already.

[Fingolfin]

Huzzah! That greatly excites me. Things are looking up! But -- um -- BMC, what exactly does all that mean? What am I measuring? Assume I'm a novice...

[bmcecosse]

Measure the thickness of the head - from top to bottom - between the machined faces........ They were all 2.750" when new.

[MarkyB]

A digital micrometer is quite handy at this point.
Watch out for silly postage charges though .

A regular micrometer is fine, as long as the operator can read a slide rule, the principle is the same, the work of a moment.
£7 to you sir.

[Fingolfin]

Should it appear 2.750" in situ, or does it need to be removed from the block? A preliminary check with a ruler returned exactly (by eye) 2.50".

I'd love seven pounds! But digital measuring instruments are available at most hardware stores in the States. I could easily obtain one...but the ruler check was so spot on, it'd almost be overkill. I KNOW it's not 2.75".

[bmcecosse]

A steel rule is usually fine. So - your measurement would suggest 250thou has been removed--------which is impossible! You will need to measure it properly.

[charlie_morris_minor]

this might be a silly question but...

has the engine been running since you purchased it? if it has does it not suggest that the correct amount has been skimmed off it?

or is it possible to run the engine without the head being skimmed?

[Fingolfin]

In a few minutes I'm going to go take some more measurements.

It has been running -- we drove the car home, and it ran nice and sweet, like a 948 should -- and it's been driven numerous times since, to a total of about 60 miles. The engine's never had any trouble.

[bmcecosse]

Yes - you can use the 295 head as is - but the comp ratio will be horribly low - especially on a 948 engine! So most of the potential performance gain - will be lost

[Fingolfin]

Well I made a shockingly dumb mistake and I hope you won't hold it against me. The new figure is 2.75", just as it should be (as close as the naked eye can tell), and this time I'm certain.

When I measured and got 2.50", I unknowingly used a ruler that had the measurement beginning offset from the end of the ruler itself (why do they do that? Does anyone know?). The offset ended up being exactly 0.250". To prove it, here's a photo with a tape measure whose markings begin at the very tip:[frame][/frame]

So...moving right along... What kind of performance gain are we talking about? Could it be figured out theoretically or would I need to test the whole shabang with a dynamometer?

[Peetee]

I ran a healthy 948 engine with a 295 head, 1.5 inch carb and water heated, alloy inlet manifold and it was a very very nice set up. Very free revving, plenty of useable power. It is a much better set up than a standard 1098 in my opinion. I run a standard 1275 now and, whilst a bit quicker, it is harsh and noisy in comparison.

[bmcecosse]

If you have 80 thou skimmed off it - the 'safe' maximum (but do a depth gauge check down the oil hole first to be sure!) and with a larger carb/good manifold it could make almost 1098 standard power = 48 bhp. But of course it will be revving 10% harder than the 1098 to get that power! If you could find a 1098 camshaft (AEA 630) that would give you ~ another 5 bhp. maybe the engine has one fitted ??? The head of course needs to be in good condition - valves all nicely ground in to smooth seats. It's WELL worth using that head - get it skimmed!