12G940 Cylinder Head

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Martlin
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12G940 Cylinder Head

Postby Martlin » Thu Sep 12, 2019 5:07 pm

Hi all,
Just purchased a reconditioned 12G940 cylinder head,all good so far.
I am an elderly,and often quite confused!
Looking at the head not only is there no provision for a bypass stub,also the heater outlet where the tap goes is blocked off!
I have had good advice how to overcome the missing stub pipe,but cannot understand why the heater outlet is blocked off.
O.K,what do you think, if I drill out the heater outlet I might as well drill and tap the bypass stub connection.
What do you think.
Thanks for bearing with me.
Martin.
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les
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Re: 12G940 Cylinder Head

Postby les » Thu Sep 12, 2019 5:23 pm

The heater outlet looks like it’s full of something, are you sure you can’t dig the blockage out?


PoolGuy
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Re: 12G940 Cylinder Head

Postby PoolGuy » Thu Sep 12, 2019 5:37 pm

les wrote:
Thu Sep 12, 2019 5:23 pm
The heater outlet looks like it’s full of something, are you sure you can’t dig the blockage out?
It's an A+ head, that's how they were.

les
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Re: 12G940 Cylinder Head

Postby les » Thu Sep 12, 2019 6:06 pm

Ah, didn’t know that.


paul 300358
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Re: 12G940 Cylinder Head

Postby paul 300358 » Thu Sep 12, 2019 6:16 pm

Martin, don't worry, drill the heater outlet out, the holes are there and threaded for the heater valve studs. Don't bother drilling and tapping the bypass.

Regards
Paul

Martlin
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Re: 12G940 Cylinder Head

Postby Martlin » Thu Sep 12, 2019 6:20 pm

Hi,
Thanks for help so far,
In reply to Les I was hoping it was crud,but is solid steel!

IslipMinor
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Re: 12G940 Cylinder Head

Postby IslipMinor » Fri Sep 13, 2019 8:30 am

The A-Plus engines used a different by-pass system that had a sandwich plate underneath the thermostat housing. This also provides the permanent feed of hot water to the heater.

Despite frequent suggestions to ignore the original by-pass hose and just block it off, no production A-Series engines were ever made with no by-pass. On standard 948 and 1098 engines history appears to suggest that you can get away with drilling a hole in the thermostat, but does that provide a by-pass or just a bleed for air bubbles? What is the history for 1275 engines?

On our well modified 1380, the heater outlet has always been permanently connected, but following the apparent success on this Board of rapid heater warm-up etc., running with no by-pass was a complete well-documented disaster. Without the circulation around the front of the engine we had multiple problems with No. 1 valve sticking and burning out.

Since putting the original non-A-Plus by-pass back, we have had no valve problems for many years and 10's of thousands of miles. The by-pass system in car cooling systems (not just the A-Series) is there for a reason! It is even more important with unleaded fuel that causes the exhaust valve to run hotter, thus the need for hardened seats and improved valve material.
Richard



PoolGuy
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Re: 12G940 Cylinder Head

Postby PoolGuy » Fri Sep 13, 2019 8:38 am

How about one of these to avoid heating the cabin in the summer? https://www.t7design.co.uk/tx2-heater-valve.html

philthehill
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Re: 12G940 Cylinder Head

Postby philthehill » Fri Sep 13, 2019 9:35 am

Not only do you need good coolant flow around the front of the head but also around the rear of the head so as to reduce the possibility of hot spots. The rear of the head is prone to having higher temperatures due to its design.
A large capacity water pump helps to push additional water around the heal so helping to reduce the chance of hot spots.
As regards the by-pass facility I have mixed views having run both with and without the bypass facility. My 1275cc blocked engines up to 1400cc have all run without the bypass facility but they have always been fitted with large capacity water pumps and bronze valve guides with good clearance between valve stem and guide. The current head fitted to my Minor has had additional water transfer holes made to help eliminate hot spots.
No two engines are the same and whilst one engine may run perfectly satisfactory another of the same spec may not.

Good coolant circulation is the secret.

Phil


paul 300358
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Re: 12G940 Cylinder Head

Postby paul 300358 » Fri Sep 13, 2019 11:26 am

If you look at the cooling page on the Carver website ( https://www.calverst.com/technical-info ... -it-works/ ) it says

"Back to thermostats for a moment. It is common practice to remove this and fit a blanking sleeve in a bid to improve cooling. If this is done, you must blank off the by-pass hose, otherwise stagnant areas of water will occur causing the dreaded hot-spots. However, the danger with fitting a blanking sleeve is that the engine may not reach proper operating temperatures, and this can be every bit as bad as running a little too hot. And the old style blanking sleeve (11G176) is not at all efficient. I would strongly advise using a thermostat in ALL road cars, of at least 82 degrees to make sure the correct running temperatures are achieved. A blanking sleeve is not the answer to over-heating problems. I always run a thermostat in my race engines unless bound for foreign shores where high ambient temperatures are experienced. Many folk think that they have to fit a blanking sleeve if they are blanking off the by-pass hose. Not so. Blank off the troublesome by-pass hose then fit a thermostat that has had six or eight eighth-inch holes drilled around the periphery. These holes allow coolant to circulate before the engine is up to temperature and the thermostat opens."

I found that one hole was adequate for a near standard 1098, any more and it was over cooled.

IslipMinor
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Re: 12G940 Cylinder Head

Postby IslipMinor » Fri Sep 13, 2019 12:17 pm

Paul,

The significance of the Calver article is the combination of no by-pass AND the blanking sleeve. With no thermostat fitted there is plenty of water circulation at all times. The whole purpose of the 'blanking sleeve' is to create a good flow around the engine, without a thermostat in place. No thermostat and no blanking sleeve leads to very quick local overheating. The description 'blanking sleeve' is very misleading, it doesn't 'blank' anything, it directs the flow around the engine, that otherwise would take a shortcut and overheat the engine very quickly.

The role of the the by-pass circuit is to provide water circulation around the engine UNTIL the thermostat opens, which then provides circulation around both the engine and the radiator.

Minors are well-known for having a good capacity cooling system, which is why, at least in part, it is possible to 'get away' with blocking off the by-pass system on a standard engine. Firsthand experience says don't try it on a modified 1275, which needs a lot more cooling capacity than either of the standard Minor A-Series engines.

My well-documented concern is the often quoted statement that the by-pass hose was removed on the A-Plus engines, so why not do the same on the Pre-A-Plus engines? Yes, it was removed, and it was replaced by an even bigger capacity by-pass system using the sandwich plate.
Richard



philthehill
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Re: 12G940 Cylinder Head

Postby philthehill » Fri Sep 13, 2019 12:31 pm

A thermostat or 'Blanking Plate' sic cannot be fitted directly to the cylinder head in question as the hole is not machined for either
To fit either a thermostat or blanking plate the sandwich plate is required.
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If you fit the sandwich plate it throws out of alignment the thermostat housing and the radiator inlet and different hoses have to used to join the two together.


IslipMinor
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Re: 12G940 Cylinder Head

Postby IslipMinor » Fri Sep 13, 2019 12:41 pm

Phil,

The head has the recess for the thermostat - why could it not be fitted directly to the head in the picture?
Richard



philthehill
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Re: 12G940 Cylinder Head

Postby philthehill » Fri Sep 13, 2019 2:40 pm

Richard
Looking at the picture again - you are right.

It should be born in mind though that not all 940 'A' plus heads will accept the direct fitting of the thermostat. My own 940 'A' Plus head has no facility to fit a thermostat and the sandwich plate has to be used if a thermostat is required to be fitted.

The casting underneath the heater outlet stub had to drilled through to allow the passage of coolant to the heater.
Phil



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