Water pump bypass hose

[jaguar68]

Hi chaps,

whilst checking which parts I need for curing the blown head gasket, I've noticed that the water pump bypass hose is plugged, as is the inlet in the head. In fact the expected inlet is missing, and appears to have been replaced by a screwed plug.

Can anyone explain the possible reason for bypassing the bypass and what are the advantages/disadvantages of running the engine in this way?

Regards

John

[bmcecosse]

Excellent to get rid of the ghastly by-pass hose - a major source of water loss = engine overheating. Richard will be along soon to tell his tale of course....... You should have 2 X 1/8" holes in the rim of the thermostat to allow some water to circulate before the stat opens.

[IslipMinor]

On cue!

Despite many postings that suggest removing the by-pass hose 'because BMC did on the Metro A-Plus', of course while they did remove the hose, they did NOT remove the by-pass system, they just designed it differently, and they never drilled holes in the thermostat!

Removing the by-pass hose can and does cause local overheating to No.1 cylinder - where did your head gasket blow? If you decide to reinstate it, make sure that you use a straight piece of hose for the by-pass, not the convoluted aftermarket version that is commonly available.

We have had our Minor in the family for 54 years, and never had a by-pass or any other hose leak or blow. (Probably will now!)

On the other hand, after I removed the bypass hose we had problems from overheating No.1 cylinder - one exhaust valve and one plug burnt out. Since reinstating the bypass hose, no problems associated with overheating! Maybe you can get away with it on a standard engine, but you cannot on a significantly modified one, which shows the there is not that much latitude in the cooling system.

[bmcecosse]

As Richard well knows - we've discussed this over and over - and his is the ONLY engine to have had a problem, and I can't in any case see the connection. Many thousands of Mini owners have done this - and Works did it certainly for the rally Minis where they retained a thermostat (to keep the heater/demister working) - the racers all had blanking sleeves fitted and every chance no bypass hose although i don't have facts on that. The two little holes in the stat are there to give some bypass - frankly not necessary IF you keep the heater connection open all the time - which I do. As soon as any heat develops in the engine - the stat cracks open and normal flow resumes anyway.

[IslipMinor]

I can't in any case see the connection

That doesn't mean there isn't one.

The blanking sleeve allows a huge by-pass, so not really relevant. If a bypass system is not necessary, why did BMC continue with one of a different design with the A-Plus?

In our case a simple series of events - engine converted to unleaded with bronze valve guides and bypass hose removed. Immediately had problems with valve pick-up and on warm-up very strange behaviour of temperature gauge readings. During the warm-up the temperature gauge would climb up to around 200°F, then a misfire, sometimes white smoke from the exhaust, and then back to normal - e.g. local overheating before the thermostat could open (82°C). After a few weeks, it seemed to settle down, but would still get a misfire under load sometimes.

Eventually (~2 years and still problems) decided to restore the bypass hose - that was 5-6 years ago and no more odd temp gauge behaviour on warm-up or misfire or problems with valves/plugs since - as a certain advert says 'thsimples'!

[bmcecosse]

I don't doubt the valve was picking up in the guide. But did you have 2 X 1/8" holes in the stat rim? They are put there to allow some circulation until the stat opens.

[IslipMinor]

I don't doubt the valve was picking up in the guide

It definitely was - No. 1 exhaust valve stem had a slightly yellowy sheen picked up from the bronze guide on the after it had burnt out, and was the first clear indication of the cause of the misfire under load. From there it was a series of steps to the final solution, the most significant one was reinstating the bypass hose.

Before that I had gone down the fuel starvation route and replaced the pump and fuel line from the tank, then ignition and swapped to a different distributor, played with the timing, different plugs, coil, leads etc., before finally going back to basics and thinking about what else I had done at the same time as getting the head converted to unleaded - removed the bypass hose!

But did you have 2 X 1/8" holes in the stat rim?

Yes I did have either one or two holes in the thermostat flange.

[jaguar68]

The gasket blow between 2 & 3 cylinders. It didn't appear to be a major leak as the rocker box wasn't filled with emulsified oil. Whipping the head off and changing the gasket seems to have cured the problem (fingers crossed). I've done about 15,000 miles in the car before the gasket blew, and god only knows how many miles it had covered before that.

I've been working on the 1275cc engine that I intend to replace the old 1098cc with and have discovered that the big valve 940 head doesn't have a bpyass fitting. Does anyone know where I can get a plug for the bypass hose or how to make one?

Regards

John

[IslipMinor]

John,

Between 2 & 3 - usual place if it's going to go!

Does the 12G940 head have the tapping for the by-pass fitting? If so Minispares have the screw in fitting - 12A2075.

[jaguar68]

No, the head doesn't have the tapped hole. I'm assuming it's a much later A+ head. I guess I could buy one of the water pumps without the bypass, but I've spent enough over the past few days, and indeed have just bought another water pump for a different engine.

I've just discovered that Minispares sell a rubber blanking cap, but are out of stock on the jubilee clips. There must be a world shortage of worn drive clips, as ESM are out of them too

Regards

John

[les]

Try a shop selling boat equipment they have nice stainless clips.

[bmcecosse]

RS Components do stainless worm drive clips. Just fit a solid wall rubber hose and plug it with a bolt.

[les]

Whilst on the subject of blocking up holes/pipes, managed to find some 'plugs' to block up the surplus clutch pivot holes (l/h drive option) in the chassis leg. Plastic wine bottle stoppers, just the right size!

[jaguar68]

Hi Chaps,

I've also noticed that the 12G940 head hasn't got a waterway for the heater take off. How do I retain the heater when using this head?

Regards

John

[bmcecosse]

Ahh - but it DOES have the waterway! Look carefully and you will find the two tapped holes - and a depression in the casting between them. Stick a drill through the depression - and run a 1/4" UNF tap down the two holes to clean up the threads.

[jaguar68]

How did the Metro, or whatever was fitted with this type of head get round not having the waterway drilled? I'm intrigued.

[bmcecosse]

They used an adapter plate with an outlet spur fitted below the thermostat cover. You can of course do that if you wish - but it is a GOOD IDEA to circulate water from the back of the head so there are no dead spots with localised overheating.

[jaguar68]

Do the 1/8" holes need to be diametrically opposed, or just anywhere? Diametrically opposed would suit my ocd

[bmcecosse]

Whatever you wish Make it 3 if you like.......