Morris Minor Owners Club

My By-pass pipe is looking rather corroded and I want to change it. I notice that a replacement with ESM has a thread on it. Does this mean that I need to tap a thread in the head when replacing, or is the present one also threaded on? (for some reason I assume it's a push fit because my only other experience with spigots/tubes like this are interference fit).
Iddy.

I assume you mean the by-pass pipe in the cylinder head - which connects to the water pump ? If so - you will find it virtually impossible to get it out of the head - maybe need to drill it out. It is threaded in - but has been there for 40 ? years now ! Rover finally realised with the Metro that this thing was a waste of space - and they eliminated it. Makes a big improvement to the heater - just drill a small hole in the rim of the thermostat to allow a little circulation in the summer - but in winter I fit an 82 stat with NO holes for maximum heater output !

If I do this, how do I blank off the holes in the head and the waterpump?

Get a Metro/ Allegro water pump, and for the head either replace that with a Metro one (not sure what that does to the compression ratio though, but at least later ones were unleaded) or tap a thread in the bypass pipe and screw a bolt in with plenty of sealant.

That's what I did, and although the car has yet to see the road, it appears to have worked fine (famous last words)

later heads had a plug screwed in the head - and on the very latest ones there is just no trace of it at all ! Yes you would need to drill and tap it BSPT - and screw in a taper plug. Suppose you could do the same with water pump - but new ones are very cheap - £10 in some of the Mini places - sometimes less on ebay !

Today I came across the same situation.I have a Marina 1275 block and with it came a head (red) 7E7.
The outlet for the heater was blocked but I opened that by drilling but to my surprise I saw that there was no pipe to connect to the waterpump.
It it not such a problem to create one but it can be difficult to find the correct tap for the thread.
But I thought to have a look at the forum first and now I see that you don't really need it.Apparently it's a Metro head.
So the best way would be to block the pipe on top of the waterpump and drill a small hole,4mm?,in the thermostat.
Is that right?
Regards Jan

I recently blanked off the By-pass on a 1275cc Midget head which I presume has the same size outlet as the minor.


Drill Size 14.5 mm. Tap: Bottom 5/8 -18 UNF. Try and get a narrow shank drill as most hand drill chucks are 13mm

5/16 allen key. 5/8 UNF Plug from Mini Spares

Blanking Plug from the water temp sender
I used the plug after cleaning up the the mating surface with a gringer
I used a new water pump from a later Mini with no by-pass.

Yes - either geat anew pump with no bypass connection - or simply plug the pump connection. A make-do job is to simply connect a bypass hose - with a bolt plugging the outlet! One 3 or 4mm hole in the thermostat rim will be plenty.

Whilst the Minor type by-pass is not fitted to the Metro, they did NOT eliminate a by-pass system. They simply changed the design of it, and it does not use the notorious rubber hose from the pump to the head.

I know that you can blank it off and all seems fine, but the by-pass is there for a reason, and that is to keep the water circulating around the front of the engine until the stat opens. With the by-pass blocked and even with small holes in the stat, you can get local overheating around the front of the engine. I experienced this immediately after fitting bronze guides and removing the by-pass. The No.1 exhaust valve was nipped by the guide during warm up, and it took a long time to find the cause and the cure, which was? Reinstate the bypass!

A similar principle arises at the back, where the advice is to keep the heater tap open all the time to allow a free flow of water around the back of the engine.

There is nothing basically wrong with the standard Minor cooling system, even with a highly modified 1380 A-Series engine - start with a complete, new set of hoses (including the by-pass - the convoluted one is fine and can be fitted with the head in place), flush everything through (if it's really mucky use some cleaning agent), use a 33% anti-freeze mixture all year round, change anti-freeze every two years and the engine hoses every other anti-freeze change. The heater hoses seem to last a bit longer, but for the cost (~£4), it's probably worth changing them at the same time.

Well - i've run many A series with no by-pass, just a little hole in the stat and had no problem. Let's face it - as soon as the engine warms up the thermostat opens and water circulates. Before that - the pump is thrashing away at the front end of the engine - there won't be any local overheating I think your guides may just have been a little 'snug' Richard.

The justification often given for removing the by-pass is that BMC did so on the Metro, therefore it is unnecessary. This is not the case and I would be concerned to advise anyone based on a false premise.

Yes, I agree, the guides could have been a little snug, but the whole saga took nearly 2 years to resolve and a number of inconveniences on the way, including a burnt out No.1 exhaust valve.

A modified engine will often find the limits of a system, and in this case it is the need for the by-pass hose, especially during the warm-up phase.

There will be many opinions on this topic, and anyone making the change needs to be aware of the potential consequences before doing so.

Thank you all for your opinions and contributions.

As I have no hole in the head ,I will blank of the waterpump.If problems arise I will know what the cause could be.I don't use the bigger engine to its limits so I don't expect troubles .I can always change the configuration and drill a hole in the head.
Best regards Jan

Just had a look at my Ital A+ 1275 engine - it has bypass hose.

Paul Humphries

The main reason to eliminate it - is for improved reliability - no daft wee hose to burst in the middle of no-where on a dark wet night!
If you think of all the problems/cost/missed meetings/late dinners that hose must have caused over all the years!!
I've seriously not heard of anyone having problems with it's removal - and it certainly does improve the heater - I can confirm that from my 1340 Mini !!

The Metro has the different by-pass system, it's the rest of the A and A+ engines have that well-known rubber hose!

I've seriously not heard of anyone having problems with it's removal

I thought I had explained it quite clearly? Removing the by-pass causes a local temperature increase at the front of the engine, particulaly during the warm-up phase. Whether this will then cause a problem will depend on a number of factors, the engine spec, ambient temperature, water pump performance etc., etc. In my case it did cause a REAL problem, for a long time, before the permanent solution was found.

I would rather have some tolerance in the cooling system, as it is designed to have, and put up with changing the by-pass hose once every few years, than risk doing damage to the engine through local overheating, which is not visible until other problems occur.

Sounds like you have been running your motor a wee bit to lean Richard, wee bit lean = more power = more heat =requiring more cooling, hense your valve gear suffering.
So can anyone tell me how the By-pass LESS heads are plumbed in?, I have 1275 mini one with larger valves that I will be fitting in the near future.
Lofty

Are there not by now ,hoses that dont split?

the metro has a sandwich plate with an outlet on it between the thermostat & head this also feeds the heater instead of the rear outlet on the minor, marina etc
I personaly wouldnt run without some form of bypass as the coolant needs to circulate around the block when the thermostat is shut or partially open to prevent hotspots

Thanks Mogwai. I must be getting flow through the head and block front to rear from pump to the heater outlet (that I leave open), it then goes through the heater, then through the heated manifold back to the bottom hose back into the pump again untill the stat opens.

Sounds like you have been running your motor a wee bit to lean

No, this was a very early check. When I first had the problem, I took it back to Aldon for a run on their rolling road, as they had done the original set up - before changing to bronze valve guides and no by-pass. The ignition and mixture settings were spot-on, just as they had been set up.

2 years later, and multiple attempts by Oselli to prevent the exhaust valve(s) nipping during warm-up and under load sometimes, I finally reinstated the by-pass and have had no problems since.

To my mind the whole cooling set-up becomes much too marginal without a by-pass. Granted my 1380 is highly modified, but I had no problems before I removed the by-pass, and none since I put it back.

Lofty, You will get good flow through the back of the head, but limited at the front, which caused the problem I had. Presumably during the Metro development they found that they could do without the permament rear flow, but needed the front, so the Metro still runs the by-pass from the front of the engine, via the sandwich plate below the thermostat.