By-pass pipe

[iddy]

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.

[bmcecosse]

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 !

[iddy]

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

[Packedup]

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)

[bmcecosse]

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 !

[janstolp]

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

[lofty1000]

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.

[bmcecosse]

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.

[IslipMinor]

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.

[bmcecosse]

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.

[IslipMinor]

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.

[janstolp]

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

[paulhumphries]

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

Paul Humphries

[bmcecosse]

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 !!

[IslipMinor]

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.

[lofty1000]

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

[PAULJ]

Are there not by now ,hoses that dont split?

[Mogwai]

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

[lofty1000]

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.

[IslipMinor]

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.