Morris Minor Owners Club

Has anybody any idea of how to remove the metal tube which screws into the bottom of the head beneath the thermostat housing? Mine was so rusted that it fell to bits when I tried to undo it so now it's flush with the head. I tapped the remaining piece in the hole and screwed in an M12 bolt, but I'm worried that this will leak or even if it doesn't then perhaps will cause local overheating. So really I would prefer to get the remains of the tube our and fit a new one - but how?

Tricky! Probably need heat and judicious use of 'easy out' - although they can be the work of devil....... Problem is they expand the stuck piece as it screws in - and if it is thin (as that pipe is) - it will bind even harder. I would leave it plugged - and plug the water pump too. Drill 2 X 1/8" holes in the thermostat to allow a little bit of water to circulate before the stat opens. It will give you faster heater action - and won't cause any overheating....... Cue Richard with tale of woe about his engine 'overheating' - the ONLY case ever heard of such overheating. It was actually just a tight valve guide........ Many many Mini owners block the bypass - without the slightest problem. It works fine. You don't even need to drill the two holes - but then it will be wise to keep the heater tap open all year round - just to allow a little bit of circulation.

It was actually just a tight valve guide

If it was, how would restoring the by-pass hose have immediately solved a 2-year old problem that has not re-occurred in the last 5 years or so?

And please don't forget that BMC NEVER had a production A-Series without a bypass circuit.

I understand you also sorted out the tight guide at the same time as refitting the bypass hose. BMC also never fitted a 940 head to a small bore engine - but many folks do now, and it works extremely well!

No there was never an issue with tight guides as such, the tolerances were checked very thoroughly. The problem of 'nipping' of the No. 1 exhaust valve stem was caused by the local overheating from the lack of bypass hose and the reduced front of head circulation. Peter Burgess suggested opening up the exhaust valve tappet clearances by 3 thou, to give the exhaust valve more 'seat' time, thus heat dissipation, exactly the same as BMC did after fitting the unleaded head - you don't suppose BMC experienced a similar problem during development??

Bizarrely I had exactly the same thing happen on a BMW M5 V8 engine, when the engine running temperatures (water and oil) increased significantly in slow moving traffic - this time multiple misfires from a number of the 32 valves! BMW diagnosed it very quickly as valve stem nipping due to reduced clearances between valve and guide - I should have thought of it, as I had only sorted out the Minor engine not long before. They found that leaves have partially blocked the air flow to the bottom of the radiator, and clearing them out eliminated the problem, rather like restoring the bypass hose did!

I have said many times that with a standard(ish) engine, you may well get way with removing the bypass circuit completely, but on a highly modified engine I did not. Competition engines did remove the bypass hose sometimes, along with the thermostat and fitted the infamous 'blanking sleeve' - huge water circulation, but doesn't do much for the heater. I bought a blanking sleeve as the next thing to try if restoring the bypass hose did not solve it - it is still in the drawer!

Any chance you two can just agree to differ?
Enough has been said and you aren't going to agree.

I do, but will not let the same old misleading statements go unchallenged.

As your argument applies to "highly modified engines" wirh brass valve guides,no doubt driven hard, maybe just respond if that's the question?

If the bolt is a tight fit, then it should be ok. I did a similar thing but on the water pump by-pass outlet.

If you have access to a welder, I 'sleeved' a big nut over the remnants of the by-pass pipe, and welded them together. Thus, I was able to undo the nut/old by-pass stub together. It took two attempts but it worked.

As your argument applies to "highly modified engines" wirh brass valve guides,no doubt driven hard, maybe just respond if that's the question?

Unfortunately it's not as simple as that.

The first occurrence was when 2 changes were made at the same time (which is never a good idea). I had the existing head converted to unleaded, including bronze valve guides and at the same time removed the bypass hose. The engine also had new rings and crankshaft bearings, so needed to be run in as well. On the first trip with the rebuilt engine I had a serious misfire under light load about 1/4 mile from home - that was the beginning of the saga, that saw the head returned to the supplier for extensive checking, the entire fuel system from tank to carburettor replaced etc. etc.

The focus later was on valve stem clearances, and one argument is that the guides wore in over time and that provided the solution, but the entire head was replaced last year, with bypass, following a crack between the valve seats, and that was fitted with new bronze guides and all new valves - no hint of a misfire.

Yes it is a highly modified engine, and that will often expose limitations that are lurking within the basic design, but with unleaded fuel being used now, which has very different combustion properties compared to the leaded fuel that the engine was designed for. Many Minor owners have modified the engines, and many post on here are about what mods to do - who is to say where the line is?

BMC retained a by-pass circuit for all A-Series engines - why should we think it's OK to do differently?

I've fitted bronze guides in an unleaded head and have had no problems, I've also got a bypass circuit.

I'm happy to accept that you had a problem with a bronze valve guide nipping up and that you feel it was the lack of a bypass that cuased it.
However, I don't think it warrents bringing up in every discussion of bypass hoses on Morris Minors.
If it was a racing forum it would be a different matter.

IslipMinor wrote: And please don't forget that BMC NEVER had a production A-Series without a bypass circuit.

Later 1990s Minis and Metros had a 12G940 head with the bypass plugged - I know, I fitted a Metro one to my Midget-engined Traveller.

No problems with circulation - the temp gauge sits about half way and heater works pretty well.

Yes they did remove the by-pass hose on the later Mini's, but they maintained the by-pass circuit using the sandwich plate, as did the Metro, between the head and top hose connection, with the thermostat on top of the sandwich to allow a permanent by-pass via the heater.

Removing the by-pass circuit completely is a bit like building on a flood plain, fine if you know both sides of the story.

My concern is when only one side is portrayed, and there is another that has the potential to bite, and bite hard.

With regards to 'agree to disagree' I suggested that back in April last year and Roy agreed not to mention it again - but he did!

Ah yes, I see what you mean. For yonks, my heater didn't work, despite changing the thermostat and back-flushing it, etc.

It was only when Roy pointed out that the thermostat should be fitted in the middle of the sandwich and not directly to the cylinder head as I had assumed it should be fitted, that I was able to recently reinstate heater operation again.

Back to the tube, I removed mine with an extractor like the one pictured and a lot of patience, and made sure to use anti-seize on the new one.

Well I've succeeded in unscrewing the bypass tube. Thanks to all for advice but especially Daveyl - I followed your advice and welded an M10 bolt into the remains of the pipe. I was then able to get really good pressure on the bolt head and thus turn the seized tube.

If you decide to replace it they are available in stainless steel on ebay.
12A2075
ebay item 281254144008.
Declan

What thread is on that pipe?

TIA, Ken

5/8" UNF - according to this thread (pardon the pun!):

http://www.minimania.com/msgThread/1091 ... hose_plugs