Morris Minor Owners Club

I have aquired a 1275 unleaded Mini head to use on my Midget engine project . It has no bypass pipe at the front . Is this a problem ? Also it has no take off at the rear for the heater pipe , but it has the threaded holes for the fitting and I asume I can drill the hole in the middle to feed the heater . Any observations would be apreciated
Phil Burley

Drill the hole for the heater, and get a Metro water pump so the bypass is completely removed.

Personally I'd drill a few holes in the thermostat to allow some circulation before it opens, or leave the heater on hot, but I know opinion differs on that.

I think you neen to drill a few holes round the edge of the thermostat to let a little water through in the absence of a bypass hose.

Someone will be along soon to say how many and what size!!

Well done losing the dreadful bypass - Metro water pump (or blank off the one you have) and just drill 2 x 1/8" holes in the thermostat rim for summer use - in winter have NO holes. And yes just drill the centre hole for the heater tap - and run a tap (1/4"unf) down the two fixing holes to clean up the threads which will not have been used up to now.

What's the point of the bypass then ? and how does the mini and metro etc manage without it ?

As I understand it, the bypass pipe is there so water will flow around the engine before the thermostat opens. The argument for losing it is that the water doesn't actually need to flow until it gets hot, and the thermostat will open when it does. I think the idea of drilling holes in the thermostat is to allow a little flow when it's closed so the hot water in the head can get to the thermostat and cause it to open.

The Metro had a slightly different circuit which allows some water to run round even when the stat is shut. In summer it's best to have the two wee holes- but for v best heater in winter - NO holes. The heater warms up much faster - and works better!

What's so wrong with the original bypass? It allows proper circulation until the thermostat opens, just like a Metro does, but it does it differently!

If you convert to unleaded, with bronze valve guides AND remove the bypass hose, you end up with sticking No.1 exhaust valve if the machine shop that does the conversion does not get the tolerances just right (very well known shop) who had three goes and all had problems, then changed back to the bypass and to Peter Burgess guides and no problems).

Which was the solution though? Proper water circulation or better guides? The answer of course is 'only change one thing at a time'!!

It was the guides!! Problem with bypass is simply none - until it starts leaking! Over the years if you think of all the ruined engines/cost for repairs/missed appointments - maybe even accidents and deaths (from car being stranded at the roadside) then it's got a lot to answer for! Without it in winter the heater starts working much more quickly, and gives more heat too! In summer - wise to drill two wee holes in the rim of the stat, does the same job as bypass, and allows you to shut the heater valve if you really want to.

Why mess about drilling holes in thermostats. Just use the Metro one with the proper joggle valve in it (which is why you don't need the bypass hose). You even get a choice of 82 or 88 degrees.

The joggle valve is there on all stats - it's actually meant to be a non-return valve if you look at it carefully. But yes - that can be one of the holes if you just remove the valve itself with a pair of pliers!

Hmm no bypass, no heater take off. More likely to be metro than mini but it makes no odds... is the area around the thermostat cover totally flat or is it sculpted? If its the latter its likely to be the larger valved version of the 12g940

Could be a 90s injection head - I'm pretty sure they have mystical plumbing (well, at least it's a mystery to me quite why it's like that), and don't use the heater take off on the end.

Lots of 940 heads are 'sculpted' at the thermostat end - and large valve MG heads are NOT unleaded! When the MG went unleaded it just used the same head as all the other 1275 engines - they 'forgot' to mention the slight power loss!

But it doesnt mean that it hasnt been converted later!

bmcecosse wrote:The joggle valve is there on all stats - it's actually meant to be a non-return valve if you look at it carefully. But yes - that can be one of the holes if you just remove the valve itself with a pair of pliers!

There's no point in removing the joggle valve, it's there to allow a small bleed through (just like the minor bypass) and there should be no need to drill extra holes. If you have a stat with a joggle valve in a minor (and a bypass hose) it's the wrong one all it will do is increase the warmup time (because you have 2 bypass systems)

My car has NO bypass - just the joggle valve hole, joggle removed. Warms up great - and v good heater (for a Minor!).

bmcecosse wrote:My car has NO bypass - just the joggle valve hole, joggle removed. Warms up great - and v good heater (for a Minor!).

I was'nt discussing YOUR car I was discussing Minors in general if you feel happy taking bits out a a perfectly good stat thats entirely up to you. The newer design using a water pump with no bypass hose and a stat with a joggle valve obviously worked on thousands of Metros.

The Metro also has another circuit that runs round through the heater all the time - it's taken off below the stat. I'm pretty sure all 'genuine' stats have had the little joggle thing, which is designed as a one-way valve although I have removed it to allow a little circulation through the hole when the stat is closed.

its flat at the heater take off end , it has the threaded holes but the central 3/4 inch ish hole is not drilled . that doesnt look much of a problem