Thermostat or no thermostat - 1275cc engine?

[ColinN]

I have a 1954 Series 2 split-screen convertible, who answers to 'Maisie'. She has a 1275cc Marina engine, disc brakes, servo and electronic ignition. She developed a leak from the thermostat housing so I ordered new cork gaskets - two are required as in addition to the t/stat housing there is another alloy housing underneath it and the whole assembly is secured with three long bolts, rather than the usual studs into the cylinder head - and it still leaks!! The top radiator hose goes into the upper traditional t/stat housing and the lower housing connects via a short hose and a length of copper pipe to the water heated inlet manifold and the bottom radiator hose. When i removed the T/stat housing i discovered there was NO thermostat fitted. I have heard that the 1275cc engine can run without one to aid cooling - with a blanking plate, but there isn't one of these either. The result is that the heater is luke warm and the whole system seems to be over-cooled.
Also the plugs fitted are Champion N7YC - are these correct for this engine? I ask as i have a problem in that the engine seems hesitant at take off and often needs a quick shot of petrol via the choke cable which suggests to me a weak mixture - i used Gunson's Colourtune to set it up but conversely the exhaust tailpipe is a sooty black, suggesting a rich mixture although the plug electrodes after a long run were just a normal, dry light brown colour - although a bit black around the edges. As well as being hesitant, it spits and bangs a bit on the over-run. The carb is a SU 1.75" HIF44 - as mentioned on a water heated manifold. Do you know what needle it should have fitted? I haven't checked the mpg - but my impression is that it is not being very economical at the moment.
Any help or advice would be appreciated.
Many thanks
Colin (Edinburgh)

[bmcecosse]

Few things here... You MUST run a thermostat - 88 degrees in winter, perhaps 74 degrees in summer, although it never gets that warm in Embra.....If it's running cold then yes it is likely to hesitate. N7Y plugs are slightly hard - I run N6Y which are even harder, but a standard engine would use N9Y. Colourtune is a useless thing on a Minor engine - there are better ways to set up an SU, but of course - it is just the idle mixture you are setting up, so not that important. The inlet manifold BTW is better to NOT be water heated. An HIF44 is quite large for a standard 1275 - or has other work been done to it? The 'performance' needle is a BDL - I'm not sure what the standard needle would be - tell us what's in there at the moment - and what type of air filter is fitted? And of course - what final drive ratio is fitted, which will have an effect on acceleration and top speed.

[IslipMinor]

Colin,

The cooling arrangement sounds a little unusual around the thermostat housing - do you have some pictures you could post? Is the bypass hose still fitted between the water pump inlet and the cylinder head? From your description, it sounds like you might have a Metro thermostat sandwich plate fitted between the head and the original thermostat housing, which may have been fitted to restore the bypass circuit IF the bypass hose has been removed. How is the heater connected to all this?

Definitely a thermostat should be fitted - have you removed it, or was it a previous owner who removed it, maybe to cover up another problem? What type of cooling fan is fitted - electric or water pump pulley mounted?

Do you know what the engine spec is? Such as what cam is fitted, compression ratio? Exhaust type/size?

Lots of opinions on whether the inlet manifold should be heated or not. Unheated could produce very slightly more maximum power, if everything else is right, heated will give better driveability during the 'warm up phase' - have firsthand experience of the difference the latter makes! Whichever you do, it's not likely to be the cause or cure of the cool or poor running you are experiencing.

I think the water system need sorting first, then basic ignition system and carburation adjustments to get it running nicely.

[ColinN]

Thanks Richard and BMCecosse.

after a bit more prodding around the carb needle fitted is a BEJ. i've attached a few photos which will show the water pipe layout - pipes everywhere! I've found a receipt from the previous owner who had a reconditioned 1275 engine fitted by Andrew Parfitt, Motor Engineers, Bingley in Yorks in 2009. it's done very little mileage since. In fact at the 2002 MOT the car had done only 54,652 and 55,264 when the 'new' engine was fitted in 2009 and its now done a whopping 56,499 miles. The receipt doesn't specify what type of engine it is but the engine No. in case it means anything to you is 12V595E-SA-H977 - which i think is ex-Marina. The heated inlet manifold is by Titan Motor Sport and seems to be on the return feed from the heater, but as there is no thermostat i'm unsure which way the water flows - presumably through the head first and then up into the heater and back through the inlet manifold into the bottom radiator hose, but that would seem to be the reverse of normal when water would only flow into the radiator to be cooled once the t/stat opened - confused.com! I don't know who or why the t/stat was removed but from what you are both saying i should be fitting one back in again - but does it go directly into the head under the alloy 'sandwich' plate or on top of the sandwich plate? There is no bypass hose fitted as such, but i hope you can see the plumbing arrangement from the photos.
I don't know what state of tune the engine is in or what camshaft is fitted or indeed what ratio of rear axle is fitted. i suppose that is one of the downfalls of a hybrid, unless you do it all yourself and you record everything. The exhaust i fear is strangling the engine as it is a small bore stainless system and think this should be at least 1.5 to 1.75" to help it breathe better. The air filter, as you can see from the photos is a cumbersome afair which straddles the carb and awkwardly hides all the adjustment screws etc - i tried a pancake on it and although it looked a lot better, the mixture was so weak that it hardly ran at all so as a short term measure the big filter was put back on. What type of filter would you recommend?
All that said, 'Maisie' made it to a charity event last Sunday at Summerlee industrial museum in Coatbridge without mishap.
cheers,
Colin

[IslipMinor]

Colin,

No photos visible!

If it is the Metro sandwich, the thermostat fits on top of the sandwich and under the original type thermostat housing. From the head upwards, the assembly order is head, gasket, sandwich block, thermostat, gasket and finally the thermostat housing. Do make sure that you use plenty of grease all the way up the studs/bolts, so that there is no corrosion to seize everything up for the next time you need to take it apart!

Is there a water take-off from the back of the head to the heater, or is the heater part of the run from the sandwich plate, to the heater, from heater to inlet manifold and into the top of the bottom hose, just before the entry to the water pump? That would make sense and is the revised bypass circuit. The thermostat will control the water flow into the radiator, but the bypass circuit must flow all the time to prevent local hotspots in the engine and particularly the head.

If that is what you have, fitting a thermostat should sort out the heater and get the water temperature up to a better level. Once you get it up to temperature, adjust the mixture for the smoothest idle (screw in to richen and out to weaken). The HIF6/44 reacts to 'weak' very noticeably, so if you find that and screw the mixture adjustment in about 1/2 - 1 turn, that should give you a good starting point. The question is, does it now drive well??

The Marina engine has the oil filter at the back of the block, up by the distributor, whereas the Midget engine has it in the same place as the 948/1098 Minor engine.

Titan Motorsport are reckoned to make one of the best HIF6/44 manifolds. What sort of 'pancake' did you try? A K & N will work very well with the HIF and Titan manifold. The BEJ needle is for a standard 1275 Metro, so should be OK if your engine is close to standard, but a bit weak if it has any 'warmed-up' bits in it.

[ColinN]

Thanks IslipMinor,

sorry about the lack of photos as all would be revealed in the plumbing dept. I've not uploaded any photos before to the messageboard so i've obviously done something wrong - they were all fairly small JPEGS. Anyway to answer your question, yes there is the usual heater tap at the back of the head and this then goes up to the heater and warms up first, then in theory flows back from the heater into the inlet manifold and then into the top of the bottom radiator hose, if it decides to take a left turn or if it decides to go right it goes back into the head through the alloy sandwich plate - or infact into the radiator as of course there is no t/stat to stop it. The pancake was an old one which i had fitted to a 1700 Marina when i had one and was not of great quality - although the Marina seemed to like it.

Thanks,

Colin

[IslipMinor]

Ah, don't like the sound of the water connections at the front and rear of the head being joined in some way.

On pre-A-Plus engines there was a bypass hose and the heater/manifold was fed from the take-off at the rear of the head, and it was always thought to be a good idea to leave this open on higher powered engines. With the Metro A-Plus the front bypass was blocked off and the sandwich plate introduced to provide the bypass circuit, which also fed the heater and manifold.

As a trial you could just use the feed from the sandwich plate to the heater, manifold and bottom hose, then block off the rear head connection altogether. Fit a thermostat and see what happens! Maybe don't go too far from home, just in case?

Can you try uploadingthe pictures again?

[bmcecosse]

Yes - I fear you are trying to feed water from both ends of the head - which will result in zero effective flow..... I would throw away the sandwich plate and ONLY use the back of head feed - but I know Richard has other ideas about that......

[ColinN]

Yes, you are both right - there is very little flow. With taking off the T/stat elbow and the sandwich plate to try and cure the leak i ended up with an air lock to make matters worse - so i disconnected one of the pipes at the inlet manifold and drew the water through with a large syringe device and once rid of the air bubbles i checked the flow and it was pretty non-existent - now i understand why. So it's a case of shutting it off at one end of the head - either the tap at the rear or by removing the sandwich plate at the front, but if there is no longer the bypass through the sandwich plate and if for some reason the tap at the rear of the head (heater supply pipe) is there not likely to be a large explosion to be heard all the way to Oxfordshire?

Why can't i upload photos - it would be so much simpler if you could see what i was talking about? I choose the picture file - JPEGS of approx 130KB which isn't large - it says it's uploading but nothing seems to happen. Perhaps i have to make them even smaller.

Thanks again

Colin

[ColinN]

Hi Richard and Bmcecosse,

i have resized the photos so here goes again. Hopefully you will now be able to see what Mr. Heath Robinson has been up to under Maisie's bonnet? By the way the grey gunk under the t/stat housing is stuff called 'Dirko' sealant as the new cork gaskets failed to seal - a bit messy i know but only temporary.

thanks

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[bmcecosse]

You're not kidding about the mess...... My view is that the bypass hose is not necessary - and this is shared by many many Mini lads. The heater tap should be kept open at all times - and usually a couple of 1/8" holes are drilled in the thermostat rim to allow some water to flow round. This all gives much faster heater warm up from cold - and eliminates bypass bursting risk. Richard disagrees - and will be along shortly If I had known about the C'bridge event - I would have come along - it's not far from me. The big airfilter will be fine - even better if fitted with a K&N filter element. The small exhaust is not great, and should be your next upgrade.

[IslipMinor]

The 'remove by-pass hose' topic is well documented. BMC/BL never removed the by-pass system, but they did change the design of it for the Metro by removing the small hose at the front of the engine and using the sandwich plate as part of the revised design. They also removed the heater feed connection from the back of the head, which is interesting as the 'common wisdom' has been that there should be permanent flow from the back of the head to give good cooling.

Having no by-pass may work for some, but it did not for me and caused me at least 2 years of grief and cost. Eventually the root cause was identified - the increased local heating at the front of the engine caused the No. 1 exhaust valve to 'nip' and misfire under load, and eventually burn out. Replacing the by-pass hose solved the problem.

So what to do as you have no by-pass hose?

Leaving it as it is is not an option, and probably why there is no thermostat fitted.

Do you know if the head has provision for a by-pass hose, but blanked off, or no provision at all. The water pump is easy, just get one with the by-pass stub 'open'. If the head can be fitted with a stub, then change the water pump and revert to the standard by-pass set-up. No sandwich plate, and run the feed from the back of the head to the heater, then manifold, then bottom hose.

If that is not feasible and because I have had overheating problems directly associated with removing the by-pass hose and drilling small holes in the thermostat, I would be inclined to block off the heater tap, turn the sandwich plate round to face out from the head (if it will, might need to open up the holes slightly?), connect it directly to the heater, from the heater to the manifold and from the manifold to the bottom hose, obviously without the 'T' connection .

Another alternative, as Roy described above, is to remove the sandwich plate altogether, drill a couple of small holes in the thermostat and run the rest of the plumbing as you have it now, again without the 'T' connection into the bottom hose. Some have tried it and had no apparent problems - has anyone tried it on a 1275 engine?

Whichever you do, fit an 82°C thermostat (could be 88°C for winter, but is it worth the effort changing it?)

[JOWETTJAVELIN]

Only slightly related, but the Allegro never had a bypass hose in 1100 or 1300 form and I have never had any problem with either.

As Richard points out, however, this engine for the Aggro does have a sandwich plate which supplies the heater.

[jaguar68]

My 1275cc A+ Ital engine is running a reasonably standard water system, in as far as the heater runs through the standard Minor copper heater pipe, an Series II type heater tap, big valve 940 head, water heated manifold (unheated), bypass blocked off (standard with the big valve 940 head) and holes drilled in the thermostat flange On Roy's advice. I'm not sure what temperature thermostat is fitted (might be an 88 degree one ) and seems to run without problems. The maximum temp. I've seen indicated on the temperature gauge is about 75 degrees (best estimate).

Not sure if any of this info helps, but Islipminor did ask about 1275 setups

(I really should find out what needle is in the carb at some point too)

Regards

John

[ColinN]

Thanks bmcecosse(Roy?), Richard,Jaguar68(John) and JJ,

There is no provision for a by-pass hose in the normal position on the head, Richard. No doubt they decided to get rid of it in the more modern 'A' series, given the grief it caused in trying to replace it when it burst. I'll try what you suggest - re-directing the water from the sandwich plate direct to the heater and back through the inlet manifold and then into the bottom rad hose and see how it goes - oh and fit a T/stat with a couple of holes as you suggest. Presumably then this makes the heater tap redundant and should now be closed as there is nowhere for the water to flow to from the rear of the head now anyway.

The event at Summerlee Roy, is an annual charity event in aid of CHAS organised by my friend Joe Kelly and last year he raised over £6,000 for the charity. There were around 75 classic cars in attendance. My other classic is a '64 Mk.2 Jag, called 'Edward' which was also supposed to attend (driven by Joe) but it refused to go out in the rain and wouldn't start!

The small bore exhaust will be replaced on the Minor asap - anyone want a stainless small bore exhaust? I also intend to replace the cumbersome air filter as well but i will probably need a richer needle? thanks for all your help - it is much appreciated and i'll keep you posted as to how it goes, although it won't be this weekend as i'm off to London.
Cheers
Colin

[IslipMinor]

Colin,

If you retain the sandwich plate there is no need for the holes in the thermostat - they are only put in to allow some flow when the stat is closed and there is no by-pass circuit.

[bmcecosse]

My almost 'full race' 1340 Mini engine ran with no bypass hose. Worked well - and the heater would be supplying good warm air within 1/4 mile from the house on a cold winter day........ I had no thermostat holes in winter with an 88 degree stat- but in summer changed it for a more normal 74 stat with 2 holes. The engine never overheated, although it would get a bit hot on a long uphill Mway (hard!) run until I fitted the smaller (ex Minor) water pump pulley.

[ColinN]

Ah, well - that's another wee job saved - no holes in the t/stat. By the way i found the very thin cork gaskets from ESM to be pretty useless as the water still seeps out - i didnt use any gasket sealant as i didnt think it would need both sealant and gasket. however the water still manged to find its way out - AND up the three bolt holes as well! thus the Dirko sealant which is pretty good stuff (made in Germany) and bought a while back from a Triumph supplier to seal the inlet manifold on my Triumph Stag V8 (combined water and fuel manifold). All that said it is still weeping slightly under the sandwich plate! Do you have any particular gasket / sealant combination you would recommend?

Cheers again

Colin

[bmcecosse]

Yes - just use a normal gasket (ie not cork) and no sealant..... Your housings may be corroded.

[JOWETTJAVELIN]

Make your own gaskets from cereal packets.

Remove the sandwich plate, clean the mating surfaces up, fit a home-made gasket, replace s/wich plate correct side up for thermostat to fit then evenly tap it down with a rubber mallet, whacking it when it's at the bottom to ensure a good seal.