I am after some advice about fitting a cylinder head that has no bypass hose to a 1275 Marina engine.
I guess there are a fair few opinions out there but i am after EXPERIENCE of fitting a head without a bypass and what the downfalls (if any) were.
I have been lent this head :<br><br>
It is a stage 3 from a friends dead 1275 Mini (tin worm!) and he has said i can try it out on my Minor as he won't need it for a while but i am worried about blanking off the bypass from the pump as i'm sure i have heard bad things about doing so!!
Also as it is only on loan then i cannot just get it machined to fit a bypass!
You could use a Metro water pump, those don't have the bypass (I think...)
Onne van der S. MMOCno 60520 Moderator
2dr 1971 White DAF 55 (with hopefully a 1600cc engine soon)
2dr 1973 Bergina (DAF 44)
2dr Estate 1975 DAF 46 in red
2dr saloon 1972 DAF 44 in Mimosa
It's excellent without the bypass - faster warm-up and better heater output. Drill the stat if it bothers you - but as long as you keep the heater valve open - all will be well.
Thanks for all your replies!
I will fit it and see how it goes then
The heater valve has been substituted for a straight hose tail anyway so there is always full flow around there!
I think Richard on here has reported he had some problem which he attributed to 'no bypass' - but it's the ONLY problem I have ever heard of like that - very popular mod in Mini world to eliminate the hateful bypass.
Although the Metro water pump does not have a by-pass hose fitted to it, there is an even larger by-pass on the Metro, running from under the thermostat (in a modified housing), through the heater and back.
This quite the opposite to what happens if it is removed altogether, even if the heater valve is left open, as there is still very little pre-stat opening flow through the front of the head.
Known actual problems? Yes, I needed to replace the water pump, so removed the by-pass hose and immediately had a severe misfire 1/2 mile from home on the first run with the new arrangement. Not making the connection with the by-pass I replaced the coil, plugs, fuel pump and fuel lines, and each time it would seem slightly better, but had continual problems for about 2 years with what would eventually prove to be the No. 1 exhaust valve 'nipping' during the warm-up phase, and even when warmed up and under load. Sometimes you could see the temperature climb rapidly just before the stat opened (82°C), and during that time the misfire would occur quite frequently. Easing off the throttle almost completely would allow the engine to warm up and then it would only an occasionally misfire under load. What a performance!
Eventually the valve burnt out and I could see a hint of yellow marking on the stem (bronze guides) when I removed it. That started the thinking process about what had I changed that might be the cause? The by-pass hose! It was allowing heat to build up at the front of the head that could not be dissipated by the restricted flow. I did have a couple of small holes in the thermostat, but they are no substitute for a real flow.
Replacing the by-pass back to standard solved the problem. That was about 5 years ago.
Many people have removed it with no apparent problems, but I would be very concerned on a modified engine that today produces much more power, and heat, than BMC could ever have anticipated with the original by-pass design. Even so, with the Metro they uprated the by-pass, not removed it altogether. At the same time though, they also removed the flow from the back of the head completely and increased it significantly from the front.
It may be the only instance, I don’t know, but it cost me hours of grief, considerable expense, lost use of the car at times and all because of that stupid by-pass hose (or is it?).
Last edited by IslipMinor on Tue Mar 03, 2009 9:39 pm, edited 1 time in total.
Richard, That is EXACTLY the sort of thing i am worried about and wanted to test the water as to any known problems as it is there for a reason as you rightly say.
I think i will look into this further now before fitting it as i don't really want to give myself loads of aggravation for the sake of a little more power!
WPR - Richard is the ONLY report I have ever seen of problems like this- it's a VERY popular mod in Mini world - don't worry about it! Once the thermostat opens, even slightly - which surely happens after about 5 minutes running - there is absolutely no difference whether there is a bypass there or not!
Well I will be fitting a head later in the year with the bypass blanked off as Roy has said in the mini community this is oten done.
I wonder if Richards problem was caused by the bronze valve guides warming up too much before the water started to flow especially as its in a fair state of tune, just a thought.
Cheers
Kevin
Lovejoy 1968 Smoke Grey Traveller (gone to a new home after13 years)
I am sure that the bronze guides exaggerated the problem, but I did not have a solution that lasted any time, until I restored the by-pass hose.
Also I am not sure the Mini experience is necessarily relevant to the Minor - bear with me!
The radiator in a Mini is known to be marginal with higher power engines, the 'S' was notorious for overheating in traffic when first introduced. Could it be that, in a Mini, when the stat opens, it opens fully as the cooling system needs all the flow it can get to keep the engine at a reasonable temperature? Full opening = full flow, so no problems?
Whereas in a Minor, the radiator is, if anything over-sized, so as soon as the stat 'cracks' there is enough flow to keep the engine cool in 'open road' conditions? At any running speed on open roads or motorways, we get a temperature of 175/180°F, which is the 'just open' level for an 190°F (88°C) stat. Enough to keep the engine cool overall, but is it enough to provide sufficient flow through the front of the head to prevent local hot-spots on a well modifed engine, without the additonal flow provided by the by-pass?
We only ever had the misfiring in open road conditions, and under load, as in town the stat will open more, and on light throttle openings the heat build-up is a non-issue anyway.
It strikes me that removing the by-pass makes the cooling a bit more marginal, which seems perfectly OK unless the engine has been modified to produce a lot more power than standard? Maybe that is the answer?
Last edited by IslipMinor on Tue Mar 03, 2009 9:43 pm, edited 2 times in total.
So - your theory is that the problem was actually caused by the over large Minor radiator ? Seems highly unlikely! I would suggest the 88 stat was the culprit - on a high power engine 74 stat is more suitable. It think it's just one of these things Richard - probably the guide was a bit tight - did you do anything else (such as grind in valves etc) when you re-instated the bypass hose ?
Don't understand how you could interpret my last post as blaming the Minor radiator? The point is that its capacity is very different to that in a Mini.
I believe that the issue is with the engine internal cooling capacity and that the A-Series head has a weakness with flow around the front of the it. Why would the Metro have an even larger diameter by-pass system than the Mini or Minor, if one was not required at all?
Consequently anything that needs a liitle help in this area, such as a serious power increase, can expose that weakness. One of the directives from Special Tuning 40/50 years ago was that if the thermostat is removed altogether a 'blanking sleeve' must be fitted - it doesn't blank anything, but it does restore the required flow to the whole of the front of the head, which is short-circuited when simply removing the thermostat. The cooling limitations in this area are not new.
The thermostat temperature is not a factor - it originally had an 88°C without any problem, was reduced to 82°C when I had the misfiring/by-pass issues, and was replaced with the original 88°C a year or so after refitting the by-pass hose 5/6 years ago.
From an engineering perspective I don't believe in 'it's just one of those things', there is always a cause and a subsequent effect.
Whether the problem is common or not is not really the point, the engine did experience severe local overheating immediately after removing the by-pass hose, which was not cured by changing everything on the fuel and ignition side, was demonstrated to have 'on spec' ignition and fuelling on 2 different rolling roads, and was 'cured' by putting back the standard by-pass hose, where it remains to this day.
In addition to replacing the entire fuel system, and trying a new coil, distributor cap etc., a number of other things were tried as well (all one at a time) - running slightly rich to have a cooler charge, opening up the exhaust tappet clearance by 0.003" to give more seat/cooling time (this worked very well) and removing the exhaust valve stem oil seals to provide more valve stem lubrication. The end result appeared to be a 100% solution for a while, but ultimately proved to be not quite!
Since replacing the by-pass I have returned the mixture to 'correct', put the orginal Lucas Sports coil back, and reset the tappet clearances back to the standard of 0.019" for 1.5 rockers and a Kent 276 cam. The exhaust valve stem oil seals have not been replaced, as that means a head-off job, which is not required for any other reason at present.
The original question asked for experiences of removing the by-pass altogether and these are the facts from my experience of doing so - I leave others to judge whether they are relevant in deciding what to do about them!
Your original post suggested 'over cooling' due to the larger Minor rad compared to Mini rad! The blanking sleeve has to be fitted to force water round the BACK of the head - nothing to do with the front of the head which is well served as standard! As soon as the thermostat open - it doesn't matter whether or not there is a bypass - so as soon as any heat develops in the front of the head - the stat will open and cool it immediately. There can be no 'overheating' in that area! I believe you made the bypass idea fit your circumstances - but i can't agree with your logic. I just think your guide was tight - and it freed off in due course.
Fact is MANY Mini owners do away with the bypass - and have much better heater action and no worries about bypass hose failure. I have done it on several A series engines - Mini and Minor - without the slightest problem. I thoroughly commend this modification - without the slightest reservation - to all my Loyal Readers !!
I followed the common wisdom and changed the water pump and removed by-pass - 1/2 mile from home had a severe misfire, which went away on light loads. drove nearly 200 miles, from Oxford to Lymington and back, the next day and every time I came to a hill, it misfired.
Replaced fuel pump, lines, tank, coil, distributor cap. Removed head for Oselli to check their guides - all ok. Changed 88°C stat to 82°C. Always seemed better for a while, but the misfire continued under warm-up and 'loaded' conditions. Never any problem at low speeds or in town, irrespective of water or oil temperature.
After 2 years of misery, with nothing else left to change, put the water pump back to standard with by-pass and re-instated the by-pass hose. No more misfire, even 5/6 years later.
Roy, I know and understand exactly what I have done, and I am sure that many have made the change successfully. I did it for exactly the reasons that are well documented, but that does not alter the fact the when I did it, I had problems that were only solved by reverting to the standard set-up.
I am sure we will continue to have different views on it, and they are just that.
But after a very few minutes from a cold start - the thermostat is open and the bypass is totally swamped by the main flow around the head - it plays no part in the cooling as soon as the stat opens! So any problems after the first few minutes - are not connected to the bypass. You must see that - surely ?
