cylinder head casting repair?
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- Minor Fan
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cylinder head casting repair?
After extensive rebuild of an A+engine, I started it and ran it on my DIY test bed, and after running for around 1/2 hour, it started belching clouds of thick blue smoke!
In all other ways the thing ran perfectly, so I have stripped the whole lot down again, and can find nothing untoward in all the relevant places, particularly the Gasket.
I can only assume that the Head has cracked (it was modified with larger valves and re porting) so have taken this to machine shop for pressure testing.
Question is.. if this is indeed the problem, can the head be saved with cast welding or other repair. The engineer at the shop was very sceptical concerning this. It's a !2G2940, and have spent plenty on it!
In all other ways the thing ran perfectly, so I have stripped the whole lot down again, and can find nothing untoward in all the relevant places, particularly the Gasket.
I can only assume that the Head has cracked (it was modified with larger valves and re porting) so have taken this to machine shop for pressure testing.
Question is.. if this is indeed the problem, can the head be saved with cast welding or other repair. The engineer at the shop was very sceptical concerning this. It's a !2G2940, and have spent plenty on it!
John
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- Minor Maniac
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Re: cylinder head casting repair?
The head can be welded but how successful the welding will be is dependent upon where the crack is.
It will also be dependent upon the skill of the welder.
At this stage I would suggest waiting until a prognosis is determined and then go from there.
Phil
It will also be dependent upon the skill of the welder.
At this stage I would suggest waiting until a prognosis is determined and then go from there.
Phil
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- Minor Legend
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Re: cylinder head casting repair?
I think it is doubtfull a welded repair would last and done properly it won't be much cheaper than doing another head. That is if it is the head, cracked heads usually lead to an obvious misfire or coolant leaks which give white steam not blue smoke, it sounds more like oil is being pulled into the intake, what breather system are you running?
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- Minor Legend
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Re: cylinder head casting repair?
It would have helped if you had tried to locate the problem cylinder.
I agree entirely with PTH - wait for the results before panicking.
I can think of other reasons for it belching blue smoke, some of which might not be attributable to the cylinder head.
What ‘relevant places’ did you investigate and dismiss? That might narrow down the options...
I agree entirely with PTH - wait for the results before panicking.
I can think of other reasons for it belching blue smoke, some of which might not be attributable to the cylinder head.
What ‘relevant places’ did you investigate and dismiss? That might narrow down the options...
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- Minor Addict
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Re: cylinder head casting repair?
Not a crack...but many years ago I put a skimmed and ported head on my Minor. The car went very nicely for about 20 miles. Then it started to emit huge clouds of smoke. It turned out that the head had been skimmed too much, leaving an oil passage with a paper thin wall.cracked heads usually lead to an obvious misfire or coolant leaks which give white steam not blue smoke
The wall held for a little while but soon broke through, pumping large amounts of oil into a combustion chamber.
I guess in your case you would have seen an oil passage that had broken through when you took the head off again.
Don
Re: cylinder head casting repair?
I once had a cracked head on a Mini Cooper, the valve heads were very close. One of the symptoms was water from the exhaust, I don’t remember blue smoke, however if the head is damaged I suppose the symptoms vary depending on where the crack is. I didn’t get the head welded, at the time welding cast iron was not a particularly successful job involving pre heating. I doubt much has changed.
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- Minor Fan
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Re: cylinder head casting repair?
Panic over! To my huge embarrassment, I found out by myself that I had fitted a 1098 gasket which over lapped the 1275 (standard) bores!
I my (limited) defence, the set was marked 1275 on the packet. I have informed machine shop, who had already tested the head and found nothing amiss. Lesson learned.
Another head query--I have another unidentified head which looks identical to a 940, but is marked 12094 ? which has no by pass or heater take offs. I know it is not rare as have seen before, but what was it fitted to and is it possible to open up the holes and re tap for correct fittings?
I have cleaned out the heater pipe adaptor fixing threads, but what about the rest?
I my (limited) defence, the set was marked 1275 on the packet. I have informed machine shop, who had already tested the head and found nothing amiss. Lesson learned.
Another head query--I have another unidentified head which looks identical to a 940, but is marked 12094 ? which has no by pass or heater take offs. I know it is not rare as have seen before, but what was it fitted to and is it possible to open up the holes and re tap for correct fittings?
I have cleaned out the heater pipe adaptor fixing threads, but what about the rest?
John
Re: cylinder head casting repair?
It could be from a 1275 Maestro. They didn't have the bypass hose and I think the heater take off in the head was plugged. I've heard of people drilling a small hole in the thermostat to do away with the bypass hose, but never tried it myself.
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- Minor Legend
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Re: cylinder head casting repair?
How does that work? There is (nearly) always a small hole in the thermostat - or the radiator would not fill if the seating was a perfect seal.
Re: cylinder head casting repair?
There's usually a small hole with a “jiggle pin” that allows air to pass through the closed thermostat. However, when system is full of water and the water pump is running, the pressure normally causes this pin to seal the hole. Some thermostats have a small groove in the seat, rather than the small hole and pin.oliver90owner wrote: ↑Fri Apr 09, 2021 1:21 pmHow does that work? There is (nearly) always a small hole in the thermostat - or the radiator would not fill if the seating was a perfect seal.
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- Minor Legend
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Re: cylinder head casting repair?
The hole is exactly what I said it was for - as well as possibly shifting a tiny volume of coolant. Not for passing coolant (in any appreciable volume). The jiggle pin is there to prevent the hole becoming blocked, nothing more. There will not be any great pressure at the jiggle pin because the bypass hose will provide a path back to the engine (so the water can circulate in the engine without passing through the radiator, thus aiding a more rapid warm-up).
The hole is necessary to allow a small amount of (cold) coolant through so that the thermostat will have hot water present, at that point, to start it opening, thereafter the hot water passing will either hold it nearly closed or open it further.
I wanted to know how making a hole in the thermostat can possibly act as a bypass, for the coolant, to take a course back to the engine without passing through the radiator. That is what the bypass is for.
The hole is necessary to allow a small amount of (cold) coolant through so that the thermostat will have hot water present, at that point, to start it opening, thereafter the hot water passing will either hold it nearly closed or open it further.
I wanted to know how making a hole in the thermostat can possibly act as a bypass, for the coolant, to take a course back to the engine without passing through the radiator. That is what the bypass is for.
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- Minor Maniac
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Re: cylinder head casting repair?
John
Your head is a variant of the 940 head and was fitted to the later 1275cc 'A' Series engines possibly the MG Metro. Several variations of 940 heads had the sculpting around the thermostat.
I have the same head fitted to my Minor but the casting number by the thermostat is 18H7.
These heads do not have a by-pass hose as per earlier heads but coolant is always circulating through the head via the later heater control valve which has a two way function - 1. Hot coolant to the heater and coolant still circulating around the head. 2. No hot coolant to the heater and coolant still circulating around the head.
It is most important that coolant is always circulating around the head otherwise you can get localised hot spots especially around No: 1 valve. If you do not have a bypass facility one must be incorporated.
The drilling of holes in the rim of the thermostat allowed some circulation of coolant around the head before the thermostat opened so alleviating any possible hot spots. A must if the head does not have a bypass hose facility.
Originally there was a sealing ring gasket between the underside of the thermostat and the cylinder head Pt No: 1G1635 which ensured that coolant only flowed through the thermostat opening and not around the edge of the thermostat. The sealing ring gasket was discontinued some time ago.
Phil
Your head is a variant of the 940 head and was fitted to the later 1275cc 'A' Series engines possibly the MG Metro. Several variations of 940 heads had the sculpting around the thermostat.
I have the same head fitted to my Minor but the casting number by the thermostat is 18H7.
These heads do not have a by-pass hose as per earlier heads but coolant is always circulating through the head via the later heater control valve which has a two way function - 1. Hot coolant to the heater and coolant still circulating around the head. 2. No hot coolant to the heater and coolant still circulating around the head.
It is most important that coolant is always circulating around the head otherwise you can get localised hot spots especially around No: 1 valve. If you do not have a bypass facility one must be incorporated.
The drilling of holes in the rim of the thermostat allowed some circulation of coolant around the head before the thermostat opened so alleviating any possible hot spots. A must if the head does not have a bypass hose facility.
Originally there was a sealing ring gasket between the underside of the thermostat and the cylinder head Pt No: 1G1635 which ensured that coolant only flowed through the thermostat opening and not around the edge of the thermostat. The sealing ring gasket was discontinued some time ago.
Phil
Re: cylinder head casting repair?
philthehill has provided a better explanation of what I was trying to say. So oliver90owner, you are quite right to point out that drilling holes in the thermostat doesn't replicate the action of the bypass.oliver90owner wrote: ↑Fri Apr 09, 2021 6:57 pm I wanted to know how making a hole in the thermostat can possibly act as a bypass, for the coolant, to take a course back to the engine without passing through the radiator. That is what the bypass is for.
It got me thinking how the Maestro setup worked. I haven't seen one for a long time, but I found some pictures below. It appears the heater take-off is on thermostat housing, but before the actual thermostat itself and the heater outlet at the back of the head is plugged. So as Phil said, this allows water to circulate around the engine before the thermostat opens and prevent hot-spots, but does so via the heater circuit in applications where a bypass hose isn't fitted.
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- Minor Fan
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Re: cylinder head casting repair?
I do have the sandwich plate with heater take off with this head, as pictured.
Have been reading on other forums which tells me that using this set up on a non Maestro application can cause flow problems due to air locks? Opinions are split as to whether it is advisable to use it or not.
Any thoughts here please? I have a choice to use it or fit correct take offs to head.
Have been reading on other forums which tells me that using this set up on a non Maestro application can cause flow problems due to air locks? Opinions are split as to whether it is advisable to use it or not.
Any thoughts here please? I have a choice to use it or fit correct take offs to head.
John
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- Minor Maniac
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Re: cylinder head casting repair?
So long as you have coolant circulation through the head you should not encounter any problems with air locks.