Greetings.... I have heard SP250 heads can have corrosion problems that might affect their usability. What might those problems be and where should I look. Also, are 2.5V8 heads and SP250 heads interchangeable?
Tim
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Cylinder head problems
Re: Cylinder head problems
Saloon and SP250 has are interchangeable.. as are right to left ... as for the corrosion.. it commonly effects the passages where water circulates between block and head with gasket in between.. corrosion around these water passages eventually breaches the head gasket and coolant can then enter the cylinder bores..(first symptom is pressurizing the radiator.. and water loss will start to be a problem) but the heads also corrode in other places, typically around the core or freeze plugs, a problem which began when they went over to convex steel plugs.. ( formerly they were alloy plugs, threaded in to the head ..as per rolls royce practice) restoring the head back to factory specs is commonplace.. and quite time consuming, hence costly..
if the coolant is changed every year and one uses the 'for life' ( red rather then green) dry mixed coolant, corrosion issues should not arise .. but given the age of these engines.. its hard to figure out whats what as regards internal corrosion without pulling the heads off..
The other issue is deck height... how many times has the head been 're-surfaced ' ??... I believe -.040" off the deck face is the maximum permitted.. and you can get away with _.060" IF you use the composite gaskets that are now available.. if shaved too much the geometry of the valve train gets out of whack..
Explaining the 'signs' to determine how much has been shaved off is better left to someone else who can post images.. perhaps others can confirm the info below ?
Im not entirely sure the actual thickness of an unshaved head ..As far as I can determine, it should be +/- 3" if 'stock' and no thinner than 2 15/16" .. if its less then 2 7/8" (-.125") its definitely well beyond specs ( I have pair that were shaved this far.. it had 1/8 shims under the rocker posts to correct valve train geometry.. and the tappet chest was modified with countersunk screws replacing the 1/2" head bolts , in order to get the inlet manifold to fit)
if the coolant is changed every year and one uses the 'for life' ( red rather then green) dry mixed coolant, corrosion issues should not arise .. but given the age of these engines.. its hard to figure out whats what as regards internal corrosion without pulling the heads off..
The other issue is deck height... how many times has the head been 're-surfaced ' ??... I believe -.040" off the deck face is the maximum permitted.. and you can get away with _.060" IF you use the composite gaskets that are now available.. if shaved too much the geometry of the valve train gets out of whack..
Explaining the 'signs' to determine how much has been shaved off is better left to someone else who can post images.. perhaps others can confirm the info below ?
Im not entirely sure the actual thickness of an unshaved head ..As far as I can determine, it should be +/- 3" if 'stock' and no thinner than 2 15/16" .. if its less then 2 7/8" (-.125") its definitely well beyond specs ( I have pair that were shaved this far.. it had 1/8 shims under the rocker posts to correct valve train geometry.. and the tappet chest was modified with countersunk screws replacing the 1/2" head bolts , in order to get the inlet manifold to fit)
Re: Cylinder head problems
typo..should read 'pre mixed' coolant.. not 'dry mixed'.. appologies..
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Re: Cylinder head problems
I believe that the modern red antifreeze coolant is acid based and is generally not regarded as suitable for older engines . Be very careful before using it . Stick to either ethylene glycol ( poisonous to some animals particularly cats ) or the stuff sold for central heating - a non-glycol one is Fernox
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Re: Cylinder head problems
This is a refurbished head...
...and this is why it needed doing....
This enlarged view shows typical waterway corrosion....
...and this is why it needed doing....
This enlarged view shows typical waterway corrosion....
Nick
"Don't bother with the Air & Space Museum - there's nothing to see.......".
"Don't bother with the Air & Space Museum - there's nothing to see.......".
Re: Cylinder head problems
As far as I have understood there is also possible corrosion that can make the heads porous and coolant can leak into the inlet and exhaust runners in the head. If this is the cause the heads are scrap as it is almost impossible to get to the porous bits for welding repairs.
And a bit of advice; DO NOT try Steel Seal to stop coolant leaks! It will cost you £40 at halfords and does not work. Trust me I have tried
And a bit of advice; DO NOT try Steel Seal to stop coolant leaks! It will cost you £40 at halfords and does not work. Trust me I have tried
Re: Cylinder head problems
the posted images of 'before' and 'after' heads will help ... Id point out the the finished one in image has been shaved close to its limit.. the tell tale is the 'ears' at the ends ( where coolant passages connect to water pump housing,,and closed by banking plates other end) which has cut into one of those ears in the image.. originally the head face does not intrude into that area .. again..measure deck height.. should be apporx 3" deep when new..
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Re: Cylinder head problems
heads that have been subjected to high heat can crack under the seat insert needing removal of same and repair before replacing the seat.
steve
steve
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Re: Cylinder head problems
When my heads were refurbished, they were subjected to a Ceramic Particle Sealing Process or micro-shot peening. I was informed that this would reduce the risk of porosity caused by the heating and working of the aluminium.
I don't know if it worked but I've had no loss of coolant in the two years since the engine rebuild
I don't know if it worked but I've had no loss of coolant in the two years since the engine rebuild
Jim in Coventry - Home of the Daimler
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Re: Cylinder head problems
Casting porosity does not necessarily mean the head is scrap. There are several firms that carry out 'vacuum casting impregnation'. Check the last paragraph on this page.Sonus wrote: ↑Thu Nov 01, 2018 8:56 am As far as I have understood there is also possible corrosion that can make the heads porous and coolant can leak into the inlet and exhaust runners in the head. If this is the cause the heads are scrap as it is almost impossible to get to the porous bits for welding repairs.
Incidentally I once salvaged a porous hydraulic pump casting (operating pressure 200 bar) by immersing it in Loctite 290. It worked a treat, but I'm not sure it would withstand cylinder head temperatures.
Nick
"Don't bother with the Air & Space Museum - there's nothing to see.......".
"Don't bother with the Air & Space Museum - there's nothing to see.......".