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MG MGB Technical - How can you identify an unleaded head?
| Hi Guys Just a quick question. Is there any way you can tell if a head, which had been removed from the block!, is unleaded or standard. What should i look for which will identify it as an unleaded head rather than just a standard head? All help is greatly appreciated. Adam |
| Adam Cooper |
| I am no expert, but the vavle seats are rings of harder material pressed into the head. You can see these rings. You can also see if the head is ported by looking into the ports and looking at the valve guides. Ported heads have a clear view of the valve guides and will have no sharp edges. If I were doing a head again, I would port it and put in hardened valve seats (I did this late) It makes a much better running car. Peter Burges wrote a book that has a discription on how |
| Frank Baker |
| adam a lot of the heads had a glued on washer or a stuck on temp gauge on the block so if the valve seats fall out because of overheating they can tell as the button will fall of or the temp gauge shows it its very diff to tell if it has been done and when you look at the original heads they are machined the same way as unleaded seats are. id take it to a head specailist to be sure theres 2 in bradford ste |
| Ste Brown |
| Adam- The MGB engine used four basic cylinder head designs during the course of its career. The fourth version of the cylinder head was a slightly modified version of the 12H 4736 cylinder head first introduced on the Austin Marina. It reverted to the original smaller 1.565" intake valve size in redesigned form (BMC Part# 12H 4211) that was used on the first two cylinder head castings, but had offset oil feed in the rear rocker shaft pedestal (BMC Part# 12H 4737) in order to accommodate redesigned cooling passages to assist in preventing overheating of the exhaust valve of the rear cylinder. This redesign necessitated the relocation of the oil passage in the rear rocker shaft pedestal, which means that if you should choose to install it on an earlier engine block you're going to need the later rear rocker shaft pedestal with the offset oil port (BMC Part# 12H 4737). This cylinder head can be readily identified by its casting number CAM1106 and is commonly found on engine numbers 18V-797-AE-L, 18V-798-AE-L, 18V-801-AE-L, 18V-836-Z-L, 18V-837-Z-L, 18V-802-AE-L, 18V-883-AE-L, 18V-884-AE-L, 18V-890-AE-L, and 18V-891-AE-L, all of which it was Original Equipment for. This cylinder head casting is sometimes referred to as the "lead-free" cylinder head casting as it was induction hardened in order to withstand the higher combustion temperatures of lead free fuel. You need to understand the reason for the necessity of installing lead-free fuel compatible hardened valve seat inserts into the cylinder head. When valves are reground and their seats in the cylinder head recut, the old deposits of Tetra-Ethyl-Lead remaining from the era of leaded fuel are removed. Without Tetra-Ethyl-Lead to both cushion and lubricate the valve seating surfaces, the head of the valve impacts upon the raw cast iron of the valve seat and forms a series of micro-welds which are torn loose the next time that the valve opens, resulting in the erosion of both the cast iron valve seat and the valve. This also occurs when a cast iron cylinder head that was induction hardened has had new valve seats cut into its surfaces, removing the layer of hardened metal. This is because in induction hardening, the surface is heated by a high-frequency alternating magnetic field that generates heat in the surface of metal before being quickly quenched, resulting in a hardness penetration of 0.060-0.080 inch below the surface. The ease and speed of this process makes it the favored technique of Original Equipment production. A lead-free fuel compatible hardened valve seat insert eliminates these problems. |
| Steve S. |
| Steve, All completely irrelevant as the CAM1106 head was never fitted in the UK! Adam, No, there is no way to identify hardened seats without cutting them - even if the head has inserts fitted, they may not be hardened ones. Original machining also looks similar to inserts! |
| Chris at Octarine Services |
| Chris- Opps! You're right about the CAM 1106 head casting being a North American Market item. However, its UK/European market equivalent was the 12H 4736 head casting which was found on engine numbers 18V-846-F-H and 18V-847-F-H, all of which it was Original Equipment for. Beyond that, the above technical information still applies. Not as irrelevant as you supposed. |
| Steve S. |
| Chris- How's this? Better? The MGB engine used four basic cylinder head designs during the course of its career. The fourth version of the cylinder head was a slightly modified version of the 12H 4736 cylinder head first introduced on the Austin Marina and also used on UK/European market MGB engine numbers 18V-846-F-H and 18V-847-F-H, all of which it was Original Equipment for. It reverted to the original smaller 1.565" intake valve size in redesigned form (BMC Part# 12H 4211) that was used on the first two cylinder head castings, but had offset oil feed in the rear rocker shaft pedestal (BMC Part# 12H 4737) in order to accommodate redesigned cooling passages to assist in preventing overheating of the exhaust valve of the rear cylinder. This redesign necessitated the relocation of the oil passage in the rear rocker shaft pedestal, which means that if you should choose to install it on an earlier engine block you're going to need the later rear rocker shaft pedestal with the offset oil port (BMC Part# 12H 4737). The North American Market cylinder head can be readily identified by its casting number CAM1106 and is commonly found on engine numbers 18V-797-AE-L, 18V-798-AE-L, 18V-801-AE-L, 18V-836-Z-L, 18V-837-Z-L, 18V-802-AE-L, 18V-883-AE-L, 18V-884-AE-L, 18V-890-AE-L, and 18V-891-AE-L, all of which it was Original Equipment for. These cylinder head castings are sometimes referred to as "lead-free" cylinder head castings as they were both induction hardened in order to withstand the higher combustion temperatures of lead free fuel. However, one should be aware that once the valve seats are remachined, the valve seats are no more tolerant of lead-free fuel than those of the earlier cylinder head castings are and that lead-free fuel tolerant valve seat inserts should be installed. Does this pass your sharp-eyed scrutiny? Comments are always welcome when they lead to improvement! |
| Steve S. |
| Steve, As far as I know, no UK market 12H4736 heads had induction hardened exhaust seats. The UK still used leaded fuel well past the demise of MGB production. Oh and in the UK it was the Morris Marina - the Austin badge was for the US market - and only the 1800 version used the B series engine. |
| Chris at Octarine Services |
| Chris- The 1800cc engines on the North American Market Marinas used an induction hardened 12H 4736 cylinder head. Perhaps the UK/European market head casting wasn't induction hardened. If this was the case, I would expect that they would have different part numbers. What does your parts list say? |
| Steve S. |
| Part numbers and casting numbers are different! The casting number 12H4736 is part number 12H4735 for UK cars. It may well have had a different part number for the US market as it had extra machining in the form of the air injector ports, the rear water take off for the water operated choke on the ZS carb and the induction hardening of the exhaust seats. The only listing I have of the US spec heads doesn't list the factory part numbers but does show that post 1974 heads are different part numbers for US & UK versions. |
| Chris at Octarine Services |
| Chris, the US heads of these period had the exhaust port air injection opened and threaded, the casting for other markets (1974 on) was not machined at the ports. There was also a different volume of chamber volume, ~ 39 ccm for US via ~ 42.5 for the rest. May be someone can check the seats of a non machined head of this production run to veryfy the material used. Ralph |
| Ralph |
| Hiya guys Thanks for all your comments, even though they have veered off over my head hahaha So i assume that the answer is no, it is not possible to visually identify a UK unleaded head? Thanks again Adam |
| Adam Cooper |
| In a nutshell - no ... 8-) |
| Chris at Octarine Services |
| Steve, The US head was part number BHM1062 - introduced in December 1974 at the same time as the new camshaft CAM1156. |
| Chris at Octarine Services |
| If the factory ever made heads with induction hardened seats for these cars, I've never seen any. I would be interested to know if Peter Burgess has seen any of these versions, as I know he's undoubtedly seen more examples than I have. Either way, I can't believe they are common, if indeed any actually exist. Sean |
| Sean Brown |
| I should mention that in addition to Peter's wonderful book (which I highly recommend), there is a short article I prepared on my website to illustrate the process of seat installation which may help some members. http://www.flowspeed.com/seat-recession.htm Sean |
| Sean Brown |
| Sean, According to Clausager, all North American heads after December 1974 were lead free tolerant. How would you know if you had seen one? |
| Chris at Octarine Services |
| Chris- Thanks! Another mystery solved, thanks to this BBS. Now, can you explain why some of the 12H4736 head castings have a water port drilled at the rear of the head for a water choke, but others weren't? What engines were the non-water-port head used for? Marinas, perhaps? Sean- The seats as such weren't hardened, the whole head was! In induction hardening, the surface is heated by a high-frequency alternating magnetic field that generates heat in the surface of metal before being quickly quenched, resulting in a hardness penetration of 0.060-0.080 inch below the surface. The ease and speed of this process makes it the favored technique of Original Equipment production. Unfortunately, when a cast iron cylinder head that was induction hardened has had new valve seats cut into its surfaces, this removes the layer of hardened metal. A lead-free fuel compatible hardened valve seat insert eliminates this problems. |
| Steve S. |
| I don't know how (or if) MG did this, but I'll relate my experiences. 1) On Ford heads I've worked with that have had this process done, it is done only in the valve seat areas. They use a special "electrode" (I'll call it that because I don't know the proper term if that is not it) which is held in the seat area. Then the head is treated as Steve explains. This leaves a hardened surface in the seat area that is again, as Steve explains. When you try to install hardened exhaust seats in this type of head the initial cutting action of the seat cutter is difficult. The material is very hard in this region and it's quite noticeable! 2) This has never been my experience with MGB heads of any kind. I will say that when porting, I have sometimes found that in the exhaust ports (at least that's where I notice it), the surface seems hard to start, with a softer parent metal. In this case Steve could be right! However the surface hardening I'm speaking of is definitely nowhere near .060-.080" deep. The deepest I've seen would be possibly .006-.008" AT BEST. I've always attributed this to some kind of high carbon case-hardening phenomenon, but that also seems somewhat silly. I have never noticed this problem in the chambers, or recall it being apparent within the inlet ports, so I can't explain it. I would say if case hardening was done as Steve says, it wasn't done very well, effectively. Sean |
| Sean Brown |
| Steve, The heads with the rear water port were used with the ZS carb which had a water operated choke. I don't know whether the Marina used the same ZS carb or whether at some point in production they deleted the water operated choke as it was troublesome and went back to a manual choke. UK spec late heads have the flat area at the rear of the head but it is not drilled out. Sean, I am not sure that Steve is right about the whole head being induction hardened - but I could well imagine that projections in the exhaust ports will become carbon case hardened - they only see exhaust temperature gas, whereas the chambers would be cooled by the incoming fuel charge. I have seen manifolds glowing red hot - certainly sufficiently hot to case harden! I will do some more research on the nature of the "lead free tolerant" aspect of the NA heads... |
| Chris at Octarine Services |
| If I was buying a cylinder head or a car with an unleaded cylinder head, I would expect the owner to have the invoice from the head/engine rebuilders stating that it had had new exhaust valve inserts, valves and guides etc and had been converted to unleaded spec.... Otherwise it a case of buyer beware. Robert |
| R J Collier |
| Sean- If you're machining recesses into the valve seats in order to install hardened valve seats, then the old hardened valve seats are almost cetainly worn out. If they're worn out, then the hardened metal is worn away, and thus you won't have any trouble machining the recesses for the hardened valve seats. Make sense? |
| Steve S. |
| Steve, I think you're grabbing at straws friend. Even if that were possible, the cutter extends beyond the circumference of the worn seat area sufficiently to encounter un-worn area. I also doubt the entire head is induction hardened, because there is little need for that. The reason Ford (where I've encountered it) uses this process, is because it is a "direct point of wear" hardening process. They don't have to heat treat an entire casting to get a hard wearing surface in just one little area. Call some machine shops in your area and ask them what their experiences are regarding induction hardened seats, I think you'll learn that my experiences are not unique. Chris, If you find anything out regarding this subject, please feel free to e-mail me about it, I would like to know as well. I've seen two marina heads and they were both 2923's. Though it's possible they had been swapped out at some point. I have also seen the heads you're talking about where there is a provision for the water choke but the holes are not drilled. Sean |
| Sean Brown |
| Induction hardening is only applied to specific areas, as Sean states. The induction hardening coil is shaped to affect only the seat. Anybody who has actually ground a valve seat so hardened will know it immediately, as Sean states. In fact, special stones (silicon carbide)were recommended for grinding these, as the regular stones (aluminum oxide) did not like to cut them. Bladed cutters won't cut them, as the induction hardened seat material will even resist carbide. Using Steve's own figures, which may or may not be correct, but which are certainly in the ballpark, You will rarely if ever grind as much as .060-,080 off a hardened seat to correct normal wear. It is extremely rare to take this much off an UNhardened seat, unless it has been run way past no compression. .060 should be good for several "clean-up" regrinds. I have many times reground seats which needed attention, and put the head back on to find that the valves still had 2/3 of the clearance they had when dismantled, or about .010 on a B series. There is some effect of a new head gasket, but certainly not enough to account for cuts of .060, or even .020. I've never met an MG head with hard seats, but I've never cut one later than 74, and the requirement for unleaded did not arrive until 75. I would expect that hardened seats did not appear until then, if ever. By the way, "hardened" is not the requirement for valve seats in unleaded operation. It is a more complex metallurgical thing, which simply happens to also result in cast iron seats being hard; they are in fact "chilled iron", which as a result of rapid quenching converts free graphite in gray iron into carbides. (Yes, the same stuff as tappets, in which hardness is also not the issue, but only a consequence of one suitable material/heat treatment.)The term "hardened seats" is largely a misnomer coming directly from the induction hardening of CI seats. Seat inserts may be the same, or any number of other metals, which may or may not be notably "hard". Many earlier inserts are high nickel steel, or some grade of Stellite, of which there are many; Modern inserts are a powder metal product. FRM |
| FR Millmore |
| OK - I asked Roger Parker (the MGOC tech expert) if he could find out anything about the NA heads from people involved at the time. NA heads post December 1974 WERE lead free tolerant and DID have induction hardened valve seats. 1% tin was added to the molten iron before casting. This led to an issue where the iron touched the mould suffered a changed molecular structure and so additional depth of material was used in modified moulds which was then machined off before the induction hardening process was applied to just the valve seat area, all valve seats. This was a complex process and applied only to the US bound engines. |
| Chris at Octarine Services |
This thread was discussed between 29/01/2007 and 05/02/2007
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