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DIY Classic Mini Cylinder Head Articles
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C-AEA526 DUAL VALVE SPRING FITTING INSTRUCTIONS
(Technical Information)
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This valve spring set has been developed to fit standard sized top caps, and cope with high rpm and high valve lifts without crushing of up to 0.570” without modifications, when fitted to a cylinder head that has standard or near standard valve spring heights. However, where possible, it is always advantageous to correct and match the valve spring heights (measured from the spring seat in the head to the underside of the spring retainer cap), as these will vary particularly where new valve seats are cut. The standard heights for pre-A+ heads are approximately 1.32” to 1.37” for small-bore types, 1.40” to 1.42” for large-bore types, and A+ heads 1.35” to 1.38” for small-bore types and 1.35”-1.37” for large-bore types. However, ...
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C-AEA527 DUAL VALVE SPRINGS FITTING INSTRUCTIONS
(Calver's Corner)
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See bottom for useful part numbers.
This valve spring set has been developed to fit standard sized top caps, and cope with racing rpm and high valve lifts without crushing of up to 0.570” without modifications, when fitted to a cylinder head that has standard or near standard valve spring heights. However, where possible, it is always advantageous to correct and match...
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C-STR1057 Group A Turbo head gasket
(Calver's Corner)
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This gasket was originally developed by Howley Racing way back in the mid eighties for what was then part of the factory Rover Group racing effort - the Group A Metro Turbo. The engines developed by Howley Racing were giving 220+bhp and 185lb ft running 16.4psi boost - quite a chunk of power in a car little bigger than a Mini! Despite 10" wide sticky slicks, the engine chirped the tyr...
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Competition Cylinder Heads
(Technical Information)
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A selected range of modified cylinder heads are available to suit a wide
variety of applications. All port and chamber modifications are carried out by
experts to current state of the art specifications. Therefore, actual
specifications may alter slightly as gas flow and port velocity efficiency
improvements are developed. Where large bore heads are used on small bore
engines (i....
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Competition head stud and nut kit
(Technical Information)
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This kit has been produced by Mini Spares to reduce head gasket problems
on performance orientated engines, especially those utilising large over bore
sizes.Standard type head studs and nuts are mass produced which unfortunately compromises the specification of the end product. Worst affected are the threaded portions which create problems during torque-down; thread deformation, stud ...
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Cylinder head - Combustion chamber shape
(Calver's Corner)
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Since the reasonably recent publishing of a certain Mini tuning, performance and maintenance guide that has strangely coincided with a batch of new readers/devotees of a certain prolifically quoted 'bible' on A-series engine modifications - the subject of all things cylinder head have bounced into the fore once more. Something I was heavily canvassed over at this years (2003) ...
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Cylinder head - Identification by casting number
(Calver's Corner)
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Number
Inlet dia.
Exhaust dia.
Nominal cc
Standard fitment
2A628
1.0625"/26.99
1.00"/25.4
24.5
850, 998 Mini & 948 Sprite
2A629
1.0625"/26.99
1.00"/25.4
24.5
948, A35 & Morris Minor
12A1456
1.0625"/26.99
1.00"/25.4
24.5
850, 998 Mini & 948 Sprite
12G202
1.156"/29.36
1.00"/25.4
26.1
997 Cooper, Austin 1100 Mk
CAM4180
1.0625"/26...
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Cylinder head - Min Tec head range
(Calver's Corner)
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Cylinder head - Min Tec head range
I'm often asked about the range of cylinder heads I do for Mini Spares/Mini Mania, so here's the low-down…
Although the following range of heads accommodate specific fitments - like pre-1992 where by-pass hoses and heater take-offs on the clutch end of the head are used and post-1992 where neither of these exist, and on SPi (...
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CYLINDER HEAD - Suitability basics
(Calver's Corner)
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See bottom for useful part numbers.
Whatever else owners do to their Minis by way of interior/exterior modifications or none at all, a very large proportion desire and search for an increase in engine performance. Now this may not be super-sonic speed-inducing power, it could just as well be for maximum economy. In either case, it's the engines volumetric efficiency (VE) under scrut...
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CYLINDER HEAD - Torque-down and head gasket problems
(Calver's Corner)
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A regular visitor to the message board, and something I am asked frequently about in my other incarnations for other technical media. Generally when something has gone badly wrong! Many folks have just as many ways of dealing with the following subjects - all can and will claim their way has worked for them for the proverbial millennia - so a few words as a basic reference and guide as I see ...
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CYLINDER HEAD - Unleaded Fuel Use
(Calver's Corner)
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See bottom for useful part numbers.
The specter of 'unleaded fuel only' - instigated in UK on January 1st 1999 and seemingly from decades ago across the rest of the world - seems to be forcing more and more folk into frightened, panic orientated action. And Mini owners are featuring heavily in this. The situation not at all being helped by all sorts of conflicting information from 'le...
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Cylinder head - What can easily be achieved
(Calver's Corner)
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Cylinder head - What can easily be achieved
The engine build I recently covered in previous Mini Magazine issues developed into a bit of an ongoing 'project'. During a discourse with the editorial staff at Mini Mag, it was decided the build feature presented an ideal opportunity to demonstrate just exactly what such an engine build is capable of in days where it's generally b...
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Cylinder Heads
(Technical Information)
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Everybody has their own opinion on this subject. The most experienced people will tell you that the best way to maintain your engine performance is to accept the fact that valve jobs need to be done 2 or 3 times more often than rings and bearings! And this data base was concluded when leaded gas was the norm! Now that unleaded is all you can get, valve jobs are needed even more often!The purpose o...
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Cylinder Heads - About Min Tec heads
(Calver's Corner)
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Cylinder Heads - About Min Tec heads.
Terminology -
VFM - Value For Money
CR - Compression Ratio
VE - Volumetric Efficiency
'Modified to give maximum performance gain for cost. Combustion chambers, inlet and exhaust ports extensively re-worked. Smoothed finish in ports - not mirror-finish polished to minimise drag. Four-angle valve seats in head. Cooper S size valve...
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High lift rocker assembly, C-AHT436
(Technical Information)
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SPECIFICATION: Material is drop forged EN16 with the
valve pad face hardened to 52.5-55 on the Rockwell C scale. RATIO: Rocker
ratio is 1.5 as opposed to 1.25 of the standard rocker.
TAPPET CLEARANCE SHOULD BE 3 THOU MORE THAN STANDARD. ON REALLY HIGH LIFT
CAMSHAFTS AN EXTRA 2 THOU AGAIN MIGHT BE BENEFICIAL.
Ensure that posts, spacers and rockers are evenly distributed...
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Offset rocker bushes, C-AEG644
(Technical Information)
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FITTING INSTRUCTIONS
Using these bushes it is possible to achieve an increase in valve lift of upto 0.030". They must be pressed into the rocker with the thick section pointing forwards, ie. toward the rocker pad. It is advisable to use bearing-fit compound (Loctite) to ensure the bush does not rotate in use, taking up wear in old rockers. Once fitted, they need to be reamed out to 9/16", ...
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Rocker Gear
(Technical Information)
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The new generation of short period, high lift cams have been developed to give the best results in large bore engines when used in conjunction with 1.5 ratio, hi-lift rockers. For the small bore range, the stock 1.3 ratio is optimum. In certain instances ratios of 1.7 to 1 are of benefit - but is really only applicable to fully developed race engines.
12G12211.3-1 ratio "Cast" rocker. Reprodu...
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Rocker gear - General compendium
(Calver's Corner)
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Rocker gear - General compendium
Whether you’re building a solid road performer or fire-breathing monster, the main goal is to improve air/fuel flow into the engine. The more you can get in, the more power you can get out. Cheapest chunk of power improvement comes from sorting the asthmatic manifolding and exhaust by applying a stage one kit. Then what?
Conside...
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Stage 2, Budget big bore head
(Technical Information)
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STAGE TWO SPEC. BUDGET LARGE BORE CYLINDER HEAD AEG592 Inlet valve : 35.6mm (1.401") diameter, standard ‘S’ spec. material CAM4601 Exhaust valve : 29.3mm (1.156”) diameter, latest lead free spec. material 12G1963 Guides : OE specification cast iron, bullet nosed C-AEA526 Valve springs : Nominal 180lb progressive ra...
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Valve Guides - Materials and Usage
(Calver's Corner)
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See bottom for useful part numbers.
Material choices for guides are down to two distinct types - cast iron and bronze. Yes, cast iron. NOT steel as described in many adverts and by vendors. Never have been, never will be. These are as fitted to the various A-series cylinder heads as standard in all applications. Cast iron is used because it is a very dissimilar metal from a...
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Valve Stem Keepers
(Technical Information)
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Call them cotters, collets or keepers, these little items are often overlooked during a head rebuild. If yours are worn and need to be replaced, make sure you order the right ones. Minis used three different versions over the years.
In general, the earliest cars used valves with a single, wide groove in the valve stem. Often called the "normal" valves, the later, pre-A+ valves u...
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