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MG MGB Technical - blown head gasket

Hi you all I'm back again with more news about the problem that i have been having with my 72 b-gt.I got the head re worked and installed with new payen head gasket.took compression readings again and found #2 still at 0 psi. Pulled the engine out and took to machinist to check it out. What he found was that #2 piston was broken at the ring groove. he asked me if i had cooked it and i told him i was sure that i had not. the pistons are .020 over and i am considering going to .030 over with matching bore. now the big question what pistons and rings do you recommend? I believe the Pistons and rings are aftermarket. He showed me one he pulled from a mercedes and it had the same failure. has anyone had this happen to them and what pistons were being used? any advice will be appreciated. thanks again.
RP Padilla

So the piston crown was not moving with the rod?
Art Pearse

RP-
It all depends on what kind of engine you're building. If the engine is stock or mildly warmed-over, then the County brand pistons are sufficient, and reasonably priced. If you're building an engine with a fairly hot camshaft, such as a Piper 285, a bit more strength is a good idea, and for that I'd go with AE/Hepolite pistons, despite that fact that they're somewhat heavier. If your engine is supposed to be a really strong performer with a hot camshaft and a Peter Burgess Fast Road specification cylinder head, then take a hard look at Accralite's forged pistons.

The piston rings are also significant, although often an overlooked matter. Buying piston rings on price alone is very bad idea. Both Deves and Hastings are excellent quality items, but I feel that Federal Mogul's Goetz subsidiary has them both beat.
Stephen Strange

The piston was still intact and moving with the rod/ It had about two inches of the ring grooves broken and the rings also looked as if they were crystalized. I will be installing 270C cam with new lifters. The head will be converted from single valve springs to the double heavy duty type. New high flow oil pump with new higher pressure (5#) relief spring. Will the AE/Hepolite pistons be ok or do you recommend the county brand? Where is the best place to get the pistons and rings, main and rod bearings? What else can I do to make this engine more reliable?
RP Padilla

RP-
Understand that a large increase in oil pressure will not, in and of itself, result in a large increase of oil flow through the system. This is due to the fact that oil pressure increases only exponentially with oil flow, thus the increase in oil flow will actually be very small. A high-volume / high-pressure oil pump will require more power in order to function and increase stress and consequent wear on both the gear teeth of its spindle gear and the teeth of its drive gear on the camshaft, as well as increasing torsional stress upon the drive shaft of the oil pump. Because such an oil pump is of additional benefit, albeit minor, only at low engine speeds when employed in the system of an Original Equipment-specification engine block, it will do little for any engine other than one whose oiling system has been comprehensively modified to suit an ultra-high performance specification. Racing engines operate at much higher engine speeds than a streetable engine, and the increased oil pressure reduces the tendency of the oil pump to cavitate at its correspondingly higher operating speeds. Racing engines also have a greater amount of clearance between their crankshaft main bearings and the journals of their crankshafts in order to reduce the possibility of overheating their lubricating oil, and that application is what a high flow volume / high pressure oil pump is intended for. However, there is a downside to this approach: because of the greater loss of oil volume and oil pressure that results from the greater clearances, the bushings of the rocker arms often suffer from decreased lubrication, especially at elevated engine speeds where the crankshaft can centrifuge oil outward into the crankcase. This forces racers into a conversion to special rocker arms that are supported by needle roller bearings. Now you know why they use them.

You can get AE/Hepolite pistons from Advanced Performance Technologies. They have a website at http://aptfast.com .

You can get the Goetze piston rings through any Federal Mogul vendor.

I'd recommend King bearings. Unfortunately, Original Equipment indium type Vandervell VP2 bearings have become increasingly hard to find, but there is a newer technology alternative which is acceptable for high performance use. These consist of an Allecular material of an aluminum, tin, silicone, and copper-plus alloy that is bonded onto a high strength steel shell. Because this material is an alloy, it maintains its properties throughout its entire depth, delivering consistent and reliable performance. Since King’s Allecular bearing layer is much thicker than the babbitt overlay (.015" vs. .0008") of tri-metal bearings, it provides eighteen times more embedability than that of a tri-metal bearing so that it can catch and hold particles so that they do not scratch the journals of the crankshaft. This is especially true for those particles that are over .0004" (.01016 mm) in diameter which are the cause of most of the damage to crankshaft journals. Other manufacturers produce bearings whose wall thickness at the crown can vary by as much as +/- .00025" (.0635 mm). King bearings are produced to a finer tolerance that permits no more than +/- .0001" (.00254 mm) variation of the desired thickness. The Allecular material’s melting/fatigue point is over 1,100 Degrees Fahrenheit (593.3 Degrees Celsius), which is almost three times that of the thin babbitt overlay in a tri-metal bearing (400 Degrees Fahrenheit / 204 Degrees Celsius). This means added protection against localized overheating due to misalignment, overloading, low oil pressure, loss of coolant, etc. The King bearing (King Part # MB520/1 for crankshaft main journals #1, #3, & #5 (Note: Grooved Bearing); King Part # MB520/2 (Note: Ungrooved Bearing) for crankshaft main journals #2 & #4; King Part # CR4403 (Note: Ungrooved Bearing) for the big end of the connecting rods has a track record of excellent performance when subjected to the rigors of racing use. King Engine Bearings has a website at: http://www.kingbearings.com .

If you're going to use a camshaft with more lift, then I'd recommend not relying on the dual valve springs alone to control valve float. A set of Crane tubular chrome-moly pushrods are a wise insurance policy. Unlike Original Equipment pushrods, tubular chromium-moly alloy pushrods do not flex at the higher engine speeds that an enhanced-performance street engine can often achieve, plus they have less reciprocating mass and thus will give more accurate valve timing at high engine speeds. This is a problem for both the early short pushrods (72 grams, BMC Part # 11G 241) used in the 18G, 18GA, 18GB, 18GD, 18GF, 18GG, 18GH, 18GJ, and 18GK engines and the later long pushrods (88 grams, BMC Part # 12H 1306) used in the 18V engines as they tend to deflect as much as 5/64” (1.98438mm) at high engine speeds, even when new. This deflection is partially the result of the camshaft being offset away from the cylinder head in order to provide room for the siamesed intake ports while allowing the use of short arm rocker arms in order to reduce their rotational mass. The greater angularity resulting from the earlier long barrel tappet / short pushrod combination created such high side-thrust loadings on the walls of the outer bores in which the tappets rotated that it was necessary to incorporate an oiling cavity into the design of the tappet to ensure adequate lubrication at high engine speeds and so ensure its rotation. In addition, the greater the angularity of the pushrod, the greater its arc motion becomes. The high load area on the pushrod moves closer to the tappet as the tappet travels up the ramp of the camshaft. This makes it even more important to use a tubular pushrod design when using large roller bearing diameters, increased valve lash, very high engine speeds, high rocker ratios, rapid valve train acceleration and high spring pressure. The reduced angularity of the longer pushrods (10.787” / 273.99mm) that are used with shorter, lighter bucket tappets results in decreased side-thrust loadings on the tappets and thus enhances their lifespan, as well as also permitting them to rotate more freely at high engine speeds.
The shorter length (1.500” / 38.1mm), lighter (47.2 grams) bucket tappets (BMC Part # 2A 13) introduced on the 18V-584-Z-L engines will also assist in the goal of reducing reciprocating mass. Due to their having identical diameters of 13/16” (.8125”), the early long barrel tappets (79.7 grams, BMC Part # 1H 822) and the later short bucket tappets are interchangeable when paired with their length-appropriate pushrods. The later Original Equipment short bucket tappet / long pushrod (10.656” / 270.662mm) assembly is 13% lighter than the earlier Original Equipment long barrel tappet (2.298” / 58.3692mm) / short pushrod (8.750” / 222.25mm) combination used in the earlier 18G, 18GA, 18GB, 18GD, 18GF, 18GG, 18GH, 18GJ, and 18GK engines. Crane’s lighter (64 grams) chromium-moly tubular pushrods (Crane Part # 905-0004) will also reduce inertia in the reciprocating mass of the valve train by about 20% when compared to that of the later Original Equipment 18V short bucket tappet / long pushrod combination and by 30% when compared with the earlier Original Equipment 18G, 18GA, 18GB, 18GD, 18GF, 18GG, 18GH, 18GJ, and 18GK engines’ long tappet / short pushrod combination. This reduction of reciprocating mass permits most high-lift camshaft lobe profiles to be employed without the expedient of using stronger valve springs in order to prevent valvetrain float at the upper end of the powerband, thus reducing wear of both the tappets and the lobes of the camshaft.
The hollow, tubular construction of the Crane pushrods also endows them with the structural advantage of greater rigidity over that of the Original Equipment solid pushrods. Because the tappets of the B Series engine are offset outward from the rocker arms, the pushrods are forced to reciprocate at an angle that increases as the tappets move upward. As this angularity increases along with tappet lift, so does the arc motion of the upper end of the pushrod, and thus bending stress on the pushrods also increase along with compression load, especially in the case of solid pushrods employed with high-lift camshaft lobe profiles. Pushrod deflection is the consequence. In turn, deflection results in the shortening of the effective length of the pushrod, and thus the accuracy of the valve lift is sacrificed. The superior rigidity of tubular pushrods all but eliminates this unwelcome deflection, as well as moving their period of harmonic vibration to an engine speed that the Original Equipment B Series engine cannot attain, thus ensuring not only accurate valve timing, but reducing fatigue stresses on the valve springs. This also means that crankshaft vibration transmitted through the drivetrain is less likely to interfere with the precision movement of the camshaft, thus permitting the engine to attain the benefits that the engineer designed into the lobe profile of the camshaft. Both end fittings are heat-treated, making for superior wear characteristics. Crane can also supply them in custom lengths if necessary in order to compensate for skimming of the deck of the engine block or of the cylinder head. Their website can be found at http://www.cranecams.com/ .
Stephen Strange

This thread was discussed between 16/04/2011 and 17/04/2011

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