HoHoHo, to Wisconsin we go....(well my block anyway)
02-14-2008, 07:16 AM
#17
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I haven't performed this operation on a motor yet, but my understanding is that notching the oil intake holes is required when using a higher lift cam. Since the tappets are hydraulic, there is some play in there, which is why the S4 and GT's can use the same tappet even though the GT has more lift. Rumour has it that there is enough hydraulic adjustment in them to accomodate an additional half mm increase in lift over a GT cam without modification. The B1's however are 2mm above a stock S4, 1mm above a stock GT, which takes them out of the safety zone, by putting the oil fill hole .5mm above the factory range. By putting a 1mm vertical notch in the lifter just below the oil hole, even though the hole itself will be closed off by the lifter bore, the notch will still be in the lifter oil feed journal, and supply the necessary oil pressure up into the oil fill hole.
02-14-2008, 08:49 AM
#18
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Cam lift itself do not have much to do with lifter notch. Its how that cam lift is achieved. Easiest way to achieve it is to take material away from cam base lobe. This raises lifter up when it follows cam base lobe. There is groove in head which feeds oil into lifter though hole on lifters side. If this hole isn't at correct height in head during cam base lobe lifter will not get pressurised oil feed it needs to function properly. Easiest way to get around this problem is to make small notch downwards below lifter hole. This will allow oil to flow into lifter even though hole itself is above oil feed groove in head.
Lash caps are needed if cam base lobe is made so small that lifter cannot take up slack space between cam lobe and valve. Byt taking off for example 2mm from cam base lobe lifter would need to extend this same 2mm further than before unless something is added between cam and lifter or lifter and valve. Adding 7xmm piece between llifter and valve brings lifter back to its normal operation range. But this do not rectify oil feed problem to lifter. So I have to dissagree with you on this John. Its cam base lobe change which causes need for lifter mod, not lash caps.
Third thing to consider is how much further down valve can be pushed before spring will stack up and do not allow valve to go further down despite cam pushing it through lifter. There is probably more than 2mm in valve spring to work with so its not a problem. From valves point of view it doesn't matter that cam base lobe has less material as lifter and possible lash cap will take up additional space and valve can't go higher up anyway when its closed. Highest lift point on cam will just result same amount of extra lift than what was removed from cam base lobe.
Lash caps are needed if cam base lobe is made so small that lifter cannot take up slack space between cam lobe and valve. Byt taking off for example 2mm from cam base lobe lifter would need to extend this same 2mm further than before unless something is added between cam and lifter or lifter and valve. Adding 7xmm piece between llifter and valve brings lifter back to its normal operation range. But this do not rectify oil feed problem to lifter. So I have to dissagree with you on this John. Its cam base lobe change which causes need for lifter mod, not lash caps.
Third thing to consider is how much further down valve can be pushed before spring will stack up and do not allow valve to go further down despite cam pushing it through lifter. There is probably more than 2mm in valve spring to work with so its not a problem. From valves point of view it doesn't matter that cam base lobe has less material as lifter and possible lash cap will take up additional space and valve can't go higher up anyway when its closed. Highest lift point on cam will just result same amount of extra lift than what was removed from cam base lobe.
02-14-2008, 08:59 AM
#19
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So I have to dissagree with you on this John. Its cam base lobe change which causes need for lifter mod, not lash caps.
If the base lobe is not changed, but you run a high lift cam (ie. welded) no notch is needed.
02-14-2008, 12:15 PM
#20
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Got it. For some reason I was envisioning this upside down. (OHV)
In order for the gap (or extra tolerance) created by the reduced base circle on the cams to be closed, allowing the cam lobe to ride on the crown of the tappet, the tappet rides on top of the lash cap which rides on the valve stem. The "boost" that the tappet is getting from the lash cap lifts it up out of the lifter bore enough so the oiling hole is out of alignment (too high). The notch beneath the hole solves the problem.
Hows that for restating exactly what the both of you just said?
In order for the gap (or extra tolerance) created by the reduced base circle on the cams to be closed, allowing the cam lobe to ride on the crown of the tappet, the tappet rides on top of the lash cap which rides on the valve stem. The "boost" that the tappet is getting from the lash cap lifts it up out of the lifter bore enough so the oiling hole is out of alignment (too high). The notch beneath the hole solves the problem.
Hows that for restating exactly what the both of you just said?