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By Andy Gough
#100244
Hi all . I have just fitted performance cams valves and pushrods to my GT but the pushrods are about 3mm longer than the stock one and there holding the valves open . I left it for an hour to see if the lifters would back off but no valves still open . Anyone else had this ?
Cheers Andy
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By stinkwheel
#100245
I'm no expert on these but aren't they hydraulic tappets? Maybe you need to turn the engine over to circulate the oil?
By Andy C
#100247
Dont know anything about the hydraulic tappets, but wondering if perhaps the crank or pump needs to be in a specific position - perhaps you need to turn the engine a bit, but be very careful if the pushrods are 3mm longer.

Just a thought.
By Bullet Whisperer
#100250
Try with the original pushrods, the hydraulic tappets might have enough 'take up' to work with them. Otherwise, the longer pushrods will need to be shortened a bit.
By Andy Gough
#100256
Hi
I fitted a thinner base gasket / 1mm thinner ,
There's no problem with take up .
I put the standard rods in today and the inlet still held open for a while but did settle in the end and she fired up really nice , don't know what the point of the Hitchcocks rods are really , they just came with the cams but can't for the love of God see why
By Bullet Whisperer
#100258
Hi Andy, the longer pushrods are supposed to compensate for the smaller base circle of the performance cams, but in a few cases I haven't needed them after shortening the cylinder barrels and fitting thinner base gaskets.
By Andy Gough
#100266
Ok thanks . I didn't shorten the barrel in the end just used the thinner base gasket but there's no play at all the the standard rods , you can just just the pushrods at full closed so think I'll just go with that .
Cheers Andy
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By Taurim
#100275
With my shortened cylinder barrel stock pushrods are too short and H's pushrods too long. I shortened H's pushrods with a lathe by the correct amount to have the rocker blocks staying in the middle of the acceptable tolerance before tightening.
Between 1mm and 2.5mm according to H's documentation so I targeted 1.75mm.

Image

H's documentation in a better English than mine ;)

Reassemble with the new pushrods following the reverse of the above sequence. It is important with the pushrod
positioned on top of the lifter with no cam lift, the rocker and rocker housings are then placed on the head with the
fixing screws loosely attached with no pressure. At this stage it would be expected for there to be between 1mm
and 2.5mm gap between the base of the rocker housing and cylinder head. (If the valves are being held open
beyond this, there is too much preload which can be solved with a slightly shorter pushrod). When you then
tighten the 4 fixings this gap will close up. Due to the oil in the lifter, it is very likely that when tightening the rocker
housing the valve will open. You must allow 10 or 15 minutes for the lifter to “bleed” before turning over the
engine. This should then allow the valves to close.

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