thailoz Posted March 27, 2015 Report Share Posted March 27, 2015 Toyota 4K I have had my cam reground and when I fitted it the tappet adjusters are at the limit of adjustment just to get the recommended 0.16" clearance. I have since read that the rocker posts need machining with the difference from stock valve lift to valve lift from ground Camshaft My questions are : 1. What is the stock lift ? 2.How do i calculate the new lift from the cam lift spec ? Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted March 28, 2015 Report Share Posted March 28, 2015 As far as I know they don't grind the 'nose' of the camshaft, as they want to maximise lift. The 'heel' gets ground away so your zero-point for lift is changed and the nose pushes the pushrod further up, as you are experiencing. The measurement you want is nose-to-heel across a stock cam lobe, and the same on the ground cam. The difference will be how much they ground off the heel. That should be the same as taking the stock lift at the cam (or at the valve, which is 1.5 times bigger) and the lift on the ground cam. The difference in lift will be what you need to machine off the rocker posts multiplied/divided by the rocker ratio. Wiki says the stock cam has 338thou lift at the inlet valve, and 356thou at the exhaust valve. Say you bought a cam with 405thou lift at the valve... For the inlet the valve is lifting an extra 67thou, so the cam has been ground 67/1.5 which is 45thou. If you machine 45thou off the rocker post it should bring your adjustment screws up by that much and back to stock level. That's my take on it, but I've never had a cam wild enough to have to do it. Quote Link to comment Share on other sites More sharing options...
coln72 Posted March 28, 2015 Report Share Posted March 28, 2015 Never bothered either...... Quote Link to comment Share on other sites More sharing options...
thailoz Posted March 28, 2015 Author Report Share Posted March 28, 2015 (edited) Thank you for your reply My Cam card says intake cam lift 0.284" exhaust cam lift 0.284" so if I multiply that by 1.5 it gives me 426 valve lift 426 - 338 = 88 88 / 1.5 = 58.7 thou to be ground of the rocker posts that's about 1.5 mm is that correct ? Edited March 28, 2015 by thailoz Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted March 28, 2015 Report Share Posted March 28, 2015 That seems right- Take a look at the rocker adjustment screws and see what 1.5mm would do to them. Are the rockers about horizontal when the valve is closed, that is, paralell to the block deck as the motor is slanted. or even pointing slightly upwards towards the valves would be better??.... skimming the head and valve stem length also affects all of this, and what you don't want is the rocker wiping across the edge of the valve stem or the rocker face.. Ideally I think they should start facing slightly upwards and go through the 'horizontal' to face downwards with the valve open. It will be interesting to see if you stick with 16thou tappet gap. Mine were noisy at that & I closed them back to stock. Quote Link to comment Share on other sites More sharing options...
thailoz Posted March 28, 2015 Author Report Share Posted March 28, 2015 Thanks for that will check it later I have built an Engine test bed so will be running it up in the next week or two at the moment just using the asian carby with a foam air filter and very short 2 inch exhaust. the motor will go in my Lotus 7 replica when done with a T50 box and ke 30 rear axle . I didn't strip the donor nor have i heard it run the car corolla it came from had been flooded so had to replace all the electrics (dizzy.coil alternator etc ) been a mission here in Thailand as i speak very little Thai so thanks again for you help . Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted March 28, 2015 Report Share Posted March 28, 2015 If you're going to motorsport the kit car, don't forget to look up Billzilla's page on how to turn the K50 gearbox into a close-ratio. It will be a challenge doing it in Thailand! Quote Link to comment Share on other sites More sharing options...
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