Hydraulic lifters, technical questions.
Discussion
I've done a bit of Googling, but can't find much of use.
If the oil viscosity changes from when cold to hot does it affect the amount of valve lift?
I reconditioned a diesel head for myself recently, as it's what I normally do anyhow I couldn't resist doing a bit of minor port work (nothing special, just a quick clean up, take some sharp corners off etc), reground the valves and the seats, put a 3 angle on where I could, but also took the valve seat out to true width. Doing this means the valve sits deeper by 1mm, so does this mean total valve lift has gone up by 1mm? I was worried the lifter wouldn't take this, but it seems to run ok. How do they know how far to lift the valve?
If the oil viscosity changes from when cold to hot does it affect the amount of valve lift?
I reconditioned a diesel head for myself recently, as it's what I normally do anyhow I couldn't resist doing a bit of minor port work (nothing special, just a quick clean up, take some sharp corners off etc), reground the valves and the seats, put a 3 angle on where I could, but also took the valve seat out to true width. Doing this means the valve sits deeper by 1mm, so does this mean total valve lift has gone up by 1mm? I was worried the lifter wouldn't take this, but it seems to run ok. How do they know how far to lift the valve?
227bhp said:
I. How do they know how far to lift the valve?
Depends on the particular valvetrain.You make no mention of pushrods.
The oil pressure from the oil pump fills the tappet, as mentioned in a previous post. This eliminates the tappet to valve clearance when the tappet is on the base circle of the cam lobe. When the tappet is on the cam ramps/flank/nose the oil galleries do not line up, so no extra pressurised oil is available to extend the tappet's valve stem seat.
Most hydraulic followers have a charge chamber which is normally full of oil fed from the oil charge drillings. The central hydraulic mech is internally sprung so that the tip is kept in contact with the valve and cam lobe. Oil pressure will fill the hydraulic mech centre via a one way ball valve, as soon as the cam starts to lift the ball valve shuts and the oil has nowhere to go, a very tiny amount of oil bleeds out down the sides of the hydraulic mech, this alows the follower to shrink by a tiny amount and adjust its length as parts expand when the engine heats up, as soon as the follower enters its latent phase pressurised oil is drawn into the hydraulic mech again to replace any that may have bled out during the lift phase.
A dirty ball valve can cause the oil to leak out on the lift phase or when the engine is not being used, this can lead to rattly followers.
Oil viscosity has an immeasurably small affect on valve lift, once the initial ramp that is designed to close the one way ball valve is passed and the follower is hydraulically locked valve lift is equal to cam lift (multiplied by any rocker/finger follower ratio).
Dave
A dirty ball valve can cause the oil to leak out on the lift phase or when the engine is not being used, this can lead to rattly followers.
Oil viscosity has an immeasurably small affect on valve lift, once the initial ramp that is designed to close the one way ball valve is passed and the follower is hydraulically locked valve lift is equal to cam lift (multiplied by any rocker/finger follower ratio).
Dave
damned auto correct led to this edit
Edited by DVandrews on Thursday 1st March 09:42
227bhp said:
but also took the valve seat out to true width. Doing this means the valve sits deeper in the head by 1mm, so does this mean total valve lift has gone up by 1mm? I was worried the lifter wouldn't take this, but it seems to run ok. How do they know how far to lift the valve?
No-one tackling this bit then? 
If valve lift was (say) 8mm before and i've sunk the valve in 1mm would I now have 9mm lift?
It's DOHC and rockers if it matters...
227bhp said:
I've done a bit of Googling, but can't find much of use.
If the oil viscosity changes from when cold to hot does it affect the amount of valve lift?
I reconditioned a diesel head for myself recently, as it's what I normally do anyhow I couldn't resist doing a bit of minor port work (nothing special, just a quick clean up, take some sharp corners off etc), reground the valves and the seats, put a 3 angle on where I could, but also took the valve seat out to true width. Doing this means the valve sits deeper by 1mm, so does this mean total valve lift has gone up by 1mm? I was worried the lifter wouldn't take this, but it seems to run ok. How do they know how far to lift the valve?
No, lift will remain unchanged, but 1mm is a hell of a deep seat cut which is clearly recessed the valve and potentially the lifter internals could bottom out with the risk of hanging the valve open.If the oil viscosity changes from when cold to hot does it affect the amount of valve lift?
I reconditioned a diesel head for myself recently, as it's what I normally do anyhow I couldn't resist doing a bit of minor port work (nothing special, just a quick clean up, take some sharp corners off etc), reground the valves and the seats, put a 3 angle on where I could, but also took the valve seat out to true width. Doing this means the valve sits deeper by 1mm, so does this mean total valve lift has gone up by 1mm? I was worried the lifter wouldn't take this, but it seems to run ok. How do they know how far to lift the valve?
Just depends how much travel the internals had to account for that sort of work.
TBH if a machine shop ever cut seats that deep on an otherwise good head, I'd be wanting them to replace all the valve seats or supply me a new head.
Surely if you have the correct clearance on the back of the lobe, then the valve will only lift by the size of the lobe (plus the valve clearance)
If you have lowered the head of the valve into the head by 1mm, this would mean you have had to increase the clearance by 1mm. If the valve used to move 8mm, it would still move 8mm, particularly on a DOHC.
And would the viscosity not be irrelevant, as operating temp is operating temp? - my Citroen said you had to check the valve clearances when hot, just above the exhaust, on a horizontally opposed flat 4, with the oil dribbling out.
If you have lowered the head of the valve into the head by 1mm, this would mean you have had to increase the clearance by 1mm. If the valve used to move 8mm, it would still move 8mm, particularly on a DOHC.
And would the viscosity not be irrelevant, as operating temp is operating temp? - my Citroen said you had to check the valve clearances when hot, just above the exhaust, on a horizontally opposed flat 4, with the oil dribbling out.
stevieturbo said:
No, lift will remain unchanged, but 1mm is a hell of a deep seat cut which is clearly recessed the valve and potentially the lifter internals could bottom out with the risk of hanging the valve open.
Just depends how much travel the internals had to account for that sort of work.
TBH if a machine shop ever cut seats that deep on an otherwise good head, I'd be wanting them to replace all the valve seats or supply me a new head.
That's because you don't understand what's been done and why.Just depends how much travel the internals had to account for that sort of work.
TBH if a machine shop ever cut seats that deep on an otherwise good head, I'd be wanting them to replace all the valve seats or supply me a new head.
I knew the wheels would fall off this within hrs.
227bhp said:
Peanut Gallery said:
If you have lowered the head of the valve into the head by 1mm, this would mean you have had to increase the clearance by 1mm. If the valve used to move 8mm, it would still move 8mm, particularly on a DOHC.
.
Decreased you mean?.
You have cut the seat down so that the valve is now sitting 1 mm further into the head than it was, this means that the back of the valve will be sticking out 1 mm more than it was, so if you did not adjust the valve clearance at all then the valve would never close. At its lowest it would be 1mm (minus whatever clearance there was) proud of the seat.
So to get around this, you would increase the clearance from minus 1mm to 0.2 mm or whatever the specs require.
227bhp said:
I have none, that's why i'm asking!
picture speaks a thousand words..or videoshttps://www.youtube.com/watch?v=lorANZ1Tptw
Peanut Gallery said:
227bhp said:
Peanut Gallery said:
If you have lowered the head of the valve into the head by 1mm, this would mean you have had to increase the clearance by 1mm. If the valve used to move 8mm, it would still move 8mm, particularly on a DOHC.
.
Decreased you mean?.
You have cut the seat down so that the valve is now sitting 1 mm further into the head than it was, this means that the back of the valve will be sticking out 1 mm more than it was, so if you did not adjust the valve clearance at all then the valve would never close. At its lowest it would be 1mm (minus whatever clearance there was) proud of the seat.
So to get around this, you would increase the clearance from minus 1mm to 0.2 mm or whatever the specs require.
On solid lifter yes, not on hydraulic. Hydraulic sets its own clearances.
'Something' has taken this difference up and I know not what, that's what i'm trying to find out. I doubt I have 1mm extra lift, but don't know how or why.
It runs fine, pulls well, no issues although it's only done circa 600 miles.
stevieturbo said:
I can find out how they work easily, finding what happens when it's 1mm closer isn't, that's what i'm asking.Mignon said:
227bhp said:
I can find out how they work easily, finding what happens when it's 1mm closer isn't, that's what i'm asking.
All the hydraulic lifter does is follow the cam lobe like any other lifter. Why would you think it is any different?Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff