Hydraulic tappets that "pump up" ... do they work?
Discussion
Just in case you can't guess it from what I'm about to ask, I know damn all about engines ...
I heard about some hydraulic tappets that "pump up". I get the impression that the idea is that at low revs the tappet has time to shorten meaning the valves open later and therefore for slightly less time. The point of this is to reduce the amount of overlap between the inlet and exhaust valve timing at low revs in order to make the engine smoother when a high performance cam shaft is fitted. At higher revs, the tappet doesn't have time to compress ("gets pumped up") and therefore the valves follow the timing of the cam shaft more closely allowing the overlaps to be increased.
Has anyone fitted these tappets? Do they work? They sound like they'd give a kind of stone-age variable-valve timing which might make it easier to live with a high performance cam. Almost sounds too good to be true, if they actually work.
I heard about some hydraulic tappets that "pump up". I get the impression that the idea is that at low revs the tappet has time to shorten meaning the valves open later and therefore for slightly less time. The point of this is to reduce the amount of overlap between the inlet and exhaust valve timing at low revs in order to make the engine smoother when a high performance cam shaft is fitted. At higher revs, the tappet doesn't have time to compress ("gets pumped up") and therefore the valves follow the timing of the cam shaft more closely allowing the overlaps to be increased.
Has anyone fitted these tappets? Do they work? They sound like they'd give a kind of stone-age variable-valve timing which might make it easier to live with a high performance cam. Almost sounds too good to be true, if they actually work.
IIRC hydraulic tappets run with no cam clearance, ie they are always in contact with the cam lobes. They are pressurised using oil, this holds them against the lobe and takes up the required valve clearance.
They run quietly, which is why they are fitted to many road cars. They do have problems at high RPM IIRC and so most competition engines run solid lifters.
*edit* I think thats the principle. the exact mechanism im not sure of though
>> Edited by chief-0369 on Thursday 22 January 15:34
They run quietly, which is why they are fitted to many road cars. They do have problems at high RPM IIRC and so most competition engines run solid lifters.
*edit* I think thats the principle. the exact mechanism im not sure of though
>> Edited by chief-0369 on Thursday 22 January 15:34
I think you're talking about Rhoades lifters. These are designed to leak down at a controlled rate under load so when the engine is going slowly the valve shuts early, at higher revs the valve is open for such a short time that they have no effect. The idea is that by closing the valve early you can make a fairly wild cam behave more like a mild one at low rpm - sort of poor man's VVC. Apparently they are very noisy at low rpm though.
"Pumping up" is a different effect, where the lifter's self-adjusting mechanism goes wrong at high revs and makes the lifter extend. Normally this causes loud tapping noises and loss of power until they've settled back down again, I guess in extreme cases it could lead to mechanical damage. You can get 'high rev' lifters which are supposed to resist pumping up, in my experience they don't help much.
"Pumping up" is a different effect, where the lifter's self-adjusting mechanism goes wrong at high revs and makes the lifter extend. Normally this causes loud tapping noises and loss of power until they've settled back down again, I guess in extreme cases it could lead to mechanical damage. You can get 'high rev' lifters which are supposed to resist pumping up, in my experience they don't help much.
Hi yeh they are the roads lifters and to be honest they do work bloody fantasticly they realy turn say a kent 234 into a kent 218 BIG BUT THOUGH!! they sound like you have a 10 foot tappet clearance below 2000 rpm which is why they are rarely used, great for getting wild cams through mot's though!!
I've got them on mine, and they do seem to work the only downside is the noise at low engine speed which when everything is running normally is livable with, however if you stop on a hot day after a run ( ie motorway for fuel) and then try and restart the car after only a short period ( 10mins / fuel stop) be prepared for an almighty clattering for the 1st minute or so as they refill. Fitting an accusump has cured this tho'.
Matt
Matt
The "pumping up" was in the original Rover V8 design to work as a sort of rev-limiter (on a carb engine!).
So it was intended you notice the power going down, and preventing to take the engine revs into the "not intended" design area (and important, to extend the engine's life).
And yes it is a very old design, and has nothing to do with for example Honda VTEC like hum-hum.
Tuning a Rover V8 takes you light years ahead of the original design (I think)...., and then you must be after other things then the Yank design logic of the fifties, the 1900 fifties.....
Rob
So it was intended you notice the power going down, and preventing to take the engine revs into the "not intended" design area (and important, to extend the engine's life).
And yes it is a very old design, and has nothing to do with for example Honda VTEC like hum-hum.
Tuning a Rover V8 takes you light years ahead of the original design (I think)...., and then you must be after other things then the Yank design logic of the fifties, the 1900 fifties.....
Rob
I've used the Rhoades lifters and they made the engine sound like a scrapper (mobile 1 didn't help either, made it worse). That said, the next time I used them it was quieter because I set the pedestal clearances properly. Now I prefer the crane product. If I tried Rhoades again I would do some proper setting up.
I've got Roades lifters in my engine and it isn't noisy at all. Maybe it's to do with choice of oil as you say. I just use plain old GTX.
They do seem to work, I've got a supposedly slightly hairy cam, but the engine idles smoothly and pulls well from low down. How much that is down to the lifters is hard to say.
They do seem to work, I've got a supposedly slightly hairy cam, but the engine idles smoothly and pulls well from low down. How much that is down to the lifters is hard to say.
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