ok can some one please tell me why its very important to have the rocker shaft shimed to the correct preload????
i understand when the heads are skimmed the hole rocker shafter will move down the same distance, and while the rush rods are still in the same place its going to push on the valves more thus maybe damaging the vavles and pistons if they hit each other!!!!!
but what about if there is clearence between the vlaves and the pistons???? is it still important to shimm it up properly????
as from my understanding when fitting and uprated cam, the more valve lift the better as it can let the air in and exhaust gases out easyer and faster!!!!!
im sure some one will correct me sortly!!!!
oh which are better to use the adjusterable pushroads or a shim kit???? i no the adjusterable P/R are about £100 more
shim prelaod
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Too much preload will mean that if the lifters pump up they will hold the valves open, this will lose you power and could end up burning the valves out.
Too little preload will mean that the inner piston of the lifter will keep hitting the spring clip. The clip will break and the lifter will fall to pieces.
Shim kits are OK but they can mean that the rocker does not bear down the tip of the valve correctly, this will cause the valve guides to wear out.
The other problem with shims is that you may not be able to get all of the preloads exactly as you want, as you have to use the same shim size under each rocker shaft support for each head.
Adjustable push rods are expensive but if you want all the preloads exactly right they're the way to go.
A lot of people reckon that the preload is not that critical but I've just bought a book on V8 lumps by Des Hamill, he reckons that if you want to rev the lump over 5.8k rpm you need to set the preload to 20 thou.
The oil needs draining from each lifter before you can set them.
So that's it in a nutshell
AJMHO
Pete
Too little preload will mean that the inner piston of the lifter will keep hitting the spring clip. The clip will break and the lifter will fall to pieces.
Shim kits are OK but they can mean that the rocker does not bear down the tip of the valve correctly, this will cause the valve guides to wear out.
The other problem with shims is that you may not be able to get all of the preloads exactly as you want, as you have to use the same shim size under each rocker shaft support for each head.
Adjustable push rods are expensive but if you want all the preloads exactly right they're the way to go.
A lot of people reckon that the preload is not that critical but I've just bought a book on V8 lumps by Des Hamill, he reckons that if you want to rev the lump over 5.8k rpm you need to set the preload to 20 thou.
The oil needs draining from each lifter before you can set them.
So that's it in a nutshell
AJMHO
Pete
ok i uderstand that bit abit more now, which brings me to my next question.....
how the hell do i set up the preload
dont worry im not that stupid ive already rebuilt engines, gearboxs, diffs etc so having got a problem doing the job, im more intrested in how its do properly, as in where do you check it from, does the cam have to be pushing on the lifters, i realy dont know????? oh and ive got an uprated piper cam in it already, its the RP4 from RPI, will the preload be different for this cam???
one thing that confuses me is that when i rebuilt my V8 about 9months ago i was under the impression that all the lifted had to be primed first by leaving them to fill with oil by leaving them in a tub of oil!!!!!! but now im been told ive got to empty them to get the rite pre load?????
the more info on this one the better so dont be shy!!!!
how the hell do i set up the preload
dont worry im not that stupid ive already rebuilt engines, gearboxs, diffs etc so having got a problem doing the job, im more intrested in how its do properly, as in where do you check it from, does the cam have to be pushing on the lifters, i realy dont know????? oh and ive got an uprated piper cam in it already, its the RP4 from RPI, will the preload be different for this cam???
one thing that confuses me is that when i rebuilt my V8 about 9months ago i was under the impression that all the lifted had to be primed first by leaving them to fill with oil by leaving them in a tub of oil!!!!!! but now im been told ive got to empty them to get the rite pre load?????
the more info on this one the better so dont be shy!!!!
Hi
if you have ajustable push rods then you can shim the pedistals to get the contact right between the rocker tip and valve correct (and the right "sweep" across the stem as the valve lifts) and then use the adjustable rods to set the preload. Preload is set on the back of the cam ie. off the lobe and is set with the oil drained out of the lifter.
Mike
if you have ajustable push rods then you can shim the pedistals to get the contact right between the rocker tip and valve correct (and the right "sweep" across the stem as the valve lifts) and then use the adjustable rods to set the preload. Preload is set on the back of the cam ie. off the lobe and is set with the oil drained out of the lifter.
Mike
poppet valves rule!
disco-v8 wrote:ok i uderstand that bit abit more now, which brings me to my next question.....
how the hell do i set up the preload
dont worry im not that stupid ive already rebuilt engines, gearboxs, diffs etc so having got a problem doing the job, im more intrested in how its do properly, as in where do you check it from, does the cam have to be pushing on the lifters, i realy dont know????? oh and ive got an uprated piper cam in it already, its the RP4 from RPI, will the preload be different for this cam???
one thing that confuses me is that when i rebuilt my V8 about 9months ago i was under the impression that all the lifted had to be primed first by leaving them to fill with oil by leaving them in a tub of oil!!!!!! but now im been told ive got to empty them to get the rite pre load?????
the more info on this one the better so dont be shy!!!!
The preload setting is generally the same for each cam, the details should come with the cam. There is quite a lot of scope when setting up the preload, from memory it's usually something like 20-60 thou.
When changing from one cam to another the preload could be messed up as the base circle may differ. Skimming the head WILL effect the preload.
As Kiwicar said shims, (which are cheap) could ve used to get the rocker sweep correct across the valve tip. I bet a lot of people dont bother with this! (You will need to google for a diagram on this).
To set the preload up you need some wire of varrious thickness, one at 20 thou. You need to bend the last 3 mm at 90 degrees. The end is then pushed between the spring clip on the lifter and the inner piston. You basically use it like a feeler gauge. Use the adjuster on the pushrod the adjust the gap with the lifter on the base circle.
To drain the oil out of the lifter you must remove each one in turn, flick out the spring clip, (watch out as the inner piston is spring loaded). The inner piston can then be removed and the oil drained out. (Don't lose the spring!).
I don't think that they need to be primed if you are not fitting a new cam, you just might have to crank the lump for a while. (You could spin the oil pump with a drill and tube that you can knock up).
If you are fitting a new cam my book recons that you should do every thing possible to get the car started as soon as its turned over. In which case you could set all the preloads, then remove or at least loosen the rocker shafts so that you can get all the lifters out, you can prime them by taking out the inner pistons and filling the lifter with oil.
Each lifter and pushrod MUST go back in the same hole in the block that it come from!
If you are fitting a new cam then you must use new lifters, these won't have oil in them. Also you must use the correct oil on the lifters and cam lobes and run them in. (Approx 15 minutes at 2000 rpm).
I've just seen a set that weren't run in, the lifters and the cam are now knackered after 500 miles. I'm sure that Rover never ran their cams in but the standard cam and valve springs are very mild. Especially the opening and closing ramps of the cam.
I have a typhoon cam and just use Range Rover lifters even though Rhoads are recommended by Realsteel. I spoke to V8 Devlopments who I have a lot of respect for and they said that the Range Rover lifters are fine.
As you can see it can take ages to do all this properly, many people don't bother and whilst their motors will probably run OK, yours will run a lot better.
HTH,
Pete
