To Shim Or Not too

[john 215]

Hi,read various threads that mention shimming the preload on the lifters and other say use adjustable push rods. What way have you guys gone?
I going to be running a Viper Typhoon in the 4.6 i am building up and am leaning towards adj push rods. The heads i am using are Real Steal stage 3 with push rod hole already opened up.Do push rods come built up or do the ends require pushing in?
Thanks for any thoughts and recomondations
John

[softdash3.9]

Checking preload on the lifters is really to ensure there is enough clearance within the lifter, i.e. not bottoming out within the lifter. the hydraulic side taking up the slack with the oil pressure. (can only be done when lifters are new and dry, i.e. no oil within)

Shimming is only required if additional clearance within the lifter is required.

Well worth checking, especially if you have had machining done head/block skim/valve mods.

It is quite easy to do, just need a piece of wire of suitable sizes, can't remember the sizes at the minute, it's on RPi's website.

I have rebuilt a couple of engines and always checked clearances, but never needed to shim the rocker shafts up I've always has too much clearance, but that's OK as long as the springloaded inner is loaded against the push rod i.e it's not loose - it could fall out and has some travel left within the lifter to min spec.

If you are running a hydraulic cam, with hydraulic lifters(which a Viper is I think?) you dont need adjustable pushrods, they are only really needed for running solid lifters or as an alternative to shimming the rocker posts I suppose if travels used up. (as racing twin plenum Rover SD1's were meant to, fitted with adjustable rocker gear for holmogation rather than adjustable pushrods, which were welded up on road cars )


Sure some others will have comments

[GreenV8S]

never needed to shim the rocker shafts up I've always has too much clearance, but that's OK as long as the springloaded inner is loaded against the push rod i.e it's not loose - it could fall out and has some travel left within the lifter to min spec.

Willing to be told I'm wrong, but I thought the preload also defined how far the lifter was capable of "pumping up" at high revs, so running lots of preload might be a bad idea even if the lifter doesn't bottom out.

[katanaman]

Depends what you have valve installed hight really. If your valves are all fairly close to each other and you have to then shimming is fine. If the valves are all at different heights then I would say adjustable pushrods are best. Reason being that all the shims on one head have to be the same so you have to shim it for the worst fit kind of thing which could leave other clearances less than desirable.

I would agree with the too much pre-load if you have too much and your lifters pump up as they are supposed to its possible something bad could happen. Never seen it happen but its possible. As for preload go with what the lifter manufacturer recommends as they aren't all the same.

[softdash3.9]

Too maybe sounds "Too" excessive excuse the pun

I have had slightly more than 60 thou (1.5mm( maybe upto 80 thou (2.0mm)

Never encountered a problem personally, but I may be wrong in my approach/understanding having read the RPi pages again.

Both engines have had heads/block skimmed , although not excessiveley and probably within manufacturer tolerances, hence no issues, but I've alway checked the preload clearances, to see there was some .

Although I would expect the "bleed down" would be more dependant on the clearances/tolerances on the bleed holes rather than the setting of the lifter in the set up (assuming there is sufficient clearance to operate, i.e.t he lifter wasn't bottoming out or hitting the retaining clip)

I'll have to take an old one apart and have a look

Here's thge RPi link http://www.rpiv8.com/engine-4.htm#preload

Please accept my apologies where required

[pitsnow]

I would give my vote for the adjustable pushrods.
It makes live so much easier if you change camshafts like underwear.
Well almost as often...
If you are likely to fiddle with you engine a lot or just want something easy, go for the adjustable. They do not cost an awful lot and would come handy should you ever want mechanical cam and lifters.
That should be enough excuses there so go on and buy them