Lets talk Lash adjustment

[Razor]

Opinions on setting lash on a flat tappet cam. Some say zero plus 3/4 turn, some say zero plus 1/2, some say zero.. some do 1 1/4 turns..

What and why, what advantage to running tighter or looser lash?

 

[Nick Micale]

When setting roller rockers on a hydraulic cam, we go between 1/8 and 1/4 turn. This has worked fine for the many years we have done them.

Have not seen any difference in performance on the hydraulic lifters loose or tight.

 

[musclecar neal]

The correct method is what ever it takes to properly preload the hyd lifter. Each manufacturer has a different spec for each series lifters.

Comp Pro Magnum .002-.004 HOT
Comp High Energy and High Tech 1/4-3/4 turn .020 -.060 preload

Crane .020 - .060 preload


Most other brands of regular Hyd lifters .020-.060

Hope this helps.

Neal

 

[Razor]

What about GM lifters?

I've always went 1/2 turn after zero. I guess just personal preference.

Tho I have heard running zero lash on the lifters with the C-clips, not the spring clip retainers.

Thanks

 

[redhotrod]

Its been awhile since I played with lash adjustment, but I used to run a solid camshaft in my big block car, which required constant valve lash adjustment without polylocks. I was told if you keep the preload tighter, it improves your bottom end torque, if they are looser, more top end hp. (Remember, this is only by a few thousandths of an inch, I don't know if it is that noticable of a difference.) But like I said, it has been awhile, it could be the other way around. Its kind of like playing with timing, if it was looser, Its as if the valves stay closed a hair longer. Same thing would go with camshaft advancement/retard. (not you)

Razor, are you adjusting your Buick rockers? The stock setup doesn't require an adjustment. Just torque the whole rocker arm assembly down to the specs. The only way to really adjust them would be to use shims.

 

[chevyII]

The trick ive found was when you get to the 1/2 to 3/4 of a turn it must be slowly done or in 1/4 increments. This helps give a little time to let the lifter collapse.

 

[musclecar neal]

Actually if the lash is tighter on a solid you have a little more lift and duration, if it's on the loose side you have less lift and duration. So what you said is really the opposite, loose is better bottom end and tighter is better top end, not by very much as the increase or decrease is quite small.

The increase in duration is more than the increase in lift.

 

[redhotrod]

thanks for the correction, after thinking about it yep, your right. When they are loose, it takes a split second longer to raise the valve so the motor can pack a little bit more punch in the combustion stroke.

 

[BobbyBuick]

I always loosen completely first.I put a dial on the lifter compressed @ half turn and I think it was about .035 so that is what I use.If my memory is correct!

 

[6SENSE]

There should be quite a bit of info on the preload subject through a search. If I remember correctly the consensus as far as a number to shoot for with our cars is around .30-.35 .
If the block is completely stock with stock head gaskets, cam, etc. etc. then of course you can safely just tourque down the spec 30 ft/lbs on the rocker arm shaft and your done. HOWEVER, difference in head gasket thickness, blocks decked, heads resurfaced, different lifts of cams all come into play with the needed pushrod length to give the proper lifter preload. Thus the need for the adjustable pushrod measurement tools to find out the needed pushrod length to get, or adjustable pushrods when such changes come into play.

musclecar neal is correct on the better topend/lowend deal. With our engine configuration/needs I wouldnt play around with it though. "Boost" your topend/lowend elsewhere, too many other ways to achieve with these cars. Too much preload, especially on the aftermarket cams that seem to have a short life already will definately lead to premature failure. Too little preload can lead to a number of issues including poor topend oiling, damage of cam and/or lifters from slapping each other, and bent/broken pushrods (I know).

 

[Razor]

Originally posted by redhotrod

Razor, are you adjusting your Buick rockers? The stock setup doesn't require an adjustment. Just torque the whole rocker arm assembly down to the specs. The only way to really adjust them would be to use shims.

Well see I made a roller setup for the TTA. Its a totally different head than the GN. As you can see, 1.7 ratio brings my little 210/205 cam to .500 on the intake.. thats some big numbers compared to .455 with 1.55.. guess thats one way to wake up a 210/205 cam huh

So in the quest, I now have a fully adjustable valvetrain, and its been 4 years since I was messing with the rollers.. hence my post. I do agree the .030-.035 for lash. Which is half turn with a 7/16 fine thread nut.

Thanks for the responses.. greatly appreciated.