8 replies to this topic

[TerrA LX]

Are you saying that with the rockers tightened down there is excessive valve lash (clearance)?
Shimming will increase the clearance, not reduce it.

What exactly do you mean by lifter collapse?

[S pack]

Please excuse the typos, usin a phone with gumby hands,

I have a set of second hand non adjustable roller rockers im putting on a 253. They go no where near sitting correctly ( lots of play when valve shut).

What is the propper way of going about shimming them ( only seen ppl use washers) and what do i do to make sure the lifters are not collapsed while doing the shimming?

Thanks for any advice

G/day LEE

When you say lots of play do you mean the rockers can be moved up and down slightly without exerting any force on the pushrods, or do you mean the pushrods can be forced down into the lifters by hand.
If there's lots play it could mean the posts on the roller rockers need machining down not shimming up.

The lash built into standard non adjustable rockers to suit a std cam AFAIK is around 1.5 to 2 turns from zero lash.
To calculate how much would need to be machined off the roller rocker posts (if that is what's required) you need to measure the free play between the roller and the valve tip with feeler gauges for each valve, record these measurements then work out how many thousands of an inch 1.5 to 2 turns of the rocker bolt is equal to and add this onto each measurement from the valves.

Clearly mark each roller rocker with its cylinder number and application (exhaust or inlet).
After machining each rocker must be used on the valve it was machined for, do not mix them up.

Another method could be to fit lash caps to the valve stem tips to take up any free play if you can get lash caps of the correct thickness to suit.

If you suspect the lifters could be faulty take them out and test them or throw a new set in to be sure.

Cheers
Dave

Edit: Ah, OK I need to learn to type faster.

Edited by S pack, 05 January 2011 - 10:18 PM.

[TerrA LX]

Are you saying that with the rockers tightened down there is excessive valve lash (clearance)?
Shimming will increase the clearance, not reduce it.

What exactly do you mean by lifter collapse?

Face palm, sorry im jibber jabbering, i did this months ago n only decided now to do somthing about it

They dont allow the valve to fully close so need to be raised. Dont hydrolic lifters squash down under pressure if the oil has ran out of them over time and u need to do something about it when putting motor back together?

Im not the engine internal king,

Ah there is no clearance, yes you can buy shim washers in different thicknesses, these washers are more uniform than a washer simply presses or punched out.
don't worry about lifter collapse, it doesn't happen till the lift is applied.

IMO working with the manifold off, and the cam on the base (off lift) install one set and chock it up with what washers (or purchase some) you have till you can torque the rocker down to the correct setting and still be able to rotate the pushrod with your fingers, without collapsing the lifter, then remove them and using a micrometer measure the correct thickness you need.

You will find that some will need less shimming than others, go on the tight side where possible as most holden lifters can handle 40tho pre load (measured around the inside of the top of the lifter where it collapses into the outside housing)

Edited by TerrA LX, 05 January 2011 - 10:36 PM.

[rodomo]

If the heads are old, valve resession (especially on the exhausts) might not let the bridge tolerate this sort of adjustment.
1/4 - 1/2 a turn preload on 5/16" UNC thread.

You can buy individual studs with posi-locks but I don't know if they would suit your rockers?

Edited by rodomo, 05 January 2011 - 10:45 PM.