Lash pads

[Brett240]

hi guys, does anyone know what height lash pad to run with this cam?

in 40/72 dur in 292 lift in .495"

ex76/40 dur ex 296 lift ex .510"

Blindly hoping... Brett

[Zedrally]

Brett,

I doubt that you can calculate lash pad height.

The way I see it, valve stem height and cam radius will both contribute to differences in lash pad thickness.

Hence the need to measure on the job, so to speak!

Not saying I'm right, over to the other experts..........

[Brett240]

stem height is standard but cam radius? i wouldnt think that would have an effect on lash pad thickness.

[Zedrally]

Have to disagree on the standard" height valve stem old chap.

I know for a fact when I had my last head job, that the new valves [the old ones where bent] where shorter than the originals, not much but enough to have new [thicker] lash pads.

I guess if your using "genuine"nissan values for that head then you'd be correct.

Cam radius will depend on the thickness of the cam lobe.

Some are ground from new billets, others from original cams. Hence the difference in lobe thickness.

[Brett240]

yeah they are genuine nissan valves and retainers with 100 pound springs. ah ok by radius you mean from the centre of the cam to end of lob tip? then your right it will have an effect. thats valve lift i think which i have above, the thing is i just dont know how to figure it out.

[Zedrally]

Brett,

There is an in depth write up on valve & timing events in one of the ""How to" rebuild books. Can't exactly remember which one, I'm sure someone else will chip in with the right name. [2many, if he reads this will know]!

Accordingly, lash pads thickness is determined by "trial & error", basically by checking the wipe of the cam over the rocker arm [not sure if thats the right name, but I'm sure you know what I mean] and adjusting the lash pad thickness so the wipe pattern is centered within the hardened seat.

Hope this helps.

[Brett240]

cheers, thanks for your help! i thought it might be something like trial and error, bugger. nothing is ever easy:classic:

[JEFF]

Zedrally has it right with centering the wipe pattern on the hardened pad of the rocker arm. Do you have access to a table grinder - On my brothers car, we ground a lash pad a little at a time to get the thickness right - then ordered that thickness of lash pads. Time consuming but it worked well.

- Jeff

[Zedrally]

I should have added, last time I did this Lash pads where like gold.

I think I got touched about $40ea. [must have seen me coming]!

So If possible get a cam thats been ground off a new billet, cross fingers and hope you can grind down your old one's. On the other hand if you can find a cheap source of supply of pads let us know.

Good Hunting.

[2ManyZs]

The book you need is the 'How to Hotrod and Race Your Datsun" by Steve Smith Autosports Publications... You should be able to get one through Amazon here on the site if you use our bookstore.

As Mike said, it is a complicated affair, and is best done when you have nothing better to do for a while....

Remember one very important thing, use new rockers with the new cam, or you run the risk of doing damage to the new cam if you use old rockers.

It is a very labor intensive job considering in the book it says that a difference of .015 inch difference in lash pad thickness can make the difference in your cam lobe contacting the rocker in the proper place, or having it run off the edge of the rocker pad.

Basically what you need to do is adjust the lash pad thickness so the cam lobe runs off the end of the rocker pad within .010-.015 of the end of the pad. If the lash pad thickness is not right, the cam lobe will run off the rocker pad too soon and will not keep the valve opened long enough, or too late and have the valve open too long, which could possibly lead to valve/piston contact on some engines....

What you need are new rockers and an assortment of lash pads in different thicknesses, hopefully if you can get them from a dealer with the understanding you can return the unused ones and only pay for the ones you use you'll be able to do this fairly inexpensively. Then you'll need a very good light and perhaps a small magnifying glass to make sure your're seeing things correctly.

One word of caution, I wouldn't try to do this with the engine still in the car.....you'd end up standing on your head in the engine compartment.

If you need, I can scan the pics to show the correct and incorrect cam lobe to rocker pad contact...:cross-eye

[Brett240]

thanks alot for your help guys!

2manyz's yeah if you can scan the pad contact that would be great, ill order that book off amazon to.:classic:

[Zedrally]

Originally posted by 2ManyZs

One word of caution, I wouldn't try to do this with the engine still in the car.....you'd end up standing on your head in the engine compartment.

I hadn't contemplated changing cams without the head off?

Is that normal?