P90 head shave and shim- Correct?

[bubbleguinea]

just aquired a VERY SWEET p90 head off ebay..stage 4 camkit, stainless steel valves, all that.

 

well, im going to shave it 2mm (.080'') and shim the cam towers up.

 

now, ive been told to use N42 valves (longer) and shim the springs up too. Being this head comes with stainless steel valves, i DONT want to change them out.

 

So to compensate for a messed up wipe patter by rasing the cam 2mm, cant i just get 2mm thicker lashpads??? they are not stock retainers, they come with the schinder cam kit!

 

is this right or wrong?

[Guest ToxicLove]

Using thicker lash pads will not compensate for the geometry adjustment made by the shave.

 

Also, if you use the stock valve stems the valves may not seat properly.

 

All the research I have done on shaving and shimming includes the following steps:

 

Shim cam towers to match head shave

Get the longer stems to maintain valvetrain geometry

Use proper lash pads to ensure correct wipe pattern (with towers raised)

 

Here is a link with good tips on head shaving mods.

http://www.geocities.com/zgarage2001/head.html

[bubbleguinea]

right, but the valves dont move! when you do a shave..the only true thing you are changing is the height of the cam above the deck..

 

to make up for that you shim the cam towers.

 

now to make up for moving the camshaft up, all you change there is the distance from the cam lobe to the rocker arm...

 

to make up for that you just get thicker lash pads??

 

once again, i NEED to keep these stock P90 valves...

[oinojo]

i dont see why not, the reason why he recommended shimming the valve springs was so the geometry doesnt need to be touched. Since your just making up the difference using valve lash pads it should do the exact same thing. Im just stating what seems logical to me, perhaps the veterans of the site will pitch in some knowledge on this subject.

[bubbleguinea]

exactly what i think----

[JMortensen]

I haven't done the shave and shim deal FWIW, but the whole idea behind it is to shim the cam towers up and use the longer stemmed valves to retain the geometry so that you don't have to mess with the lash pads.

 

You should be able to do the same thing with the lash pads to get the geometry back to stock if you want to keep those valves. The only things that I would be concerned with are excessive seat pressure with aftermarket springs or coil bind with stock springs, and valve retainer to stem seal interference.