Valves or rockers problem

[damicotile]

I had been have this problem with lash caps popping off.
I have Scat 1.25's. I had them shimmed out with 2 shims, the thick one is .055 and the thinner one is .030. Together they are .085 on each block.
Plus they hit the covers just slightly so I took out the shims, re-did my geometry, ordered new push rods to the new length and just installed them back in.
I started it up and it sounds like the valves are hitting the pistons.
Is this possible?
It's a w-120
When I put the stock rockers on, no problem.
How close are the valves to the pistons?
_________________
'73 SB
82x94
W-120 w/ CB light weight lifters
Silicon bronze sleeves
Scat 1.25:1
CB H-Beams
Straight cuts
42x37 Steve Tims
44 IDF's
9.2:1
A-1 Sidewinder coated

__________________________________

[Dougy Dee]

Sounds like your retainers may be hitting the top of your guides.

[damicotile]

I put the valve at full lift and am able to move the rocker arm about an 1/8 inch more. There is no coil bind going on either.
Perplexed.
I am wondering if the vale is hitting the piston.
Anyone know how much clearance there is supposed to be with my setup between the valve head and the piston top?
I'm sure all the people that know this stuff are out doing other things but I'll take any advice I can get.
_________________
'73 SB
82x94
W-120 w/ CB light weight lifters
Silicon bronze sleeves
Scat 1.25:1
CB H-Beams
Straight cuts
42x37 Steve Tims
44 IDF's
9.2:1
A-1 Sidewinder coated

__________________________________

[stoneloco808]

I would pull that cylinder head and look for any distinguishing marks on the piston. I would also pull the valve from head and check it out.

I personally like a minimum of 0.120" valve to piston clearance with stainless steel valves. But with titanium I prefer a minimum of 0.090".

[damicotile]

[stoneloco808]

Well lets, start off on square one, my memory of these different builds on this site is not the best, consider it selective memory.

What valve is breaking these rockers?

I guess you have the pad style rockers and not the swivel foot type. Do the lash caps fit tight on the valve? Does it come off easily?

Do you have access to some sort of borescope? Just take a sneak peak at the top of the piston for any markings of a valve making contact.

If not, pull the engine and pull the cylinder head for inspection. As there is no way I know of to check while its on the car.

Off the car it requires a valve spring compressor, light springs(like the ones used for checking geometry), dial indicator w/stand, and a degree wheel.

[volksnut]

On my Scat rockers (1.25 pro comp with blue washers) my final measurement for the rocker was 1.33....so with my 380 cam lift came out to 505 at valve...how tight is your deck

[nsracing]

YOu mean you did not check valve-to-piston clearance?

If the heads were not flycut deep then should be okay. But your guide tops might be hitting the retainers. If it is 1/8 inch....that is not much of clearance. YOu can easily float the valves and kill the guides and/or/both retainers.

[damicotile]

My deck is .055, the chambers were step cut to 60cc.
Brothers machine did all the case and head work and took into account for the piston and valve clearances. I called them and asked.
I'm up and running right now, the sound is gone. I'm thinking that the rockers may be to blame for all this grief.
The cups are not machined smooth like one would think. They're Scat rockers.
No rocker arms broke, the caps are a loose fit and they came off just twice on 2 different valves.
I changed the length of the pushrods and geometry cuz the rockers were hitting the covers. No shims.
Anyway, it runs great now. Just some minor linkage adjustments and A/F adjustments and I should be ready for the Bugorama.
_________________
'73 SB
82x94
W-120 w/ CB light weight lifters
Silicon bronze sleeves
Scat 1.25:1
CB H-Beams
Straight cuts
42x37 Steve Tims
44 IDF's
9.2:1
A-1 Sidewinder coated

__________________________________