Dale1990

Speaking of geometry, one of the potential causes that was thrown around was that the guide and seat might not be "lined up" properly - I think it was referred to as valve seat concentricity. If that was off from the factory, does your step of machining the seat correct that? What kind of tolerance is there for that process? Sorry of this is a dumb question, I'm not a machinist.

Thanks!

0C_Williams@RPM

every new head that i've seen has excellent seat concentricity and those with good guides maintain this. gm does an excellent job on all the LS heads in this regard.


it's when the guide wears that valve face to valve seat geometry goes awry.

john_g_46

Thanks.

Dale1990

Thanks for the info!

Chalky

Charlie:

Nice work. Just curious but based on this statement, are you inclined to believe this is a stock guide issue with the LS7 or a combination issue with guide and exhaust valve?

0C_Williams@RPM

That's the 64,000 dollar question..up until the LS7 we just didn't see this type of wear - in fact, it was rare to find a guide issue on a LS1, LS2, LS3, etc. - and in the LS6, GM opted for sodium filled exhaust valves.

The obvious differences with the LS7, as I'm sure you know, is the implementation of the 1.8:1 ratio rockers arms and rev limiter moved to 7100 RPM. So, at least in my mind, unless there has been a material or tolerance change in the guide/valve combination, the increased rocker ratio or increased red line (or combination thereof) are likely at the root of the issue.

Keith N

RPM Motors recently did my heads and a valve job along with porting the intake & throttle body on my 2006 Z06 with 30,000 + miles. They have a full service shop and do excellent work at reasonable prices. My Z06 is running great and very strong.

JetBlue427

is 1:8 pretty much the highest rocker ratio out there? the one thing i have always noticed is that the quide wear is the highest at the bottom of the measurement...could the aggressive ratio cause increased wear like that.

0C_Williams@RPM

Thanks Keith

here is the data from your heads...before rework of course

john_g_46

Is there a feature in the head that controls the height/depth of the valve guide?

carnutsx2

How much is the valve job w/o r&r?

0C_Williams@RPM

Comp valve job is $250

thanks,

charlie

0C_Williams@RPM

yes, a small step is on the guide

john_g_46

Thanks.

I'll be doing my heads a week from Friday. When I changed plugs this past weekend, I noticed 6 and 8 were very wet with oil.

88,000 miles on the engine.

I'm convinced there is a geometry problem. You can't get excessive wear unless there is significant side force on the valve stem.

Among other things, I'm going with roller rockers...can't get side loads with rollers.

JetBlue427

How exactly are guides usually matched to the valve stem diameter? do they all come to that specific diameter that you need...or is it just a general smaller guide diameter that gets honed to the size you need? or are they just honed because they get mushroomed from pressing them in place?
Curious of any theories on what step they may have screwed up from the factory?