johnplogii
Senior citizen
- Joined
- Aug 13, 2005
So, what is entailed in setting preload on adjustable t & d's? You guys have me thinking I better check mine. How much, 1/4 turn, 1/2 turn?
Thanks
Thanks
lifter preload
- Thread starter gsbuick65
- Start date
turbodave231
Moderator
- Joined
- May 24, 2001
I beleive the adjuster screws on T&D's are 3/8-24 thread. One turn equals
.0417". So half a turn from zero lash should be about right.
Lee is right about adjusting rocker tip to valve stem geometry. Buick shaft mount rockers are not adjustable. The geometry can be changed by changing valve installed height. (installing longer or shorter valves or installing valve seats)
Dave
.0417". So half a turn from zero lash should be about right.
Lee is right about adjusting rocker tip to valve stem geometry. Buick shaft mount rockers are not adjustable. The geometry can be changed by changing valve installed height. (installing longer or shorter valves or installing valve seats)
Dave
turbofabricator
Well-Known Member
- Joined
- Mar 7, 2004
True, that using shims (or washers) is not the "BEST" way. However, I have done this on MANY, MANY Buicks over the last 18+ years, and have NEVER had a single issue.
Here is a pedistal mount a friend made. I haven't tried it, as it really isn't needed.
Rocker geometry needs to be verified on EVERY engine that is built. Production tolerances are so vast that adding a .016"/.032" shim will rarely negatively effect geometry. What is usually done with valve stem heights?........usually just cut them even (IF that
), and "hope" that it is close enough.
I use to mill away 1/4 of the rocker pedistal to pin the decks on a 8445 casting (to center the "deck pin" over the fire ring of the gasket on the intake side-between the head bolts), and the pedistals never broke, even with a 150+lbs of seat pressure. The stock pedistals are pretty strong, and we don't run these things with 350 lbs on the seat and at 8500rpm. The majority of the load is in a vertical plane. Here's a pic of the pinned deck, too. (now, we just fuel the engines and the gaskets live fine )
The best way to "fix" pre-load is to purchase a set of roller rockers and do it right. BUT........you still must check rocker geometry on them, too.
Absolutely nothing wrong with over caution, though. As an aircraft mechanic, my life revolves around over-engineering.
Here is a pedistal mount a friend made. I haven't tried it, as it really isn't needed.
Rocker geometry needs to be verified on EVERY engine that is built. Production tolerances are so vast that adding a .016"/.032" shim will rarely negatively effect geometry. What is usually done with valve stem heights?........usually just cut them even (IF that
), and "hope" that it is close enough.I use to mill away 1/4 of the rocker pedistal to pin the decks on a 8445 casting (to center the "deck pin" over the fire ring of the gasket on the intake side-between the head bolts), and the pedistals never broke, even with a 150+lbs of seat pressure. The stock pedistals are pretty strong, and we don't run these things with 350 lbs on the seat and at 8500rpm. The majority of the load is in a vertical plane. Here's a pic of the pinned deck, too. (now, we just fuel the engines and the gaskets live fine
)The best way to "fix" pre-load is to purchase a set of roller rockers and do it right. BUT........you still must check rocker geometry on them, too.
Absolutely nothing wrong with over caution, though. As an aircraft mechanic, my life revolves around over-engineering.
