Rage

What is the maximum valve lift that a 496HO will mechanically tolerate with the stock roller lifters and assuming special valve springs for reducing spring solid height as necessary?

Rage

Crane says that the 496HO cannot tolerate more that 0.570" max valve lift becaue the stock roller lifters will become disengaged from the lifter alignment bracket at higher lifts and that will allow the roller lifter to rotate thus causing problems with the cam lobe and roller lifter roller alignment.

Crane roller lifters allow more lift and the special Crane lifters with a link bar connecting two lifters eliminates this issue entirely allowing max valve lift of 0.6+.

Nordicflame

iTrader: (4)

Rage, your piston to valve clearance will be an issue well before your lifters create any grief.
The stock lifters are working fine in many applications up to .632 lift with forged/relieved pistons on the 496HO.
Dave

Rage

Dave,

That is very interesting to hear and why I keep asking questions until I see some consensus from multiple independant sources. In all fairness to Crane they did say that this information was for the GM 496 420hp and I assumed that this would be the same for the Mercruiser 496HO.

Crane also said that the stock GM (not Mercruiser) cam for the 496 has a max valve lift of 0.480" intake and 0.483" exhaust. I have also seen some (3) Comp Cams advertized for the 496 all with max valve lifts of 0.510". Comp Cams tech line said that the 0.510" max valve travel limit is do to the valve guide and valve spring retainer clearance limit.

Actually I am much more interested in the max valve lift limit do to the valve to piston clearance issue. Do you know what the max valve lift the 496HO stock piston will safely accomodate?

Nordicflame

iTrader: (4)

Rage,
I haven't been able to find any info on this motor on the Crane sight. They have always used this standard statement on all of the Gen VI stuff...

"CRANE 16535-16 LONG TRAVEL HYDRAULIC ROLLER- LIFTERS MUST BE USED WITH GREATER THAN .570 LIFT CAMSHAFTS TO PREVENT ALIGNMENT BAR- DISENGAGEMENT"

I'm not so certain that it applies to the 8.1L motor however.
I have heard that a set of the regular aftermarket hydraulic roller lifters were installed on a 496 (8.1) and it created a "very" serious oiling situation

I think Raylar has mentioned .520 lift max with the larger valves, others .590 with stock valve size, etc.. so in that ball park I would assume. Just get some clay and check it out to be sure.

I don't have enough "hands on" with this motor (YET ) so take these as observations.

Dave

Rage

The clay check out is coming. I am here the boat is at the lake. Doing what I can in the mean time from the keyboard to sort it out. Thanks for the observations and comment on the Crane site info.

What kind of 'oiling situation'?

Nordicflame

iTrader: (4)

I'm assuming it was an alignment issue (lifter oil hole to the block oil supply)