how much pre load with bbc 1.7 roller rocker with crane cam conversion kit ?

 

It has been several years since I did my 460 with the comp cams BBC roller tips (1.72) and the Crane conversion kit. The kit converts it over to a stud arrangement and not a pedestal mount. I did not have any "preload" figures except the old standard of rolling the pushrod between your fingers to determine when the slack was gone. From there, the standard 1/4 to 1/2 turn to establish preload. I think that works to ~.040----cant recall, depends upon the thread pitch. From there, you need to be sure the tip is correct on the valve tip. Thats a pushrod length issue. I think I cranked the engine and adjusted each rocker to 0 tick plus 1/4-1/2 turn down. On the old 460, it was not a hi-po motor, so I was not all up in arms if the travel was not perfect.
I still have a new conversion kit and a new set of comp roller tips, BBC.
LOL

 

I determine the push-rod lenght with a push-rod lenght-checker. The stock one are 9.5" and now i need 9-3/8. It's 5/8 shorther! Could that be possible ? Just shave the block 0.010 and just clean up the heads a few thousan. Maybe 0.015 at most and now 5/8 shorther push-rods.

 

the difference between 9.5" and 9 3/8"(9.375") is only 1/8"(.125")

 

sorry 9 3/16. 5/16 short for the intake. 9-3/8 on the exhaust side,1/8 short. I have 2 differents lenght on one head and 2 different lenght on the other head ? I guess the deck block, deck head and the valve job change everything.

 

I keep preload at .020", you can go out to .040". You need to add in the preload figure to the push rod length you came up with before you order them.

 

I did make 1/2 turn preload on the rocker, i watch a couple movie on you tube for proper adjustment. Did i still need to add lifter preload on push rod lenght ? driver side intake 9 9/32 and exh 9 13/32. Passenger side intake 9 3/16 and exh 9 3/8.

 

preload is really negitive lash. A pushrod checker will most likely tell you length at zero lash. I prefer a preload of .040 -.080 . the hyhdralic mechinism in the lifter usually has a travel of about .100-.180 or so.
If you have too much preload shims are available form people like Crane and Comp Cams.

 

I really doubt with .080" preload that an engine would even start, much over .040 and you are going to have lean snaps back through the carb.

 

80 thou is just a skosh over 1.5 turns of a 7/16"-20 adjuster, or maybe just a hair under 1.5 turns of a stock 5/16"-18 pedestal bolt... it is quite a bit

i've found that my engines are more happy to rev with the least amount of preload

 

Of course it will start, because the valves will be seated. lifter won't be bottomed out at .080 .Most all lifter have about .125 of total travel.
The hydralic mechinism will regulate the the las at zero. and then compensate for temp and over time compensate for any wear.

Laen snaps?? lets say the valve wouldn't seat. Just how does theis effect the mixture?

 

These are Crane Cams words about excessive preload :
"With excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat. This will cause the valve to be open longer and the lift to be higher. This will decrease the cylinder pressure, lowering the performance of the engine. If the preload is excessive it may cause "backfiring" from the engine."

 

It is a common practice in some circle track series that require hyd.lifters to bottom out the lifters and back it off 1/4 turn.
It does not take to many RPM for a pump to start bypassing oil pressure.
I have seen on the dyno that oil pressure is not going up after maybe 3-4000 rpm. After that the pressure relief valve is dumping oil. So I have no clue what Crane is thinking to make that statement.
I have done and seen it done with no issues.
These engine will run in the mid 7000 rpms.

 

What it really says in the Crane Cams catalog:
In theory, a hydraulic lifter can pump up.....

Have you proven this theory?

I worked for years with the men that wrote those words. Many times they wrote to make things understanbdable for the masses.
Do the math of the oil pressure in the lifter exserts on the pushrod and then look at the proper valve spring and you will see the valve spring wins the push of war every time. (oil pressure X square area of the lifter mechinisim<> valve spring X rocker ratio) I know I can't spell well

I think that many blame "Hydralic lifter pump up" problems that are really more to do with improper vavle springs. When you get into true valvefloat it doesn't take much to pump up lifter and create these ghost problems.
People have actully swaped lifters and or cam and lifters when the real problem was the springs.
Although a very rare situation, I have seen a very high speed video of the valve spring harmonics on a BBC engine. This profile was mainly a marine proflie and the harmonics were really bad between 5100-5300RPM the guys at work call it the "slinky on drugs video"
At a steady 5200 rpm this cam would just eat springs. but that a different story altogether.

 

We could debate this issue till the cows come home but I'll always set mine at .020. You can set yours where ever you want.