This is a topic that I continue to get conflicting info on, even from different people within the same company. I am aware of the need to adjust lash once the motor is hot. But I am looking for something very close, because of the combo.

This is for the large combo. Background: 447 cubes, D1X supercharger (sitting over drivers valvecover), solid roller cam, no stud girdle, Jesel shaft rockers, 18° Chevy heads, tall deck block.

CC recommends 0.016"/0.018" hot lash on int/exh respectively. My reasoning has always been that with the expansion of the lifters, pushrods, rocker studs, & valve tips, the cold lash should be set "loose" (+0.003"). Per conversation with tech at TPIS, recommend setting lash "tight" (-0.003") due to expansion of block and head material. Later conversation with TPIS, contradicted first comments. CC tech could only say that lash must be set "hot". I would like to get this fairly close, as I will have enough difficulty in getting all the DFI mapping somewhat right on initial firing.

Any thoughts as to the correct thought and why would be appreciated.

Aaron

 

I did an experiment with mine a while back. I found that the lash needs to be set .003" tight when cold. I have verified this a couple of times and .003" has always been right on my setup. For example, I set the valves hot(.018"), come back when the engine is cold and they are .003" tighter (.015"). Hope this helps.

By the way, does the D1 fit without hitting the hood? Any pics yet. Sounds like a killer setup. Where did you find the headers, or did you have them made?



[Modified by 91tpi-zf, 10:07 PM 2/23/2002]

 

You need to go tight, .004 when cold, for start up only. The block and heads expand a whole lot more than the valve train, moving the rockers away from the pushrods.


[Modified by 7Bob3, 8:17 AM 2/24/2002]

 

I used to know the answer to this. There are a couple of rules that vary depending on the block and head materials. I would do what 91tpi-zf did (not so much what he said to do), and set those that you can get to, hot. Then come back when they're cool, check these and set the rest accordingly.

 

It would appear that the requirements are 15-20% reduction in lash for a "cold" setting would be appropriate. I have a tight lash cam, so the requirements would be 0.013-0.014" intake / 0.015-0.016" exhaust. As for comments on adjusting hot, this is a starting point for firing a fresh motor. I would hope that I can remove the blower and A/C compressor in the allocated time while still warm.

Thanks for the responses.

Aaron

 

I must have missed something. I didn't realize it was a first time start up. I would have simply adjusted it cold, to the hot specs. It certainly couldn't hurt anything. If you have better information, go with it.

 

There are rules of thumb, but vary depending on the materials involved.

Iron heads and iron block call for one specific setting

Aluminum heads and iron block a different setting

Aluminum heads and aluminum block still a third setting.

If I recall, they are listed in either Crane's or CompCam's catalogs.

If you don't have those and need their recommendations, let me know and I'll dig mine out and post their recommendations.

Jake

 

This is always a fun topic, and everyone has their own way. But since you asked....

I always have set mine cold and left it alone. Now let me explain.

The absolute best perfect way is to set them hot. And I mean consistent hot. It is very difficult to achieve real consistency setting them on a hot engine unless you have super easy access to pull the covers and work very fast. My experience has been that most people work way too slow and by the time you get done running them all, the temp. of the valves, heads, block, rockers etc etc has changed enough to negate all that precision you planned to get.

Now on a dyno you can do it and you get two people doing it on opposite sides. Not very practical in the car.

Now if you set them tighter when cold ( my experiments on my motor consisted of setting them cold then driving it for and hour and then quickly checking them. I needed .006 tighter when cold.) you are absolutely certain that everything is at the same temp. At least you have that consitency. Now there are variations in cylinder to cyilnder temps etc, but I believe in most cases this will provide the most repaeatable setting.

With your blower set up I assume it's pretty tough to get to them all. That will just make it worse.

Jim

 

Like Jim said you will always set them tighter when cold. An all iron smallblock and heads will gain about .002 lash. With aluminum heads around .004 will be gained and an aluminum block AND aluminum heads will usually need .008 to be in the ball park. This is from setting them hot on the dyno and then checking them later when the engine's cooled overnight. So to counteract this you set them the same amount tighter when they're cold since you know they are going to loosen up when they're hot. :chevy

 

go to crain cams web site http://www.cranecams.com/master/adjustvt.htm


[Modified by white 91 roadster, 3:44 AM 2/27/2002]


[Modified by white 91 roadster, 3:52 AM 2/27/2002]


[Modified by white 91 roadster, 3:58 AM 2/27/2002]

 

I was told to set them .005 tighter when cold. Like Chad said...set them all cold, then go back and check at least one when hot. That shoud give you how much tighter they need to be lashed when cold.