I was running Comp Aluminum Roller 1.7 rockers. I went back with the Comp HiTech Stainless Roller rockers mostly for the strength. After talking with some drag and circle track guys, they all gave up on aluminum rockers b/c of failures. Many still run aluminum Jesel, but that is a different league. What sucked the worst is the aluminum is not magnetic, so it was a pain to clean all the aluminum junk out of the heads, valley, and pan. I basically had to wash the motor down.

 

ouchy

 

i was thought the other way round as well. the heat will cause the valvestem to lenghten which closes the gap

 

I understand about the expansion. I would think that too, but the article from Crane's old site says:

"Compensating for a Cold Engine when Adjusting Valve Lash
When installing a new cam, the engine will be cold but the lash specifications are for a hot engine. What are you to do? There is a correction factor that can be used to get close. We mentioned that the alloy of the engine parts can be affected by thermal expansion in different ways, therefore the amount of correction factor to the lash setting depends on whether the cylinder heads and block is made out of cast iron or aluminum. You can take the “hot” setting given to you in the catalog or cam specification card and alter it by the following amount to get a “cold” lash setting.

Iron Block Iron Heads Add .002"
Iron Block Aluminum Heads Subtract .006"
Aluminum Block Aluminum Heads Subtract .012"

Remember this correction adjustment is approximate and is only meant to get you close for the initial start up of the engine. After the engine is warmed up to its proper operating temperature range, you must go back and reset all the valves to the proper “hot” valve lash settings."


This makes it sound like the lash should be set tighter cold. Here is the link http://69.20.53.62/faq_mlifter.php

 

when i learned about this there was no aluminum heads on the car. the chart says to add there. seems to be the other way round with aluminum :-)
If I wouldn't know better I would do exactly as the crane cams website specifies. they constantly have to deal with valve lash questions i guess.

i wish someone who knows chimes in on how to set the cold lash. Stil I wouldn't deviate from whatever your specs are by manufacturer on hot lash

 

IIRC, the cold lash is .022". Aluminum and iron have different coefficients of expansion. However, I cannot believe the difference is significant between the block and the rocker arm. If that were true, aluminum heads would be constantly blowing head gaskets.

Bottom line: Start with .022 cold, and go with .018 hot. If your cam maker recommends otherwise, go with that, but these 289HP numbers should be good.

 

so if your card says .016-.018 you should set them at .012-.014 (I'd go .012 on IN and .014 on EX)

if you look back i had mentioned most lash adjustments are in the .010-.012 range - now that you look at what your specs should be cold you'll see i was between .000-.002 within where they should be (see, i'm smart and stuff)

 

My head hurts. I know they are at .016/.018 cold right now or at least they were before the first heat cycle. I will heat it up tomorrow morning and then check the lash to see if the lash is more or less than 16/18. Maybe that will shed some light on this. My thoughts where the block and heads heats up and expands some, causing the pushrods to act shorter thus creating more lash when hot than cold. Here is what comp says and it contracts Crane and follows what you guys were thinking.

First, check the spec card that came with your cam for the correct valve lash specifications. All COMP Cams® valve lash settings are “hot” settings (set at normal engine operating temperature) but will work for initial start-up as well. Turn the crankshaft in the direction of normal engine rotation until the exhaust pushrod of the cylinder you are adjusting begins to move upward, opening the valve. Adjust the INTAKE lash by tightening the intake rocker nut with the correct thickness feeler gauge inserted between the valve stem and the rocker tip. Tighten the rocker nut until there is a slight drag when moving the feeler gauge. Next, rotate the engine until the intake pushrod fully opens the valve and then goes half-way back down. Adjust the EXHAUST rocker nut (with correct feeler gauge) using the same procedure. Repeat for all cylinders.After setting your valve lash with the engine cold, start it and follow the appropriate break-in procedures. Due to thermal expansion, your valve lash will now be tighter than it was when the engine was cold. Repeat the adjustment process to ensure that your valve lash matches that specified by your cam card at normal operating temperature.

They also say to contact them for aluminum head settings. I guess I will do that now.

 

Found this on Comp's website under the FAQ for Rockers...wish I would have seen that a year ago.

1. Why is steel better than aluminum as a material for rocker arms?

Aluminum, unlike steel, has no safe stress point. With aluminum, every cycle endured is one cycle closer to failure. To make things worse, the failure point of aluminum is very unpredictable. The advantage of high quality steel is that as long as it cycles at less than its maximum failure point, it can be run for virtually a lifetime without failure. Steel just doesn’t have the same cycle failure problem that aluminum has.
http://www.compcams.com/Technical/FAQ/FAQRockerArms.asp

 

Buick GS 350 engines had aluminum rocker arms. They discovered that if you went just a little over on the oil change interval, the rockers were trashed. All the replacements from Buick were steel.

Aluminum aircraft have a very strict no-exceed service life. If they are stressed too much, or too often, they can fail catastrophically before that life is met. This is a cold way of saying the crew dies.

http://www.youtube.com/watch?v=PK49QALNj-0