Im ready to run my new engine on a test stand to break in the cam and check for leaks. Im suppose to run .018 on the intake and .021 exhaust hot. Well the engine is cold and I need to set it to fire it up. What do you all recommend? Its an aluminum head 360 with a solid flat tappet cam. Thanks

Set it to .020 to .022 range fire it up--after it is hot go over the lash--set to correct specs -- always set your lash hot from then on
No matter where you set it cold for that first run it will be fine no worry
In the future any cam you don't know the specs set to .022 cold and never look back it will run fine
Good Luck

I never set mine hot. With aluminum heads set the int .006"/ exh .005" tighter cold than the hot spec. Warm it up and measure a few intakes and exhausts. Recheck those same valves after it sets overnight. How far did they change from the measured hot setting to the current measurement? Then do the math of the change. Now when you set them cold they'll be where you want hot.
Doug

What matters: NO MATTER WHAT you do not have negative lash at any temperature. Even zero is safe until you keep the valve open even that tiniest little bit.

This works for me. Also agree, a little loose on break in will not hurt.

I always set mine at .016-.018 dead cold. Not a big fan of setting them hot unless you use a temperature probe and set them the same every time. I really don't understand why some cams spec at anything wider than .020 Can somebody enlighten me?

Gus

Reassuring, I have just set mine cold at 16, I will check them again after 20 miles or so and I'll be setting them cold.

As per Comp

"All COMP Cams® valve lash settings are “hot” settings (intended to be set at normal engine operating temperature), but will work for initial start-up as well."

How I've always done it. I don't run it for an hour. Just put some heat in. Maybe 150, that's around where I come out of the lanes. Have to be organized so you don't take all afternoon to do it.

On your deal I would set them .006 tighter at room temps. than what the lash should be hot and then run it for 20+ minutes at or above 1500 RPM to break in the cam and then check two or three pairs of valves on one side or the other to see how much they opened up when hot
Not all aluminum heads gain the same height as others when warmed up

My cam calls for .018 & .020. I set Them cold at .013 & .015; Ive found them typically on the tight side of the spec numbers when checked warm.

Real race engine builders know and understand that initial start up--It does not matter as long as you have some lash OK?
But they also know that if you understand Anything about an engine or racing or cams or this business that you set valves hot Period! That is IF you want it right--so since that thing will run with about any setting folks start getting cute and come up with all this BS calculations etc from cold to hot etc and decide they know more than the engineers that designed the engine and or parts Well...you don;t--you get a pass because the engine will run with the valves open a little or with .040 lash so you wind up thinking you are on to something--you are--Not following age old guidelines that are designed to help you get it Correct

In the past i used some Cam motion cams that were inverse radius designs--the low spot on the lobe was NOT on the base it was up the side--so setting valves was tricky--I remember a 500 CI big block that was running 5.10's after delivery then a couple weeks later was winning rounds but running 5.40's owner had set valves WAY too tight and valves were not closing--we re-set lash and it went right back to 5.10's no harm done
OK you set them at .040 and guess what ??It runs but sounds like two skeletons screwing on a tin roof--yes it can and will harm the unit by bashing the lifters but my point is
IF you want to know something about this subject just follow the CORRECT procedure for setting mechanical lash and do it HOT or ...produce your engineering degree thesis you did on why your way is "better"

Gees! This is an easy subject that gets lots of argument from people that just will not listen

I believe that the reason for that I have already stated --an engine will run with almost any lash but each lobe design has very specific lash settings based on lifter diameter and opening and closing ramp designs as well as many other factors so WHY fight the engineers that built the part??????????

OK you set it correctly HOT and then check when cold so you have an idea --makes life easier I get that but honestly please just derive that info from a HOT setting will ya?

If a valve does not close that cylinder is out.

Right but even with some negative lash and valve not closed tight tight a rookie will not know except when looking at ET slip based on my personal observations in that one case
Theory and answers it takes to get an 'A" on the test are not always dead on except on paper
For sure it is awful to run like that and has all kinds of consequences but ......
That tale was to aid in enlightenment and flesh out my entire argument

I greatly respect your knowledge--- I try and help where I can adding in real world experiences--reading a book about how to swim is a good start but you can't read that book and jump off a pier or you will go to the bottom--

So educate me. If its checked hot, then cold. Do the math as to the difference in lash dimension cold/hot. Then what does it matter at which temp I check them? When its cold we have a starting point that is always the same. Just subtract the difference. At what oil temp do you check? 125,150,180? Am I missing something?
Doug

Right! Base it off the Hot reading

I set mine just like you are thinking but always always based on Hot reading

Hot is full engine temp like 5-10 minutes after a run Yea it ain't fun but then you know what it really is

FWIW after the first few times they all should settle down and you don't need to get in there but every so often just to check--I like to keep after them so I catch a lifter wheel or lobe getting into trouble before it gets to Code Red

Why don't you want heat in the engine? Burn your fingers? Gas expensive? Why do engine builders use deck plates and run hot water through the block when boring & honing? Cam manufacturer says HOT. My junk is 140-150 going into the water, not 70. I just going to warm it up, let it heat soak for a few minutes and run the valves. Then I know and not guessing.

Just lashed my valves on the 511 with victor heads. First time since last august when i lashed them cold at .016" for the engine/cam breakin. Spec hot is .020" on both int and ex. I relashed them hot at 180* doing one side at a time then reheat for other side. Only had to relash 4 valves on driver side and they really didnt need it. just trying to get them all exactly the same. 2 valves on pass side. All very much the same at .020", but 1 was a little tighter than i like. The HS rockers held the lash good and the flat tappet broke in well from what i see.

Again if we measure hot. Then cold, check the difference. Then lash cold with the math. It's not rocket science. It's easy. It's in a controlled eviroment, instead of outside in wind and dirt. What's the down side? Show me the upside.
Doug

I have a mid 1970 Crane cam catalog that has a chart in it for setting the initial lash on their new cams, the chart calls for setting it .002 loose cold on a iron headed iron block, .006 tighter with a aluminum head on a iron block motor and .012 tighter on a aluminum water block with aluminum water heads
I used those settings on the first all aluminum blown street Hemi gas motor I assemble for a customer, they worked out great compared from the .012 tight room temp setting to the 170F water temps with 160 F oil temps setting on the dyno
My stupid pump gas Duster 400 stroker motor with Eddy RPM heads only changed .001 from hot to cold
The message I got from that stupid motor was to check every motor for what it does, write it down and use it

It's my routine. Always has been. Doing it someone else's way may work fine. Never said it was wrong. I don't typically open the engine up at the track. This is shop maintenance. Once a fresh engine has settled down, I don't do it every week. Warm it up, throw a light on it to make sure nothing has moved. Check the trans. Run the valves. Look everything over. I can do the valves in a few minutes if nothing's out of whack. Upside? IDK. Taking care of all this at once. No fudge factors to forget.