FE valve lash hot vs cold

[poboy427]

I have a alum Shelby block and Dove TP heads. I am running a Comp Cam solid roller and they specifiy .020 for lash and I am sure that is a hot spec, cam card does not say.

I always set my lash cold. Primarily because I am slow and the engine is cold by the time I get set up.

Question. Several guys here are running alum FE's with solid roller cam-probably even some with Comp Cam's Magnum roller, 308R.

What would the cold lash setting be if hot is .020. Expansion rates are differant for each block/head setup.

Comp cams will give me a big block Chebby best guess but I would like to see what the alum FE guys say.

-Ray

[Jac Mac]

When doing any alloy block/head builds I set initial cold lash at 0.015" then run motor up to full temp & recheck when hot. Now your cam card suggests 0.020" hot so say the hot lash checked out at 0.022" then we would know to set the cold lash @ 0.013" to arrive at a hot check of 0.020". Virtually every combo & application is different, so doing it like this and keep it that way for 'your car' makes it simple.

[Anthony]

I'd set the lash at 0.010" cold to start with, and then recheck it when hot. But I bet it's going to be about 0.013" tighter when cold, so the lash would then be set at about 0.007" cold.

[ERA Chas]

So in Jac's explanation, is .007" a good rule of thumb for the hot/cold variance?

[Jac Mac]

No, the 007" is not necessarily 'the' figure to use. Each application will vary to some degree and the FE alloy block/head combo could be expected to have a slightly larger variation due to the block height as compared to say a BBC for example. I gave the 0.015" cold setting as an example only. The main thing is to check for the 'difference' between hot/cold & allow for that when setting cold. Its a lot easier than doing them hot. I would expect the actual difference to be similar to Anthonys figure of 0.013" in real life.

Sort of precludes the idea of running some of the 'tight lash' cam, profiles we used in the past with clearances around 0.012"/0.015" hot- would make a preheater mandatory prior to start-up

[ERA Chas]

With an iron block/ally head combination I have run .016 int., .018 exh cold. Never checked hot lash but I will. Mike LeFevers, who was at Shelby when I bought my heads suggested the cold spec and felt it would open up to about .023 / .025, which was the original cold spec of my Ultradyne cam. Has run fine for many years set this way. I check lash every season but only have to adjust 2 or 3 every 2nd or 3rd year.

[Barry_R]

I set my alloy engines up kinda scary tight when cold. Down around .003-.004. they open up to about .016-.018 hot.

[ERA Chas]

Barry,
Does that make the cam "bigger"?

[Ronbo]

I'm curious why the gap expands, the only thing I can think of is the valve face expands from combustion chamber heat? (pulling the valve farther into the chamber)

Is this correct? Just curious.

[Jac Mac]

Alloy expands at a greater rate than steel etc, in a pushrod motor the block/head will expand/grow while the pushrod stays much same creating most of the extra clearance, Plus the cyl head alone grows more than the length of the valve stem to create a bit more & in the case of the exh valve head dia growth also contributes slightly [ that valve head will also do the same on an iron head as well though, so not really relevant to this discussion ].

[Barry_R]

I like my solid rollers to be fairly tight lash. Seems to help them live longer in street/sorta street applications. I'm also kind of fond of roller springs with a narrow spread between open and closed pressures - the oval track Nextec stuff is a good example with seats in the middle 200s and only 600 open - at least 100 pounds less open than a true drag race spring.

[Clois Harlan]

For what it is worth I set my lifters cold at .010 and then recheck them after warm up. My Comp Cam recommended gap is .018-.022 with Edelbrock Performener heads and vintage block. I am usually spot on .020 with that procedure and I usually check everything before going to the track or at least 4 or 5 times a year.


Clois

[RICK LAKE]

poboy427 Ray I run hydro lifters and have no worries and it's a shelby block and heads. These motor expand about .0012-.0015" from just heating up. Every motor has a sweet spot for power and adjustments. If you have the time, and money, go to a good dyno shop and do thw valve lash setup for what the motor wants. I agree with tight lash on a street motor. This will extend the life of the lifters and camshaft. This is also with a good oiling system that puts the oil where it needs to be. IMO idling a solid lifter cam is just killing the rollerwheel and needle bearing in the housing. Also the pushrod is being bounced back and forward between the lifter and adjuster on the rocker. If you are looking for the most power, run a wider lash. If you are looking for less maintainance run tighter. If your lifters are pressure oiling this will extend there life longer than not. Watch for any blueing on the pushrods. This is a sign of poor oiling to this important contact point. Who's rockers are you running and do you have limiters for the rockers in the heads. Make sure that the valve springs are at least 1/2 of the way in oil. This helps control the heat they produce. If you are running a HV oil pump, over fill the motor by 1 quart. It will not hurt anything. Limit your rpms to 6,500 or 6,700 rpms on your stroker motor. This will extend the life of the motor too. There is alot of weight spinning around in the bottom of that block. Rick L.

[vector1]

i would do what barry r said and set them on the tight side at least initially. too loose and they hit the sides of the lobe and miss the takeup ramp for lack of better terms.

my 351 block ex opened up about 8-9 thou on avg., int about a thou less.

idle in the 1000-1200 range will help the lifters live longer lives i've read. mine idles at 1200.