LM318 solid lifter valve lash help please

[Little GTO]

Hi Guys,
Working on my Century MKII with an LM318 engine. Had a burned exhaust and intake valve replaced and now want to set the valve lash on this solid lifter engine. I can't find any info on what clearance they should be set to. The other cylinders seem to be around .020" so I set them at this but it sounds awefully rattley like this.
Can anyone let me know what valve lash a 1972 318 with a solid lifter cam should be set to?
If not, is it better to err on the loose side or tight side.
Thanks
Paul

[Warp Speed]

If unsure about suggested valve lash from cam manufacturer, it is always best to error to the tight side. As long as there is some lash cold (not holding valves open upon cold start up) there is no dissadvantage, except maybe a couple of lb/ft of torque.
The negative to excesive valve lash is the slap, and resultant speed of valve opening (harder on valve train components), and also the area on the lobe that the lifter / lobe starts to see load.
The first, as lash increases, the harder the lifter is excellerating before meeting valve spring resistance. This can be good for torque, but is very hard on parts as things slap together violently. The second, the bigger the lash, the farther up the ramp the lifter is before encountering resistance. Get too far up this ramp, and the edge of the lifter (flat tappet) can start to dig into the lobe creating instant failure. On a roller, this increased lash is also extremely hard on parts (most rollers usualy have faster opening/closing rates already), and the farther up the lobe the lifter travels, the more the cam tries to push the lifter out of the side of the block.
Valves should ALWAYS be lashed at operating temprature. Depending on cylinder head material (iron vs alum.) and cylinder head height (short stock type head vs tall racing type) the difference between cold and hot lash can vary greatly, and is seldom cosistant from cylinder to cylinder.
On a stock type cast iron, you may only see .004-.007 of lash growth between cold and hot (depending on normal operating temp). On a tall, race type aluminum head, you can see as much as .014-.018 change from cold to hot. Again depending on running temp. The higher the operating temp from ambient, the larger the growth.
This being said, the cam manufacture suggest .024/.026 lash. You set to this cold, when things get to operating temp, now you have .038/.040 depending on head type and material. This is a recipy for destruction, especialy upon break-in.
For all of the above reasons, I would always rather set the intitial lash a little tight, and find I need to open it up a little during hot lash than versa visa.
If unsure about suggested specs, .018-.020 will be good (safe) on most all grinds flat tappet or roller. And will be easy (relatively speaking) on parts.
As always, not the gosspel, but our cent and a halves worth!
Warp Speed

[steelcomp]

Warp is exactly right, except that I might add an even more critical issue with excessive lash. IMO, even more critical than the opening events he described, are the closing events. One of the most importsnt functions of the cam lobe are to as quickly, but as gently as possible, set the valve on the seat. There are a number of reasons for this, but mainly so that the valve dosen't bounce. Excessive valve bounce will lead to catostrauphic failure faster than most anything else. This will occur with excessive lash for the same reason, but on the closing side of the lobe. A lot of work has gone into designing proper closing ramp speeds, and too much lash will allow the lifter to free fall long before the ramp has had a chance to do it's job, allowing the valve to slam into the seat. This will always result in severe valve bounce..as much as .030"-.050" as seen in spintron testing. Now you have a whole bunch of problems. The valve isn't sealing like it's supposed to, so gasses are still flowing when they shouldn't be, which leads to loss of power. The valve can't transfer heat while it's bouncing, and even though we're talking fractions of a second, the valve can ultimately overheat and fail. It dosen't take long to wipe out a set of guides and a valve job with excesive valve bounce either, and finally, the valve can just fail from fatigue. A broken valve is usually the proverbila hand grenade.
Everything else he said I agree with 100%.
Just my .02
(I cahrge more than he does) :D