Solid cam lash

I am not an expert just very experienced in solid cams over several decades. As a rule of thumb, the tighter the lash the more lift and duration the valvetrain sees, before the engine is completely built it is helpful to know how much clearance the piston to valve combination has. Once you have established that there is sufficient clearance then you can proceed to tune the lash on a running engine,car combo. Lash should not go over about .030 or under about.012 (loose rule of thumb)try setting it loose to start with and then tightening in .002 increments while driving it soft and hard to see how the engine feels and drives. When the engine does not feel happy or does not drive smooth anymore then back off to the last setting that worked, bear in mid that other things will come into play while doing this process such as carb jetting that m ay need to be adjusted and/or timing issues particularly where the all in figure of advance is. There is a great deal of power that can be gained by tweaking this along with other tuning. This was how it was done old school when we did not have access to dynos or other modern equipment that can aid in this. If you find that the engine is still making more power when you get to the tightest setting(s) then the cam is probably too small for your particular combination. 396Wheelstand

 

Hi thanks very much for that info. I don't have access to dyno tuning either and want to learn how to do everything myself. I haven't pulled the old motor out yet because I need to concrete my 'carpet on shingle' garage floor lol. the motor went in on that... never again.

I will buy a book on valve trains before I attempt anything to reduce the chance of wrecking anything. I also have a set of 1.6:1 roller rockers which were previously used with these world heads and higher comp KB pistons with a bigger lift cam than this. I'll definately be checking clearances though. what piston to valve clearance do you recommend? I suppose that depends on RPM? The bottom end is stock (if it flies apart I have a mint standard bore 305 with 416 heads I can swap parts to). I want to put this motor together so I can start competing at the drag racing instead of just watching every one else. It will also be used on street but I don't care if it's a pig lol.

 

piston valve clearance

I dont like to see less than 100 thousands to 120 of piston-valve clearance. Check the springs to make sure they are strong enough for the rpm range you intend to use. Recheck them regularly. Floating a valve is probably one of the primary grenade mechanisms for racing engines. Remember the higher the rpm and more times you go there the quicker the springs go away.

 

Thanks a lot for your advice, I've bookmarked this thread.

I have a set of springs that were used with a cam very similar to this (slightly more duration and 106º lobe separation), but haven't had them checked yet. On the cam spec sheet for that cam they recommended comp cams 985 springs at 1.8 = 150 lbs (which I presume is what I have) do you (or anyone) know if this pressure is suitable for the cam I have? Sorry for so many questions, I have a lot to learn...

 

cam

Solid lifter cams have what is called a lash ramp ground into them. Until just a few weeks ago I thought all solid lifter cams had them. But I was at a seminar and Steve from Erson cams told the group that some guys grinding cams, that do-not know what they are doing will grind them with-out the lash ramp.

So if the cam was a production grind, or done by a reputable cam grinder it should have a lash ramp. If you are good with a dial indicator you can find out reasonably close what that ramp is. Then take that number times your rocker ratio and you will have a real good lash number.

To find the lash ramp with the dial indicator you need a solid lifter, just like your going to run on the cam. Set the dial indicator on the lifter and rotate the engine in it’s normal direction. Once the lifter is on the base circle of the cam set it to zero. As you rotate the engine in it’s normal direction watch the indicator, at first the movement (lifter rise) will be slow.. and then it will “take off” . That slow movement distance is the lash ramp. It may take a few try’s before you see what I am talking about.


Keith