Valve lash

If  you get the valves too tight you are going to burn one of them and could cause idle problems. If you are setting your intake and exhaust valves at .016 cold, you are getting them about as tight as I think you should. I am assuming that you are still using a cast iron block? I doubt that the valve adjustment as you have it set is causing an idle problem. You might want to consider for safety, setting your exhaust valves at .020 and your intakes at .018. 

have you been running proper oil for flat tappet cams in it?

I can tell you this. I am using a Compcams, solid lifter 294s series cam. It has .605 lift, 110 centers, 248 duration @ .050, 74 degrees of overlap. I'm running A3 Ford aluminum heads, iron block and Weber carbs.

It idles at 850rpm, gives me 13 inches at idle. Lifter specs are .022.

Compcams told me to adjust them cold (70 F air temp). Because of the aluminum heads, set them at .016. Their comment was "we guaranty they will be right on spec at running temperature".

I have been told by some that they are too quiet for solids. These are all Chevy guys so you need to take that into consideration because in their case, a solid lifter Chevy generally sounds like a broken typewriter at idle and to boot, won't hold the adjustment for more then 500 miles.

Does mine rev like a dynamo? I never though of it that way but I'd have to say yes. Of course there is other engine noise involved back there with the 180s and the Webers but kinda' sounds like a Formula One car when you rev it.

You can usually play with solid lifters with a plus or minus .002" safely. The looser they get, the nosier they get and the more stress they will put on the valve train components generally resulting in faster wear. The biggest concern of failure is going to be on aluminum roller rocker arms , the push rods and the rocker arm studs. They are only safe up to a certain valve spring load. They will snap. I use the Compcams chrome molly steel rocker arms and ARP studs.

I would think that a shaft rocker arm like Jessels or the equivalent would be safer with a full comp cam, as far as long term dependability is concerned? I have heard that they wear out quickly with roller cams though.

Now to your answer. For you to have only 7 to 8 inches at idle, you most likely have a camshaft with 80 to 82 degrees of overlap and it may also be a 108 ground center. In my view, that's a full competition cam. Power is going to be in the 8,000 to 8,500 rpm range and gives away lots of torque under 2,500 to 3,000 rpm.

I'm not the Pied Piper of cams. If you like yours, fine. Leave it alone but 7 inches is probably correct for it's timing events.

What method do you use when you set the lash?

dmfinley posted:

i have a 351 with the Yates heads and Ford high rise. Solid flat lifters. I do not know what the cam is. Guy I bought it from had engine built but couldn’t find cam info. Ran about three thousand miles and ran fine. Summit 750 carb. Idled decent and had brakes all the time.  Didn’t put a vacuum gauge on it. First mistake. Noticed the other day valve train was pretty noisy. Pulled covers. Lash cold was about .029-.030.  Not knowing cam specs did a lot of research and guessed on .022 hot. Everyone said to subtract .006 for cold so .016 it was. 

Started up and when warm sounded like the “sewing machine”   But the idle was rough and adjusting screws little effect. Bought a vacuum gauge. Idle at 700 is 7 inches!  Thought I had a vacuum leak but I checked everything no leaks. Runs great down road but idle quality way worse than before. Can tightening the lash .013-014 make that much difference?

I even pulled the power valves which were 9.5 and put in 3.5.  I see no difference. Idle screws still make almost no difference. 

What am I missing?

Thanks

David Finley #3659

 

You might find out that you are going to be cutting out sometimes by using a 3.5 power valve. If you have about seven inches of vacuum at warm idle, it may take too long for the 3.5 power valve to open. It might not happen all of the time and altitude and air temperature could be a factor. Perhaps a 5.5 power valve would work better for you.