valve settings

[we kool]

ok might be a dumb question but all I read on big blocks I have a 555 with a 748 lift and 284 duration on intake and 296 on exhaust comp cam says adjust at .028 but they don,t say cold or hot and alot of other manufactures say .030 cold anybody have any suggestions on adjust hot or cold and set .028 or .030 alittle on the loose side ,Im looking to get one lousey 10th out of this thing any help would bee greatly appreciated thanks

it ain,t over till the fat lady sings

[Bob West]

My Comp solid roller calls for .016 hot, XR286R. I set them at .011 cold with aluminum heads, a little on the tight side.

[JohnDougherty]

Tighten them up by .004"

The problem changing lash comes when you loosen the lash up. If you go too loose you can increase the valve seating velocity and valves can bounce on the seat.

The clearance ramp height can be different between manufacturers and even between lobe profiles from the same company.

.011" cold is maybe .015" hot on the intake side. Take .015" divide by 1.7 (rocker ratio) and you have .0088" at the cam lobe. Im curious what the duration is at .0088" :)

[sunsation540]

Most every cam co states hot valve settings. a bbc with alum heads and std rockers moves about .006 and with jessel stuff its around .004. hot to cold. if you want .026 hot set them at 0.22 cold depending on rocker type. don't get to worried about .001 loose or tight it takes .004 to make any diff on the dyno or in the car. as for .0088 each .001 has the same effect on duration opening and closing points. ex a cam that is advertised at 295 duration with .026 lash.is 300 duration with .021 lash this changes adv duration as well as 0.50 numbers... like with 1.7 vers 1.8 rockers is diffrent the seat timing won't change just the veloicty it opens the valve and the total or net lift..

[dadnova]

You may want to check with you Head company. I have Jessel rockers and AFR heads on my SBC. If I set them at .026 the rods come out. Probably due to Jessel small cup. AFR says the 227 head grows .010 when hot. So I set them cold at .016 and when the engine is warm the lash is at .026- .027 and the rods havent come out again. Heads differ as my freinds big block AFR heads dont grow for some reason. Cold to hot is .001 - .002 differance. In my opinion the Jessels are not worth the money, nothing but problems with the small cup size.

[we kool]

Hey thanks for the info guys ,a While back car craft had a how too on valve adjustments and there way was totally screwed up with the base circle on the cam and what to adjust ....like with 1,3,2,4 cylinders closed ,you could adjust those valave etc and it was not even close to where it should have been ,no mention of hot or cold etc..does anybody who reads the magazine follow them ? Hope not ,the only good articles in those books pertains to bodywork and thats about it ,thanks for info

[ytnova]

I think for the average mild motor, using that method is fine, but once you start running a cam with alot of lift and duration, you might as well chuck it out the window, not to mention if you have a 4/7 swap cam. Call me old fashion, but I am more comfortable with doing them one at a time. I use a ati balancer with timing marks all the way around and starting at tdc and #1, I just turn the motor 90 degrees at a time and set the valves in order with the firing order, it takes longer, but I know its right.

[aitch o]

my afr 220 sbc heads grow .005 when they are hot. therefore i set the valves at .020 cold which is right at .025 hot and right on the cam motion suggestions.
i have tried to mess with the lash in hopes of picking up just a little. tightened it down to .020 hot and it put just a little duration in the cam and maybe another 200 rpm in the torque curve. ran the lash up to .030 hot and it put just a touch bit of lower end torque in it, maybe moved the torque curve down 150 rpm from baseline.
so, after this long story, and several attempts at using a buddy's cam that was close to my combination, i determined it was definitely worth the 300-400 to call cam motion and have them grind one to my specific combination. it was usually worth 1-2 tenths in the 1/8th and 2-3 in the 1/4.
(set the lash 1 pair at a time, and keep rotating the engine so you can keep track of the pairs in order.)

[we kool]

Hey thanks for the reply WOW 2-3 tenths now that,s alot but you have aluminum heads mine are steel so expansion and contraction are not as great think your suggestion is going to work for me on steel heads again thanks yt nova are you running a big or small block?

[ytnova]

Aluminum headed bbc

[sunsation540]

for 20 years i did the #1 tdc rotate 90* and follow firing order hell i watched warren johnson do it at indy in 1986 must be right .... as lobes and duration and so many things in cam design have changed in the last 20 years so has this... the tdc-90 works on cams under 300* duration less overlap the correct way not the only way just the safe way so if you runing your valves with a 268 h or a friends 905 lift roller the way for both is, when the exh starts to open set intake,continue to rotate in running direction until intake opens and starts to close at least 1/2 back to close and set exh. HOT then let cool completley recheck for cold number why guess...