This is slightly directed at F250 Restorer, because I believe he has one installed.

I have been trying to order this camshaft for a month now. There have been some confusion on my part regarding part numbers, but that is mostly sorted out. I always thought this was a milder camshaft, so I was a little surprised when my machinist had some doubts about the strength of the valve train.

I called him today and he said that the pressures required by that camshaft warrant new valve springs and require the studs be pulled and their holes tapped to fit stronger, threaded studs. He said I would be looking at an additional four hundred dollars for this job.

I can't remember reading anything about this in other people's rebuilds. This has taken me by surprise. My machinist said he would look into another manufacturers camshaft with similar specs for me and give me a call back Wednesday. I thought this Isky 256 was a tried and tested idea.

Is this normal?

 

Hello. I do run the 256. It is a nice cam. Any cam with larger specs (valve lift, duration, etc.) than oem, will put more strain on your valve train. And most cam makers require a specific v.spring for any cam. I know Isky says to use their double spring v.spring with 145lbs at the seat. That is crazy. I went that route and ended up removing the inside spring to get me 120 lbs at the seat.

But back to your concerns: You do need at least 110 lbs at the seat. Because of that added stress most guys replace the oem studs with stronger screw ins. What gets me is that your machinist wants $400 to do it. My shop charged me only $100. I used ARP studs for a sbc for $55. You should also go with metal/metal t.gears. I would find another shop. That guy is charging too much. You can get that head ported for about $350!!!!! Always replace the lifters. Also, install a new, $10 hardened oil pump shaft.

The nice thing about the new studs is that if you go 3/8 to 7/16, you can buy a set of used roller rockers from on ebay for a bbc that will bolt right on for $100.

 

"...new valve springs and require the studs be pulled and their holes tapped to fit stronger, threaded studs..." That is not just normal but consider it required. Some engine builders won't reman an engine without changing to threaded studs on stock engines...they don't ask...they just do it.

 

Isky uses steep ramp profiles to "snap" the valves open & shut quickly. Still a short duration cam for low RPM, but the valves move as if on a wilder motor, hence the wilder valvetrain.

 

ALL aftermarket cam manufacturers sell kits to upgrade your valve train. If any valve is opened more than oem, you have more spring tension, stress on the system. Also, I'm laughing about how you described the Isky cams: "steep ramp profiles to 'snap' the valves open quickly. You make it sound like Isky is the Darth Vader of cams.

 

Sure. Sounds like op bought just the bare cam. In addition to lift & spring tension, the faster rise rate means faster instantaneous valve speed and stiffer springs to prevent the valve/rod/lifter from overshooting & flying off the cam lobe at peak lift. Like wearing a seatbelt when sitting in the back of the bus to keep from hitting your head on speedbumps.

I was going to call the Isky "squarelobe", but someone might take that literally. The isky 248 & 256 have way higher seat pressures than a comp/crane, IIRC.

 

Pretty much all performance cams have steeper ramps than stock. I don't know that Isky has more or less than an equivalent Comp or whatever. They all get the valves off the seat and closed in a hurry vs. the stock set-up.

Pressed-in studs would probably work with a mild performance cam kit, but screw-in are relatively cheap as far as insurance goes.

 

For the same .050 duration, Isky has a shorter advertised duration. Thats all the info I have, and could be incorrect.