Aluminum heads, eh? Recently I have been helping a friend with his 1968 Road Runner with a 383 that was punched out to 512cid. The prior owner built the engine himself, using a machine shop as needed. I guess y'all might know where this is heading... Anyway, a little while after buying the Road Runner he began to have problems with the starter. A local shop insalled a high performance starter motor, and immediately the new starter caused grinding noises when the engine waws cranked over (I am getting to the aluminum heads, I promise. I am just trying to set some context here). The shop told him "they all do that with replacement starters."
I told him that the shop is right, they all grind like that with starter replacements, IF THEY LEAVE OFF THE METAL GASKET (aka metal shim)! I made a few calls and found a place with their last two metal gaskets (shims), and had them ship them to me. My put the car up on my lift, and installed the shim. Surprise, surprise! No more grinding sound! But, I noticed a ticking sound that occured as half-speed, indicating a valve train issue. "Oh yeah, that started after brought it home. I figured I just had to let it break in a bit more." I broke out some vibration sensors and recorded sounds coming from several places hear where the sound seemed to be coming from, and used an elecronic stethoscope to test some other areas. I recorded the sounds on a multitrack recorder, along with a set of inductive leads that sent a signal any time spark plug 3 fired, and any time the ignition coil fired. When analyzing the sound waves I used the #1 plug firing signal to ascertain exactly where the ticking was coming fro - #5 cylinder, exhaust valve. We pulled the valve cover, and found #5 pushrod had popped out of position. Other pushrods on valves not being opened at the moment (engine off) were loose, but not yet enough to pop off. My friend said, I guess we need to adjust the valves. I told him I thought the need was deeper.
As I began to look at the valve train, with the rocker shaft and adjustable rockers (roller tip, nice high performance rockers), I found the rocker shaft mounting bolts were all loose. I suggested we pull the bolts and look at the threads, but by then my buddy was grabbing his torqaue wrench, looked up the torque spec, and began to tighten the bolts. 4 of the 5 bolts tightened well enough, but one of then ended up pulling the threads out. I told him the way to correct the issue would be to heli-coil all five bolt holes, then get some high grade studs with NC threading for the head end, and NF threading for the rocker end.
I ordered a nice SAE/Metric Heli-Coil kit and showed him how to heli-coil the damaged threads, as well as some high grade studs with NC threas at one end, and NC threads at the other. I also ordered some high grade lock nuts, and even some stainless steel split lock washers. Once I went back to his place with all the goodies he really did not want to heli-coil and stud the other bolt holes, as he felt they were now tight and properly torqued. I voiced my recommendation, but told him if he wanted to go no further I would not interfere. The one damaged thread took the heli-coiling very nicely and the heli0coiled stainless steel threads accepted the stud perfectly. The NF nut tightened down nicely, and the stud accepted the torquing with no issues. I figured aat worst he would end up heli-coiling and studding the head anyway if the bolts loosened again. He went out for a test drive and upon returning told me the engine was running better than it ever had.
I suggested we check the rocker shaft mount bolts on the other head, and the valve adjustments. The other head mounting bolts for the rocker shaft mounts were fine, but the valves definitely needed to be adjusted, as all has aa little valve lash, which forr hydraulic llfters, even hydraulic roll lifters, is not what we want. The engine sounded and ran really well after the valve adjustments were made. But, I was not convinced the rocker shaft bolts were going to say tight on the driver side of the engine. I reiterated my recommendation we heli-coil and stud the fasteners for the rocker shafts on both side, mostly because for aluminum heads using sudes instead of bolts helps keep the threads from wearing with such a soct metal. Nope, he felt we nailed the problem, so I told him the other studs, nuts, lock washers, and heli-coil inserts would be waiting for him in the event they were needed. Long story short, they were needed, but only on the one side of the engine. The other side nothing loosened up.
Shortened story made a little longer, omitting details... We studded the mounts on the one head after installing heli-coil inserts in the bolt holes. We left the other head alone, and I am betting this coming car Season when he takes the car out, we will end up needing to stud the other head also.
So, why all that info? To help lend support to my suggestion that with aluminum heads and/or blocks all bolt holes for non angled mounting parts the bolt holes be drilled and tepped for heli-coil stainless steel inserts, then studded as opposed to using bolts. Some situations will not allow for studding, such as mounting the intake manifild as its bolts are not perpendicular to the head's mating surface - so studs will not work out very well.
Okay, that's all I had to say about the bolting on of parts to aluminum heads or blocks.
