Tuesday, June 26, 2007

Starting to look like a motor

The intake and exhaust make it look much more like a motor. Intake was pretty easy once I figured out that I was trying to put the throttle body in upside down. Which is to say right side up. I think my polymer intake is lower than the stock upper, causing the throttle cable bracket to interfere with both the fuel rail and the valve cover when installed in the normal way. I found incontrovertable evidence that the throttle body was previously installed upside down, so I put it back that way. Looks OK, but I'm a little worried about the throttle bracket and hood clearance.

I was going to try to finish up my fuel lines, but realized that I needed to know exactly where the right-side exhaust was going to be first. So I put that in. Now I know why everybody was chatting about how to tighten the exhaust header bolts. None would take a socket. Some were easy with a box-end wrench. Some required an open-end wrench, because they're so close to the pipe that you can't even get a box-end around them. One was so close to the pipe that the open-end wrench had well under 60 degreees of travel. That one is just not going to be tight.

Monday, June 11, 2007

Intake manifold installed

Well, that was easy. When I pulled the manifold back off, I found that the broken bolt still had about 2 threads sticking up above the head, and was not tight at all. So I was able to remove it with nothing but my fingers. Close inspection revealed slight but distinct necking of the bolt, on the thread right below where it broke. There's no way I put enough torque on it to create any necking, so it had to have been overtorqued previously. That's a little scary. I took a look at the other bolts, and they looked OK, though I didn't reuse any of them.

Hmm. I forgot to publish this post. Oh well, here it is.

Monday, June 04, 2007

Restarted, I hope

I got e-mail last week from a guy named Warren, of Heber. He is thinking about building a coupe and wanted to come by, look at the chassis, sit in it, etc. So on Saturday I went out and spent a couple of hours cleaning up my shop and getting everything looking good. Show-and-tell went great, and the clean shop got me inspired to do some work on the cars.

First, of course, was swapping the winter tires back to the summer tires on the van. Then I fixed the coolant leak in my RX-7. (I hope!) But finally, I went to install my intake manifold, which has just been sitting on top of my motor since I did the cam swap.

The intake manifold has 12 bolts, and you're supposed to tighten them in a specific sequence, first to 8 ft-lbs, then 16, then 22-24. I don't think my torque wrench is trustworthy at 8 ft-lbs, but I just went snug, then 16 then started to do 24 and SNAP!

One of the Grade 8 manifold bolts broke. Brittle failure, on a 5/16" bolt at something less than 24 ft-lbs. Weird. OK, let's do a little calculation. A 5/16" bolt should have a stress area of .0524 in^2. Grade 8 means minimum tensile strength of 150,000 psi. So that's a maximum load of 7860 lbs. Now according to my sources, a torque of 25 ft-lbs on a dry 5/16"-18 bolt gives a clamp load of 4720 lb. But assume my torque wrench is off by 20% to give and the threads were lubricated by some residual oil. Now we've got 7550 lbs. Hmm. That's getting close.

Well, now I'm paranoid about the other bolts, so I ordered a complete set. Haven't pulled the manifold back off, so I'm not sure exactly how difficult it is going to be to remove the broken bolt. But I'm hoping that it should come out pretty easily, since it's not like a bolt that was frozen and snapped off when I was trying to remove it. It shouldn't even be tight in there.