Installing HeliCoil Threads, The Restorer • November/Decemter 2003
As is his custom, my dad, Jim Spawn, doesn't hesitate to draft me into various Model A related activities - sometimes against my will. lt's nothing new. He's been doing it since 1 was 12 years old - about the time he got his first Model A. Whenever he needs a third hand or a strong back, I've bccn the designated helper. 1 don, mind. It gives us a chance to work together and more often than not we end up with some ivIodel A progress and satisfaction. And so it was during my most recent visit...
Dad's latest project, a 1930 Murray Town Sedan, developed a serious performance problem. He had researched all the obvious woes - fuel, carburetor, timing, etc., before I arrived. The engine started fine and would idle like a Champ. But under pressure it would bog down and the top end seemed to rattle. We concluded that a stuck valve, blown head gasket, or worse, was to blame. We pulled the side valve cover to determine that all the valves were free. I figured that since my three-day visit was short, h. let me off the hook at that point. Not so.
He produced not one, but two, new head I'll be the first to admit that HeliCoil gaskets and announced that we had to pull threads should be used as the last resort. the head.
Surprisingly, the head came off fairly easy. A quick review showed no signs of a bad head gasket. We searched for more serious problems - cracked block, busted piston - all seemed to be fine. While removing the old head gasket we noticed one of the studs was loose. It wouldn't tighten up either. After removing it We saw that the tlweads were in bad shape. Many were rounded indicating that it had been loose for a while. We cleaned up die threads the best we .uld a. it seemed to hold. On went the new head gasket and the head. However, when tightening the head bolts that stud started pulling right up out of the block! And so tile one on the opposite side of the engine! This must be our problem.
The combination of bad threads in the block and on the cylinder stud prevented the system from holding tight. It was clear to me that we had only one choicc
For us, it was the last resort. The engine number and frame number match on this ear and Dad wanted it to stay that way. I'd used HeliCoil threads coil before. It had saved the day on a .ky rear end banjo a few years back.
allows you to screw in new stainless steel threads. It comes in a kit. So while Dad szdos,pal::eaned up for the
Wom cylinder stud on left no, stod rn,nt
We used the Balkamp HeliCoil Thread Repair Kit 77.3047 - Size 7/16-14. The kit comes with everything you need except the drill bit. In this case, a 29/64 (.453)) bit is required. Wc bought a new reduced shaft bit, as it is a fairly large bit and . wanted to insure that it would fit into Dad's antique electric drill.
The steps to install HeliCoil threads are fairly simple. Here's how we installed OUTS:
• When working on an engine block, tape off the piston area. We used duct tape leaving only the hole we were working on exposed. This prevents metal shavings from finding a way into the pistons.
• To insure that you drill thc old threads out straight and al. gauge the depth of your drilling, it is a good idea to bolt the head in place temporarily. Mark the drill bit with masking tape to gauge the depth of the cut so there is less chance of drilling through to the water jacket under the stud. The 29/64" drill bit is somewhat loose in the head and you can wrap it with tape for a snugger fit. Go slow and only go as deep as necessary to remove the old threads. Use a vacuum cleaner to remove metal shavings and old threads from around thc area.
• The HcliCoil kit comes with a for the size indicated on the kit. Use a Tee handle if you can, to help you go in straight. Lubricate the tap and go slowly. Cut fonvard clock-wise and then back off. Then go clockwise again. Since you are working in a clean hole, the tap cuts pretty easily. Let the tap do the work rather than horsing it in.
• Remove thc tap several times to check your depth and once you have cut threads to the bottom of the hole remove it and again clean up all loose metal.
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one of the stainless steel inserts (part number RI 185- 7). It screws right in until the little driving tang engages on the bouom of t. insert.
• Then screw the insert into the newly tapped hole. When it hits the bottom, snug it up and back out the installation tool leaving the new threads in place. The top of the insert must be 1/4 lo 1/2 tum below the top surface.
• U. a punch and hammer to break off the little tang on the bottom of the coil. Remove the tang from the hole.
• Finally, install a new head bolt stud and tighten. At this point, don't take any chances by trying to use the . old beat up onc.
• We reinstalled the head and naturally held our breath while tightening the head bolts to specs — 55 ft. lbs. Sure enough - they held. Once all the usual parts were reinstalled, the engine ran great, We're convinced that the loose studs allowed compression to leak even though it didn't blow the head gasket. Remerober to re-torque the head bolts after testing the engine.
1. 29164. reduced shaft drill bit. 2. Tap 0819.7 3 Installation tool. 4. Stainless steel thread inserts.
I recommend that when you're finished, you put the 29/64" drill bit and a couple of new head studs into the HeliCoil packet. That way, if you ever need to do this again, you'll have everything you need right in the kit.
Thanks to this repair, yet another Moclel A Ford was fit for travel. The smile on my Dad's face was handsome pay for this job. Who knows what he'll have waiting for me next time?
November/December 2003 The Restorer