I have a low head that the plug threads are shot. I am sure this is nothing new . What if anything can be done to save this head. One hole the plug can be bottomed out with using my fingers to thread the plug in. Actually just wiggle the plug and it drops all the way down. It has been suggested to cut it in half and make book ends. Any suggestions would sure be appreciated.
Bill, there's a lot of old low heads laying around in some of these guys shops with good threads. Call Andy Loso, he can probably help you out or take a look at helicoils.
I had nothing to loose on this head that had striped threads, drilled to fit a plumbing 1/2"to3/4" nipple adaptor, screwed with loctite and milled the nut off, all 4 plugs.
Bill, I don't know if there is anything like a half inch pipe thread helicoil, but if worst came to worst, maybe you could install a set of 14 mm spark plug adapters using threadlocker if you had to and use 14 mm plugs until you could find a usable head.
Kerry beat me to it, but he may have the best suggestion.
Kerry, how did you cut new 3/4" pipe threads in a cast iron head?
Kerry let me more specific. I once tried to drill and tap a Z head that originally had 14 mm spark plug holes. I drilled and attempted to tap for a 1/2" pipe thread. It was so hard to turn that tap, I darn near gave up.
Nice work Frank! I also want to know...
Richard, The tap on top of the head is a 3/4" pipe thread tap, just re-drilled and tapped, cast iron is very easy to work with.
Pipe thread tap sets are easily available on Ebay, I actually had bought mine from USA ebay.
Kerry, you da man. I will do the drill and tap. Like you said nothing to lose and a heck of a lot cheaper. Thanks , Bill
Richard use plenty of cutting oil when re-taping in cast iron the higher the sulphur content the better imho
I was taught to machine, drill or tap cast iron dry except when doing high speed work, then use a fluid for cooling.
I have a rare primer cup head that had striped spark plug holes.The local machinest made new 3/4 bushings with fine thread on the od and drilled and taped the head to match.Perfect! Bud.
MSC sells Helicoil inserts for 1/2" NPT.
Would a helicoil insert work? Just doesn't seem to me that it would seal the way you need it to.
Yes they work ,I have used them.
I too was taught to drill and tap cast iron dry. My teacher went to work at Ford in 1928 in the Pattern Shop. Dave
I'll have to agree with G.R.--Use a lube. Unless you have a gorilla helping you turn the tap, lube helps a lot. A 1/2" NPT tap is over 3/4" and 3/4 NPT is right near 1" and they're tapered. If you don't ream the hole with a tapered reamer, you'll need a breaker bar to turn it.
Tap dry, cast iron cuts all together different from steel. KGB
No Helicoils !!!!!!!!!! They will not hold up to the heat. They will pull and loosen up. All they are is a stainless coil spring and they offer no strength.
There is a high quality hardened steel insert."Thread Certs" are the reccomended and approved way to install permanent threads in to blocks, heads and especially spark plugs.
These hardened inserts are threaded on the outside(oversize) and have a flange on the top. You buy a kit which included the oversize tap, the chamfer tool and the installation tool. Mc Master Carr has them and if you go on line and type in Thread Cert you can find other suppliers
Following the simple instructions you can easily install the insert in a short while. Simple hand tools and follow instructions. This is a permanent fix for a nasty problem.
We have used these on Subaru's for over 25 years and never had one fail. We use then for head bolts, exhaust studs and spark plug holes.
I have an aluminum head that had 1/2" pipe helicoils installed from the manufacturer. I bought the head back in the 70's and have run it on a regular basis since (most recently, today). The helicoils work perfectly and always have.
Whatever you are tapping threads into by hand, most likely you need to just turn into it as far as you can easily, then back up and, then go again, no matter whether you are tapping steel, cast iron, aluminum, stainless steel, etc. I have the utmost respect for Ken, but you don't need lube for tapping cast iron, I have done that many times. There are different tapping fluids for different materials. JMHO. Dave
I am always wary of using helicoils in open holes like spark plug hole in heads and king pin holes in front axles. In blind holes the coil winds in and stops. One one front axle to which I tried to fit a helicoil, it repeatedly wanted to wind out the bottom when the kingpin was screwed into place.
This can't happen with Thread Serts. I feel much more at ease using them in open hole applications.
Just my tiny mind at work.
Allan from down under.
My opinions are to tap or machine cast iron dry. Clean the tap often. Tap till it is hard, remove tap, clean tap, and tap some more. Thread certs are my only choice after I started using them. Heli coils probably will work but thread cert are in my opinion a better system. KEENCERTS are another brand I use often. They have 4 keys that you drive into the treads after inserting the insert. They will not ever back out. But they are removable by using the proper size drill bit to drill the insert and then "pick" out the keys. Good luck. I always like to see someone trying to save the old parts, instead of just throwing them away and buying new.... or another one
Please excuse my ignorance, but why do you tap or machine cast iron dry? I'm nowhere near a master machinist, but something about that just doesn't make sense to me. Is there a scientific reason cast iron is cut without lube?
Jared, cast iron is relatively soft and somewhat granular when machined or tapped, almost self lubricating so to speak. It doesn't take anywhere near as much pressure to be machined as other metals, so there isn't near as much heat buildup. Sometimes lubricant (depending on what is used) can cause the cuttings to jam up. Dave
Brass car guy, I agree. I used thread certs and was very impressed with them. Calling them helicoils was a wrong choice of words on my part. It seems as I get older I show these tendencies for using the wrong nomenclature for what I'm attempting to describe. Thank God I've got old age to blame for my ignorance.
Jared, typical cast iron contains a lot of graphite, so it's like self lubricating.