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Next came the sketchy task of carefully removing the old Helicoils. Usually, if the end of the coil can be grasped with a needlenose plier, most times pulling up on the coil will unwrap it and it comes right out. But in aluminum, it usually takes some of the part out with it. Because we have deeply recessed tandem inserted coils and have so little original material left to hold our repairs in place, we had to think of less intrusive ways to get the old coils out. This kit, manufactured by Hanson and sold under various brands, has saved my ____ many times!



It consists of well thought out and even better manufactured reverse direction spiral flute extractors and if those don’t do it, several cobalt coated HSS reverse twist drills with aggressive flute angles and extremely sharp cutting edges:



The method here is to try the extractors first, by hand using a tap handle, to grab the near end of the Helicoil and turn it out. The extractor will catch the coil and twisting it in the reverse direction loosens the coil from the insert threads in the head, so once it starts coming out, it keeps getting easier to remove the rest of the way. If the coil doesn’t catch with the extractor, the reverse twist drill will gouge into the coil, and then twist it out. Do this at very slow speed in a controllable electric drill motor – a cordless drill is probably best. Don’t use an air drill!



Next time (couple of days), I’ll explain our custom thread repair inserts and how to make them:

That's not a time/sert that is some sort of big/sert i have a lot of these but would never use them in that location, you can get time/serts with the same external thread as the helicoil and in various lenghts they have a lip at the top which can be ground down slightly to allow it to go down the locating dowel holes, there are only two locating dowels per cap in diagonal positions well on older models at least, it looks like you have your work cut out on that one due to some previous owners botching, years ago i made some inserts with the dowels built in for someone in Norway it took multiple attempts to get it right but it was successful . good luck with that one.

More than a couple of days….had to get some other stuff done, and damn, it is cold here.

First, yes, I have called the Barrel type insert a “Time-Sert” type insert. Sorry, that isn’t entirely correct. A true “Time Sert” is the same idea, but is recognizable as a “Time-Sert” by having small steel prongs protruding from the top that are used to lock the barrel insert in place after being threaded in to the correct depth. I have the habit of calling all barrel type inserts “Time-Serts”. The one in the picture in my previous posts looks like one of the type available from McMaster Carr’s catalogue. McMaster’s price is about 1/10 of what our local retailers charge for those. But the outside threads are 3/8 NC, way too big to keep the alignment pins intact.

Someone else on here said they could get solid thread repair inserts the same outer diameter as a Heli-Coil…where? I have never seen such a beast. In fact, all the inserts I could find would require destroying the dowel pin holes. Do the math here, and in order to get a threaded insert inside the 8 mm diameter dowel pin holes, you will end up with an insert with minimum wall thickness of 0.021”. Under normal circumstances, that thickness of steel would easily break when torqued to 9 ft-lbs (108 in-lbs).

So here is the theory behind what we are doing. The idea is to use a common thread type for the outer part of the inserts. This is so a standard size tap can be used in the head. We chose 5/16” NF, as it is readily available, and so is grade 8 or better grades of high strength steel threaded rod. McMaster Carr to the rescue, we order the stuff in 3 ft. lengths. 5/16” NF was the best compromise, as the largest size of rod that is smaller than the 8 mm dowel pins (knock pins to many, BTW), and the fine thread kept as much insert wall thickness as we were going to get.

But what about that 0.021” wall thickness? Well, that does present some difficulties. First, if we had tried to simply drill and thread the inside of the 5/16” NF rod to M6 x 1.0, the stresses of running the tap would almost certainly have broken the thin steel if the rod wasn’t re-enforced somehow while the threads are being cut. So we made an internally threaded sleeve out of ½” diameter free machining steel stock to go on the outside of the rod while drilling and tapping the inside. The sleeve keeps everything in place and prevents breakage. Also, the sleeve was made 0.800” long, the length of our finished inserts. Handy for cutting the 5/16” rod to length after drilling and threading each insert.

Second, we still have a relatively weak 0.021” wall insert. Well, that won’t be a problem for two reasons. One – we will carefully bond the inserts in the head using high strength lock tight thread adhesive (red Locktite). That should make them nearly as strong as a stainless steel Heli-Coil insert. Two, because we will be using studs rather than bolts to fasten the cam bearing caps, the peak stress on the inserts will be considerably reduced.

On to making the inserts (for this head, we needed 15 of them). First, here are the basic tools. One each quality HSS taps.
• 5/16 NF Plug or Taper
• 5/16 NF Bottoming
• M6 x 1.0 Plug or Taper
• M6 x 1.0 Bottoming
• Edge cutting fine flat file the same thickness as your flat blade / slotted screwdriver used to turn the inserts into the head later – shown is a wedge file. A flat jeweler’s file will work.
• A test M6 x 1.0 bolt
• Our 5/16” NF threaded sleeve.



Step 1, make our threaded sleeve. O.D. is ½”, drilled and tapped through the center 5/16” National Fine, on a lathe. 0.800” long.



Step 2, thread sleeve onto threaded rod until flush with the end, then chuck rod (not insert) into the lathe chuck with the sleeve butted up tight against the jaws. If the end of the rod needs to be faced square, leave enough rod protruding to face flat to end of the sleeve.



Step 3, center drill to guide the tap drill. Here you can see how the sleeve is NOT in the chuck.



Step 4, drill to the correct tap drill – for M6 x 1.0 that is listed as 5.00 mm, or a no. 8 drill. No. 8 is actually slightly oversize, so we used a no. 9 drill to keep as much wall thickness as possible. Drill only 0.900” deep, as it is necessary to end face the rod and start a new center – drilled hole in the unused portion of the threaded rod every time. Otherwise, the drill will tend to wander off center with each additional insert made.



Post broken here for size limits, continued below…

Continued from above….

Step 5, cut internal thread M6 x 1.0, using only a sharp tap. An aside – how do you know if a tap is sharp? Easy – how much resistance is felt when cutting threads.



And a warning – as an experienced former tool and die machinist, this is the best advice possible for taps and dies. For making new threads, only buy high quality high speed steel (HSS) or better taps and dies from an industrial supplier of machine tools. Always buy at least two at a time, for each size you need for the job. Only use one at a time (keep unused ones new in their containers until the old one is worn out), and mark used taps as used. Use plenty of the correct type of tapping / cutting fluid for the material being tapped, and clean out chips and debris often with compressed air or a strong shop vac. The old “turn 1, back out ¼ turn” isn’t really true. Actually, with abrasive materials like cast iron, mild steels, and aluminum, constantly backing out the tap will quickly dull the cutting edges. Some expensive taps are manufactured to go in all the way without any backing required. So most of the time, only back out when you feel chips binding the tap slightly. Then remove the tap completely, clear all the chips, re-oil, and continue. A tap is getting dull when it STARTS to resist turning / cutting easily. As soon as you notice an increase in the force needed to turn the tap (or die), remove and discard the tap. Don’t believe for a second that you should keep it around – throw it in the scrap bin right away. Dull taps are the ones that break off inside your most valuable parts in the worst possible locations. Don’t use your expensive HSS taps to thread chase previously tapped holes, either. Buy proper thread chasing tools for that.

Step 6, carefully cut off the rod at 0.800”. We used an ordinary hacksaw following the rule that at least two and preferably three teeth of the blade are in contact at all times, so we used a 48 tooth / inch blade. Clean up the cut end with a file, use your thin file to cut a slot in the filed end as shown below, and test fit by threading the completed insert over your test bolt.



Repeat for as many inserts as needed (we made one extra in the end). You can see here that the completed inserts fit neatly into the 8 mm dowel pin holes



So 8 down – 8 more to go…



Next, tapping the head for 5/16” NF….

No eBay APP ID and/or Cert ID defined in Kunena configurationIn your picture you have a big sert this as you say will destroy the locating dowel holes, in the link i have put up is time serts these have the same external thread as helicoils and are solid, the top lip just requires machining down slightly to enable it to be used without destroying the hole, if you wish they can then have a slot put in them to allow the use of a screwdriver to apply them, i would rather buy these as they are only a keyboard away , they will do the same as the inserts you are making and will leave more time to get on with other jobs on the motor, the shouldered stud system in my previous post was done around 14 years ago and is still going strong, and the whole time i owned that particular bike i thrashed it hard .

That is interesting kevski, I never knew of those before. The synchronized threads are a plus, making the wall thicker on average. Doesn't say what tap to use, but I'd imagine M8 x 1.0. I hope not the damn expensive and hard to get Heli Coil taps, anyway.

Good alternative for anyone without machine tools with only a few stripped threads to fix, but still requires modifying the inserts for screwdriver install, removing the lip if it interferes, trimming off the locking portion, etc. All the holes on this head were damaged, and unsuccessfully repaired before, so lots of work to do no matter what inserts we use. This head is on it's 10th life already. It has been more than just thrashed - it went through at least 3 rebuilds and has been off the bike and stripped and re-assembled / valve seals at least a half dozen times, and cams in and out dozens of times. And a 125 mph impact and rebound off of a guard rail at the race track....if it weren't a bathtub with a fresh valve job, porting, polished chambers, relief cuts for big cams, dry block oil feeds, surface machined, etc... we wouldn't bother with one this bad.

I still prefer our custom inserts for a few reasons - we control how long / deep, and there will never be a problem with installing them or securing them (I don't like / trust the "locking from the bottom by expanding the last few rolled threads into the base metal" as the time - sert specs say), and ours are still cheaper....just takes a little more time (I'm counting the time to order them, picking up the parcel and paying customs, taxes, and duty, shipping and handling....

And, we have the machines and materials already....

Nifty repair work! Nicely done.

Did you use thread locker on the outside of the insert before install? Sink it to below the dowel recess? How many threads did you lose due to the installation slot?

How tight do the inserts need to be, and how tight do you set the nuts that hold it all together? Cam cover clearance ?

With the time-serts if you buy the kit and follow the instructions and use the supplied tools it will lock into to the hole you are repairing.

The time-sert external thread is a 7mm fine pitch i believe which is the reason they are able to synchronize it with the standard 6mm used in these and most other Jap engines, they come in various lengths and can be trimmed to suit if you are confident enough to do it.

I have the kit to make inserts just find it time consuming, when i could be doing other things, so would rather get pre-made ones.

I have never used thread locker, even on my own stud system, but with those every one is bespoke and when tightened in lock themselves in place due to the shape of the stud and the lower part of internal thread.

It's good to see how others get around these problems when they arise, we need more thinking outside of the box ideas to keep these old motors going, i have come across people that are so blinkered that give up when issues happen.

The owner of this head finished up drilling and tapping the head for the inserts on a Bridgeport - style vertical milling machine this past weekend. It went very well. For anyone interested, the spacing of the cam cap bolts (each cap) is 38 x 40 mm, and I'll have to go back out to the shop in a few days to get the spacing between the caps (I forget). It is bitterly cold here (-33 C overnight), so I've shut the main heaters off and left the shop at just above freezing until it warms up a bit outside. I'll sand / prep bodywork in the basement of the house, and fix tattered wiring looms in the kitchen until then....

A few notes....

1. We are going to run the studs through the H cover, just tall enough with drilled and spot faced cover, sealing washers, spacers, and external nuts and use them to hold the cover with a few of the original cover bolts blocked off (the owner's plan is to use 12 point ARP nuts for appearances). The studs will be installed thus: coat the stud threads with moly grease - turn the stud in by hand until it bottoms - back the stud out 1/2 turn - install cam bearing caps, washers and nuts - gradually tighten each nut 1/2 turn evenly until all the caps are fully seated on the head - torque to 8 ft-lbs. (96 in-lbs) in 2 stages - install top spacers above nuts - install cam cover and gasket- install sealing washers and top nuts - torque top nuts to 70 in-lbs.

Not for everyone, we know, but this is more a race engine than daily commuter. There are other ways to use studs without putting holes in the cam cover....I'll explain some of those in a later post.

2. We must use permanent thread lock adhesive (such as red Lock-Tite) when installing the thread inserts. We make sure each insert will fit properly (test fit) before cleaning the parts with contact cleaner, then apply the thread locking adhesive. The adhesive is necessary as the top of the holes where the Heli-Coils had pulled out didn't have much aluminum left to cut new 5/16 " UNF threads. The fact that our inserts go in all the way to the bottom of the holes, are one-piece solid parts of high strength steel, and are "glued" in place will make them much stronger than the original threads,

3. The owner was doing all the work drilling and tapping the head, and didn't take nearly enough photos. I was too busy cleaning and rebuilding old Amal Concentric carbs and trying to get rusted / seized Norton "Iso-Elastic" engine / transmission mounts, and swing arm pivots out of a bike that sat (and rusted) since 1986. I have to earn the money to keep the heat and lights going somedays. I'll get some photos of the faux milling machine set-ups and do a proper write up when the weather improves a bit.

4. The inserts still have to be test-fit and glued in place. The owner will order the studs from the manufacturer soon. For now we will be using the standard bolts to check our work. I also have to plasti-gauge the cam bearings to be sure the alignment of the caps is acceptable. If not, I'll have to work carefully to precisely correct or re-locate the dowel / knock pins. I'm hoping that won't be needed!!!!!

5. I will be using the same stud system on my own KZ-J 1394 big block and my "Beater II" 's new street / strip KZ-J 1170 engine (made out of discarded used / reconditioned racing parts). My heads don't have stripped threads, so no need to install the inserts. The studs will keep the original threads safe from damages over the harsh life my "experimental" racing engines will see in the future....

Nessism wrote: Nifty repair work! Nicely done.

Did you use thread locker on the outside of the insert before install? Sink it to below the dowel recess? How many threads did you lose due to the installation slot?

Hi Ed, thank you.

Yes, thread locker is a must. The inserts are installed flush to the bottom of the dowel recess, and extend all the way down to the bottom of the holes in the head. The total depth we used to drill and tap is 1.125". The dowel recess is supposed to be 8 mm deep, but this head varied from 0.302 to 0.330". The screwdriver slot cut into the end of the insert doesn't really affect the insert once installed, so not really losing any thread engagement / height. the slots are cut two threads deep (at most 3) into the inserts, and are 0.050" wide.

I have some spare virgin low mile bathtub GPz1100 engines and heads I've been hording for future projects, and the owner of this damaged one wanted to buy one of those from me to replace his goofed one. I said I preferred to try and fix his old one (and all the good performance work that has gone into it prior to discovering how hopelessly bad the cap threads were) before parting with one of my nice unmolested spares......

kevski wrote:
I have never used thread locker, even on my own stud system, but with those every one is bespoke and when tightened in lock themselves in place due to the shape of the stud and the lower part of internal thread.

It's good to see how others get around these problems when they arise, we need more thinking outside of the box ideas to keep these old motors going, i have come across people that are so blinkered that give up when issues happen.

I generally stay away from thread locker, gasket glue, RTV, etc. but sometimes it is unavoidable....

Heck, I obtain most of my "discount" parts from others "so blinkered that give up when issues happen" - they see insurmountable problems - I see affordable opportunities with a good challenge and some potential fun...

Besides, after spending more on tools and shop equipment than I spent on my first house and car, I can't really justify any excuse why I can't repair stuff like that.....