I was torqueing down bolt 10 on the exhaust cam retainer- and wouldn’t tighten to the specified torque of 180”/#’s. Instead it stripped inside the stud hole of the engine head- i saw metal shavings in the bolt's teeth. The bolt must have stretched and therefore was too thin to make the appropriate contact. The replacement bolt is 6x37mm.

What’s the best way to fix this? Do I have to take off the whole cylinder head from the engine and bore/tap/thread a wider hole??

 

What yr, make & model bike is it first of all? You will need to install a heli-coil or a time sert to repair the hole. The cam cap will need to come off & the hole will need to be dilled & taped for the heli-coil.

 

The first thing I would do is see how deep the hole is. Many times, the threads are machined much deeper than what the bolt reaches too. This means you may be able to simply use a longer bolt and get into good threads again. For that dia bolt in an aluminum hole, your going to want about double the diameter of bolt in legth which would be 12 mm. In this case, if you can get a 6x45 to tighten, you should be fine.

take a piece of wire and bottom it out in the hole. Hold your finger in the spot that it stops and remove the wire. Now measure the wire and see how deep the hole is compared to your bolt. If you have an extra half inch or more, you can probably get a bottoming tap and get enough threads for what you need.

Or, you make that threaded hole into a stud. Chances are very good you still have a few good threads. You can buy some high heat cold weld,(jb weld works really well on aluminum), buy a really long m6 bolt, load it up with jb weld and thread it into the hole. Bottom the bolt in the hole and use a decent amount of torque, but not enough to strip out the remaining threads. Let it harden over night. Now cut off the bolt head leaving enough of the stud to go through the header flange and to put a washer and nut on. Put the nut and washer on and torque to your specs. The remaining threads combined with the cold weld will create and extremely strong bond that should far exceed the torque specs.

If none of these methods work, you will have to go with drilling and tapping as already suggested. Personally, I like the keyserts the best. They can never back out once they are installed. I've never had good luck with heli-coils, especially with aluminum. I've never used the timeserts, but they look like they should work well.

 

Yeah... don't do that ^^^.


A crap bodge at best.

 

The JB weld is an option, but I would try the heli-coil or time sert first. No need to gob a bunch of stuff in the hole if it can be repaired propperly. Heli-coils are a good, reliable repair if done correctly. Time sert actually replaces all the threads in the hole. Locktight it in & you will never have a problem again. If you just install a longer bolt you run the risk of pulling the rest of the threads out of the head. The lack of threads will hinder you from achieving the propper torque safely. As stated, find out how deep the hole is, remove the cam/s, cover any open part of the head with some rags so no shaving get into the engine, & drill & tap for heli-coil or time sert. If that doesn't work then I would try the JB weld option. Seen too many bad JB weld repair jobs that I wold recomend only as a last resort. What kind of bike is this?

DON'T drill the hole to double the diameter. That is simply a BAD idea & could ruin the head altogether. The bolt is a 6x1x??. 6mm bolt, 1mm thread pitch, & the question is how long the bolt is.

 

Thanks for so many good suggestions - and none of them involved removing the head which is good.

Bike is a cbr600f3.

The honda bolt is (6X1x37) 90016-KT7-000. I got out the digital caliper and the old bolt was 5.75x 37.2mm - pitch 1*. Measuring the diameter of the threads it was 5.75 whereas a new bolt measured 5.88.

I measured the stud and it was 47.2 mm deep*. I was able to lightly bolt down a new 45mm bolt. So bolting in a new bolt would catch 8mm virgin stud. Also it have 0.13mm more girth than the old bolt, catching some of the damaged stud threads. Do you think that will be enough to hold when I apply 180"/# and ride it?


Side notes
* almost all the bolts on this bike have a 1 pitch - though there was a bolt holding the exhaust that was 1.5 - but that was probably installed with the aftermarket exhaust

* The cam chain cover is over bolt #10 which acts as a washer making the effective depth of this stud a little longer than the others.

 

It all depends on what you are working with. If it prevents you from removing the head and holds up for as long as you own the bike, how is it a crap bodge? I would certainly try this versus removing the head to drill and tap the hole. Not to mention, having to have at the very least a drill press, but ideally a mill to ensure the hole is going to be located correctly. Not equipment most people have access to. If you used just a hand drill in aluminum, you would end up with an egg shaped hole that would more than likely not be straight. A stud that has 10mm of thread is enough to hold the load on its own, the cold weld is mearly there to prevent the stud from backing out and adding a little strength at the same time. And whats the worst that will happen. The stud loosens up and a little exhaust leak is created. This is not a structural part that sees a ton of stress.Its main stress is heat and vibration. Nothing wrong with disagreeing, but you may want to actually add some ideas instead of just negative comments. That doesn't help anyone.

As for the longer bolt holding. Its hard to say. Since the original one did not hold, the lower amount of threads engaged probably won't hold long either. Unless of course it was stripped due to over tightening or corrosion. Many times, a steel bolt will corrode in aluminum and as the bolt is removed, it takes away some of the threads in the aluminum. Then when the bolt is put back in, it strips easy. As a general rule of thumb, you want at least the same amount of thread engagement as the dia of the bolt for steel. Aluminum should be nearly double. I guess what I'm saying is, it may hold, it may not.

 

Where should I buy all new bolts for the exhaust cam retainer? Any good sites for hardened steel bolts? Last time I tried nappa and they didn't even carry any flange bolts that would fit.

Def don't have access to a drill press... but it looks like I can still do the insert approach while leaving the head on. - Just widening the hole should be ok with a carefully applied drill. I DO worry however about metal shavings falling into my engine, and would have to buy a M6 tap kit, and right angle adapter to get the drill bit into a tight space.* I think I'll wrap the engine with plastic wrap and have a shop vac running while I drill can help minimalizing collateral shrapnel damage.

Seen a bunch of vids of folks using a 'free hand' drill. If an egg shaped hole is what is worrisome I would imagine that the helicoil would be preferable to the TIME-SERT since the former can go deep into the stud cavity where the hole should be nice and straight.

I heard that if the bolts aren't torqued correctly the cam retainer can warp or crack, and the heads and the retainers will have to be replaced. And the heat and cooling is what can make the bolts loosen over time- so the damage could happen 10K miles into the repair. So even if the bolt initially handles the torque it could fail later.

Yeah it didn't fail because of rust... these bolts are into the head so they are exposed to nice clean oil NOT moisture. My guess is that 40K miles of heat/cooling cycles stretched the bolts or there was a weak bolt that stripped the threads of the studs 'cause it was too thin and not having great tooth to tooth contact.

This isn't a repair I wanna do again given how much work it would be to repair a SECOND time ... it's probably worth a bit more time to do it right the first time.

So how comfortable are you with the thread engagement larger than the bolt diameter rule of thumb? If I get the perfect size bolt I could have up to 8mm of virgin stud which is more than the 6mm bolt diameter, so it should work? Just don't know if that rule would hold given the heat, vibrations and torque 180"/# factors.

SO I'M LEANING TOWARD the insert approach... and leaning toward using two helicoils so I can get contact deep in the newly threaded hole. When I break the little tang out of the bottom of the coils, do I just leave it in buried in the stud below the bottom of the bolt or is it important to try to fish it out? Like say using a magnetically charged phillips screw driver?

As a sanity check- if I were to disassemble the head and get it to a machine shop how much would they charge to bore a new stud and apply an insert?

* Notes- potential tools/parts:
Here's the link to the right angle adapter to widen the hole:
Amazon.com: Milwaukee 49-22-8510 Right Angle Drill Attachment Kit: Home Improvement

Heli-Coil 55466 M6X1 Metric Kit:
Amazon.com: Heli-Coil 55466 M6X1 Metric Kit: Automotive

Time-sert:
Amazon.com: TIME-SERT M6 X 1.00 Metric Thread Repair Kit 1610: Automotive

JBWeld cold link:
Amazon.com: Customer Reviews: J-B Weld 8280 Industro Weld 10 oz.

Another promising adhesive approach except it only works to 300 degrees:
Loctite Form-A-Thread repair kit
Amazon.com: Loctite Form-A-Thread repair kit, grey - 4.8ml: Sports & Outdoors

Loctite ® Form-A- Thread ® Stripped Thread Repair - Henkel

 

You don't meed a drill press to do this repair. To install a heli-coil you will the kit, a drill, & a 1/4" drill bit. You will need to retrieve the little tang from the hole.
To use a time sert you just need the kit as everything is included in the kit. If the hole is oval or egg shaped I would definitely use a time sert as it will make the hole round again. They also come in longer lengths. The insinde (spark plug side) bolt length is 35mm, & the outside (exhaust or carb side) length is 45.5mm.

We are talking about a cam cap not an exhaust flange here. An exhaust leak is the least of the OP's concerns right about now.

The information I have given here is not bad info. In no way, shape, or form do you want to double the diamater of the hole to 12mm as started earlier. You will create more problems for yourself.

 

If there is doubt about it holding then it is a crap bodge. I get the impression you think this is a bolt holding the downpipes to the head, it is actually a bolt holding aluminium cam guides over the top of the cam shaft, if it fails so does the engine.

If it was an exhaust stud then the heat would be too intense for JB weld.


Without mixing my words, it is a crap bodge either way.