Bolts (now a serious problem)

If a bolt should “not exceed 40Nm of torque.”

And you tightened it to 40Nm by the torque wrench.

And some time in the future you go to the bike and see no bolt.

How tight should you fasten the replacement bolt when it arrives?

And what do Honda use to make their spacers that they charge £12.12 for one?

But does an engine really need to be held in the frame anyway?


I guess the answer is 40Nm and a dab of loctite.

I had a similar issue with a yamaha £14.40 nut but the extortionate hardware seemed to be the solution.

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Shall i take a guess …
R&G crash.bung bolt ?

Buy nuts, bolts, spacers, washers etc from a dealer and you’re paying for the whole 9 yards of warehousing, storage, summer holidays and then some.

In real life 40 Nm tips the scales at about 30 lb-ft. Interestingly enough that is about the same breakaway torque of cured Loctite 243 (the blue stuff) the difference being the Loctite 243 will not succumb to vibrations.

I’ll take a punt here that we’re talking about a steel bolt in a threaded aluminium casing. The problem is the steel can and more often than not will weld itself into the aluminium. Then when the bolt is withdrawn it pulls parts of the aluminium thread away resulting in the obvious weakness. We know we should be cleaning and examining the threads of all fasteners when taken apart but how many of us really do that?

All is never totally lost, bolts can be replaced and any damaged threads can be repaired with an insert. A careful inspection is required before re-assembly to avoid another bolt going AWOL.


I had not even considered the thread being damaged. Obviously I still have the original bolts, so tomorrow I will try one if the thread looks okay just to be sure that is all okay.

The bolt has never been withdrawn by me, would it have been removed when being serviced? Hopefully it was just vibrated loose, I am assuming from Tim’s astute guess it it is not an uncommon problem.

And when the spacer arrives I will measure it to see if I can find some knock-off versions to keep as spares. At least then I could have used one of the original bolts for now. Though a replacement bolt is only £3.40 though, and surely they cost more to produce than drilling a 10mm hole thought a short cylinder.

The replacement should be tightened to 40Nm still because they will be into threaded aluminium, overtigthening will result in tears pretty quick. Worth checking in the owners manual if there’s a particular tightening pattern. For example with my Saab, there’s a particular tigthening order for up to finger tight, then another quarter turn, and then finally with the torque wrench. It felt ridiculously excessive when I was doing it, but was probably a way of getting the head cover to seat well and then get consistent pressure on all bolts. This may be true with yours

Well the thread seem to be okay, I can tell because the rest of the bolt is still in there!

I cannot imagine how, but it must have snapped in two. Although I have never done anything to put any external pressure on it, and the bike has not been parked anywhere that anyone else could have either. So that only leaves the engine vibrating against the frame?

So how serious is it? Can any decent mechanic just drill it out?

I assume the bike would be safe enough to ride a few miles carefully to one, given I have no idea where along a 277 mile journey on Friday it broke off but got home without realizing.

funny, as I was reading through these points I thought that may be the case. happened to me once on my old hornet. it was an engine mounting bolt too if my memory serves me correctly. an instructor pointed it out shortly before I was due out on track at a trackday! I hadn’t even noticed it. luckily it was at brands hatch so I whizzed down to T3 and they used an ez-out and drilled it out.

you’ll want to go to a decent mechanic if you can just to stop it turning into a horrible mess but shouldn’t be too much bother. good luck

When you retrieve the bolt shank the thread will be far from fine. Its a common enough problem caused by the very nature of the materials used and/or some monkey boy who felt 40Nm wasn’t near tight enough. Any half decent workshop should be able to sort it out for the cost of half an hours labour. Once out I’d be inclined to drill it oversize and fit an insert to minimise any risk of any further occurrence of the same. The aluminium threads are probably fubar anyway.

Sorry I just realised what you are talking about. I wouldn’t worry about it I’ve had it happen a few times. Vibrate out that is. It may have been missing for a few days you just didn’t notice it. I wouldn’t worry too much about it for now if the other one is tight (for now as in I would get it to the weekend). Drilling the entire bolt out would be a bad move as you’ll not be able to keep the drill tracking straight. My favourite solution is to weld on a nut or allen key to the bolt. You also have stud extractors which I have always had mixed experience with. Failing that, left handed drills but your bolt will be too big for this.

If welding something on the bike, DISCONNECTING THE BATTERY is paramount - your mechanic will know this but worth making this clear all the same.

I thought we were talking about an engine block bolt - just a mounting bolt the torques are more of an art than a science. I would still 40Nm it, but a healthy dosage of loctite would be a smart move. Note this is one of the bolts that ought to be checked in those pesky 4000 mile service items that I always ignore

Point of order it is science and it works something like this - When steel comes into contact with aluminium there is a risk of electron transfer which causes the two metals to weld together. The risk increases over time and with higher torque settings, contaminated assemblies, distortion of threads, ingress of moisture and contaminates etc.

The idea of using a thread lock adhesive such as Loctite 243 is two fold. Firstly it bonds the threads together achieving a greater break away strength for a lower torque setting and less compression. Secondly it provides insulation between the steel and aluminium. All of which reduces the risk of electron transfer and the welding together of the two metals.

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Within the context of cylinder head bolts, it is an art and the torque wrench in your forearm will tell you if you’ve done it right

Let us know how you get on!

More points of order we’re talking about a steel engine mounting bolt, the risks and the reasons associated with failure when assembled into aluminium (engine) casings. Yes, these same principals would equally apply to steel cylinder head bolts where they’re assembled into an aluminium block. However, of interest and so as not to mislead anyone steel cylinder head bolts fitted into aluminium blocks should be assembled with a molybdenum disulfide oil. This is in part because of its low electrical conductivity which acts as an insulation reducing the risk of electron transfer between the steel and aluminium which in turn helps prevent the metals from welding together. Whoops, sorry more science :wink:

The advice ‘not to worry about it’ (‘it’ being a failed engine mounting bolt) is… no matter this is the internet after all.

Cylinder head bolts important for maintaining compression. Engine mounting bolts just for keeping engine roughly in the right place… mine hasn’t fallen out yet! YMMV

Is that the same thing as my big tub of grey lithium grease?

No action today as I have been waiting for the new bung and bolt to arrive. They did not, but the spacer did. So I measured that up to now try to find some cheaper 7.6mm ones for spares.

As I cannot sit around all day waiting on the post tomorrow, I will call around to see about getting the broken bolt out as I can use an original one in the meantime. The bike has never fallen on that side, but I am sure it will without protection, though. It has been that sort of year.

Molybdenum disulfide oil or grease? Is an anti-seize paste such as Molyslip’s Alumslip or Permatex anti-seize and completely different to your tub of lithium grease. Copperslip is a similar product but not as effective in reducing galling and seizure within steel fasteners into aluminium casings.

Anti-seize and thread lock are not interchangeable. Use an anti-seize to prevent galling and seizure (which is probably what you have here) use thread lock to prevent fasteners backing off due to vibrations. Note when using either anti-seize or thread lock dry torque settings need to be reduced to allow for their lubricating effect.

Ahh, actually looking at the lithium grease it contains molybdenum disulphide (CV Lith Moly), so I half remembered what it said.

Anyway, I called Frank Dunstalls, who were recommended on the forum way back and I have happily used on occasion. He was a bit concerned about drilling the bolt out, that it might need special tools and the damage it could do. But I am taking the bike over tomorrow morning so he can take a look at it. At least then he can give informed advice if not do anything himself.

Although the Lithium grease contains the all important molybdenum disulphide it remains less suitable as an anti-seize because it probably contains too little and is too thick, the correct consistency will be nearer to tomato ketchup. That said back in the day my father, who owned a Honda franchise when there were such things, had just one tub of grease in the workshop and he’d use it for everything including wheel bearings, anti-seize, drive chains and gasket goo!

Frank Dunstall’s are right to be cautious because drilling too far off centre could weaken the aluminium casing sufficiently for it not to be suitable to accept an insert.

Looking at your picture it appears that the centre of the sheared bolt shank is a cleaner shearing to the surrounding area. Leading me to think the bolt has previously been fractured but not completely sheared and that vibration over time has finished the job.