Advice needed

[darkember]

Actually the stud length is 18mm so loosing 3mm should not be an issue. The stresses on those studs are definitely not excessive as the nuts behind them are only torqued to 12Nm just enough to compress the copper seal. The thread on the engine stud end is 8mm & its torquability is far in excess of 12Nm. I believe its excessive thickness is to combat the heat cycles it needs to endure.

[tony.mon]

One thing many many MANY experienced people have told me in the past and something I have become to truly believe is that the japs are fantastic are building bikes (and cars for that matter) and anything they put on a bike, they do so for a reason. Putting on more than necessary costs more and therefore reduces profit margins.

Another thing I am learning (doing a BEng at the moment) is that things aren't randomly chosen when being included in the design of a machine.

Obviously, other people have cut away (what appears to be 3mm) from the engine and haven't seen a problem but this genuinely concerns me. Surely, cutting away 3mm from where the stud is placed means you have 3mm less of thread acting on the manifold and against the forces subjected to that (not just gases traveling at just shy the speed of sound but also every time you hit a bump, gear changes, braking etc all act on all parts of the bike, gravity ensures it!). So if you only have 10mm thread on the stud and remove 3mm from its housing, you only have 7mm doing the same job 10mm is expected too. I'm not suggesting your going to run into problems as it's you likely wont, but I am suggesting that cutting bits of engine away from the bike should be last resort business.

That might be valid if each part were designed for that particular model. But as it is, the same head castings are not only used for both front and rear heads, with just the CCT position machined differently, but also on the XL1000 Varedero series. Those are the ones we know of, it may of course be that Honda had several other models in development that also used the same head castings.
Very clearly, from the diabolical CCT situation, Honda don't make a new part for each model variant. There's a financial reason to raid the parts bins, and make do with a part which will do the job but isn't specifically engineered, stress tested, and pared to meet the exact specifications and life expectancy for that application.

The tensile strength in the remaining section of thread is plenty strong enough. Remember that the exhaust clamp, as is shown in the thread above, isn't clamped to a solid surface, but applying a force to compress the O ring gasket- indeed the plate that goes around the header and which the studs go through will also deform a little, especially once it has rusted and thinned a little, as they all do.
The head casting material is an aluminium alloy, and is quite hard, able to take the strain of a reduced thread length without failure, imho.

Lastly, if the thread DID strip, no biggie, as the casting is big enough to be tapped oversize and a custom stud inserted, alternatively a thread insert can be used. But I've not known one strip, tbh. Even with a reduced thread depth, you can't generate enough rotary force to strip the larger thread; the smaller section of the stud shears first.

[Bleh]

I could fish out some old notes with relative formulas on to calculate the studs maximum torque ability IF we could find any modulus' in relation to the material it's turned out of. Can't remember it off the top of my head (as there is so many) but there may be engineers on here who do so ad it would be interesting, purely out of interest/ curiosity.

I doubt the 12 N/m torque setting is to benefit the stud which will undoubtedly have a considerable shear strength. 12 N/m is what? It's equivalent to just over a single kilogram held out at a meters length so it would be safe to assume the setting is purely to benefit the thread in the aluminium head to prevent over tightening and potentially stripping it. Ali with a thread pitch of 0.5-1mm (?) isn't going to withstand a massive force at all, especially when getting to the temperature the head can get to. Not even the 6061 grade I built a set of billet yokes out of a few years ago took much effort to cut a thread into and that's some tough ali.

I have no intention of criticizing anybodies techniques if they work, just trying to maybe offer a consideration that others may not have thought of.

Not long back, a few lads I know had trouble getting the flywheel/ stator off the crank. They broke two pulleys trying to get it off (quite common with the R1 apparently) before they came up with the bright idea of CUTTING it off. I couldn't stand by without offering my opinion and i said to them 'lads, you may believe that cutting things up is your only choice, but once you've cut the majority away, what have you got? You still have a section attached to the crank so still in the same boat! Plus, if you cut that little to far by accident, you're looking at replacing the crank, bedding it in and hoping you do a good job of it for when it's rebuilt'. I tried to persuade them to try 101 things before they cut it away, freezing it, heating it, brake more pulleys, anything but cut into it...
They inevitably f**ked it up and the engine remains in bits to this very day.

I know there's a significant difference between a piece of manifold mount and crank/ stator but I really am not a fan of cutting near or on engine parts, I try to encourage any and many things before resorting to such, which, is some circumstances, may be the only option but there is always options before getting to that point...


If the japs decided they need (structurally) 18mm of thread in place to hold the exhaust in place, they did so for a reason. It could be for benefit of the life of the part(s) or because at 12 N/m, 18mm of thread would compress the copper gaskets sufficiently with out putting excessive stress on the thread in the head when under load (external forces etc) and reducing this to 15mm will change the requirements of such settings to achieve the same results that are necessary. The japs didn't guess it, they did it because it was what was best for the bike and I for one am not going to argue with them, they can build a better bike than I can (for now ).
Performance wise, fair enough, bikes are tuned to our british 'terms and conditions' and we all enjoy tinkering with this, but as far as what they intended for the structure of such components, I'll listen to their recommendations every day of the week, but maybe that is just me!

make do with a part which will do the job but isn't specifically engineered, stress tested, and pared to meet the exact specifications

They may get some generic parts from 'the parts bin' I assure you, every single part that goes onto ANY vehicle from a reputable company is tested and traceable to the original element it is produced from, so detailed it is, if needs be they can trace it as far back to the mine the ore came from.

They wont provide this sort of information to me or you as we are mere mortals, but I am highly reliably informed that this is the case from people who have/ had jobs we may only hope to have one day!

[macdee]

i love it when you talk dirty blehhhh

[Virt]

i love it when you talk dirty blehhhh

I don't. I've never felt more stupid in my life than when reading that It all WHOOSHES over my head

[tony.mon]

I'd love to have access to some of their test data; if nothing else it would save a lot of dyno cost playing with variations in airbox sizes, designs, etc.....
Honda, if you're listening, I'd keep it to myself, honest....)

The trouble is, all manufacturers have their own set of production values; they simply won't just build the best bike they can- cost, weight, emissions, and sometimes not taking sales from another model in their own range.
Not to mention leaving a little in reserve to increase sales in the "new" model, 2bhp or a Nm of torque over last year's one never hurts sales figures of a new model.

And after all, you're buying a design engineer's idea of what you want, modified by the accountants and marketing folk.

That's why I modify bikes- to get them nearer to what I want.

[darkember]

I could fish out some old notes with relative formulas on to calculate the studs maximum torque ability IF we could find any modulus' in relation to the material it's turned out of. Can't remember it off the top of my head (as there is so many) but there may be engineers on here who do so ad it would be interesting, purely out of interest/ curiosity.

I doubt the 12 N/m torque setting is to benefit the stud which will undoubtedly have a considerable shear strength. 12 N/m is what? It's equivalent to just over a single kilogram held out at a meters length so it would be safe to assume the setting is purely to benefit the thread in the aluminium head to prevent over tightening and potentially stripping it. Ali with a thread pitch of 0.5-1mm (?) isn't going to withstand a massive force at all, especially when getting to the temperature the head can get to. Not even the 6061 grade I built a set of billet yokes out of a few years ago took much effort to cut a thread into and that's some tough ali.

I have no intention of criticizing anybodies techniques if they work, just trying to maybe offer a consideration that others may not have thought of.

Not long back, a few lads I know had trouble getting the flywheel/ stator off the crank. They broke two pulleys trying to get it off (quite common with the R1 apparently) before they came up with the bright idea of CUTTING it off. I couldn't stand by without offering my opinion and i said to them 'lads, you may believe that cutting things up is your only choice, but once you've cut the majority away, what have you got? You still have a section attached to the crank so still in the same boat! Plus, if you cut that little to far by accident, you're looking at replacing the crank, bedding it in and hoping you do a good job of it for when it's rebuilt'. I tried to persuade them to try 101 things before they cut it away, freezing it, heating it, brake more pulleys, anything but cut into it...
They inevitably f**ked it up and the engine remains in bits to this very day.

I know there's a significant difference between a piece of manifold mount and crank/ stator but I really am not a fan of cutting near or on engine parts, I try to encourage any and many things before resorting to such, which, is some circumstances, may be the only option but there is always options before getting to that point...


If the japs decided they need (structurally) 18mm of thread in place to hold the exhaust in place, they did so for a reason. It could be for benefit of the life of the part(s) or because at 12 N/m, 18mm of thread would compress the copper gaskets sufficiently with out putting excessive stress on the thread in the head when under load (external forces etc) and reducing this to 15mm will change the requirements of such settings to achieve the same results that are necessary. The japs didn't guess it, they did it because it was what was best for the bike and I for one am not going to argue with them, they can build a better bike than I can (for now ).
Performance wise, fair enough, bikes are tuned to our british 'terms and conditions' and we all enjoy tinkering with this, but as far as what they intended for the structure of such components, I'll listen to their recommendations every day of the week, but maybe that is just me!

make do with a part which will do the job but isn't specifically engineered, stress tested, and pared to meet the exact specifications

They may get some generic parts from 'the parts bin' I assure you, every single part that goes onto ANY vehicle from a reputable company is tested and traceable to the original element it is produced from, so detailed it is, if needs be they can trace it as far back to the mine the ore came from.

They wont provide this sort of information to me or you as we are mere mortals, but I am highly reliably informed that this is the case from people who have/ had jobs we may only hope to have one day!

The above all goes out the window as you tune your machine to higher BHp's according to what you are arguing. So if i were to setup my bike to 130 Bhp my exhaust studs are still going to be the same. The way you are speaking is as if any mode is detrimental. These machines are under stressed as it is due to the nature of their Vtwin configuration.

[Bleh]

The above all goes out the window as you tune your machine to higher BHp's according to what you are arguing. So if i were to setup my bike to 130 Bhp my exhaust studs are still going to be the same. The way you are speaking is as if any mode is detrimental. These machines are under stressed as it is due to the nature of their Vtwin configuration.

Yes your exhaust studs will be the same but the flow of gases CANNOT exceed the speed of sound (unless you add some fandango kit) therefor the forces being applied to the headers remains the same with the exception of more gases being exhausted hence upgraded exhaust systems to aid in dealing with this. If you wanted to tune your bike to 130 bhp, you'd be firstly looking at getting more air and fuel in for bigger bang (so valves, springs, cam, timing/ ignition, overlap etc) and then critically your frictional losses as this is where most of your power loss is, in fact over 60% by the time you get to final drive in a majority of cases but I'd guess you already know this?!

Please don't misunderstand, I'm not saying modifying your machine is detrimental but just structurally, I wouldn't personally take parts of an engine but as I also said earlier, people seemed to have done it with no issues. It's just personal preference!

Tony, I'm slightly confused by what exhaust studs have to do with Dyno testing but eh, if you ask, the worst they can say is no... Or, you could jump on a relevant engineering course, learn all the mathematics related to engines (I've been at it two and a half years and still learning new formulas every week) then build excel models to calculate what power gains you get from certain modifications and THEN stick it on the Dyno to confirm/ establish how accurate your changes are. At least, that's how it's done in the uni I attend with open access to an engine Dyno (rolling road apparently on its way).

And funny you should mention Honda sharing their technology. The christmas before last (so, 2011) we had a guest speaker by the name of Neil Spalding (assuming you know who he is). He spent a few hours discussing GP technology, in particular, the naff Ducati chassis at the time and the quality Honda were developing. Neil is fortunate enough to have privileges where he gets to see a lot of behind the scenes stuff in GP and speak to a lot of top top people within the sport (we also have a part time lecturer who works for Tech 3 as Bradley Smiths data analyst so maybe doesn't see as much as Spalding).

One thing I found particularly interesting is the fact that Honda were displaying their CURRENT GP bike for all to see at a function (whereas most teams cover the bike best they can to hide theirs), and the reason they were doing this? To encourage other teams to follow suit so they could have some genuine competition.

He's back down here on the 12th December to give another presentation which I am really looking forward to. I'm hoping to get a word with him about the Tigcraft chassis he used to race with which we currently have and are developing with a CRF450i for supermono championships, hopefully, that will be finished by or before May 2014.

In fact, a few students are running a race team with a VFR 400 (Team V4 Racing if you're interested) and have had some responses from Honda in relation to tuning the engine, but have never asked for test results of the shear stress experiments for the exhaust studs. Any Fast Bike readers should see an article on the team and uni over the next month or two (or three) as there was a journalist with us one day last week doing his thing for the magazine!

[MacV2]

The Fast Bike article should be a good read then...How much does this bike wheelie & what tat can we bolt on to it...

[tony.mon]

The CRF project sounds fun.
To be honest I've never had to Dremel anything off mine, as I'm just as happy, if the stud shears flush with the cast boss surface, to take the head off and use a pillar drill to remove the old stud with a broken stud extractor or similar. An as I have a few spare heads laying around, too, so it just isn't a problem.
All I was saying is that I wouldn't have thought that the forces you can put on the stud by tightening the nut on the header clamp wouldn't be sufficient to pull a stud out of the head, even if it were 3mm shorter.

And if it goes while you're riding, nothing dreadful will happen, you'd still be able to ride it home, so it's not critical.
Sure, an exhaust leak could make the engine run leaner, increase heat, etc, and fail an MOT, but it won't kill you.
I'd be happy enough riding with it.

But if you stick with the Honda must know best mantra, surely your bike would be standard, even down to the tyres?

I've ridden a fair few standard ones, prefer mine, though

[Bleh]

The Fast Bike article should be a good read then...How much does this bike wheelie & what tat can we bolt on to it...

Let's hope it is, we are apparently the best in Britain if not Europe for what we do and the quality of graduates coming out.
It's already tatt'ed up quite a bit with TYGA sending bits over (for the benefit of it potentially being seen on the bike in the article). The rider is a student who also races in italian super stock (think he currently has the MV) and wheelies a lot as well as falls off a lot (joked about 'a lot'). The boys have worked hard on it in fairness and seem to have new carbon fibre panels in the auto-clave on a frequent basis.

I don't buy any magazines usually but will likely do so when this one is published.

[VTRDark]

If none of the suggestions works for you it will be a head off and have it drilled out and a machine shop and new head gasket too .

That's what I ended up doing after trying heat, drilling etc. Mine was snapped near enough flush with the surface

If you get too pissed off with it, then as a temporary bodge you could get a spot weld in there instead of the nut. That should last just over year......because of the forces from going over bumps Which brings me onto the following.

And if it goes while you're riding, nothing dreadful will happen, you'd still be able to ride it home, so it's not critical.
Sure, an exhaust leak could make the engine run leaner, increase heat, etc, and fail an MOT, but it won't kill you.

I can vouch for that. I rode over 100miles with the front downpipe hanging off.

(:-})