Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Erwin83 on July 08, 2020, 07:08:06 PM
-
For lack of another word...
My CB466f turned quite smokey recently. I determined that the head nuts (especially the 4 surrounding cil2, the one smoking) were not torqued down anymore. So either they came loose, or the head came down during break in, and I was too late re-torqueing them.
I replaced the head gasket yesterday and found something that I find strange:
I torqued all nuts in proper order to 20 Nm, next to 25 Nm, finally to 30 Nm.
Now, even after applying 30 Nm, I can still twist the nuts a little if I apply less than 30 Nm of force. You can see the nut AND the stud itself turn a little. They will come back to the original position however. Hence the “elasticity”: the stud twists a little.
This happens on pretty much all head nuts.
Is it normal?
-
30Nm is approx 20 ft/lb, which sounds very high. Did you remove the head studs as part of the rebuild?, Have you stripped the threads on the bottom of the studs? have you got the correct size copper washers in place, because if they are too thin, the nut can come down too far on the thread and not hold. Are they standard head studs or stainless steel?
-
16 ftlb is the spec, so I overshot it a bit with 30Nm. Still the flexibility is weird to me.
Nope, studs have not been removed, hence standard stuff.
I have the correct washers 10 thick copper ones, and 2 with the rubber insert.
-
16 ftlb is the spec, so I overshot it a bit with 30Nm. Still the flexibility is weird to me.
Nope, studs have not been removed, hence standard stuff.
I have the correct washers 10 thick copper ones, and 2 with the rubber insert.
🤔🤔🤔 As you say, the flexibility is very strange and anything that flexes can't really give a good hold. Unless by tightening to 30Nm has stretched the studs a bit, dont forget the equivalent of 16ft/lb is the absolute maximum torque. I think mine are done at about 12-14 ft/lb.
-
By the way, the spec I found was 16 ftlb for the 350, 18 ftlb for the 400f
So I’m still a little high, but not as extreme.
I guess I’ll leave it for now, let the bike run a couple heat cycles and than do the trick with quarter turn loose and retorque.
-
If the studs had gone past their elastic point they would keep on stretching till they bfoke. The torsional load is what you are really talking about and they are acting a bit like 450 twin valve torsion bars. Did you put oil/lube under the washers/nuts if so you shouldnt have as book doesnt say so and it will alter the torque
-
Agree with above regarding torque max, I've got 30nm as 22.16 ft lb which is quite significantly over spec.
But feel that they should turn as you experience (although mostly that's not generally tried) I think most would if attempted.
The reason for using the washers they have is partly to seal them, but also that the torque to turn the nut against a washer is lower than that to tighten the nut on the threads else you'd be measuring friction torque at the washer nut interface instead of between the two threads.
As the nut is tightened it's threads compress, making the thread pitch smaller. But the stud threads are being stretched longer, the mismatch as it accumulates causes the torque required to keep turning it to rise. That final figure is arranged to give the correct tensile load on the stud structure.
But as Bryan says, raise the torqued level too high and you'll risk permanently stretching the stud.
Probably ok to do as you plan to run and reset, it'll let you know one way or another.
-
If the studs had gone past their elastic point they would keep on stretching till they bfoke. The torsional load is what you are really talking about and they are acting a bit like 450 twin valve torsion bars. Did you put oil/lube under the washers/nuts if so you shouldnt have as book doesnt say so and it will alter the torque
I haven’t lubed anything, but the area is a bit greasy with engine oil.
A torsion bar is exactly what it seems like.
-
Agree with above regarding torque max, I've got 30nm as 22.16 ft lb which is quite significantly over spec.
But feel that they should turn as you experience (although mostly that's not generally tried) I think most would if attempted.
The reason for using the washers they have is partly to seal them, but also that the torque to turn the nut against a washer is lower than that to tighten the nut on the threads else you'd be measuring friction torque at the washer nut interface instead of between the two threads.
As the nut is tightened it's threads compress, making the thread pitch smaller. But the stud threads are being stretched longer, the mismatch as it accumulates causes the torque required to keep turning it to rise. That final figure is arranged to give the correct tensile load on the stud structure.
But as Bryan says, raise the torqued level too high and you'll risk permanently stretching the stud.
Probably ok to do as you plan to run and reset, it'll let you know one way or another.
Thanks. This makes a lot of sense. I know of (one-time use) head bolts that are stretched to a certain lenght by torqueing and turning them, to get that specific load on the head.
The studs obviously work the same, but I’ve never actually seen it like this.
By the way, going from 25 Nm to 30 Nm is not even 1/8 of a turn of the nut. The ‘stretching’ of the stud is therefore pretty minimal, should that come into play.
Anyways, the bike started right up this evening. I let it idle a bit and took her for a little ride.
Smoke and burned oil smell seems to be gone. 8)
-
I just don’t get why you would torque the bolts in the “correct order” but to the wrong spec? If you’re going to use a torque wrench surely you need to check what value to set it to....otherwise why bother, you might just as well use any old spanner.... ::)
-
We're back to this oil don't oil the threads debate. If you did a full rebuild the threads would be dry on assembly, if you did the head on a bike that's run all the threads will be oiled and there's not much you can do to remove it. What's the correct torque for oiled threads because I suspect we are all doing it wrong on repairs?
-
I just don’t get why you would torque the bolts in the “correct order” but to the wrong spec? If you’re going to use a torque wrench surely you need to check what value to set it to....otherwise why bother, you might just as well use any old spanner.... ::)
You never make mistakes?
I only have a workshop manual of a 350f, so for the 400 I searched and found a torque spec of 29 Nm. Must have been the wrong bike or the wrong source. :-X
-
Your not the only one, I make mistakes constantly. Sometimes repeating the same mistakes over and over. It's the price I pay for getting older, just have to check and double check everything I do. Mistakes happen to everybody at some point.
-
An old bosses saying was
" Him what don't make a mistake don't do bugger all"
-
"The studs obviously work the same, but I’ve never actually seen it like this.
By the way, going from 25 Nm to 30 Nm is not even 1/8 of a turn of the nut. The ‘stretching’ of the stud is therefore pretty minimal, should that come into play."
It's difficult to feel any changes this small, but if you pull this type of thing on a test rig they start a very benign stretch first, followed by a big bang as failure comes fast, you just can't separate the phases as its such a small dimensional change.
It's that angle change multiplied by the thread pitch that gives more elongation as the stud top travels away from it's base fixing point. The change is distributed over the entire length though (as Honda designed it properly with waisted central section) but we don't know a yeald figure at which point the material stretches beyond elasticity, making it a guess as to how close you got.
I'd try them again after running for a while exactly as you've done now "see if they turn at the correct maximum torque rating" and not release/ reset them. If they are still holding torque ok (you can't separate gasket squish from torque release to clearly see) then they should be ok to leave alone.
-
We're back to this oil don't oil the threads debate. If you did a full rebuild the threads would be dry on assembly, if you did the head on a bike that's run all the threads will be oiled and there's not much you can do to remove it. What's the correct torque for oiled threads because I suspect we are all doing it wrong on repairs?
You're right Roy, in that you'd have to have them all clean or all lubricated to firstly make them even, and secondly take account of the difference. Best case data indicates that dry to oiled gives 10 to 15% more tensile loading for the same rotational torque.
In effect if you went for maximum spec torque number dry and take off 10% for lubricated, it would essentially pull the stud to the same loading. How close it is to material yeald we don't know.
It's a problem illustrated by occurrence in other places. The stud often used to hold cam belt tensioners in place is a good example because of this variance. Most tensioner are now supplied with a new stud (because they just don't know what's happened to the last one) and then they torque the nut to a very low figure around 5 ft lb , they then turn the nut 90 or180 degree to get the loading they require. You in effect get low error total from the torque setting (even if completely cocked up) followed by exactly the correct elongation from prescribed angle.
-
Just wondering if the nuts were oily on the gasket replacement, the torque would be too much with the wrong setting plus 10 to 15% and that's caused the stretching.
-
Well, this was truly only a head gasket replacement, done in a single evening. So everything was a bit greasy, but the nuts themselves... not so much I would say. However there is definitely oil on the copper washers.
-
Mmmmm this thread has got me thinking........when the Factory assembles Engines, they usually don't use any lubricants on the fasteners........they don't have the time - or the inclination - and bollox to the poor sods down the line who have to take them apart later.
Some years down the line poor sods like me often use some kind of grease/ oil/ copper paste etc etc etc on fasteners so that they will come apart more easily in future, especially where dissimilar metals are bolted together such as a steel stud in an alloy casing or a stainless nut on a steel stud. Where components are subjected to the heat cycles of the engine, this criteria is also important. The use of washers (of various materials) may also pose potential Torquing discrepancies, but I suppose if the Parts diagram shows a particular washer, then the Factory has allowed for that in their recommended Torque settings.
So the question is........how accurate or critical is the Torque setting if a lubricant has been employed, and is there a rule of thumb be used when determining the Torque setting that is used in a rebuild with regard to lubricants being used ?
-
So, couple months (and just a few kilometers, really) later. I'm back at square one.
Again, Cilinder 2 is smokey. I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.
I'm going to retorque the head again, first without changing the gasket. Remember last time I found 'loose' head nuts.
Could there be anything wrong with my Studs, or Head?
Is there any harm in using an extra ring under the head nuts, just to make sure the nuts are not bottoming out on the studs (because of the aforementioned elasticity)?
-
So, couple months (and just a few kilometers, really) later. I'm back at square one.
Again, Cilinder 2 is smokey. I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.
I'm going to retorque the head again, first without changing the gasket. Remember last time I found 'loose' head nuts.
Could there be anything wrong with my Studs, or Head?
Is there any harm in using an extra ring under the head nuts, just to make sure the nuts are not bottoming out on the studs (because of the aforementioned elasticity)?
I can't immediately remember but someone on forum had one of these head with crack in casting allowing oil to leak into exhaust port to smoke on #3 I think ?
It was long convoluted chase through all the other possibilities, but ended definitely with this outcome.
-
Well I'm hopefull it's not that. Afterall, replacing the headgasket and (re)torquing the head nuts stops the smoking completely.
It appears to come back only after riding hard (full throttle up to red-line).
I think my issue is with the studs/nuts, as I have this 'elasticity' on torqueing, and headnuts that appear to come loose after a short while of riding (couple 100 km).
-
So, couple months (and just a few kilometers, really) later. I'm back at square one.
Again, Cilinder 2 is smokey. I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.
I'm going to retorque the head again, first without changing the gasket. Remember last time I found 'loose' head nuts.
Could there be anything wrong with my Studs, or Head?
Is there any harm in using an extra ring under the head nuts, just to make sure the nuts are not bottoming out on the studs (because of the aforementioned elasticity)?
I can't immediately remember but someone on forum had one of these head with crack in casting allowing oil to leak into exhaust port to smoke on #3 I think ?
It was long convoluted chase through all the other possibilities, but ended definitely with this outcome.
That was me on the 350F. It was a real head scratcher problem. I ended up rebuilding the top half three times. In desperation I took the head to an NDT place who gave it to a chap called Eddie Current. He was good, he found a crack next to a valve guide that was invisible cold but opened up when hot. I replaced the head with a really good low mileage one off eBay and problem solved. It's never smoked since.
Sent from my Pixel 6 using Tapatalk
-
When I rebuilt my 125s I torqued the head down properly (circa 16ft lb iirc) and I distinctly remember looking at the manual multiple times thinking is that it?! Is that the correct figure, have I misread something? That torque seemed way to low to me after having worked on car engines with aluminium heads countless times when your generally over 50ft lb on head studs.
However the 125s studs are on the small side so I thought OK that must be correct and duly proceeded to finish off the build. After about 400 miles of riding I noticed oil seeping from the cylinder base gasket. So I duly re torqued the studs and noticed exactly the same as what you did, the stud would turn with the nut for a couple of degrees, then go tight allowing the nut to turn on its own. I put it down to everything just settling in.
Only for it to happen again at about 1000 miles. This time I thought, this is really strange I've never known this to happen before so I approached one of the engine builders at work and asked him for advice. He said the torque spec does seem very low but if that's what honda specified then it must be correct.
We work on vintage/pre war cars so are used to dealing with worn out and re used parts. He suggested that perhaps the threads in the crankcase were stretching / already stretched and the studs and nuts likewise. Therefore although torqued to the correct setting they were able to fret loose with engine vibration due to the wear on each component. I had after all re used my studs and nuts which were original.
So I asked what he would do and he said come here my boy....... and pulled out a 12mm spanner from his drawer. Go home and tighten those nuts as hard as you can with the ring end of this spanner. I suggested that I might run the risk of over tightening them if I did that, to which he replied you can't, this 12mm spanner is this length for precisely that reason.
So I did what he said and a few thousand miles later hey presto all was well. I'm not suggesting that you do this to your engine, merely sharing my similar experience!
Sent from my SM-G780G using Tapatalk
-
Took the valve cover off last night and found that the 2 nuts on the intake side of cil 2 (the smoking cilinder) were indeed a bit loose again.
I've tightened them up, but one would not stop with the 'elastic' feel once torqued. So I added another ring and that helped (for the feeling of stretch at least). Maybe this nut is binding on the threads or binding in the dome of the nut?
No idea, but I'll put everything back together this weekend and see what happens.
-
Took the valve cover off last night and found that the 2 nuts on the intake side of cil 2 (the smoking cilinder) were indeed a bit loose again.
I've tightened them up, but one would not stop with the 'elastic' feel once torqued. So I added another ring and that helped (for the feeling of stretch at least). Maybe this nut is binding on the threads or binding in the dome of the nut?
No idea, but I'll put everything back together this weekend and see what happens.
I see it as one of two reason, either the nut is backing out by rotating to release load or the stud has been stretched beyond it's normal elastic point of integrity and now in a failure state. If it's stretched beyond normal limits it will keep getting longer each time it's tightened until it snaps, indication of this is that the stud is getting higher than the other examples on the engine.
-
Tensile load failure looks like this
[attachimg=1]
Classic failure of too much loading by over tightening.
-
Just been out on the 350F (not used it for ages) and noticed when I got back an oil weep from the head gasket that wasn't there before. Also it's blowing fumes out of the breather tube. It is slightly overfilled with oil, could that be causing the fumes. The oil weep is probably time for a head re-torque I guess, I will also take some oil out of it at the same time. Runs really well though.
-
So, couple months (and just a few kilometers, really) later. I'm back at square one.
Again, Cilinder 2 is smokey. I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.
I'm going to retorque the head again, first without changing the gasket. Remember last time I found 'loose' head nuts.
Could there be anything wrong with my Studs, or Head?
Is there any harm in using an extra ring under the head nuts, just to make sure the nuts are not bottoming out on the studs (because of the aforementioned elasticity)?
I started riding, nice and easy. No smoke. Once everything was nice and up to temp I gave the ol'girl the beans and cilinder 2 (I have a non-balanced 4-4 exhaust, so easy to diagnose) started smoking again. Looks like head gasket again.
Hi Erwin,
There may be some oil overheating/thinning occuring, which will promote oil burning.
If you have a 466 bored out engine you would be running hotter than normal and definitely need oil cooling.
On a standard engine you will maintain about 90 to 105 degrees C oil temp with normal riding - give it the beans and you will soon be up to 120 C, with oil thinning. I think this causes oil degradation and probably why Honda specified 1500 miles oil changes.
Just another factor to consider. FWIW
Dennis
-
At the risk of sounding daft I have felt this sensation decades ago when tightening Helicoiled threads back in the early days of Helicoils.
Are all the head stud threads in the block as per original ?
-
A question to the OP, can you turn the nuts with your fingers when they are not torqued/tightened ? In other words can you twist them down with your fingers easily until they touch the washer and then just needing to be tightened with a socket from there ?
Thinking we may have interpreted the description of "elasticity" wrongly. If they are tight right from putting the nut on the stud then that will give a torque requirement without even clamping the head sufficiently to start with.
Thinking out loud really as they should stay tight once assembled with no real problem.
Are they the original nuts that are in use too ?
-
At the risk of sounding daft I have felt this sensation decades ago when tightening Helicoiled threads back in the early days of Helicoils.
Are all the head stud threads in the block as per original ?
OK, I did not think of that before. I'm using Bell Ray EXL 10w40 (mineral). Should I move to another oil type?
I was not planning on putting on oil cooler on this bike to be honest...
-
At the risk of sounding daft I have felt this sensation decades ago when tightening Helicoiled threads back in the early days of Helicoils.
Are all the head stud threads in the block as per original ?
Yes, the studs have never been removed from this block. Also did not come loose accidentily when undoing the head.
A question to the OP, can you turn the nuts with your fingers when they are not torqued/tightened ? In other words can you twist them down with your fingers easily until they touch the washer and then just needing to be tightened with a socket from there ?
Thinking we may have interpreted the description of "elasticity" wrongly. If they are tight right from putting the nut on the stud then that will give a torque requirement without even clamping the head sufficiently to start with.
Thinking out loud really as they should stay tight once assembled with no real problem.
Are they the original nuts that are in use too ?
Yes, I'm using original nuts, although I may have mixed up some 350 / 400 parts as I have been working on both these engines simultaneously for years.
All the nuts go on smoothly. I normally use a long socket to place the nuts and reduce the chance of the nuts falling in. They all feel normal when turning them the first couple windings with my fingers on the socket.
-
Runs fine now, have not seen even a puff of smoke.
https://youtube.com/shorts/v9xFpDdq0PY?feature=share
-
Runs fine now, have not seen even a puff of smoke.
https://youtube.com/shorts/v9xFpDdq0PY?feature=share
So how did you fix it or have I missed the cure?
-
I retorqued the headnuts and placed one extra ring under the one nut that I found 'loose' again. Idea was that maybe the tread on the one with the most elasticity was not perfect and the extra nut ensures the use of cleaner thread. Or if the nut bottomed out, the extra ring gives more space and makes sure the nut clamps down on the head for sure.
In any case, the elasticity is now gone...
I have not taken the head off. Just retorqued with the head in place.