Author Topic: Head + Rocker cover torques...  (Read 2706 times)

Offline Lobo

  • Lobo
  • SOHC Master
  • Posts: 1568
  • Lobo
    • View Profile
    • Lobo
Head + Rocker cover torques...
« on: March 21, 2019, 02:32:53 AM »
Guess one for the builders here, Gents...
Slight oil weep on the ‘400, emanating within the fins / RHS. The engine was rebuilt about 500miles ago, and so figured I’d simply re-torque the head.
Which is what I’ve now done...
Have to say, and using ‘Clarkson parlance, “poo was coming out” as I slackened, and re-torqued each to the book figure (15 ft-lb). Fingers crossed the slight weep has been remedied.
The Rocker cover however, was a different matter, and I noted at least 3 thread inserts already in place. And whilst I couldn’t bring myself to use the book figure this time (6 ft-lb)... bloody #12 (the last bolt!) failed to tighten... even to my calibrated elbow.. and well below 5ft-lbs.
So... that thread has an insert now, and job fettled... til next time.
Q - any comments here wrt using book figures on 40 yo engines which may have indeed been apart more than once.  And if so... given how soft these heads are... what are you typically torquing to? There seems to be a finite number of times these motors can be taken apart and put together!

Offline Bryanj

  • Grogu
  • *
  • Posts: 10694
    • View Profile
Re: Head + Rocker cover torques...
« Reply #1 on: March 21, 2019, 08:05:43 AM »
Never used torque on the 6mm bolts just "feel" but all critical bolts(head,rods,mains et) need to be torqued and i always use the highest number and never had a problem

Offline Harold 400/4

  • SOHC Associate
  • Posts: 71
    • View Profile
Re: Head + Rocker cover torques...
« Reply #2 on: March 21, 2019, 08:51:24 AM »
Lobo. I have exactly the same issue with my 400/4. Once the rocker cover is off, can you get at all the bolts to tighten down without dismantling camshaft etc etc? I was planning just to torque up, but see you slackened off before torquing? What is the reason for this?? Many thanks
H

Offline Lobo

  • Lobo
  • SOHC Master
  • Posts: 1568
  • Lobo
    • View Profile
    • Lobo
Re: Head + Rocker cover torques...
« Reply #3 on: March 21, 2019, 11:27:17 AM »
Hi Harold,

Yep, you can easily access all 12 bolts to torque the cylinder head. Spark plugs 2 & 3 will need to be removed, as will a couple of oil spray bars. (They just lift out). You might want to stuff a lint free rag abouts the cam chain sprocket tunnel area, as anything dropping down there will surely spoil your day.

Note there’s a gradual tightening sequence up to full torque... basically working from the centre of the head (and indeed rocker cover) out.

Didn’t see it written anywhere.. but you probably want to consider loosening all the tappet adjusters to allow the rocker cover to naturally fit onto the head prior to buttoning it all back up.

You’re asking the wrong person here as to whether you need to ‘slacken’ each head bolt first - my logic was that ‘stiction’ would possibly screw the process, and that a gentle continuos tightening to required torque would give a more accurate setting.

Thanks for the comment Bryan... fits in with my gut feeling given the head’s made of something akin to butter...

 Btw - took it out for a run this arvo... and so far all looking good. Phew..

Online K2-K6

  • Grogu
  • *
  • Posts: 5234
    • View Profile
Re: Head + Rocker cover torques...
« Reply #4 on: March 21, 2019, 11:54:32 AM »
Reference the bolt/fixing integrity for rocker cover.

From an engineering point of view I don't feel that they wear out, as such.  It's the case that the steel bolts can very easily exceed any torque aluminium castings can tolerate.

In tightening them,  if the torque used succeeds in fracturing the threads ( in essence detaching the thread form from its root anchored to the surrounding metal)  then they are scrap from that point onwards. It doesn't matter if it's the first, or many times its been used.

That joint is unusual in how it's viewed from a technical point.  Using its two faces to provide the tolerancing for cam bearings,  it only has to be tightened until the surfaces touch by which time the o-ring shouod have long been compressed into its sealing function. The remainder of tightening after this point is just to provide a "shakeproof" torque on the bolts. It really doesn't need much to do this.

There's anther factor that's not really considered,  which is lubrication of the bolts and the affect it has on torque rating. I think Bryan made this observation about whether to lubricate the thread's some years ago (that was in relation to head studs, that I remember).
As I understand it,  thread torque used is given for a dry thread UNLESS a lubricant is specified.
If you add a lubricant to this equation it requires you to use LESS measured torque to achieve the same clamping force, but the load on each thread goes upwards toward failure. Torque is just measuring friction and has to be qualified for the friction in place.  Change the friction,  and you change the measurement of torque as it's rotary and specifically doesn't measure the clamping force.

It follows that if you use oil and maximum torque specified,  then you'll come closer to the materials capabilites to resist failure.

The general interpretation would be to reduce torque by 10 to 15% indicated by figures I can find. 

Offline Bryanj

  • Grogu
  • *
  • Posts: 10694
    • View Profile
Re: Head + Rocker cover torques...
« Reply #5 on: March 21, 2019, 12:02:28 PM »
Havent got time to look it up for you but try looking for wheel torque and detached wheels on HGV. They usually discuss oiled or not

Offline Laverda Dave

  • SOHC Jedi
  • Posts: 2531
  • Health is wealth
    • View Profile
Re: Head + Rocker cover torques...
« Reply #6 on: March 21, 2019, 08:40:52 PM »
Interesting point you've raised Nigel. I always brush copperslip grease on all threads (although not big end bolts) to make it easier to remove the bolts should I have to. I do this through bitter experience stripping threads trying to remove bolts that have siezed through steel/aluminium reaction. I didn't know this affects torque figures and will work to this in future. Thanks for the information.
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Lobo

  • Lobo
  • SOHC Master
  • Posts: 1568
  • Lobo
    • View Profile
    • Lobo
Re: Head + Rocker cover torques...
« Reply #7 on: March 22, 2019, 12:26:00 PM »
... the stuff you learn on this forum... so many clever folk here.

Question Nige.. will the threads maintain integrity if never torqued beyond the book figure... or will repetitive torquing eventually take its toll?
If the former, must we assume that over-torquing regularly occurs?

And as Harold asked.. is it good - or poor - practice to slacken any nut / bolt slightly before re-torquing it?
Cheers.
Simon

Offline Bryanj

  • Grogu
  • *
  • Posts: 10694
    • View Profile
Re: Head + Rocker cover torques...
« Reply #8 on: March 22, 2019, 02:30:54 PM »
As a time served engineer on big stuff to guarantee correct torque you should work in stages and on the last stage DO NOT STOP between starting to move and attaining required torque as the friction between nut and washer/head frequently takes more "torque" to get movement than the static fastner is at.

On the re-use of studs/nuts/bolts as long as you stay within the "elastic" limits of the metal involved you can use them till the thread wears out, this is why on most modern car/truck engines bolts have to be changed every time as they are not "torqued" but tightened through a set angle after initial seating which takes them very close to the "elastic limit point". Old Triumph motorcycles used to specify a "stretch" amount on big end bolts rather than a torque.

Are you now all suitably confused?--------- Good cos Swansea just sent me a letter telling me my licence is to be retuned to me in another letter so when it arrives i can go back to work!!!!!

Offline Nurse Julie

  • 1977 CB550/4 Mongrel Brat. 1974 UK 500/4 K1. Honda CD250u.
  • Grogu
  • *
  • Posts: 8206
    • View Profile
Re: Head + Rocker cover torques...
« Reply #9 on: March 22, 2019, 02:36:49 PM »
Great news on returning back to work Bryan.....keep healthy now x
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Bryanj

  • Grogu
  • *
  • Posts: 10694
    • View Profile
Re: Head + Rocker cover torques...
« Reply #10 on: March 22, 2019, 03:28:53 PM »
Thanks Julie, Teri, my beloved wont have it any other way!!

Offline Laverda Dave

  • SOHC Jedi
  • Posts: 2531
  • Health is wealth
    • View Profile
Re: Head + Rocker cover torques...
« Reply #11 on: March 22, 2019, 04:36:26 PM »
Good news Bryan and thanks for the update.
A friend of mine had a modern MG (the one with the K series engine). Like all these engines the head gasket blew. The garage changed the gasket but not the stretch bolts, the gasket blew again a coupe of weeks later. To do the job properly cost £1,100!
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Online K2-K6

  • Grogu
  • *
  • Posts: 5234
    • View Profile
Re: Head + Rocker cover torques...
« Reply #12 on: March 23, 2019, 02:37:27 PM »
That is good news Bryan, hopefully after the "rebore" you'll get no more trouble  :)

The technical points:- as you say Dave,  the bolts are a real problem if corrosion gets into the threads.  The zinc plating is the part that protects them originally,  but as we all know when exposed to salty winter roads it will strip that off over time.  The zinc is sacrificial so that when you see them going white in early stages of their life you are observing that process in operation. Once gone though,  it starts on the components to give that siezed stage that can destroy the parts. Using something to avoid this is sensible as you do with coppaslip,  just have to be aware of the effect on measured torque.

Bryan picked up on scale with things like this.  it seems to trip up the unaware in not acknowledging the very small scale that is involved, many just don't believe that they are working with such small numbers, for both tolerancing and torque settings.

To elaborate on the cam cover bolts Simon, yes it should be true that if never over torqued they should be ok for most eventuality.  They have more to them than is generally appreciated I believe. I mentioned earlier about the torque on the threads,  what Honda have done on these though is to design in a wide head/flange on the bolt. The increase in the surface area is the principal element in how the torque is built up.  If tightened correctly it'll reach the measured specification just from this surface and not overstress the thread area. As mentioned,  the joint face is not compressed like a gasket,  so once the two metal components come into contact that is job done,  the bolts just need the torque setting to stop them backing out during use.
It's one of those assemblies in which some very subtle elements combine to give an integrated whole component.

Retightening head bolts,  it's one of those things that I don't think can be answered definitely as to method,  unless the original manufacture gives a prescribed routine.
Faced with trying to retourque them means it's already compromised the gasket to some extent,  else it would not be required. Agree with Bryan in releasing first then tightening again to get a correct reading.
I'd do them one at a time so that the head casting is not released and in the original pattern of engine build if doing them all.
It's one of those things that you'd hope to get it to seal,  but may have to accept it needs replacement if not effective.

That K-series engine Dave, as far as I remember they have bolts that go right through the whole assembly and hold crank main,  pass through block,  then the head to squeeze the whole assembly. It's quite a clever design,  but like many things considered in that way, sometimes mis-understood.
They are definitely "stretched" bolts, in that they are pulled during tightening past elasticity into primary yeald to set them correctly and need replacing if taken apart.
Great irony of those engines is it's not this construction that causes the fault in the first place,  but often gets blamed. The overheating usually originates with failure of water system sealing to the inlet manifold as I understand it. They run a fairly small coolant volume and will readily overheat because of this problem,  by which time the head gasket is compromised.



Offline Laverda Dave

  • SOHC Jedi
  • Posts: 2531
  • Health is wealth
    • View Profile
Re: Head + Rocker cover torques...
« Reply #13 on: March 23, 2019, 10:00:47 PM »
Great explanation Nigel.
Yes, the K series was known as 'ladder construction' I believe. I remember Suzuki made a big thing about it a few years ago with the GSXR engine even though most motorcycle engines are built using this method!
I've just bought a new Sealey 1/4 torque wrench as I think my SP one is out of calibration after 25 years!
1976 Honda 400/4
1977 Rickman Honda CR750
1999 Honda VFR 800FX
1955 750 Dresda Triton
1978 Moto Morini 350 Sport
1978 Honda CB400/4 'Rat' bike
1982 Laverda 120 Jota

Offline Bryanj

  • Grogu
  • *
  • Posts: 10694
    • View Profile
Re: Head + Rocker cover torques...
« Reply #14 on: March 23, 2019, 10:27:02 PM »
All you need to check calibration is a vice a rule and a spring balance-------and before sombody tries to correct me there is only one ruler in this country and she lives in a big house at the end of The Mall in London!!

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal