Valve adjustment as per factory manual

[EuroIron]

look guys......... show me backing off any about or specified amount as proper procedure for these engines........ I'll accept it from Porsche or VW too

from a valid source

I can sure show any of you factory manuals for certain engines that clearly state if you back off any head bolts.......... replace head gasket....... and some specify head bolts too.

I don't consider Terry a valid source, read plenty of his posts.

[niall4473]

Hi all,
Been watching this post a couple of days and poor old EuroIron seems a bit beleagered, so can I say that in my humble opinion, he is exactly right.
People have stated, on this thread, the necessity of getting the "torque" exactly right on a head in service as if that is an end in itself.
Well, its not.
The purpose of the torque spanner is to apply a measured turning moment (torque) to the fastener, so that, taking into account the lead of the screw thread and the modulus of elasticity of the bolt, a given loading is put on it to clamp the two components (in this case the barrel and head) together. Given that many other variables can affect it (temperature, the surface characteristics of the thread, lubrication or lack of etc), that would only be achieved accurately under toolroom conditions with all new parts.
Don't get me wrong, the torque spanner is an invaluable tool which should be used wherever possible, but no one should build an altar on the workbench and worship it.
In general engineering bolt stretch is measured wherever possible, in fact British manufacturers used to publish the figures for big-end bolts etc.
Where the torque spanner really wins out is in getting the clamping pressure across joint surfaces EVEN, especially if you don't have any recommended torque figures. (Incidentally, as an apprentice I had to spend quite a while learning to tighten bolts evenly, and in sequence, until they were bang on when checked). But you can manage without it, if you have to. For instance, take a look at the Norton Dominator/Atlas head fixings, no way to use a torque spanner on some of them, and yet the head hasn't been off mine for 20+k miles. Boxer BMWs probably have the easiest heads to work on of any bike.
Back to the question above, don't fix what isn't broken. With a new head gasket, torque them down to the 25ft/lbs (for an R60 if memory serves) then, as the gasket settles down, do it again, possibly twice, at 250/500 miles then once it has stabilised leave them alone. Check tightness when you have the rocker boxes off, by applying that same torque as before, but really, if they move then there's something wrong.
By backing off the headbolts then re-torquing, if there's any corrosion in the open thread under the bolt then they might not actually be as tight as they were before you touched them. Also bear in mind that all bolts have a service life, not just the sacrificial "stretch bolts" used in cars (which are used to avoid having to re-torque like above), and by continually slackening and re-stressing them you reduce this considerably, bolts like everything else in life from advertising to sex suffer from the law of diminishing returns, and checking with a thread gauge will only tell you if they are on the point of total failure.
I was once told about a test to check bolts used in high stress applications and with an unknown history:- throw them in a bucket of water, if they sink, scrap and replace them.
Got to go to work now.

[schrader7032]

Niall (I think that's your name) has certainly defined the proper way to measure the torque...it's a measurement that must be done with the nut and bolt moving relative to each other. I might be reading too much into he said. He said "turning moment (torque)" of the fastener. To me that means that the torque can only be measured while the fastener is in motion. This is the only way to do it, and no manual is going to specify this process. It will simply state to torque the head bolts...it's implied that everyone knows how to apply the torque and measure the value.

I also agree with his approach for torquing the head bolts after use of a fresh head gasket. Once the gasket seats, there should be little reason for a retorque of the heads. There's still some confusion about what should be done at each valve adjustment, despite what the manual might say. Once they're stable, the head bolts tend to need little attention.

I guess a question still remains in my mind and was essentially what started this thread. It is the process of checking for tightness of the head bolts. If the proper way to measure the torque value is to read the value while the nut is moving against the threads, how then, is it possible to "check the tightness" of the existing nut/bolt union WITHOUT loosening the nut and repeating the process for torque application? If one uses the torque wrench, set for 25 ft-lbs, pulls the wrench around so that 25-ft-lbs is measured (beam wrench, clicker, whatever), you have only determined that the static friction (or torque) of the nut on the threads is at least 25 ft-lbs. It takes more torque to overcome this static condition in order to get the nut moving on the threads. Then you can measure the torque.

I certainly don't advocate completely loosening all 4 or 6 head bolts and repeating the process of retorquing the heads. This will only serve to hasten failure at some point by application of extra load cycles on the threads and associated attachments. Once tightened, the attachments see load cycles much smaller in variation, due to heating and cooling of the parts. But to loosen a single nut 1/8-1/4 of a turn, dropping the torque to maybe 75% of maximum value and then retorquing seems like the only way to know for certain what the actual torque is. And I can't see where this small reduction in torque will have any significant or measureable effect on the status or health of the head gasket. Nothing will be disturbed with 1 of 6 bolts being slightly loosened at a time. If something is affected, the cumulative affect will take so long to be noticeable that by that time, the heads will have come off for a completely different reason and the whole torquing process is started from scratch.

My understanding is that torque is a measurement done as a running or sliding movement of the nut on the threads. The only way to check for tightness is to recreate the sliding process which requires that each nut, one by one, is loosened slightly and then retorqued.

Now, I will occasionally put the torque wrench on a nut and check the tightness without loosening...if the nut moves at all, there's a big problem. If it doesn't move, I'm satisfied that probably everything is OK and I'll wait for another time to properly check the torque. I still don't know what the torque is, but it isn't loose and that's a good thing.

Kurt in S.A.

[EuroIron]

again, your 'sliding washers and moving on the threads' premise is incorrect

and if BMW wanted you to do this......... the procedure with it's proper sequence would be clearly laid out for you in there service manuals

why do you think BMW recommends to check the torque value of these cylinder flange nuts and head fasteners prior to doing the valve adjustment procedure?

do you think you can measure a difference in valve clearance if the bolts are at 25% of their recommended torque spec instead of spot on? short of using some NASA owned optical comparator?

now if their methods are to be questioned.......... it would be to question why they fail to recommend measuring installed stem height every 4K along with their other specified procedures........ as well as making the head so that it readily lends itself to checking this critical measurement with ease

heck....... you vintage bmw guys want to invent something useful not found in the manuals....... go invent rocker geometry stuff from the VW manuals......... try checking it sometime on your BMW...... you'll be surprised how many of yours are off by a long shot


perhaps I can even open up my offer for you to show me factory published procedures, which support your notion of how head bolts should be checked for proper torque, to include any and all air cooled engines for aircraft.........

can you pony up something if the field is made that wide open?

how about include any and all air cooled engine manufacturers?

I am waiting

[Allan.Atherton]

I check valve adjustment and headbolt torque about every 2000 miles, and I cannot remember ever feeling "stiction" with my beam-type torque wrench. What I have frequently felt over the years, more often after rebuilds, as the pointer gets to 20 lbs, is that one or two of the bolts begin to move smoothly, so I take it to 25 lbs.

[EuroIron]

does anyone care to speculate what it would mean if one consistently found any cylinder flange or head fasteners under-torqued at the specified intervals? assuming they were checked for tightness and corrected per the factory specifications?

I'll give you a clue, automatically assuming you should loosen these fasteners prior to retorquing totally undermines and erases the intended beneficial benchmark of this exercise and also will absolutely, to some extent anyhow, lead to premature fastener fatigue or yield.


then comes the million dollar question.......

at what point of looseness can a bolt be properly retorqued?

from 10 pounds to 25?

from 15 pounds to 25?

from 22 pounds to 25?

from 24.5 pounds to 25?

all of the above?

sure, if not BMW and every other manufacturer would have, again, given you very clear procedural instructions

[saintclair2703]

Please, what ARE those instructions? I don't remember the manual going into that much detail. (I'm still looking for my manual, however...)

[EuroIron]

Every 4000 miles (6000 km) with the engine cold and before adjusting valves clearances, the cylinder flange fixing nuts and the cylinder head bolts must be checked for tightness to a torque of 24 ft/lb (3.5 mkp). This work should be left to the BMW service workshop.

you want me to put the neato stuff about feeler gauges, metric cap nuts, and things in too?

[saintclair2703]

Hahahahaha...
That's what I thought.

I don't think people would be so patient with you if you weren't so good looking.

Now, how about a quote from the ASE folks, too. A sprinkle of MIT wouldn't hurt either. Maybe some Dr Goddard is you have him, too.

Here's one of my favorite quotes;
"Ol' doc Einstein abolished time, but they haven't got the word at Sing Sing yet."
-Archy

[EuroIron]

ditto kiddo

tell the long legged lady I said hullo