Over Torqueing Cylinder Head

[n/a]

I was quite happy in retorqueing head and adjusting valves when a terrible thought occurred to me.  Did I torque (I backed off head bolts first)to 72 foot pounds or 100 foot pounds?  I think I might have torqued the latter as that is the equivalent brit value Nm's and might have torqued 100 foot pounds because it was on my mind at the time.  Any real down side to this?  Dr Dan? Your thoughts please?

Thanks!

James

[Malc]

Er,
On my rally car I have always tweeked the bolts up over that specified value, and haven't had any problems, head,gasket, or otherwise.

My only suggestion would be the next time you do this I would use new bolts

Finally I have had my "good" torque wrench calibrated and I found that it was out at the top end (set at 120 ft-lbs actually 110) but good at the bottom end

Malc

[rwmastel]

Where would one get their torque wrench calibrated?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[A Dalton]

<<Finally I have had my "good" torque wrench calibrated and I found that it was out at the top end (set at 120 ft-lbs actually 110) but good at the bottom end >>

 It is quite common to see them out on the top end and that is why it is good pactice to use a torque wrench whose medium range is equal to the spec you are looking for .

 IE., if you want to torque at 110ft/lbs, it is better to use a 0-250 wrench than a 0-125 wrench........

[George Davis]

Torqing fasteners is really a somewhat imprecise surrogate for measuring their stretch.  There is an ideal stretch for each size/type of bolt to provide maximum clamping force, but if it's stretched too much the bolt 'may' become weakened and no longer clamp as well as we'd like.

Being the paranoid sort, overtorquing by much more than 5-10 lb/ft would worry me.  Since they all seem to have tightened up ok, they are probably not overstretched, but I'd still loosen them and retorque them to 72 lb/ft, paying very close attention to how they feel as they tighten.  If any of them feel funny, like they're getting easier to turn as they tighten, stop immediately, back it out and replace it.

Just one paranoid opinion...

George Davis
'69 280 SL Euro manual

[Raymond]

I'd love to hear how the heck you're supposed to measure stretch on a head bolt.

Ray
'68 280SL 4-spd Coupe

[TheEngineer]

First, get your torque wrench calibrated. You can do this by making yourself a little fixture and using a bathroom scale (or an electronic scale like they sell at the post ofice). You may find that 100 ftlbs on your torque wrench is actually less.  There are also "Calibrating Instrument Services" Look in the yellow pages. Calibration is a requirement for many contracts. Also, it makes a difference when you put grease on the threads and under the bolt heads. There is less friction and a given torque will produce more clamp.

[Benz Dr.]

Re do them to the right amount always starting at the middle of the head and work out from there.

You can measure how long the head bolts are but only when there removed. Sine they're not stretch bolts I don't see how this would work out. The rod cap bolts are stretch bolts and you can measure this amount in the necked down area and after you tighten them. I think they stretch about .001'' when tight.

Daniel G Caron

[Cees Klumper]

If I am not mistaken the rod cap stretch bolts have to be measured for thickness with a micrometer, not when they are installed but 'loose' - apparently they can be overstretched/overused and the neck area then will become permanently too thin. There's a minimum thickness that's in the Data Manual.
I suppose the head bolts do stretch out, from the head down to where the bolt goes into the block, i.e. the full height of the cylinder head - because there is no thread there.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[Malc]

quote:Originally posted by theengineer

 Also, it makes a difference when you put grease on the threads and under the bolt heads. There is less friction and a given torque will produce more clamp.

Agree but.......
Be very careful when applying grease and or oil, if the bolt is going into a blind hole you can get "hydraulic" lock and the bolt will not tighten down properly. You end up compressing the oil or grease in the bottom of the hole. This can fracture a block :?

I ALWAYS make sure the block bolt holes are blown out,clean, and dry. I use a tiny amount of "copper anti-sieze", applied with a clean paint brush, on the threads of the bolt.

Having "whipped" the head on and off the rally car engine numerous times this practice has worked for me.

In regard to stretch bolts these are usually torqued to a certain value and then tightened again by angle, VW diesel engines use this method. NEVER reuse stretch type bolts on a cylinder head, usually they are cheap enough to replace. If any stretch bolts are used in a component I usually replace them as a matter of course.

Just my way of doing things
Malc

[A Dalton]

113 'M'-10 head bolts are not stretch bolts
 'K' is stretch designation [ used on some bottom end parts]
 TTY [ torque to Yeild] are stretch bolts and they are usually tightened to a specific torque and then turned a number of degrees
[ 1/4 turn. 1/2 turn, etc,]  usually in two steps with a resting time in between...
 Head stretch bolts are a one time use bolt...

[DaveB]

Malc,
Is copper safe to use in aluminium heads? I know boatbuilders won't mix copper and aluminium.

>I use a tiny amount of "copper anti-sieze", applied with a clean >paint brush, on the threads of the bolt.

DaveB

[Benz Dr.]

I only use engine oil on the threads and under the flat washer for the head bolts. Any part on the engine that I have to tighten I use a bit of oil on the threads to help it pull down smoothly.
Only use nickel anti-sieze on aluminum. This wouldn't be a problem on the cylinder head as the bolts go right through into the block. I always use a tap on every threaded hole in the block before I start assembly and use new fasteners that hold the oil pan on.

Daniel G Caron

[Malc]

Actually I use what's known as "pipe dope". It's used in the oil industry for drill pipe..
It comes in 25Kg drums and I "obtain" a little now and then from work [:p]

Agree about copper and ally in boats, put them together in sea water and you have a wonderful corrosion problem. I actually live near the sea and my land rover with an ally body on a steel chassis wants to dissolve all the time!

That said I use this stuff to stop alloy wheels "sticking" to steel hubs seems to work with no problems so far

Cheers
Malc

[DaveB]

Thanks for the tips Malc & Benz Dr. Malc have you heard of another marine product called DENSO tape (may have a different name elsewhere). It's a waxy cloth tape excellent for wrapping up metal parts in storage - they'll never rust.

DaveB