a novice fitting glowplugs

[mikeWalsall]

Thanks ... for the explanation ...

It's just to my mind ... if you torque a bolt down to down to say 256 lbs foot .. then use an angle gauge .. you are simply apply more torque to 'stretch' the bolt anyway ..

So I could not see why a simple three stage tightening sequence with the torque wrench would not have achieved the same effect ..

[g8dhe]

Using a torque wrench only ensures that you don't over tighten a bolt, its a measure of the rotational force that has to be overcome to turn the bolt due to friction.
Angular tightening is about applying a clamping force along the length of the bolt, as it is stretched by the length that Steve described previously.

[rita]

I think you will find that when the bolt starts to stretch the Torque required may well REDUCE, by angle tightening you force the bolt to stretch by a given amount in length.

The reason it's done by the angle tightening is as Geoff said, that is when the bolts actually START to stretch. The bolts are made of a very strong material (high tensile) which, for a given stretch produces are finitely known grip force. The actual bolt stretch is very small yet the grip force is identical in each bolt. VERY PRECISE.
The ONLY place I disagree with Geoff is the torque.. It certainly DOESN'T reduce in the final tightening. It goes WAY beyond the initial torque setting. Take my word for it Geoff. Been there - Done that. There is no way you can do the final 'stretch' using an ordinary torque wrench.
We had to use a 5 foot pipe to complete the final 2x90 degree setting, and then it took some force.
We followed the Mazda manual to the letter, even applying oil to the threads as specified (which makes a significant difference).

The head we replaced has now done in excess of 2000 miles and all seems well. (Head bolts were re-checked after 600 miles as recommended)
As far as overtightening of the glowplugs is concerned, you are far safer sticking to the Mazda recommendations (15~19Nm). Why? - Aluminium Just my opinion though.

That's very interesting,how did you check the bolts after 600 miles.?

[widdowson2008]

I think you will find that when the bolt starts to stretch the Torque required may well REDUCE, by angle tightening you force the bolt to stretch by a given amount in length.

The reason it's done by the angle tightening is as Geoff said, that is when the bolts actually START to stretch. The bolts are made of a very strong material (high tensile) which, for a given stretch produces are finitely known grip force. The actual bolt stretch is very small yet the grip force is identical in each bolt. VERY PRECISE.
The ONLY place I disagree with Geoff is the torque.. It certainly DOESN'T reduce in the final tightening. It goes WAY beyond the initial torque setting. Take my word for it Geoff. Been there - Done that. There is no way you can do the final 'stretch' using an ordinary torque wrench.
We had to use a 5 foot pipe to complete the final 2x90 degree setting, and then it took some force.
We followed the Mazda manual to the letter, even applying oil to the threads as specified (which makes a significant difference).

The head we replaced has now done in excess of 2000 miles and all seems well. (Head bolts were re-checked after 600 miles as recommended)
As far as overtightening of the glowplugs is concerned, you are far safer sticking to the Mazda recommendations (15~19Nm). Why? - Aluminium Just my opinion though.

That's very interesting,how did you check the bolts after 600 miles.?

When we did the head bolts originally, we put paint marks on them to help going through the 90 degree tightening sequences. All we checked was that the paint marks hadn't moved from the original tightening.
One needed tweaking to get it in-line with the rest (very minute amount), but otherwise nowt to do. Couldn't see what else could be done. Engine still running sweetly though so we must have done things right. (I hope)

[teenmal]

I think you will find that when the bolt starts to stretch the Torque required may well REDUCE, by angle tightening you force the bolt to stretch by a given amount in length.

The reason it's done by the angle tightening is as Geoff said, that is when the bolts actually START to stretch. The bolts are made of a very strong material (high tensile) which, for a given stretch produces are finitely known grip force. The actual bolt stretch is very small yet the grip force is identical in each bolt. VERY PRECISE.
The ONLY place I disagree with Geoff is the torque.. It certainly DOESN'T reduce in the final tightening. It goes WAY beyond the initial torque setting. Take my word for it Geoff. Been there - Done that. There is no way you can do the final 'stretch' using an ordinary torque wrench.
We had to use a 5 foot pipe to complete the final 2x90 degree setting, and then it took some force.
We followed the Mazda manual to the letter, even applying oil to the threads as specified (which makes a significant difference).

The head we replaced has now done in excess of 2000 miles and all seems well. (Head bolts were re-checked after 600 miles as recommended)

As far as overtightening of the glowplugs is concerned, you are far safer sticking to the Mazda recommendations (15~19Nm). Why? - Aluminium Just my opinion though.

Hi Steve,
What do you recon the torque on the bolts are after the final tighten.

Cheers.

[widdowson2008]

Hi Steve,
What do you recon the torque on the bolts are after the final tighten.

Cheers.

Absolutely no idea. Couldn't even hazard a guess - sorry. Just followed the Mazda manual instructions.
All I know is that it is WAAAYYY above the initial torque of 29Nm.
As a very rough guide, Jeff did the final tightening (and he is an extremely fit bloke). We had a 5 foot long bar and he had to exert full body weight to it to achieve settings.

[dandywarhol]

I don't understand why the bolts are rechecked @600 miles.
The principle behing stretch bolts is to eliminate retorquing the head thus extending the initial service intervals of the vehicle. Before stretch bolts were invented, engines used conventional high tensile steel bolts which had to be retorqued at the first 1000 mile service - pretty labour intensive.

If you were to retorque stretch bolts, then you are resetting them from the stetch - thats a no no cos you should never reuse stretch bolts......................................

[teenmal]

I don't understand why the bolts are rechecked @600 miles.
The principle behing stretch bolts is to eliminate retorquing the head thus extending the initial service intervals of the vehicle. Before stretch bolts were invented, engines used conventional high tensile steel bolts which had to be retorqued at the first 1000 mile service - pretty labour intensive.

If you were to retorque stretch bolts, then you are resetting them from the stetch - thats a no no cos you should never reuse stretch bolts......................................

I am a bit confused as well,

"Quote from Steve...(Head bolts were re-checked after 600 miles as recommended)

I dont know any other way of checking the bolts other than checking the torque setting.

[widdowson2008]

I don't understand why the bolts are rechecked @600 miles.
The principle behing stretch bolts is to eliminate retorquing the head thus extending the initial service intervals of the vehicle. Before stretch bolts were invented, engines used conventional high tensile steel bolts which had to be retorqued at the first 1000 mile service - pretty labour intensive.

If you were to retorque stretch bolts, then you are resetting them from the stetch - thats a no no cos you should never reuse stretch bolts......................................

Sorry Dandy/teenmal - getting old (and feeling it) .
It wasn't the head bolts we checked - it was the tappet settings.

[teenmal]

I don't understand why the bolts are rechecked @600 miles.
The principle behing stretch bolts is to eliminate retorquing the head thus extending the initial service intervals of the vehicle. Before stretch bolts were invented, engines used conventional high tensile steel bolts which had to be retorqued at the first 1000 mile service - pretty labour intensive.

If you were to retorque stretch bolts, then you are resetting them from the stetch - thats a no no cos you should never reuse stretch bolts......................................

Sorry Dandy/teenmal - getting old (and feeling it) .
It wasn't the head bolts we checked - it was the camshaft pedestal bolts, simply because it was suggested by a mate - no other reason.

Great stuff,I will sleep better tonight

[widdowson2008]

I don't understand why the bolts are rechecked @600 miles.
The principle behing stretch bolts is to eliminate retorquing the head thus extending the initial service intervals of the vehicle. Before stretch bolts were invented, engines used conventional high tensile steel bolts which had to be retorqued at the first 1000 mile service - pretty labour intensive.

If you were to retorque stretch bolts, then you are resetting them from the stetch - thats a no no cos you should never reuse stretch bolts......................................

Sorry Dandy/teenmal - getting old (and feeling it) .
It wasn't the head bolts we checked - it was the camshaft pedestal bolts, simply because it was suggested by a mate - no other reason.

Great stuff,I will sleep better tonight

Cocked up again. It was the TAPPET settings we checked. I'm not paying attention.