Thread: Bolt Torque - clutch/flywheel bits

I think one is talking ft/lb (imperial) and the other metric

Originally Posted by rijidij

My manual says, Flywheel to crank - 105-125 ft lbs lubed with eng oil, and flywheel housing to eng - 90.4-112.1 ft lbs (that's for the 2 piece housing)

Murray
.

What year is the manual? Genuine ISUZU?

Rob - not sure what you mean, everyone has been quoting ft.lb / lb.ft

Murray,
Sourced it semi-locally in the US. The local Isuzu truck place was not 'allowed' to look up the flywheel housing part number. I went to an Isuzu Industrial dealer who was able to find the only one in the US/CAN.

-Paul

Originally Posted by rijidij

My manual says, Flywheel to crank - 105-125 ft lbs lubed with eng oil, and flywheel housing to eng - 90.4-112.1 ft lbs (that's for the 2 piece housing)

Murray

ps. Paul, where did you end up sourcing the flywheel housing.

Originally Posted by isuzurover

So which is right???

John, since you are the expert on bolted joints, I would be keen to know which method you think is preferable (not that I am about to pull my engine back out, but it would be good to know for next time...)

Originally Posted by Bush65

I had a look in a different manual and copied the following (see pic), which also says to apply engine oil, and tighten to 115 ft lbs.

Originally Posted by isuzurover

What year is that manual? Mine is 1988.

An Isuzu truck service manual - October 1988.

The engine section was scanned by someone else into pdf format. I tried to upload it into the files section of this forum, but kept getting page load errors. I tried firefox, safari and internetexplorer. Also tried with firewall turned off.

The values given in my earlier post were taken from another Isuzu manual, IDE2140, I don't know manual date, but it says for 4BD1 and 4BD1T, 1986 ~.

Edit: pic added

Originally Posted by Bush65

An Isuzu truck service manual - October 1988.

The engine section was scanned by someone else into pdf format. I tried to upload it into the files section of this forum, but kept getting page load errors. I tried firefox, safari and internetexplorer. Also tried with firewall turned off.

The values given in my earlier post were taken from another Isuzu manual, IDE2140, I don't know manual date, but it says for 4BD1 and 4BD1T, 1986 ~.

That is interesting.
The manual I scanned the above section from is a:
Workshop Manual
N Series
applicable to all vehicles in all countries except USA and Canada
Manual applicable to 1985 and later model years
First Edition, September 1988 1008-25K-1
PN: LG4BE-WE-58G

Originally Posted by isuzurover

John, since you are the expert on bolted joints, I would be keen to know which method you think is preferable (not that I am about to pull my engine back out, but it would be good to know for next time...)

In most cases with bolted joints, the thing which is important is the pre-tension in the bolt.

Tightening torque is one method for achieving a required pre-tension, but because the tightening torque is resisted by friction between the mating threads, and between the underside of the bolt head (or nut) and the joint/washer, only a fraction of the torque contributes to pre-tension.

The friction increases as pre-tension increases and also varies greatly from one bolt to another.

Research has shown that the accuracy of achieving desired pre-tension is in the order of +/- 25% when torque control is used. In many cases this is not acceptable and other methods are used, such as part turn method. For critical applications, one of the best methods is direct measurement of bolt stretch.

Australian Standard AS4100, Steel Structures Code, Clause 15.2.5.3 does not permit torque control to be used for tightening bolts in structural joints. With steel structures (e.g. buildings), bolts may be either snug tightened of fully tensioned depending upon the design requirements.

Machinery is usually intended to be disassembled and reassembled, so bolted joints are usually designed for bolts to be tightened to approximately 65% of their proof load. In some instances when loads are high and larger bolts can not be used the design will require higher pre-tension up to 100% of the proof load - these bolts should not be re-used.

The fatigue strength of bolts subjected to cyclic tensile loads, is increased when the pre-tension is considerably higher than the maximum applied tensile load.

In the case of the flywheel connection bolts, the torque load is carried by the dowel in shear and the friction between the flywheel and the mounting face on the crankshaft. Note the bolts are not loaded in shear - they can only be loaded in shear if the dowel and friction joint fail first (in which case the bolts will also fail).

To transmit the necessary torque through the bolted connection, the required friction is achieved through the pretension in the bolts clamping the mounting surfaces together.

There are a number of factors (including: shank diameter, thread pitch, thickness of plies, size of bolt head and depth of bolt engagement into the crankshaft) that determine the part turn angle to use for the required pre-tension. Also a number of factors for the relation between tightening torque and pre-tension.

So it is difficult to determine resulting pre-tension from those published figures, but having confirmed that Isuzu published these, and mistakes in interpretation were not made, then I would use the part turn angle method.

I know from experience and investigating many cases of bolt failure, that insufficient bolt pre-load leads to more bolt failures than over tightening. Failures due to over tightening usually causes bolts to fail while they are being tightened (in which case the bolt can be replaced immediately). - BTW, the last revision to the Australian Standard for nuts was changed to be inline with ISO and revised some nut thicknesses to ensure that bolts would break, before threads would strip, so that failure due to over tightening would be obvious to the person tightening the bolt/nut.

Taking into consideration the normal practice of specifying tensions of 65% proof load for machinery, I like to err on the side of over tensioning.

I got a manual with my 1982 second hand Isuzu Rover and hope it is the correct one. Have recommendations changed or does it vary with the year of manufacture? If I need bits isthe Isuz dealer my best hope, or should I go to Landrover?