Z24 Re-torque head bolts hot, cold, doesn't matter?

[MaddieCycle]

Are people retorquing their head bolts when the engine is hot or cold? Does it matter? I am worried about snapping a head bolt when loosening them, also thinking about how to get this and the valves all done while the engine is still hot.  I think iron and steel have similar thermal expansions so probably does not matter, yes? Also, is it worth as insurance for the future replacing all of the head bolts when I do this on my 35 year old truck?

[datzenmike]

It's only the Z24 blocks that suffer most from head gasket failures every 100K. The best prevention is to keep the head tightly clamped to the block by loosening a head bolt and tighten to 60 ft. lbs. Never loosen more than one bolt at a time. Do this once a year. Do in any order you like. 

 

If the head bolts are undamaged they are re-usable

Iron and steel are close for thermal expansion but the head is aluminum and it will expand about twice that of steel.

Always loosen and then re-torque on a COLD engine. This is the temperature that the Z24 bolts were originally torqued under.

 

If setting the valve lash, put the valve cover back on and warm the engine for at least 20 min. Or do another day.

 

On a hot engine I like to remove the valve cover and turn the engine to TDC on the #1 cylinder using the crankshaft pulley mark on the timing scale. Check that both #1 cylinder valves are closed. Adjust both valves on #1 cylinder, intake on #2, the exhaust on #3. Turn engine ONE full turn up to TDC. Adjust exhaust on #2, intake on #3 and both valves on #4. Done this way there is no endless bumping of the starter and fast enough to do before cool down.

[MaddieCycle]

Thx. Do you use a breaker bar on the camshaft nut to turn the engine?

[DanielC]

Turn the crankshaft to turn the engine.

 

[datzenmike]

You could, but you risk loosening the torque on the cam sprocket bolt. I think the crankshaft bolt is 27mm. A large adjustable wrench would work.

 

Take the exhaust side plugs out. This will make turning the engine easier.

[MaddieCycle]

I did the head bolts and nothing snapped, but some weird things happened.  The bolts were all on very tight.  A couple of them would not budge loose even with a breaker bar and I could sense that if I put any more torque on them I'd snap the bolt. The ones that did move had a lot of resistance.  I suspect these have never been moved before.  I torqued them to 57 ft lbs which is the middle of the 54-60 range listed in the FSM.  Maybe there is some funny business going on inside there, but I'd rather wait for the head gasket to blow than snap off a bolt now.

Turning the crank bolt is going to be a pain as this truck has both AC and power steering and there is a lot in the way to get to the crank bolt.  I think I will set my torque wrench at a low setting, take out a plug from each cyl, and try turning the engine with the cam bolt.

[datzenmike]

AC is off so the pulley is free wheeling. The PS pump is very easy to turn by hand.

 

You could try warming the engine and try loosening. Heat will expand the block metal making the holes larger and maybe loosening it's grip on the bolts... but let cool down before torquing.

[MaddieCycle]

The issue was not so much the drag from the A/C and PS, but the lack of any clear access to the crank pulley from above or below.

In any case, I was not happy about using the cam bolt, so I just did the old crank-the-starter, verify cam lobes are down, verify piston position with a probe in the spark plug hole method.  I have not been able to find a clear mark on the crank pulley to line up with the indicator anyway. 35 years of grime and rust.  After all of this fuss only 3 valves needed adjustment, and they were loose by only 0.03mm. 

[MaddieCycle]

Finally the truck for a spin after finishing this valve adjustment. It runs like a new truck. Huge increase in power, quieter, easier to start. What a difference 0.03mm makes.

[datzenmike]

Placebo effect. 0.03mm is just over a thou and not significant. Sure it wasn't 0.3mm??? Maybe wires were on wrong and you put them back on correctly?

[MaddieCycle]

No it was definitely 0.03mm.  However, this also was the first real shakedown cruise since I did a full front end refresh, alignment, and fixed a couple of vacuum leaks. So that could be part of it.  Still, when you have such a marginally powerful engine to begin with, I would imagine it needs every little bit dialed in just right.  Also, I just put in a Rodeo seat so it is actually comfortable and that could be swaying me as well.

[datzenmike]

16 minutes ago, MaddieCycle said:

   Also, I just put in a Rodeo seat so it is actually comfortable and that could be swaying me as well.

 

There's nothing like being comfortable when driving. Plugs will self clean as you drive too. The more you drive it the better it drives.