Re-torque cylinder head

[johnny250]

After doing about 750 miles since the full rebuild, and noticing that I have a 'little bit of seepage...' oil from around cylinder head, do you think that a re-torquing of the cylinder head nuts might be called for? (yes I do have the external rocker feed too)

If so should the nuts be slackened off first then redone, or just tighten them down, if they will go? Looks like I will have to remove the rocker shaft to get at them too....

thanks

john

[Guest Wyn]

John,

 

I'm about to re-torque mine after approximately 100 miles. The rocker shaft will have to come off. I would slacken first and then re-torque, although opinions may differ. After reading quite a bit about it and having excessive oil consumption caused by worn valve guides, I have removed my external oil feed. Time will tell whether this was correct.

 

Wyn

[88V8]

From all I've read on many types of car, yes, back each one off in turn, in the original order of tightening, and retorque it. Should be no need to drain the coolant.

Ivor

[BrianC]

From all I've read on many types of car, yes, back each one off in turn, in the original order of tightening, and retorque it.

Shouldn't that be "in the reverse original order of tightening"?

It's also a good idea to slacken off the adjusters on the rockers before refitting the shaft (don't ask me how I know this )

[johnny250]

Thanks gents,

I will slacken and tighten each in turn otherwise I assume I'll be back to how it was when first fitted!

 

john

[Guest ntc]

Hi John

Don't forget the engine needs to be stone cold ie min 6hrs after running and reset the tappets while your there

Regards

Neil

 

Ps Thanks for the PM

Edited August 19, 2008 by ntc

[88V8]

Shouldn't that be "in the reverse original order of tightening"?

Well, one is tightening the head more, which in effect is what one did when first fitting it.

So I've always taken it that one works in the original order of tightening.

 

Thanks gents,

I will slacken and tighten each in turn otherwise I assume I'll be back to how it was when first fitted!

Oops, sorry, yes, each in turn

 

Ivor

[johnny250]

All done OK, but I reset the tappets a bit wider after reading that a fast road cam needs more than the standard 0.010".....? but not as much as 0.024" (0.6MM) as that seems too big a jump to me, and it has been running fine at 0.010"

Also tapped the external feed banjo bolt to 4mm and then loctited a threaded stud drilled for 2mm as a restrictor, as I like the idea of SOME extra oil to the rockers...having seen the state of the originals when I stripped the engine during the rebuild.

 

john

[Eyetee]

Johnny250

does the engine have a means of breathing, a pipe going to a catch tank which is then piped to the ground?

A mate bought a spitfire recently and the engine had to breather pipes that both went to the catch tank that had no way of equalizing with the atmosphere, making a sealed engine. When run the dip stick would get fired out.

The extra pressure made from enhanced engines increases the chance of oil sepage, as well as ejecting dip sticks.

[BrianC]

Well, one is tightening the head more, which in effect is what one did when first fitting it.

So I've always taken it that one works in the original order of tightening.

 

 

Oops, sorry, yes, each in turn

 

Ivor

Whoops, my misunderstanding

I was thinking of backing all off and then re-torquing which is not quite what you were saying.

I guess it's not a good idea to back them all off as this could jeopardise the head gasket seal, so your method is probably the safest. In retrospect, I think this is how I used to do it (a very long time ago), but it's one of those simple jobs one does subconsciously and is difficult to describe.

[Nick Webster]

Whoops, my misunderstanding

I was thinking of backing all off and then re-torquing which is not quite what you were saying.

I guess it's not a good idea to back them all off as this could jeopardise the head gasket seal, so your method is probably the safest. In retrospect, I think this is how I used to do it (a very long time ago), but it's one of those simple jobs one does subconsciously and is difficult to describe.

 

I have just re-torqued some head bolts and I too was concerned about backing off to re-tighten. However in order to start the nut moving in the tightening direction, more torque seems to be required than if the nut was continually tightened up from slack to full torque without stopping. I am sure there are some good scientific reasons for this involving friction etc. Having said that, when replacing a cylinder head, I have always made it a practice to tighten all head nuts to a certain torque (say 50%) and then go round the sequence again and then again etc. For reasons I will not bore you with, the head I have just done was not mine when it went on but looking through paperwork I realised to my horror the mileage was way over what it should have been after an overhaul and I was suspicious the gasket seal was a bit borderline. So I opted not to back off the nuts, even one at a time (which would have been a preference) and went for a very cautious "over torque". I'm not a great fan of the type of torque wrench that has a pointer against a scale, favouring the "snap" type, but the pointer type does allow you to see the variations in torque, up and down, as you tighten.

 

Nick

Edited August 20, 2008 by Nick Webster

[BrianC]

...I opted not to back off the nuts, even one at a time (which would have been a preference) and went for a very cautious "over torque". I'm not a great fan of the type of torque wrench that has a pointer against a scale, favouring the "snap" type, but the pointer type does allow you to see the variations in torque, up and down, as you tighten.

If you initially torque to the lower setting in the recommended range (e.g. 100 lbs.ft. if range is 100-105), then when it's time to re-torque, I've always assumed it's safe to go to the upper limit without backing-off. I wouldn't attempt this with a bendy-bar torque wrench (mine was long since relegated to the bowels of the toolbox) and would use the same torque wrench each time. Doubtless, a real engineer will point out the error of my ways (never too old to learn).

[marvmul]

If you initially torque to the lower setting in the recommended range (e.g. 100 lbs.ft. if range is 100-105), then when it's time to re-torque, I've always assumed it's safe to go to the upper limit without backing-off. I wouldn't attempt this with a bendy-bar torque wrench (mine was long since relegated to the bowels of the toolbox) and would use the same torque wrench each time. Doubtless, a real engineer will point out the error of my ways (never too old to learn).

Maybe not an engineers way of doing this, but it seems very sensible to do it this way.

I would not go beyond the upper limit because this can make the seal weaker because the engine block can be pulled upwards around the studs, especially when uprated nuts and

studs are used (ARP type).

[Andy Moltu]

It would be best practice to slacken off & retorque the nuts one at a time to the recommended settings - I don't see the point of going higher you may end up damagint the threads or stretching the studs for little gain in terms of preventing head gasket failure.

Ideally in the correct sequence but for retorquing - the order is less critical with a cast iron head than an alloy one.

 

The tappet gaps will need resetting afterwards.

The gaps for the standard cam are 10 thou" but with after market cams you really need to go with the suppliers recommendations.

The reasons why a different gap from standard may really be for one of two reasons-

1) To make sure the valves open at the correct time - reducing the gap to the standard 10 thou" may result in the valves opening too early and making the engine less efficient - for example if the exhaust opens too early you may find that this is before combustion is complete & you end up with a load of unburned hydrocarbons coming out of the exhaust pipe.

2) The gap may also allow the cam to start lifing the follower at the correct point on the cam lobe rather than hitting it at the wrong point whre the lift rate may be higher and thus subject the lobe and follower to higher forces, shortening cam life in the process.

[johnny250]

It would be best practice to slacken off & retorque the nuts one at a time to the recommended settings - I don't see the point of going higher you may end up damagint the threads or stretching the studs for little gain in terms of preventing head gasket failure.

Ideally in the correct sequence but for retorquing - the order is less critical with a cast iron head than an alloy one.

 

The tappet gaps will need resetting afterwards.

The gaps for the standard cam are 10 thou" but with after market cams you really need to go with the suppliers recommendations.

The reasons why a different gap from standard may really be for one of two reasons-

1) To make sure the valves open at the correct time - reducing the gap to the standard 10 thou" may result in the valves opening too early and making the engine less efficient - for example if the exhaust opens too early you may find that this is before combustion is complete & you end up with a load of unburned hydrocarbons coming out of the exhaust pipe.

2) The gap may also allow the cam to start lifing the follower at the correct point on the cam lobe rather than hitting it at the wrong point whre the lift rate may be higher and thus subject the lobe and follower to higher forces, shortening cam life in the process.

 

Thanks for that Andy, as a matter of interest I opened up the tappets to 15 thou after re-torquing the head (from 10 thou) and the engine now starts to pink under load. If I select the 3 degrees less advance map setting (megajolt) it stops the pinking.... unless it's a coincidence and just the latest tank of fuel ?although from same pumps (always used supermarket cheapest unleaded with no problem)

 

john

[marvmul]

The pinking after widening the valve clearance can mean that the cam is more efficient now : better filling of the cylinders will result in higher pressure at the end of the compression stroke, hence more prone to pinking.

[Guest Wyn]

Did you not get details of the V/C from where you got the cam?. For what it's worth, mine is high lift with Inlet 0.014 and exhaust 0.016.

 

Wyn

[Guest ntc]

The pinking after widening the valve clearance can mean that the cam is more efficient now : better filling of the cylinders will result in higher pressure at the end of the compression stroke, hence more prone to pinking.

 

Sorry marvmul the only reason the cam is more efficient now is that it is given more float to find its optimum timing. As I have said before v/c should be in the equation when timing the cam

[marvmul]

Sorry marvmul the only reason the cam is more efficient now is that it is given more float to find its optimum timing. As I have said before v/c should be in the equation when timing the cam

I think it's just that what I mean and not that pinking=more efficiency of course! More valve clearance is making the cam duration shorter, when it is a rather hot cam, the volumetric efficiency will be better with shorter duration, at least in the mid or low rpm where pinking is most likely to occur. It may well be that in the high rpm zone, the cam will loose efficiency, knocking is less likely at high rpm and btw high speed knocking is something you won't hear.