What's the right way to un-torque a head?

[dragoon]

What\'s the right way to un-torque a head?

One of my engines is being lifted in order to replace a piston that was damaged earlier in the season by a broken valve.

The head was overhauled by Powerdrive in Portsmouth (who I can recommend BTW), and I don't wish to damge it in disassembly.

When I put the head back in it was torqued up according to the workshop manual in stages of 60, 90 & 130nm.

The question is, what is the right way to go about undoing the bolts in order to minimize risk of stress/bending. Obviously I can follow the pattern of tightening (i.e. which bolts first), but can I really un-do the bolts in stages of tightness? I can't see how at least.....?

The engines are TAMD40Bs. If anyone has any suggestions, I'd greatly appreciate it.

Cheers,
Paul

 

[Kawasaki]

Re: What\'s the right way to un-torque a head?

Start in the "middle" and "fan out" if you get My drift.
Crack/nudge/persuade the bolts/nuts.First.
Go from side to side and work your way"outwards".
Don,t think undoing is quite as critical as assembling,imho.
Gentle and even is the way to go.
Carefull/ slowly/don,t rush etc etc etc.
Well you know that anyway, sorry!
Stripping is easy, it,s all about putting it back in. Right. /forums/images/graemlins/blush.gif

 

[bdsweeting]

Re: What\'s the right way to un-torque a head?

I would have thought that the staged tightening was more to do with the stretch of the bolts and compression of the gaskets but am prepared to be shot down.

 

[Stoaty]

Re: What\'s the right way to un-torque a head?

Slacken them off in reverse of the tightening order, ¼ of a turn each, then repeat with another ¼ turn, then in order remove them.

 

[dragoon]

Re: What\'s the right way to un-torque a head?

Thanks everyone who replied. I'll be tackling that during today.

Cheers,
Paul

 

[spannerman]

Re: What\'s the right way to un-torque a head?

The Volvo workshops just use a windy gun same as at your tyre shop in same sequence as tightening, the heads cast iron so never gives any problems, only critical when tightening down.

 

[oldharry]

Re: What\'s the right way to un-torque a head?

Stoaty is right - always follow the tightenin sequence in reverse to avoid warping. Staged tightening ensures that during tightening, no individual bolt is tightened enough to cause distortion of the casting. i.e the difference between 60n and 90 nm is not enough to distort the head, whereas going straight from 60 to 130 would.

 

[chuckaduck]

Re: What\'s the right way to un-torque a head?

[ QUOTE ]


Thanks everyone who replied. I'll be tackling that during today.

Cheers,
Paul

[/ QUOTE ]

Make sure the engine is cold if warm the head can warp

 

[dragoon]

Re: What\'s the right way to un-torque a head?

I slackened the head off today. I followed a collection of all the advice above.
The engine (block) is now in a position to be lifted into the wheel-house (tomorrow morning) and I'll be fitting a new piston as soon as it arrives.


Thanks to all who replied.

Cheers,
Paul

 

[hlb]

Re: What\'s the right way to un-torque a head?

Just as a matter of interest. I've always wondered how engines are removed from under the sallon on say shaft driven boats. Now dont get me wrong. I can think of the way I would do it, providing there was not a massive long reach fork truck available that would just poke through the patio door and lift it for fun. Maybe with a block and tackle on the end. Or are you taking the head off in sittue to loose weight??

Just wondered in case I ever have to do it.

 

[dragoon]

Re: What\'s the right way to un-torque a head?

Hi Haydn,
luckily Dragoon's engines are right under the wheel house with loads of access so they could come up with the head in place if needed. However, since I'm not planning to take the engine home, I've turned the wheelhouse into a temporary workshop and just want to lose weight to make moving it around more managable. Also, Dragoon's interior is completely mahogany so I want to ensure that the lump I have left is as controllable as possible to avoid destroying any wood.
Tomorrows lift is actually with a crane, through one of sliding sun roofs.

That said, I've always wondered the same thing with engines that get buried under the saloon or the aft cabin. I suspect a lot of manufacturers almost build the boat around the engines. I guess it's sheer determination that gets them out in many cases ;o)

Cheers,
Paul

 

[[2068]]

Re: What\'s the right way to un-torque a head?

Didn't one of the magazine boats have an engine out a couple of years back?

They used some sort of long reach crane and took it straight thru the patio doors and out the back as if it were a box of chocolates.

dv.

 

[rich]

Re: What\'s the right way to un-torque a head?

Like this, It took me nearly a week to take the boat apart, but it was worh it in the end. [image]

[/image]

[image]

[/image]

And back in /forums/images/graemlins/smirk.gif

 

[hlb]

Re: What\'s the right way to un-torque a head?

Yes. I see how it could be done, by a masive crane with a long reach jib, would still need block and tackle at the end though, to lift engine high enough. Sure it's simple with the right equipement. No problem with stern drives, done that a few times.

Would think with my boat, you would need about twenty foot horizontal reach, less taking the davits off. Say half a ton at that distance, maybe equates to fifty ton straight lift. /forums/images/graemlins/confused.gif

 

[dragoon]

Re: What\'s the right way to un-torque a head?

I got the engine lifted today, and removed the broken piston and sleeve. Pictures below - the man pictured is Mick, my neighbour.

Cheers,
Paul



Before:

Immediately after the lift;

With the sump removed;

 

[spannerman]

Re: What\'s the right way to un-torque a head?

For flybridge boats with big engines we used a enormous purpose made square shaped 'C' frame which we suspended from the crane with the engine hanging at the lower end of the C, and it had a counterweight to offset the weight of the frame so it hung level and then the lift point was directly over the engine but about 15ft above so we could get it into the saloon with out fouling the flybridge.