240 head removal

Throttleton

Well-Known Forum User
I want to take the head off a 240 engine, I have a Haynes but the timing chain marks are not explained very well. I have trawled the past threads but to no avail.
The manual says to look out for 2 'bright' links to line up with the 'marks' on the cam sprocket.
My timing chain has one bright link, one link which is bright in the middle only and another which is not bright but with a notch in the centre.
The sprocket has numbers stamped on from 1 to 3.
What exactly am I lining up with what??? before I jam a bit of wood down to stop the tensioner moving. I really don't want to have to pull the front off yet and set the timing up if I get it wrong.
Thanks if any suggestions.
 

rallymanDP

Well-Known Forum User
Craig
What you should be looking for is the small notch at the rear of the Cam Sprocket, and ( with the help of a torch ) there is a corresponding horizontal line about 4mm long on the retaining plate to the front of the Cam. Hard to see, but if you read again the Haynes Manual, you can see pics of what you are looking for.
You need to align those two marks together when one of the bright Chain links is positioned where the wheel is marked No:1 and you have the Engine rotated to position it where No.1 Cylinder is at TDC ( i.e both the Valves are closed & the cam lobes form a '10 to 2' position ). May need a few turns to do it.

Then you can shove the Wood down into the Chain tensioner area to make sure that it can't move, and then remove the Chain sprocket and the Head can be removed safely.

When re-fitting - make sure that the Cam is turned to exactly the same position and then the Chain will go onto the correct Cam Sprocket tooth.
 

Mr.F

Inactive
Would recommend a copy of "How to Rebuild Your Nissan/Datsun OHC" by Tom Monroe - many of the official Nissan manuals had it wrong to start with (corrected in later editions) and I'm not sure that Haynes copied the right one. Also, most aftermarket chains don't have bright links which are for setting up anyway...
On reassembly, it is important to ensure that the tensioner hasn't moved / popped out - there are many on here that will confirm this can happen even with a "bit of wood shoved down". Check the template for the correctly shaped tensioner retaining tool.
Reassembling the oil pump and distributor drive shaft in association with the correct cam timing is key to a sweet running engine and timing marks that work as expected...
If I had a fiver for every phone call that has started with "I had my head off and now I can't get the chain back on the sprocket", I'd have retired years ago...
 

Throttleton

Well-Known Forum User
I am assuming you are recomending the Tom Monroe book over the Haynes Mike??
If so have you any in stock or access to one??
I just want to get the head off without interfering with the timing at all.
Tensioner retaining tool.... is that something I need to get to be safe before I stuff something inappropriate where it doesn't belong?
Duncan is close ish to me so he has kindly agreed to have a look at the head but too far to lug the whole engine down coz I'm feeling scared to take the head off properly.
 

Mr.F

Inactive
Monroe book is (IMO) the definitive guide - although not completely devoid of errors! I can't do links at the moment, but if you follow the mjpshop.net link below you'll find the book listed on page 3 of the book listings. That will allow you to buy securely through Amazon (don't forget to select free postage unless you need it urgently!).
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
Craig, buy the book and have a go. These engines are very simple to work on and a head off is not a difficult task but of course the first time is always a bit scary.

One thing I do these days that's possible with modern digital cameras is to take lots of close-up good quality pictures of components in their current positions before you dismantle. It was very useful with washing machine wiring etc recently. It's very reassuring to know how it should look when it's back together and it can save a bit of time!

Cam chain tensioner - yep fully understand where it is, how it works and how to keep it in position. I use a piece of wedge shaped wood attached to stiff coathanger wire.

Apart from the cam chain tensioner all you have to do is put 3 components (cam, sprocket, chain) back together as they came apart and without rotating the crank.
 

Mr.F

Inactive
Don't underestimate the importance of the oil pump / drive shaft / distributor alignment...
 

Albrecht

Well-Known Forum User
If you've got the engine out of the car, now would be the best time to give it a full strip down, clean up, hone & rings, crank polish & new brgs etc etc.

In which case you would not need to worry about cam timing, cam chain tensioner wedging and all that......
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
Don't underestimate the importance of the oil pump / drive shaft / distributor alignment...

Mike, if Craig doesn't turn his crank or touch the distributor all will remain in the correct place won't it? If he put the head back on with the cam rotated so he was on the wrong stroke then I can understand the problem.

When I've take my head off I've never even thought about the distributor drive.
 

SKiddell

Well-Known Forum User
All of this assumes the engine is in good condition, Alan makes a very valid point If the engine is out, take the opportunity to recondition it, its a relatively small cost as most parts are easily available plus its a great opportunity to inspect things more closely, find potential issues and learn new skills.
I wouldn’t recommend a head off procedure on an engine that’s been standing around unused or neglected for any period of time.

Robs advice for a digital camera or camera phone is excellent; I do this…..a picture is worth a thousand bits of fag packet.

Mikes recommendation re the alternative book “How to rebuild your” is golden, the Haynes manual is sadly lacking in certain areas, neither are without slight errors and omissions.

If the engine has been recently overhauled and requires a head off only procedure
here’s a few tips (not a definitive “how too”)

Don't get too hung up with the shiny link malarkey, just look for the dot on the outer diameter of the cam sprocket and mark the nearest link both on the sprocket and the chain (see below)

When making a chain wedge (there are internet templates around), the best thing is a piece of poly prop or nylon, if you don’t have that to hand use a bit of wood that doesn’t splinter or shed bits easily (you don’t want wood splinters in your oil ways)

On a stock cam sprocket engine, when the engine is a TDC there is a little “window” on the cam sprocket and through that you will see a notch on the back diameter of the sprocket and a “dash” mark on the cam retaining plate these two “match up” (approximately) depending on which sprocket location hole is used (Nissans mechanism to compensate for chain stretch) and the wear on the chain.

If you don’t disturb the cam/crank relationship when taking the head off then it should go back together fairly easily (that’s no excuse not to check things though).

Heres a "sort of" procedure
Rocker cover off, plugs out, battery disconnected and assuming all of the induction/exhaust is disconnected etc.

Take engine to TDC on the timing marks on the crank pulley (real TDC not the overlap cycle) so that the cam ears on cylinder 1 are up a la Mickey Mouse.

Note the notch and dash on the cam sprocket mentioned above (take photo)

Note which hole the cam sprocket location dowel is using (take photo)

Look for a dot on the outer diameter of the sprocket and use a paint blob/tippex/scribed line to identify the chain link nearest it (take photo)

You can make a piston lock (old spark plug with a radiused end jacking bolt going through it) this can help prevent engine movement and reference TDC.

Put your chain wedge down in between the rising and falling links, make sure it is very well seated and pushed home as this is the most important thing you will do (make sure you have a mechanism for retrieval such as the coat hanger mentioned)

Once all is secured (check again that the chain wedge is securely fitted as you only get one shot at this), remove cam sprocket bolt whilst using a large spanner on the “ears” on the cam shaft body” to prevent any rotational movement of the cam (less work later on to re-align everything)

Remove the cam sprocket from the nose of the cam, it should come off fairly easily, a soft mallet and a light tap may be needed.

Drop the chain down into the large oil way at the front of the head, it can’t go to far, the chain wedge stops it. You need to be able to get the chain back out once you put the head back on, I use a magnetic retrieval tool, string works just as well.

Get some ultra clean rag and use it to cover this large gap up, its not uncommon for all manner of bits to drop in here, if that happens then you will definitely be taking the front cover off.
 
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SKiddell

Well-Known Forum User
In addition, during a strip down you can fit the Kameari modified chain tensioner, this has a retaining bar preventing the infamous popping out scenario.

Or you could fit the dual sprocket setup which is one of the best bits of Z kit ever made, neither is cheap but worth their weight in gold
 

Ian Patmore

Well-Known Forum User
In addition, during a strip down you can fit the Kameari modified chain tensioner, this has a retaining bar preventing the infamous popping out scenario.

Or you could fit the dual sprocket setup which is one of the best bits of Z kit ever made, neither is cheap but worth their weight in gold

Certainly is, and no worring about shimming the cam towers either (if used) I love the rattle/whir they make when the engine is running....
 

Throttleton

Well-Known Forum User
Alan/Steve, the engine is out of the car.
I was in the short term just going to put a new head gasket and water pump on but what is the point of asking for opinions on here then ignoring them....
So a full strip down it is then....Gulp!
I will no doubt be pestering you all when it comes to re-build and new parts upgrades.
Thanks
Craig
 

zpuppy

Well-Known Forum User
Dont worry to much about it just proceed without haste and take lots of pics ! You'll most likely enjoy it and there is no better feeling than having rebuilt it and driving to the next meet ! :thumbs: If you want I have L24 Su 240z engine overhaul manual on file, send me your email and i'll send it along,,,although as Mr F says, there are some minor issues with some nissan manuals. :confused: :driving:
 

MaximG

Well-Known Forum User
Certainly is, and no worrying about shimming the cam towers either (if used) I love the rattle/whir they make when the engine is running....

I was under the impression that the need to shim the towers arose if the head had been skimmed to realign Cam geometry. The alternative to this is to change the lash pads?


Mike B
 

Throttleton

Well-Known Forum User
Thanks zpuppy it's frpcraig@hotmail.co.uk
Taking the head off tomorrow and as It's a full strip down I will try not to worry about the timing!
Although plenty of pics will be taken.
When I was looking through the old threads I noticed a couple of people had a problem with the odd bolt snapping off. Are there any tricks to avoid this. I know not to just rive them out and turn back a bit then loosen a bit more but should I try to tighten an eighth of a turn first or is that an old wives tale.
I have access to heat but was worried about locally heating the alloy head and nackering it.
Also the exhaust manifold bolts are horrible. Do I get the head off with the manifolds left on then tackle on a bench??
 

Throttleton

Well-Known Forum User
I'll take pics throughout the stripdown and rebuild and keep the thread going.
I am sure it will come in handy for others who haven't done it.
There will be questions where I imagine most of you will roll your eyes but I think a full stripdown and rebuild thread by someone not to familiar with the engine would be a help to others like me who want to have a go.
 

zpuppy

Well-Known Forum User
Thanks zpuppy it's frpcraig@hotmail.co.uk
Taking the head off tomorrow and as It's a full strip down I will try not to worry about the timing!
Although plenty of pics will be taken.
When I was looking through the old threads I noticed a couple of people had a problem with the odd bolt snapping off. Are there any tricks to avoid this. I know not to just rive them out and turn back a bit then loosen a bit more but should I try to tighten an eighth of a turn first or is that an old wives tale.
I have access to heat but was worried about locally heating the alloy head and nackering it.
Also the exhaust manifold bolts are horrible. Do I get the head off with the manifolds left on then tackle on a bench??


Soak hell out of every bolt for at least a 24 hr period with wd40 or equivilant ,,,and get down your hand tool supplier an get a good set of " EZ Outs " They'll know what you mean, cus you will most likely need a set and they are not expensive. ;) ( broken stud removers ) By the way thats been e-mailed to you :)
 
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SKiddell

Well-Known Forum User
Mike B said:
I was under the impression that the need to shim the towers arose if the head had been skimmed to realign Cam geometry. The alternative to this is to change the lash pads?

The head gets skimmed for 2 main reasons

1. Slight warp correction
2. Reduced chamber size increasing compression

In the 1st case a mild shimming of the towers takes out any excess chain slack that the tensioner couldnt cope with, sometimes you can get away with no shims.

The second case is the more common, taking 30 - 90 thou off a head may need lots of shims under the towers to bring things back into line, this lifts the cam higher and as a result increases the lobe to finger distance, this is exacerbated with reground cams as the base circle is much reduced, which in turn means increasingly thicker lash pads are needed however you can't do this ad infinitum as once you get to a certain size lash pad the entire relationship between the lobe and the finger is upset and cannot be easily corrected.

That is why the Kameari dual sprocket system is the dogs danglies, it removes the need to shim the towers, never having to take the front cover off to re set the tensioner and acting all smug on the forum to boot:D
 
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