Yanmar 1GM problem - nut securing valve gear

blackbeard

blackbeard

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... so, following much advice on how to do it, I have begun to partially strip down the engine preparatory to taking the head off and getting rid of what I suspect to be a great deal of carbon.
I have got as far as the valve gear which I now need to take off the engine. It's held in place by a single nut , which I now need to remove and to then remove the valve gear prior to lifting off the cylinder head.
Problem is that I can't remove the nut. I have tried WD40, PlusGas, heat (carefully!) and brute force, but the nut will NOT turn - seems absolutely solid.
Can anyone help? As a last resort, is it possible to remove the head without taking the valve gear off?
 
blackbeard said:
... so, following much advice on how to do it, I have begun to partially strip down the engine preparatory to taking the head off and getting rid of what I suspect to be a great deal of carbon.
I have got as far as the valve gear which I now need to take off the engine. It's held in place by a single nut , which I now need to remove and to then remove the valve gear prior to lifting off the cylinder head.
Problem is that I can't remove the nut. I have tried WD40, PlusGas, heat (carefully!) and brute force, but the nut will NOT turn - seems absolutely solid.
Can anyone help? As a last resort, is it possible to remove the head without taking the valve gear off?
Click to expand...
How large is the nut and are you sure that you have determined whether is is right or left handed? I'm not sure which nut you're referring to but if you can get a socket on it with a breaker-bar then it will undo. Provided the nut is not rounded and you have good access you can exert more that 300 ft lbs with a bar and a 1/2 inch drive.

You may well be able to remove the head if you can see that you have clear access to all the head bolts/nuts. However, you will not be able to check/lap the valves which would be a wasted opportunity. Unless access is poor at the moment, releasing the tight nut once the head is removed might be even more difficult.

Richard
 
blackbeard said:
... so, following much advice on how to do it, I have begun to partially strip down the engine preparatory to taking the head off and getting rid of what I suspect to be a great deal of carbon.
I have got as far as the valve gear which I now need to take off the engine. It's held in place by a single nut , which I now need to remove and to then remove the valve gear prior to lifting off the cylinder head.
Problem is that I can't remove the nut. I have tried WD40, PlusGas, heat (carefully!) and brute force, but the nut will NOT turn - seems absolutely solid.
Can anyone help? As a last resort, is it possible to remove the head without taking the valve gear off?
Click to expand...
RichardS said:
How large is the nut and are you sure that you have determined whether is is right or left handed? I'm not sure which nut you're referring to
Richard
Click to expand...

This one (M8) I guess. Id not expect difficulty. It should only have been tightened to 27 ft-lbs. Yes you can remove the head without removing the rocker assembly

Google will find you a couple of links to the workshop/ Service manual.
1618518633355.png
 
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You will need to remove the rocker assembly to grind in the valves and it is easier to do this with the head on the engine. Try a ring spanner on the nut and taping the free end of the spanner with a hammer. Sometimes just tapping the side of the nut with a drift helps it start to turn. If you're going to use a lot of force it's always better to use a hex socket than a twelve pointer. It's often better to use the Tee Bar for your socket set than the ratchet, pushing on one side and pulling on the other.
 
Topcat47 said:
You will need to remove the rocker assembly to grind in the valves and it is easier to do this with the head on the engine. Try a ring spanner on the nut and taping the free end of the spanner with a hammer. Sometimes just tapping the side of the nut with a drift helps it start to turn. If you're going to use a lot of force it's always better to use a hex socket than a twelve pointer. It's often better to use the Tee Bar for your socket set than the ratchet, pushing on one side and pulling on the other.
Click to expand...

+ 1 for a gentle tap with a decent sized hammer
but I was wondering if all else fails :
Once the head is removed the rockers will slide off then will it be possible to get the spring retainers and springs off with the rocker support still in place ? If so it will be possible to grind in the valves .



(
 
Topcat47 said:
You will need to remove the rocker assembly to grind in the valves and it is easier to do this with the head on the engine. Try a ring spanner on the nut and taping the free end of the spanner with a hammer. Sometimes just tapping the side of the nut with a drift helps it start to turn. If you're going to use a lot of force it's always better to use a hex socket than a twelve pointer. It's often better to use the Tee Bar for your socket set than the ratchet, pushing on one side and pulling on the other.
Click to expand...
I would recommend avoidance of the ring spanner as it will almost certainly be twelve sided. Access permitting, as you say, a hex socket is the way to go. T-bars are not as common as they used to be but even a breaker bar can be applied is such a way that the force is applied rotationally rather than laterally.

Richard
 
fwiw, when I took apart the cyl head on my 2GM, these nuts were astonishingly tight for such a small lump, but did let go using the techniques listed above. Don't be afraid (with a hex socket!)
 
6 point deep hex socket after a good dollop of penetrating fluid and a rap with a suitable Drift and hammer and it will come free.
 
I would be wary of shearing the stud, which then takes you into a whole new world of pain.
Can you cut down the side of the nut, being careful to miss the stud threads and you should be able to remove the nut. Obviously a new nut is then required.
 
In my experience the stud usually winds out where the nut we are talking about won’t come free.
Be gentle but firm and apply gradual force with the right
 
Thanks to all for advice.
Nut (and associated valve gear, and cylinder head) are now OFF, following a week or so marinating in Plus-Gas, plus a deep hex socket spanner with a very long bar (courtesy Halfords). I noticed that the washer beneath the nut (according to the manual) was absent without leave, which may have added to the problem ...
 
blackbeard said:
Sounds like the voice of experience .... haven't had a good look yet.
At first sight the combustion chamber looks OK but I will have a closer look.
Now to find a valve spring compressor ....
Click to expand...
Bitter experience. The machine shop chap to whom I took my head (and who found the crack) said he had never seen an un-cracked one. You normally see it by getting the exhaust valve out and looking with a glass at the seat nearest the inlet valve. The good news is that replacing the head is easy. The bad news is that it's astonishingly expensive: over £700 for the head alone and by the time you've bought the other stuff you need (gasket) and may as well do at the same time (precombustion chamber bits, valves) you won't have much change from a thousand quid.

When I did mine I reduced the cost by half by buying in the US and getting a friend to bring it across. US dealers aren't allowed to sell to the UK.
 
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