Engine Servicing

[jimbo]

I see the point you are trying to make but, the only time you can adjust the valve clearances is when the piston is at TDC on the compression stroke. This is when the rockers are 'rocking' ie both cam lobes are at their lowest point, both valves shut

[senator]

at which point one of the other valves will be totally shut, assuming Sea Gem has straight 6's each engine has 12 valves, if valve 1 of 12 is fully compressed then valve X, possibly 7 will be fully closed as that piston will be at TDC and the cam lobe will be in the correct position to give maximum clearance on that tapit.

[jimbo]

Hmm! This is getting lost in the fog now The point I was trying to make is..............You can adjust both inlet and exhaust on the same cylinder at the top of the compression stroke! It is possible to adjust them at other points in the cycle, but why make life difficult? As far as the term 'Rocking' is concerned, a valve is either opening,closing or 'rocking'.

[senator]

Interesting to me as I know sod all about diesels but I can't see any fundamental difference to a petrol OHV in this instance, while it is technically possible to do as you say the tapit can rock as soon as the tension is off both springs but unless the cam shell is in exactly the correct position the clearance on both would be different, by turning the engine until a valve is fully compressed, something you can see visually, you can be sure that the valve referred to is fully decompressed without the need to match up timing marks

[jimbo]

The reason I gave that example is that service manuals, such as the one I presume Wayne is using, usually give a point at which to start adjustment and it is usually with Piston 1 at TDC. In a petrol engine, it is very easy to whip a spark plug out and check when the piston reaches this point, not so easy on a diesel.

I may have misunderstood his question all together, but as long as he checks the adjustment when the cylinder is at TDC of the compression strokes, he wont go far wrong.

[senator]

We are both singing from the same hymn sheet Jim but I am missing a few words.

As I say I know sod all about diesels but how do you check a piston is at TDC on the compression stroke, do you have to take out an injector to drop a dowel down or something? or are you into timing lights? in which case does it not make sense to have a valve order and just adjust the clearance's as per the workshop manual?

Think the big thing is interpreting Rocked rather than Rocking in the terminology, I would take that to be down or compressed but that would be very obviously wrong if the rocker arm on the valve they are telling you to adjust is not rocking.

[mjt]

If I can add my twopenn'orth my understanding of 'rocking' is the point at which the exhaust valve is closing and the inlet valve opening, i.e. around TDC at the end of the exhaust stroke. In my 4.108 manual this is also referred to as 'valve overlap'. Thus if the valves of no.1 are at this point then no. 4 will be around TDC on the compression stroke and it's clearances can be set.

with no. 2 valves 'rocking' no. 3 clearances can be set,

with no. 4 rocking no. 1 can be set,

with no. 3 rocking no. 2 can be set.

On some engines I have worked on the method has been to turn the engine until one of the valves is fully open and then adjust the relevant valve in another cylinder (I can't remember the sequence). In this case 'rocking' would be the point at which the cam follower passes over the peak of the cam.

[Antares_9]

Much easier with OHC, you can see exactly when each individual cam lobe is at 180 to the lifter.

[wayneakp]

Thanks all - still

I'll have a play - it will probably be obvious once the penny drops - just seems to take a little longer these days

regards

Wayne

[jimbo]

I set 1 at TDC both valves closed timing mark lined up. Then simply follow the firing order of the engine, in my case 1-3-4-2.

The harder question hasn't been asked yet! "Which valve is an inlet and which an exhaust"

[mjt]

That ought to be obvious from looking at the manifolds.

[wayneakp]

The harder question hasn't been asked yet! "Which valve is an inlet and which an exhaust"

Ah..that bits easy - there is a picture in the book with arrows

[jimbo]

Ah..that bits easy - there is a picture in the book with arrows

Cheat!

[Morris Man]

I was always told in a 4 cylinder engine with 2 valves per cylinder you always used the count of 9, that is when no 1 valve is fully opened you set no 8 no 2 open set no 7 and so on, by open I mean the valve is open.

Hopes this helps,

Robin

[wayneakp]

Hi Thanks for that - yes I have found a similar reference to the rule of 13 for the 6 cyl. engines .I will have a play

Wayne

[Stranger]

Hi Wayne the rule of 9 and 13 can only be used on some engines, if u use it on ones where it is not recomended by the manufacturer if they are designed to be set at TDC you can over adjust them and end up with bent pushrods as i have seen done on chrysler engines or worse valves and pistons come in contact so use the manual and take it as a word from God lol

[wayneakp]

The mystery of setting tappets is solved, i found out if you read the book properly, then turn the engine in the correct direction it is actually quite easy !

[Antares_9]

That's the spirit Wayne, when all else fails RTFM

[senator]

to be honest as long as you don't have outdrives there is not much on a basic engine that anyone with a bit of practical ability can't do.

I have to do it to make boating affordable but it also means you can fix it when it needs fixing.

[Guest DAYTONA-BILL]

to be honest as long as you don't have outdrives there is not much on a basic engine that anyone with a bit of practical ability can't do.

I have to do it to make boating affordable but it also means you can fix it when it needs fixing.

Making boating affordable? ............... You`re avin a larf , Just not such a money pit, that`s about all . Regards ............Neil.

[jimbo]

I have to agree, I personally have saved hundreds of pounds by doing the work myself. Plus I enjoy doing it