Tappets

tom52

tom52

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'owdo all,

Can anyone tell me what the sequence is for adjusting tappets in a three cylinder diesel ?

You know the kind of thing when 3 is 'rocking' adjust 2 etc. From memory there is usually some kind of formula like " when valve No.X is rocking/fully closed ( can't remember which ! ) adjust No.X+2 " or +3 or something.

Thanks

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If you don't get any luck with this I'll check my VP2030 manual next time I'm down the boat.

Rgds
Tom

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Depends upon the firing order and the crankshaft configuration. What engine is it?

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion
 
Steve - I had a similar query on a Mitsubishi M3.10/Vetus M3.10 which is also 3 cylinder diesel. Any idea of order of adjustment?

I know in a car it normally works from when one rocker arm is completely down the other rocker arm clearance is adjusted. Is this the same with a boat diesel engine?

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Thanks everyone.
I have now found the info for my engine.
Sorry if I have started something.
If its any help to anyone else the answer for the three cylinder Volvo 2020 is
When both valves for No 1 are closed continue turning the engine until the marking of the flywheel shows 0 degrees. Then adjust both No 1 valves and the outlet valve on No 2 .
A further turn of 240 degrees anti clockwise ( seen from the front ) then adjust both No 3 valves and the inlet valve on No 2.
The clearances for all 6 valves is O.20mm ( cold).

However......

I still believe that there is some simple rule.
Which I believe is something to the effect that you deduct 1 from the number of cylinders to get the magic number. In which case for a 3 cylinder engine the magic number would be 2.
You add the magic number to the number of the fully closed valve to find which to adjust.
So if 1&2 are closed adjust 3&4 and so on.

Can anyone confirm or correct my dim and distant memory.

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I think, for a four cylinder car, that it was the "rule of 9" -i.e. you would adjust No.1 rocker when No.8 valve was fully open, then No.2 when No.7 was fully open and so on with each pair of values adding up to 9. I have no idea whether you can do something similar with a 3 cylinder engine but all you're trying to do is to ensure that the tappet you're actually adjusting is directly over the "heel" of the camshaft (i.e. opposite the highest point on the lobe of that cam). If you can make a note of the camshaft position (if you can see one end of it) mark the point where the valve you want to adjust is fully open and then turn the engine until the cam has done half a revolution from that point. If you can't see the cam, you can do it with the crank but the cam will most likely turn at half crank speed so you'll probably have to turn the crank one whole turn from when that valve was fully open.

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For any 4 stroke engine, when the valves are rocking the piston is at TDC. turn the flywheel 1 complete revolution and the valves can be adjusted as the piston it at TDC compression stroke. Treat each cylinder of a multicylinder engine individually.

The 7 rule worked on older 4 cylinder engines, which I did on an almost daily basis when I was reconditoning them for 4 years, late 60, early 70s. However I came unstuck a few years ago, when I tried to adjust a modern engine (sorry forget what it was) and found it didn't work.

I too seem to remember hearing of a 3 cylinder rule, but never needed to use it.

<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://www.angelfire.com/rnb/malcsworld/>http://www.angelfire.com/rnb/malcsworld/</A>
Take a look at my boating pages.
 
IThe formula used to work for the old 1-3-4-2 firing order engines, but people have now started swappiong things around, and producing such monstrosities as 1-2-4-3 firing orders. 3 Cylinder engines are often be configured on a Y basis, meaning that if the valves are rocking on one cylinder, the others will not be anywhere near TDC, and the valve gaps obtained will not be correct.

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Wether or not the other rocker on a cylinder is open or closed isn't the issue. What you want is the cam follower on the "back" of the cam, ie opposite to or near opposite to the lobe of the cam. In a 4 cylinder engine usually, when one cylinder pair of rocker arms is "rocking" ie one opening and the other closing then it is Ok to adjust both the paired cylinder's clearances. Whichever IS the paired cylinder depends upon the firing order and crankshaft shape (ie are alternate big end journals on opposite sides -one up, one down, one up, one down or are the middle two together but opposing the end ones -one up, two down, one up)

If your firing order for a 4cyl is 1-4-3-2 then you should adjust 1 when 3 is rocking (&VV) and 3 when 1 is rocking (&VV).

Three cylinder engines may have all the big ends in the same plane (two up and one down) or at 60 degrees to each other so it is vital to know the shape of the crankshaft.

These are guides for the unskilled and infrequent adjuster of course, a skilled mechanic can tell when the followers are on the back of the cam by turning the crank back & forth (with decompresion of course!

Steve Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion
 
Thanks Brian. I just copied someone without thinking. I set so many engines this way, it became second nature. These were usually Ford 1200 or 1500, and then crossflow engines, with a few minis, vauxhalls, imps, and 1725 Roots thrown in.

I think it was when manufacturing techniques allowed better casting and heads were made with true crossflow i.e. the valve sequence if inlet exhaust inlet exhaust etc. instead of siamesed exhaust inlet, inlet exhaust ect. that messed this up. I remember finding it not to work on a 1986 Fiesta in 1990. Up til then I had been running a Mk1 Escort with a 1300 crossflow for a number of years. And apart from the annual service, I had little to do with engines for a longish period.

<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://www.angelfire.com/rnb/malcsworld/>http://www.angelfire.com/rnb/malcsworld/</A>
Take a look at my boating pages.
 
i dont quite see what the effect of cross flow engines had on the idea, the valves open and shut at the same time as an ordinary engine.
ford 4 cylinder engines fire 1243 and the rest 1342, these are the only two combinations. 2 pistons must always be opposite the other two for balance reasons.

think about it, 1342, 1 and 4 go up together and then 3 and 2 go up together, so 1 goes up with 4 and fires, so 1 will have both valves closed and 4 will be rocking. next 3 and 2 go up, 3 fires and 2 rocks next 4 and 1 with 4 firing and 1 rocking and then 3 and 2 with two firing and 3 rocking.

so rule of 5 works. if the cyliders add up to 5 one will be rocking and tight tappets and one will be loose tappets ready for setting.


<hr width=100% size=1>http://www.beneteau-owners-association.org.uk
 
Sorry we are going slightly off topic. Go to the parts department, or a scrapyard and take a look at a camshaft.

When No1 lobe is vertically up, No8 is vertically down.

When No2 is vertically up, No7 is vertically down.

No3 up, No6 down

No4 up, no5down.

They are opposite each other.....however with altering the positon of the valves in the head, the camshaft is a different configeration, so you cannot set the tappets using this method.

Pm me if you like, and I'll try and explain more cleary, and find some pictures.

<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://www.angelfire.com/rnb/malcsworld/>http://www.angelfire.com/rnb/malcsworld/</A>
Take a look at my boating pages.
 
its the position of the pistons that dictate when the tappets are in the right position.
when 1 and 4 are at top dead centre, which is where one is rocking and one is loose, is the point where you set the tappets. sorry old chap you are barking up the wrong tree, if you alter the position of the lobes you alter the valve timing.
the position of the valves is compensated for by the length or angle of the pushrods.
dont forget all ignition and valve timing is always set by reference to degrees.
stu


<hr width=100% size=1>http://www.beneteau-owners-association.org.uk
 
as far back as i can remember (early 60s) ford have always used 1243 as the firing order other wise i agree
stu

<hr width=100% size=1>http://www.beneteau-owners-association.org.uk
 
I'd have thought this might not always be true! When the piston is at TDC, the valves will probably both be shut but depending on the valve overlap, the follower (in an OHV engine) might not be directly over the heel of the cam at this point. I agree that marine diesels probably won't have really "wild" valve timing but they still might not be over the heel of the cam at TDC. I'd still be inclined to set the tappet clearances when you KNOW the follower is directly above the heel of the cam i.e. 180 CAMSHAFT degrees after the valve is fully open. I think you might otherwise end up running the risk of setting the tappets too tight because although the valve is shut, you don't know how close it is to starting to open.

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To garantee being on the back of the cam, rotate the engine until the valve is fully open. Turn the crankshaft 360 degrees (one full rotation) The cam is now in postion to set the tappet on this valve.

Complete this operation for every individual valve in the engine.

This will work for any conventional 4 stroke, regardless of number of cylinders, firing order, or number of valves per cylinder.

Some Yamaha motorbikes have 5 valves per cylinder, 20 valves for a 4 cylinder engine. You need to take it slowly and do one at a time to be sure to get them all correct.

<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://www.angelfire.com/rnb/malcsworld/>http://www.angelfire.com/rnb/malcsworld/</A>
Take a look at my boating pages.
 
cam.jpg


I have managed to find a picture of a camshaft, and have written the number of the valve, and the position of the lobe.

You can see No.s 1 & 8, 2 & 7, 3 & 6, 4 & 5 are 180deg.
So when No1 valve is fully open, No8 is fully closed, so the valve is on the back of the cam, and you can set the tappet.
It is the same for 2 & 7, 3 & 6, 4 & 5.

Valves 1, 4, 5 & 8 are exhaust, and valves 2,3,6 & 7 are inlet.

If however the head is designed with valves 1,3,5 & 7 exhaust,
and valves 2,4,6 & 8 inlet,
then the lobes on the camshaft will not be 180 degrees, so this method of setting the tappets cannot be used.

I hope this helps clarify any confusion.

Of course modern engines with overhead camshafts are easy, as you can see when the rocker is on the back of the camshaft. Unless they are adjustde with shims.

<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://www.angelfire.com/rnb/malcsworld/>http://www.angelfire.com/rnb/malcsworld/</A>
Take a look at my boating pages.
 
Heavens!

But Sonsy Lass is saying that not ALL engines have the usual firing order/layout.....so the cranks & cam's & therefore "if one is rocking, adjust x" rule doesn't work for every engine.


Must say I've always followed manufacturers guides when setting valve clearances on bikes, sometimes these are "tdc" ,sometimes back of the lobe.

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