Piston Ring Gaps / Flying Farmers New Project

[Klaus Schlueter]

Hi Neil and Edd and of course the other experts,

in "Flying Farmers New Project" you discussed the location of the piston ring gaps (post #258 + 259). I admit that I didn't understand all of it.
Is it possible to explain in which direction the ring gaps should point by using the attached sketch with the coordinates RH 1 to 4 and LH 1 to 4?

Klaus


DSC04356.JPG

[dasadrew]

The Triumph ROM says to spread the gaps evenly between 1 & 3 on the "4" side of the piston, i.e. between 1 and 4; 3 and 4.

The Grants Rings Instruction says also to spread the oil control rings top and bottom about 90° apart from one another so that they don't align and equidistant from the overlap or joint of the oil control ring spreader.

[flying farmer]

Unfortunately I assume there is a cock up in the Triumph ROM and the Haynes manual as it says the non thrust side of the piston is the inboard
side, which would be position 4 in the above diagram.

However, for this to be the case the arrows on the piston crowns would have to be pointing in opposite directions on the left and right cylinder
banks and they don't, they all point the same way. This means that the thrust side is on the same side, the right hand side looking from the
rear of the engine, which means the thrust side is inboard on the left bank and outboard on the right bank.

As to the actual effect of fitting the gaps on the thrust side of the piston, I have no idea at all. I would have thought that logically the piston
being forced to the side of the bore where the ring gap is located would have had the effect of covering the gap with the ring lands and therefore
reducing blow by. The fact that this position is not recommended obviously means that I am unaware of the reason why!!!!!

Neil

[Ian Durrant]

I am confused, what is the "thrust side"? it obviously doesn't mean crank thrust. ISTR that one of the sets of rings I fitted recommended setting the ring gaps at 120 degrees ( 3 compression rings) but its a long time ago when I last rebuilt an engine.

[flying farmer]

The thrust that is being referred to is caused by the angle of the connecting rod relative to the piston as the piston travels down the bore.

Because the connecting rod is at an angle to the piston it pushes the piston sideways into the bore. To help counteract this, the gudgeon
pin is also offset slightly to one side which is why the pistons are marked with an arrow that points to the front of the block.

My old uncle who first taught me engine building also said to put the ring gaps at 120 degrees, but that was on diesels with three compression rings,
and that is exactly what I did when I rebuilt one of my tractor engines a few years ago

Neil

[edd]

The usual fast replies this forum is better than google well done guys
Edd

[wilf]

So, if I have this right, looking onto the front of the engine, the thrust faces should be:

LH bank - "outer" cylinder walls
RH bank - "inner" cylinder walls

Correct?

[Klaus Schlueter]

Drew: are the green dots the position of the ring gaps based on the ROM?

Wilf and Neil: do you mean pos.2 on RH and 4 on LH is the thrust side where the gaps should be situated?

Klaus


DSC04360.JPG

[flying farmer]

So, if I have this right, looking onto the front of the engine, the thrust faces should be:

LH bank - "outer" cylinder walls
RH bank - "inner" cylinder walls

Correct?

Oh dear, now you have me confused. Looking from the front it would be that way round,

but to save confusion Triumph cast LH and RH onto the front face of the heads.

If we work on the principal that the side that has LH cast on it is left side, then on that side it is the inboard cylinder wall,

and on the side it has RH cast into it then the thrust side is the outboard cylinder wall

Neil

[flying farmer]

Drew: are the green dots the position of the ring gaps based on the ROM?

Wilf and Neil: do you mean pos.2 on RH and 4 on LH is the thrust side where the gaps should be situated?

Klaus

Klaus,


[ATTACH=CONFIG]25192[/ATTACH]

Klaus,
It is the non thrust side the ring gaps should be situated according to the manual, this is position 2 in your diagram
above for the left bank, and position 4 for the right bank

Neil

[dasadrew]

Klaus, as Neil has pointed out, the ROM contradicts itself. I hadn't actually spent time to work out what is the thrust side and discover this inconsistency for myself.

Putting it clearly:

The ROM says "Ensure that the piston ring gaps are spread evenly on the non-thrust side of the piston - inboard"

As Neil said earlier, the Thrust Side is where your LH '4' is, and where your RH '2' is. So the non-thrust side is where your LH '2' is and your RH '4' is. In other words, piston ring gaps are fitted LH outboard and RH inboard.

I'm pretty sure I fitted all my gaps inboard but quite spread out as the separation of the two oil ring gaps already occupied 90° of the circumference. If my engine explodes on one side, then I now know what the error was. Doesn't mean I'm going to strip it down again now!

Regarding what is LH and RH I've never encountered any vehicle on land, sea or in the air during my stay on this planet where LH has been anything other than the left side facing in the direction of travel.

[wilf]

Sorry guys if I inadvertently introduced a new way of defining left and right!

[staginhiding]

Klaus, as Neil has pointed out, the ROM contradicts itself. I hadn't actually spent time to work out what is the thrust side and discover this inconsistency for myself.

Putting it clearly:

The ROM says "Ensure that the piston ring gaps are spread evenly on the non-thrust side of the piston - inboard"

As Neil said earlier, the Thrust Side is where your LH '4' is, and where your RH '2' is. So the non-thrust side is where your LH '2' is and your RH '4' is. In other words, piston ring gaps are fitted LH outboard and RH inboard.

I'm pretty sure I fitted all my gaps inboard but quite spread out as the separation of the two oil ring gaps already occupied 90° of the circumference. If my engine explodes on one side, then I now know what the error was. Doesn't mean I'm going to strip it down again now!

Regarding what is LH and RH I've never encountered any vehicle on land, sea or in the air during my stay on this planet where LH has been anything other than the left side facing in the direction of travel.

So if when you are talking about the engine as you reverse down the drive ,do things change.. just being difficult Drew take no notice of me..most don't by the way..

Sam

[dasadrew]

So if when you are talking about the engine as you reverse down the drive ,do things change.. just being difficult Drew take no notice of me..most don't by the way..

Sam

Don't worry, the Mother Ship is arriving soon to pick me up anyway.

[edd]

Another problem some will face is what type of piston clamp you use .If you use a rachet type they tend to grap the rings and pull them into another position , its very frustrating. Its almost laughable as most of these complete rebuilds will only cover very few miles and in actual fact see us all out , so i wouldn't worry to much.
Edd