Piston Rings (Question)

[mwmackenzie]

Where is the best place to have the gaps for the best seal... Fitting new rings to my pistons and then fitting them to my liners tonight hopefully!

[mac]

IIRC it's 90degs from the oil control rings - but it could be 180deg........




Mac

[roadboy]

Fit each consecutive ring so the gap is on the opposite side of the piston to the previous one and make sure that the gaps are not on the thrust faces. With the oil control rings, the top and bottom rings should have the gaps opposite each other and the join of the middle ring should be slightly offset from one of the ring gaps but again not on the thrust face.

HTH (and makes sense)

Dan

[mwmackenzie]

Top work gents... Thank you very much! still cleaning the piston tops so I can see the arrows so I know which way to pop them back in

[roadboy]

The markings on the conrods/big ends go towards the exhaust side.

Saves you having to find the arrows.

Dan

[mwmackenzie]

I knew it was worth having you (an Englishman) on here for something! Great info, thanks!

[roadboy]

Pah! I just fill in when the Oracle (Robin) is busy.

Dan

[mwmackenzie]

Well that's that done, pistons now fitted to liners and ready to be fitted to my freshly skimmed block (thanks to Stu160 for sorting liner heights and robin for providing the bottom end)

This is what i did... bottom oil control ring is to one side of gudgeon pin, centre is to the other side of same end of gudgeon pin, top of oil control ring is at 180 degrees or other end of gudgeon pin. lower piston ring is 180 degrees to top oil control ring and the top ring is at 180 degrees to that one so nothing is working on the thrust face of the piston.

Does that sound about right or do I need to strip it all down and start again??

Thanks guys

Mark

[robin]

What Dan says is right. The manual is more detailed, but you end up with the same effect ...

The lower ring (oil control) should be placed such that the ring gap and spring gap are 30 apart centered around the gudgeon pin axis (i.e. the ring gap should be 15 degrees clockwise from pin axis on one side and the spring gap should be 15 degrees clockwise from pin axis on other side).

The two compression rings gaps should be 120 degrees apart on the exhaust side (i.e. one is 30 degrees clockwise from gudgeon pin axis on one side, the other 30 degrees counter-clockwise on the gudgeon pin axis on the other side).

The rings should be free to rotate.

Presumably you identified which way up the rings goes (i.e. that the compression side of the rings face towards the piston crown).

Did you bother with any of the tolerance and ovality measurements - given the cost of new pistons+rods you might not want to know

Cheers,
Robin

EDIT: PS, there is some ambiguity in the manual - it says that the gaps should be away from the thrust side but then draws the picture with them on the thrust side, then says that the gaps should be on the left if the piston is viewed from the front (which would place them on the inlet side of the gudgeon pin, I think) ... anyway, if you've placed yours inline with the gudgeon pin then it'll be symmetrical and so you've managed to sit on the fence in this regard

[roadboy]

A good poost by Dave Andrews on SELOC about it, says what I was going to post here but, being Dave, manages it so much more eloquently.

To be honest it is a convention rather than a necessity, the rings will turn in service as a matter of course so there will be times when the gaps line up, the idea is that having the gaps staggered will mean the cylinder will sustain less leakage and oil control will be marginally better. In practice there is no definitive evidence to support this. However it cant do any harm..

Dave