18 replies to this topic

[Sprocket]

I would't worry about ring gaps too much, with a new set of rings, as long as the gap is not below minimum limits. The size of the gap above minimum doesn't really matter that much in the great scheme of things, so long as the piston to bore clearance is acceptable, since the rings create what is called a labyrinth seal anyway.

It's the ring tension that makes the biggest difference to piston ring blow by. Old used rings with a big gap are a bit of an unknown quantity since you don't really know what the initial ring gap was, therefore, you cannot work out by how much the rings have worn, nor will you be able to tell by how much the ring tension has slackened off. This is the most likely scenario for excessive blow by, not the actual size of the gap.

The ring gap size is not really the best way to determine whether the bore is worn or not, more so if you are using old and used rings, since you will be measureing wear on the rings as well as the bore. Bore wear, needs to be measured directly, in the bore. The piston skirt then needs to be measured and if the clearance between the two is above maximum limit, its time for a re bore. if the clearance is within limits a new set of rings can be fitted so long as the bores are honed. An overly large ring gap will have no ill effect.

The ring pictured above with a step is actually pictured upside down. It is technically called a Napier ring and is the second, or middle ring.

The top ring is technically called a torsional twist ring, it is pictured in the correct orientation. It is important to measure the ring lang clearance with this type of ring since it is designed to 'twist' in the ring grove, and can sometimes wear the ring lands on the pistons.

[grahama]

I decided to take the piston to my local engine reconditioner and he gave them a once over. He has all the old books with ring sizes and tolerances in, measured mine and they were worn so I have ordered a new set. will see what gap a new.set of rings gives me and report back.

by the way, measured mine using a piston, at the top, middle and bottom of each bore and got a range of 19 to 22 tho on both top rings. pretty consistent but a little large.

should get them tomorrow or Monday, interested to see now!!

Thanks for all the help,

graham

[grahama]

Hi all,

just to see what you think, I have got my set of rings and they have reduced the end gap.

On the top ring it has reduced from 22 tho to 18 tho

Middle ring has reduced from 20 tho to 13.5 tho

Bottom ring is less than middle.

I have a four ring pack for my 3 ring pistons as my rings are now obsolete as I thought. However the extra ring in the pack is tighter than the new top one. Should I use the tighter ring (13 tho) rather than the new top ring ??

Is it ok to swap and change rings?? (would be swapping the third ring down for the top one)

A good reduction on the middle and bottom rings and only just over for the top one.

Is the top ring meant to have a greater end gap??

Thanks,

Graham

[Sprocket]

On a four ring piston the third ring is a scraper ring, not a compression ring. If the rings are made from the same material and have an idential profile, then you could possibly get away with swapping them round, however if they came in seperate packets labled up for each groove, chances are, they will be different, since if they were all the same, why all the packaging? But as I explained earlier, the actual size of the end gap on new rings is of no real concern, so long as your piston to bore clearance is below the top limit, thats the bit that will allow the piston to rock in the bore, too big and you loose the seal on the ring across its entire length, not that tiny little end gap. The ring tension is also a major player in ring seal. Compare your old rings to your new rings and you may well find that your newer rings are a lot more springier than the old ones. Fitting new rings? have you had the bores honed?

http://www.diagnosti...wledge Gaps.php

Edited by Sprocket, 24 January 2012 - 12:03 PM.