Piston rings

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Try breaking one of the oil rails, near impossible.
1/ It is an expander
2/The ends of the EXPANDER should always touch in the bores
3/ AND I reckon this is probably the most critical point the assembly shouldn't touch the bottom of the groove, it should still float in the ring groove when pushed into the bore.
Rapid bore wear /oil ring wear will occur if it doesn't float, always assemble up in your hand and check the oil ring is down below the piston skirt level
If it don't fit in the groove it wont fit in the bore
Check very carefully if changing from pistons that originally came with the one piece oil ring

Off topic you should be able to bore an engine without the pistons because they should be to the correct required size ,whats the point of having set sizes if nothing will fit,you should also check the clearance before you fit them regardlass , the ring gaps will normally give you an indication of your bore clearance. If you buy a set of STD fitment pistons that require less or more clearance there is possibly some thing wrong with them, most will have max clearance if bored to the std oversize, if you bore it under book size and it seizes any manufacturer will tell you to fackoff and do the job properly
 
+1 trimming the expander is a recipe for high oil consumption. as stated its job is to put pressure on the two rails against the cylinder wall to scrap oil, give a path through it so it can drain from the ring groove and not let the rails bottom in the groove. if you have ever had an engine apart from an oil consumption and found the expander ends overlapped you would know why it used oil. trimming is a fools game from some one that THINKS thy know more than the OE.

splatt said:
Try breaking one of the oil rails, near impossible.
1/ It is an expander
2/The ends of the EXPANDER should always touch in the bores
3/ AND I reckon this is probably the most critical point the assembly shouldn't touch the bottom of the groove, it should still float in the ring groove when pushed into the bore.
Rapid bore wear /oil ring wear will occur if it doesn't float, always assemble up in your hand and check the oil ring is down below the piston skirt level
If it don't fit in the groove it wont fit in the bore
Check very carefully if changing from pistons that originally came with the one piece oil ring

Off topic you should be able to bore an engine without the pistons because they should be to the correct required size ,whats the point of having set sizes if nothing will fit,you should also check the clearance before you fit them regardlass , the ring gaps will normally give you an indication of your bore clearance. If you buy a set of STD fitment pistons that require less or more clearance there is possibly some thing wrong with them, most will have max clearance if bored to the std oversize, if you bore it under book size and it seizes any manufacturer will tell you to fackoff and do the job properly
Click to expand...
 
Again, I don't agree. The expander is there to hold the scrapers against the upper and lower oil ring lands. Or course there must be clearance with the assembly as the scrapers have to be free to slide in and out of the groove. If the expander has no gap (or overlaps, as in the photo) when pressed against the cylinder wall, it's too big and should be replaced or trimmed. There should be a small heat expansion gap when the expander is held against the inside diameter of the ring groove and if the scrapers wear to the point that they no wider than the area from the flare of the expander to the front, they are shot.


And boring a cylinder without precise measurement of the piston that goes in it is a crapshoot. Moreso than trimming an oil ring expander.
 
and just what is your credentials to make you thing that trimming the expander is the right thing to do? how many engines have you built and how long have you been doing this ? yes it is a spacer to keep the rails separated the correct amount top to bottom also BUT it is to put outward pressure on the rails so that the RAILS can remove the oil from the cylinder wall. when you reduce that pressure by either having the ends over lap or by trimiming it you are very well likley to have oil consumption issues. as to boring to size do you think having the pistons in hand is how the major manufacturers and production rebuilders do this? if so you are living in a dream world!!! tho only ones that do it this way is if you have a specialty piston or race engine builder looking for something out of the normal production realm.

PS I have been around this for 40 years and done hundreds of engines and NOBODY i have been around has ever trimmed expanders because it does not fit the bore. it is NOT supposed to fit like a compression ring or one piece oil ring.

Danno said:
Again, I don't agree. The expander is there to hold the scrapers against the upper and lower oil ring lands. Or course there must be clearance with the assembly as the scrapers have to be free to slide in and out of the groove. If the expander has no gap (or overlaps, as in the photo) when pressed against the cylinder wall, it's too big and should be replaced or trimmed. There should be a small heat expansion gap when the expander is held against the inside diameter of the ring groove and if the scrapers wear to the point that they no wider than the area from the flare of the expander to the front, they are shot.


And boring a cylinder without precise measurement of the piston that goes in it is a crapshoot. Moreso than trimming an oil ring expander.
Click to expand...
 
bill said:
and just what is your credentials to make you thing that trimming the expander is the right thing to do? how many engines have you built and how long have you been doing this ? yes it is a spacer to keep the rails separated the correct amount top to bottom also BUT it is to put outward pressure on the rails so that the RAILS can remove the oil from the cylinder wall. when you reduce that pressure by either having the ends over lap or by trimiming it you are very well likley to have oil consumption issues. as to boring to size do you think having the pistons in hand is how the major manufacturers and production rebuilders do this? if so you are living in a dream world!!! tho only ones that do it this way is if you have a specialty piston or race engine builder looking for something out of the normal production realm.

PS I have been around this for 40 years and done hundreds of engines and NOBODY i have been around has ever trimmed expanders because it does not fit the bore. it is NOT supposed to fit like a compression ring or one piece oil ring.

Danno said:
Again, I don't agree. The expander is there to hold the scrapers against the upper and lower oil ring lands. Or course there must be clearance with the assembly as the scrapers have to be free to slide in and out of the groove. If the expander has no gap (or overlaps, as in the photo) when pressed against the cylinder wall, it's too big and should be replaced or trimmed. There should be a small heat expansion gap when the expander is held against the inside diameter of the ring groove and if the scrapers wear to the point that they no wider than the area from the flare of the expander to the front, they are shot.


And boring a cylinder without precise measurement of the piston that goes in it is a crapshoot. Moreso than trimming an oil ring expander.
Click to expand...
Click to expand...


I never recommended trimming the expander, I recommended sending the wrong parts back and getting the right ones. Some folks have obviously gotten away with trimming the incorrect expanders and I won't discount their good fortune in not fucking it all up, but what you can get away with is not always what you should do. Please read the entire thread and argue with those who HAVE trimmed expanders. Personally, I would never do it. Your 40 years of experience evidently doesn't include reading throroughly and comprehending what you've read.
 
Danno said:
Again, I don't agree. The expander is there to hold the scrapers against the upper and lower oil ring lands. Or course there must be clearance with the assembly as the scrapers have to be free to slide in and out of the groove. If the expander has no gap (or overlaps, as in the photo) when pressed against the cylinder wall, it's too big and should be replaced or trimmed. There should be a small heat expansion gap when the expander is held against the inside diameter of the ring groove and if the scrapers wear to the point that they no wider than the area from the flare of the expander to the front, they are shot.
Click to expand...

Ei, yei, yei, yei, yei! Where do you get this stuff?
 
pierodn,

There is nothing wrong with one piece oil control rings. I do prefer the three piece though, because I feel the scrapers, being steel may be gentler on the bore and last longer as well. One piece oil rings are cast iron.
 
Biscuit said:
Danno said:
Again, I don't agree. The expander is there to hold the scrapers against the upper and lower oil ring lands. Or course there must be clearance with the assembly as the scrapers have to be free to slide in and out of the groove. If the expander has no gap (or overlaps, as in the photo) when pressed against the cylinder wall, it's too big and should be replaced or trimmed. There should be a small heat expansion gap when the expander is held against the inside diameter of the ring groove and if the scrapers wear to the point that they no wider than the area from the flare of the expander to the front, they are shot.
Click to expand...

Ei, yei, yei, yei, yei! Where do you get this stuff?
Click to expand...

It doesn't come out of your ass like your posts do.
 
Biscuit said:
pierodn,

There is nothing wrong with one piece oil control rings. I do prefer the three piece though, because I feel the scrapers, being steel may be gentler on the bore and last longer as well. One piece oil rings are cast iron.
Click to expand...


Depends upon your definition of "wrong" One-piece oil control rings generate more friction and cause more bore wear than three-piece. They're not "wrong" they-re just obsolete. Sort of like your pool of knowledge.
 
i too had to shorten an expander ring on a special piston in a BSA b44 engine ,,,,,,,,,,,,,,,,,,baz

Bill and Biscuit would like to see your "credentials" that enabled you to do this.




....And to apply the pressure against the walls needed to seal the bores...........Biscuit


Bullshit

I also think main reason for the expander is to keep the scraper rings separated.........B+Bogus


This


An expander pushed into the bore and held to the cylinder wall should have a pretty good gap as it is not meant to touch the bore in use, only establish the equivalent of lands for the oil scrapers. If it doesn't, it's the wrong part. You could get away with trimming it, but how do you know what the gap should be without the proper part to compare to? Sending parts back is a major pain, but nothing compared to re-doing your rebuild. If anything, it should be checked held tight to the circumference of the oil ring groove in the piston, where it should still show a slight gap for heat expansion. But, again, how much?-Me

If you don't understand english, Google Translate can help.
 
Thankfully ring manufactures supply fitting instructions
One piece oil rings don't create any more bore wear, they do however restrict oil flow back through the piston marginally, and I would guess are more expensive to manufacture, also most of them use an EXPANDER behind them to, or is that just a wedge that goes between the piston and bore ?
It's strange how the obsolete rings are used in most of the worlds heavy diesel engines.
 
Bullshit


An expander pushed into the bore and held to the cylinder wall should have a pretty good gap as it is not meant to touch the bore in use, only establish the equivalent of lands for the oil scrapers. If it doesn't, it's the wrong part. You could get away with trimming it, but how do you know what the gap should be without the proper part to compare to? Sending parts back is a major pain, but nothing compared to re-doing your rebuild. If anything, it should be checked held tight to the circumference of the oil ring groove in the piston, where it should still show a slight gap for heat expansion. But, again, how much?-Me

If you don't understand english, Google Translate can help.[/quote]p

It wont touch the bore in use because the rails will, if fitted as the manufacture intended
There should be no gap because it is a spring, it requires the two ends to touch in place to hold the whole assembly under tension when assembled it requires no heat expansion gap , the rails do
YES it does hold the rails apart, but what you're preaching is that a WWWWWWWWWWWWWWWWWW shaped spacer between the rails with no extra outwards pressure exerted would do the job, have you ever seen the rails fitted to a modern engine, they have no radial tension
There used to be horrible 4 piece rings that worked closer to your special needs, it had a flat pressed spring in the bottom of the groove, a WWWWWWWW shaped spacer and two rails, the spring would break and the rails would no longer scrape the bores
 
Cast iron oil control rings have their place but rarely have I seen them applied in modern high speed IC engines. There are exceptions and the original and replacement pistons in my long stroke Nourish had one piece cast iron oil control rings. If I were to have custom pistons made for the Nourish I would go with the three piece oil control ring - unless someone could make a compelling reason not to. One concern I would have with one piece cast iron oil control rings is (my opinion here) their being prone to flutter at high speeds (shear mass) and any resulting premature ring land wear.

Diesels tend to be low to medium speed for a variety of reasons so flutter would be a non issue in these applications.
 
Dances with Shrapnel said:
Cast iron oil control rings have their place but rarely have I seen them applied in modern high speed IC engines. There are exceptions and the original and replacement pistons in my long stroke Nourish had one piece cast iron oil control rings. If I were to have custom pistons made for the Nourish I would go with the three piece oil control ring - unless someone could make a compelling reason not to. One concern I would have with one piece cast iron oil control rings is (my opinion here) their being prone to flutter at high speeds (shear mass) and any resulting premature ring land wear.

The oil ring isn't subject to any combustion pressure, so no gas is getting under it and making it float, it will have nice oil cushions .

There seems to be a strange group on this forum that are obsessed about getting 10000rpm out of a 50year old motor I suppose in the end it all helps to the long term reliability for everyone, JimS post on the winningest Norton is a good example , also some good 3 piece ring photos to
Click to expand...
 
splatt said:
It wont touch the bore in use because the rails will, if fitted as the manufacture intended
There should be no gap because it is a spring, it requires the two ends to touch in place to hold the whole assembly under tension when assembled it requires no heat expansion gap , the rails do
YES it does hold the rails apart, but what you're preaching is that a WWWWWWWWWWWWWWWWWW shaped spacer between the rails with no extra outwards pressure exerted would do the job, have you ever seen the rails fitted to a modern engine, they have no radial tension
There used to be horrible 4 piece rings that worked closer to your special needs, it had a flat pressed spring in the bottom of the groove, a WWWWWWWW shaped spacer and two rails, the spring would break and the rails would no longer scrape the bores
Click to expand...

I think we have exhausted practically all the ways to explain the way three piece oil control rings work.

Mr Dano will never get it. Leave him in peace to continue to put together his trimmed to suit, fluttery oil ring installations. Besides he's just getting nasty now.

To answer his query though. A degree in automotive engineering.
 
Fair enough splatt. Differential pressure is a contributing factor to ring flutter and oil rings should not be exposed to the diff pressures of the top ring so ...........are the only readily identifiable benefits of a three piece oil control ring over a one piece cast iron oil control the 1.) reduction of reciprocating weight and 2.) maybe better drain back.

There seems to be a strange group on this forum that are obsessed with people that are obsessed about getting 10000rpm out of a 50year old motor ................... in the end it all helps to the long term reliability for everyone. It is called racing where rpm is only a means to more torque, more power and less weight. I would think that some would be interested. I find it interesting that the Nourish race engines come with cast iron oil control rings and they go like the wind without having to rev to 10,000 rpm.

Too the point, is there a compelling reason to go with cast iron rings in most non diesel automotive and motorcycle applications if a suitably designed three piece is available. I have a bias towards three piece rings only in that most others tend to use three piece in high speed (and this can mean regular road going automotive) IC engines.
 
Dances with Shrapnel said:
..........are the only readily identifiable benefits of a three piece oil control ring over a one piece cast iron oil control the 1.) reduction of reciprocating weight and 2.) maybe better drain back.
Click to expand...
Probably cost as well, a good cast ring would normally have chromed scraper lands as well, better oil control, no manufacture will sell a car that pollutes except VW
There may be lower friction from the one piece ring

Dances with Shrapnel said:
in the end it all helps to the long term reliability for everyone. It is called racing where rpm is only a means to more torque, more power and less weight. I would think that some would be interested. I find it interesting that the Nourish race engines come with cast iron oil control rings and they go like the wind without having to rev to 10,000 rpm.
Click to expand...
I always look at the posts on the racing development and enjoy most of them but normally the guys winning aren't overly radical they are just well built well prepared machines
What does the nourish engine rev to, is that an 8v motor?
 
Splatt,

Thanks for the response on the rings.

Your assessment of race bikes and riders is pretty good. A decent bike with an excellent rider has the edge over an excellent bike with an average rider; Dave Roper and a few others in our race organization are excellent examples, yet some of us strive for the Valhalla of engines. The Nourish I cited is an excellent reliable power platform. In my opinion, it offers one of the best of engine power and reliability for vintage racing in the class.

http://www.nourishengineering.co.uk/page.php

The Nourish is a parallel twin cylinder purpose built air cooled race engine. It is made in a variety of displacements and crank phases. The notoriety of the motor is that it is one of a few vintage period four valve per cylinder race engines. Mine is an 88.5mm stroke and really has nothing to add after about 7,000 rpm in stock configuration. It can easily go to 8,000 rpm yet has been very reliable. For me, reliability translates to more track time.
 
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