Topic: Piston ring 101

[Raul CB750K1]

I'm about to install new rings in my CB350 pistons, and in order to make sure I do everything right I've done a search through all the old posts. I would like to make a summary so you please fill what is left:

1. In order to avoid the piston slap, what should the piston-to-cylinder wall clearance be? I guess there should be two different measures as the piston is slightly oblong.

2. Ring gap. Put the ring halfway through the cylinder, pressing with the piston itself so it gets perfectly perpendicular. Piston gap was between Honda specs, so no need for filing. That also implies that the cylinder diameter is fine, as I didn't have an inside-caliper to measure it. I knew there was some standard clearances depending of the inch of bores. Mike, could you post again how much was it?

3. Ring installation. The mark on the piston must face up. That means, it should face the piston top, not the piston skirt. Which of the ring tools pictured below are best? I broke one of the old rings when disassembling and I'm getting paranoid about breaking one while assembling.

4. Order. The oil ring is clear: at the bottom. The other two, one have a distinctive lip (scraper). It should be in the middle position. The remaining one at the top.

4. Staggering. The gaps should be apart 120 degrees one to each other, in such a way that none of the gaps is in direction or perpendicular with the gudgeon pin, because those directions are where the bigger forces are applied.

5. Ring clearance. There should be a given clearance between the ring and the groove. Is there a "rule of thumb" when there are no specs? If it's necessary to file a ring, it should be done on the above face because the side below is the one that "does the work". Am I right?

If I have forgotten something please advice.

Raul

[Raul CB750K1]

BUMP! I guess that no replies means everything is OK. I hope to have time today to install the pistons and rings. Will keep informed.


Raul

[750goes]

Raul,

I have no information, but if you are worried about braking a ring on installation, a little tip that may help.

Put the rings into some really hot water for a few minutes before installing them..it will help them bend a bit, hopefully allowing a few more mm,, then no more snapped rings. don't burn your fingers picking them up..or you could put them in the oven on a really low heat for 10 minutes...

I am just starting to look at a 350/4 in OZ, anything I should look out for (bike is complete, not been running for a few years).

[SteveD CB500F]

Did you forget "Orientation" ? ie "which way up?

Any markings or numbers on the rings should go UP

[superchode]

alright.. i've got this job coming up fast as well... i've got 4 new sets of rings to put on my 750 - but i don't know which ones are which.  it seems that only two of the 4 rings have marks on them (appears to be a 'R') - so i know that side should face upwards, but i don't know where each ring is supposed to go.  i'd guess the two thin rings surround the fancy wavy thing in the lower piston groove - and the two thicker rings end up in the upper two grooves... but (as you can probably guess from my poor terminology) I don't know what's what.  the manuals (clymer and honda) are suprisingly sparce on info in this regard.

[upperlake04]

Super - the rings in my F3 were like this-
  Top - marked on top, beveled outer edge, shinier edge compared to second ring
   Middle-  marked 2n on top side, shiniest flat on bottom
   Bottom - 3 piece oil

[superchode]

does orientation matter on the bottom oil rings?

[SteveD CB500F]

If I recall they come in three parts.  Just spread each part around (120 degrees)

[superchode]

right, but when it comes to the oil rings... it doesn't matter which side you have up?

i also don't have a ring compresser tool, at this point... can it be done without? is there a method to get it done reliably without a special tool? where does one get hold of an appropriate tool, if it is necessary?

[SteveD CB500F]

I don't recall there being a top on the oil rings.

I never used a piston ring compressor.  Set the crank so that you have two up and two down (ie don't try to fit all four at once!) add copious amounts of oil and slip the barrels down over the rings. The base of the barrels is tapered to help this. I always "helped" the rings close a little with my fingernails. Never broke one.

[Dusthawk]

Thank goodness for this thread. I just found out I probably need rings on my 750. The scraper or second ring has that lip on it, shouldn't that lip be on the bottom?

The base of the barrels is tapered to help this. I always "helped" the rings close a little with my fingernails. Never broke one.

Steve, never broke what, a ring or a nail?? Just kidding ya

Peace,

Jeff

[MRieck]

Raul
  .004" of ring gap per inch of bore.  3" bore = .012 of gap fpr 1st and 2nd rings.

[Noel]

Don't take this as gospel, because I've only done it once. The guy who bored my cylinders, however, was an ancient old speedman who liked to talk, so I think I got some good information.

1. In order to avoid the piston slap, what should the piston-to-cylinder wall clearance be? I guess there should be two different measures as the piston is slightly oblong.

I'm unsure of the clearance. I do believe the piston measurements should be taken at the bottom of the skirt and about an inch above the bottom of the skirt, in line with the pin holes.

3. Ring installation. The mark on the piston must face up. That means, it should face the piston top, not the piston skirt. Which of the ring tools pictured below are best? I broke one of the old rings when disassembling and I'm getting paranoid about breaking one while assembling.

I used a tool identical to the yellow-handled one on the left. The ancient old speedman used his fingernails.

4. Order. The oil ring is clear: at the bottom. The other two, one have a distinctive lip (scraper). It should be in the middle position. The remaining one at the top.

In answer to whoever asked, yes, the three piece ring goes on the bottom, with the wavy bit sandwiched in between the two thin rings. I didn't see a lip on any of the 500 rings; but was told the chrome one goes on top.

4. Staggering. The gaps should be apart 120 degrees one to each other, in such a way that none of the gaps is in direction or perpendicular with the gudgeon pin, because those directions are where the bigger forces are applied.

I understand the gaps should not be position 90 degrees from the pin holes either.

I didn't use a ring compressor either. I meant to use something to hold the pistons so I could insert 2 and 3 first and then 1 and 4. Forgot, so ended up doing all four at once. Kind of stupid, but it worked.

[superchode]

threw the rings on, as instructed by the fine folks higher up in this thread... no issues.  hopefully i get the head back in the next day or two and the rest of the engine can go back together.

[SteveD CB500F]

Steve, never broke what, a ring or a nail??

Never broke any piston rings Dusty.  It's a real bugger with those nail extensions though - and the chipped varnish...

The ancient old speedman used his fingernails.

QED !

[Raul CB750K1]

OK, rings are in place, no issues. I put some oil on the piston to help the rings slide into position. I didn't trust that big ring tool and used the small, yellow handle one. Much better.

The original Honda oil ring is not a three piece affair; it's just one piece. The ring-to-groove clearance whas also between specs.

Pistons are already in place, with the cylinder ready to slip into position. I will post in the "meta in my oil" topic something I found about the chain tensioner...


Raul

[Bob Wessner]

Those pistons look sooo shiny and new now.. aren't you just going to hate mucking them up with burning fuel and dirty oil? 

[Raul CB750K1]

Those pistons look sooo shiny and new now.. aren't you just going to hate mucking them up with burning fuel and dirty oil?

mmm a touchy subject. If you remember I asked about whether reusing the old ones. They seemed fine and tolerances were between spec too, but I happened to find a set of new ones on eBay and bought them for about 20 bucks + shipping.

I was planning to keep them as spares, but they are .025 overbore as the old ones. Then I said to myself : "OK, the 40 bucks are spent. Where will the new pistons be more useful? Inside a box in the cellar, or inside the cylinder? If I keep them as spare, chances are that next rebuild a new rebore is necessary and no use for the pistons"

So I decided to use the new ones and keep the old ones at the moment. They are manufactured by ART. I was hesitating about the quality, until a close look at the original Honda manual showed me a picture of a piston with the ART logo... 

Old ones were ART too, but the engine had been rebuilt in the past.

Does anybody have some feedback on ART pistons?

Raul



new vs old piston...

[SteveD CB500F]

I seem to recall in a post by Mike Rieck that all Honda pistons were made by ART (?)

[MRieck]

I seem to recall in a post by Mike Rieck that all Honda pistons were made by ART (?)

I'm not sure if all Honda pistons are made b by ART but certainly the majority are Steve. ART also makes most OEM pistons for the Kawasaki. Yamaha and Suzuki

[Raul CB750K1]

I seem to recall in a post by Mike Rieck that all Honda pistons were made by ART (?)

I'm not sure if all Honda pistons are made b by ART but certainly the majority are Steve. ART also makes most OEM pistons for the Kawasaki. Yamaha and Suzuki

Hey Mike, I take this that ART are then trustworthy pistons, aren't they?

Truth is that, and I know it because of a piston that Mike turned into a pencil holder and sent to me, there are pistons with the "Honda" engraving.. 



Raul

[bryanj]

Raul, bit late to the party but if you use Honda rings and pistons you will never have to file anything as long as the re-borer did his job right!. ANY marks , including sizes, go upwards and the chromed ring is always in the top groove. From memary all the 250/350 had solid scrapers as they didnt have the oil burning initial problems of the fours.

[superchode]

replacement pistons for $20 a piece... nice work.  if that was an option for me i would have done it instead of spending a couple hours per piston scrubbing carbon deposits off.  they look nice now - but it wasn't a fun job.

[Raul CB750K1]

Raul, bit late to the party but if you use Honda rings and pistons you will never have to file anything as long as the re-borer did his job right!. ANY marks , including sizes, go upwards and the chromed ring is always in the top groove. From memary all the 250/350 had solid scrapers as they didnt have the oil burning initial problems of the fours.

Your expert advice is appreciated anytime Bryan. Those are ART pistons but the rings are original Honda. I didn't do any filing, because I remembered you mention they just go in. I checked the clearance just in case and everything was between specs.

I put the ring marks upwards, that is, facing the piston top -not the skirt-. As you can see in the pictures, the top ring had a silver side colour, while the middle ring is almost black. BUT, the top ring body is the same colour as the middle ring, there is no difference. You can identify them by the particular scraping profile.

Piston pins (gudgeon pins) were also scored so I bit the bullet and bought new ones. At 6 euro each is a fair price for peace of mind.


Raul

[Raul CB750K1]

replacement pistons for $20 a piece... nice work.  if that was an option for me i would have done it instead of spending a couple hours per piston scrubbing carbon deposits off.  they look nice now - but it wasn't a fun job.

You know, you always find cheap what you don't really need... 

Raul