Piston rings / shaving fins

[mr_misfit138]

Hey everybody,

I've got 2 questions that I hoping to get a little enlightenment on.

First, I'm going to be starting my grand tear down and leak stopping adventure this week, and I bought new piston rings to go along with all of the new gaskets I got and was just wondering about whether or not I'd have to do a break-in after putting them. I read a whole article on breaking-in the engine when it's brand new (which I'm pretty sure we don't have to worry about here), and after the cylinders have been honed and new rings installed, but it didn't say anything about just adding new rings. I'd imagine that there would be some sort of a break-in that would need to happen. Has anybody on here done just a piston ring swap that can chime in with some advice?

Second, I'm also planning on blacking out the jugs, and then "shaving" the fins a little to bring the aluminum back on just the tips, but I was wondering about the best methods there too. I was just planning on hand filing them just until I'm through the thin coat of paint, and maybe squaring the edges off a bit, and then following up with a sanding block and progressively finer grit sandpaper until they started shining. Has anybody else shaved their fins? If so, what method did you use, and what recommendations do you have? To me is sounds like "shaving" should utilize something other than a file and sandpaper, and I'd like to avoid taking them to a machine shop to mill them.

Thanks in advance for you input.

[DAVINCI]

I would not install new rings without at least breaking the glaze. You will never get a good seal unless the rings and cylinder walls are broken in together. That said, yes, you would have a 'breaking in' period as the new rings seat to the cylinder walls.

About the fins, hey whatever does it for you.

[DGXSER]

If your going to the trouble of installing new rings, I would definitely lightly hone the cylinders as well like Randy suggetsed. That is the best way to ensure they seat in correctly.

As for the fins, I did something similar on my valve cover. repainted it and just taped off the raised areas, then used very fine sand paper to polish and remove any paint from the surface when completed.

[MPittma100]

Rings

Be sure NOT to use synthetic motor oil when breaking in new rings. May want to read the sheet that comes with the rings (or call the manufacturer) to see what finish on the bores they recommend. Different finishes for different rings. An example: Chevy High Performance recommends leaving the bores alone (shiny) when using chrome-moly rings. Just a good idea to do your homework first.

As far as removing material from the fins, keep in mind that they are there for cooling purposes - especially if there is no oil cooler.

MP

[natemoen]

I agree with MP that different style rings desire different finishes, but I also agree that with these engines and rings available you will have to do at least a hone on the cylinders first. You won't get a good seal if you don't.

[mack]

Honing tool

So what size and grit is recommended for our stock cylinders. Do we have a link for this tool? Just a thought, these would work on rotors too wouldn't they?

[mr_misfit138]

As far as the fins go, I know they're for cooling, and the more surface area the better. I'm not talking about taking them down to stumps. I'd probably only end up taking of ten to twenty thou off the edges, if even that much. I just want a definite contrast between the blacked out block and the shined up edges of the fins, and masking them would be impossible. And I do have an oil cooler, so there definitely shouldn't be any cooling problem. I was just wondering if anybody had suggestions on better ways to do it than a file and a sanding block.

As for the rings, these are Yamaha OEM ring sets. It's sounds like I'm either gonna have to hone the cylinders, or leave 'em alone for now, and hold onto the rings for the spare engine I've got. So now my question changes to how well would the current rings reseal if I pulled the jugs off and put them back on? I would think that this would be just as bad as not honing the cylinder, if the rings rotated slightly. Thoughts?

And it sounds like I'll be getting a paper with the rings that says how the cyclinders should be honed, since all rings are different, but just in case I don't, does anyone know how it should be done for the OEM rings?

[natemoen]

I used a ball hone when I replaced my rings. Don't remember the grit, I could look if you really want to know.

[ViperRon]

Rings replacement is for correction of 2 problems, loss of compression or burning oil. These two problems can also be caused by valve problems so when you put new rings in it only makes sense to do the basic checks on things in the head. First of all define the problem you are looking for. If it is compression loss that is easy to check for on the head when the it is off. Take the head fully assembled and turn it upside down level and pour the plug valve area full of a then oil or as I did mineral sprits. Leave it set for some time and check for any loss. If you do not see loss of fluid the valves are sealing good but I would still take the time to replace the seals on the valve stems just to avoid a future repair or oil burning.
If its burning oil you will need to examine the stems and guides for wear along with the seats in the head. Just ask here and you will get the information on all things to check.
Usually oil buring from rings comes from the second ring on the piston being worn or cylinder imperfection scratches out of round etc. There is a wear tolerance for the rings in the manual using ring gap. Take a new ring push and push it squarely into the cylinder and measure the gap of the ring in three positions both in rotation arround the cylinder and also top, middle, and bottom of cylinder. Check for any small amount of light from arround the outside of the ring. Another way to check for out of round is use trans fluid or something with color you can see and smear it around the wall of cylinder and push a ring down to see if it cleanly wipes the surface.
If it has a large ring gap and you see an issue with a good ring not fitting the cylinders tight then honing the clylinders and putting in new rings may not resolve problems. They make different stones and tools for honing cylinders. If you are installing standard rings you need to use a really fine set of stones and lightly hone cylinders with some light oil so as to not remove a lot of material. They make a ball hone that does a good job breaking glaze but does less to even cylinder imperfections.
Check top ring gap (compression ring) for each cylinder at the 9 locations 3 around at top middle and bottom after honing. If your gap is at max you may want to get oversize rings and cut them to fit so you do not loose compression and or have severe oil buring. Remember it typically will smoke some till the rings reseat
If gaps vary greatly between cylinders you will likely have compression differences once assembled. The closer to even it is mechanically the easier and smoother you can get it to run.
Remember there is a procedure to install rings on pistons in cylinders with gaps offset this has a great effect on compression and oil buring.

Hope all this helps some and this is just a portion of the things to check while the engine is appart. It sounds like a lot of work but that is what it takes to repair problems.

As far as breaking in as mentioned using a good break in oil is important changing it after a break in period (I use 500 miles) and the filter to clear all particals is just as important. Break in is good to allow all parts to adjust to each other. I have seen several people increase compression on an old engine and run the $ell out of it with no break in and have them throw a rod. Is also suggested to run at different RPM's at break in using several quick accelerations and decells to help rings seat properly.

[mr_misfit138]

I used a ball hone when I replaced my rings. Don't remember the grit, I could look if you really want to know.

If you used the OEM rings, and you're not having any engine problems, that'd be great. I've got a machinist buddy, but he's not at an automotive machine shop, so any extra info I could give him for when he does this would be awesome.

What kind of compression should I expect after the ring swap/break-in? The standard for our bikes without swapping out pistons is 142 psi, and a max of 156 psi at sea level. Should I be expecting to see closer to the max level if the break-in is done right? The air pressure at my altitude is about 95% of what it is at sea level, so my numbers might be a little lower, but theoretically I should see the higher end of the range, right?

[ViperRon]

The most common ball hone is a 180 grit but because of the design you can not compare to stones. A 400 grit stone hone typially removes more material than a 180 grit ball because of tension and design. When using either move the hone quickly up and down in the cylinder and clean the cylinders and or hone often.

[mr_misfit138]

Rings replacement is for correction of 2 problems, loss of compression or burning oil. These two problems can also be caused by valve problems so when you put new rings in it only makes sense to do the basic checks on things in the head.

I'm mostly pulling my top end off because I know that my valves need done, I've got a broken exhaust stud, and I've got some small intake/exhaust leaks that aren't allowing me to dial my carbs in, so while I was in there, I was just going to do everything I could think of. I've got new cylinder, head, and head cover gaskets, various seals, new CCT gaskets, exhaust gaskets, I even got new Midnight Special exhaust pipes. I just got the piston rings because I figured that if I did all of that work, put it together, and then started getting pressure blowing back through the rings, I wouldn't have the gumption to take it all apart again and fix it. It's ran good and plenty strong in the past, but the clearances are a off a little, and there's some popping and sputtering going on, and it revs a bit when I spray WD40 by the carbs, and I've already replaced the old boots with shiny new ones, and am going to get rid of the paper gaskets on those, and RTV them on and seal around the brass fittings, and then see if there's any more popping issues. The pistons and rings might actually be fine, I'm just trying to be prepared for whatever it is that needs to be done. I'm doing a complete make-over, so whatever's going to get done, is going to get done this winter. I'm already into it about $700 in parts so far, so there's no point is half-assin' it now.

[crazy steve]

...What kind of compression should I expect after the ring swap/break-in? The standard for our bikes without swapping out pistons is 142 psi, and a max of 156 psi at sea level.

Yamaha low-balled the 'official' compression numbers IMO (probably for warrantee reasons) so expect to see considerably higher numbers. It also depends somewhat on how the test is done: with or without the carbs installed, all plugs out or just the one you're testing, etc. I've personally seen compression in the 180-190 range on pretty much every motor I've tested, with '78-79 motors going as high as 200. This was with the carbs off the motor, all plugs removed, and using a car battery with it's higher current delivery to spin the motor. Note that these numbers were gotten after adjusting the valves; valve clearances can drastically effect compression, with the higher numbers coming with the early 'loose' clearance amounts.

[MPittma100]

Cylinders

As has been suggested, you must verify the integrity of the cylinders prior to just replacing something. Compression test is the only test that you need to do if all numbers are good. However, if you have a cylinder(s) showing low numbers, then you need to know where the loss is going. This means a cylinder leakage test. The sources of leakage are valves/and or rings. If numbers are good, no need to pull cylinders. You are also better off keeping the same (numbers matching) engine in the bike. Fix that one instead of replacing it. Bike will be worth more that way.

As far as honing cylinders, I suspect Yamaha suggests doing so. A ball hone has been mentioned and they are fine, but they do come in different grits. I would be ok with either a 280 or 320 grit.

If compression is good and you are pulling the head, you will be able to closely inspect all cylinders visually. If they look good (still have the cross hatch pattern), leave them alone.

MP

[DGXSER]

You are also better off keeping the same (numbers matching) engine in the bike. Fix that one instead of replacing it. Bike will be worth more that way.

This point I have to disagree with. Honestly, you can typically find a decent to good runnibg engine for less than the cost to do the repair work on one. And the numbers matching would only be a consideration on a truly restored bike. On a daily driver type bike the buyer typically is not going to care. More than a few of these bikes have repacement odometers anyway, so the milage is a guestimate to start with. on top of that, the average person buying one would not even know to look at the engine numbers.

Now if your shooting for a complete restoration, showroom condition bike, and looking to sell it for the premium dollars, then yes, the numbers matching will matter.