Topic: Can piston rings be "re-used"?

[Magpie]

I'm tearing a CB750 motor down and wondering if, once the pistons have been removed from the cylinders, I must replace the rings with new ones and not just reinstall the pistons with the "old" rings. I had a leak down test done and the mechanic said it was loosing less than 10% air which was quite good. The bores look ok, one piston had a nasty top ring which broke when I tried to get it out. I cleaned up the ring groove and it all looks good.
Thanks in advance,
Cliff.

[gnarlycharlie4u]

I'm tearing a CB750 motor down and wondering if, once the pistons have been removed from the cylinders, I must replace the rings with new ones and not just reinstall the pistons with the "old" rings. I had a leak down test done and the mechanic said it was loosing less than 10% air which was quite good. The bores look ok, one piston had a nasty top ring which broke when I tried to get it out. I cleaned up the ring groove and it all looks good.
Thanks in advance,
Cliff.

short answer; no.

[markb]

I agree with the short answer but, (don't tell anyone) several years ago when I was putting my K0 back together I was using new rings and while installing the cylinders I broke one.  (Don't even remember which one, probably oil ring).  I used the best looking one of my used ones instead and no apparent problems.  But I'm not proud of myself for doing it. 

[Magpie]

Ok, new rings and a light hone it is. Thanks guys! Cliff.

[Bankerdanny]

Rings are relatively cheap, so why not replace them as long as the engine's apart.

But that said, if they are in good shape and when re-installed the end gaps are correct, I don't see why you couldn't re-use them.

[fmctm1sw]

My 750 engine has compression like this:

1: 170
2: 170
3: 170
4: 100

I'm reusing 1-3 once I find out what's wrong with #4...

[gnarlycharlie4u]

Ok, new rings and a light hone it is. Thanks guys! Cliff.

I thought I needed a "light hone"

Honda told me that it still required new pistons.

[gnarlycharlie4u]

Rings are relatively cheap, so why not replace them as long as the engine's apart.

because the new ones may not set themselves like the old ones did after years of wear, even after the new ones are broken in properly.

[KRONUS0100]

honda wants your money.  you only need new pistons if you are boring it.

[MCRider]

Rings are relatively cheap, so why not replace them as long as the engine's apart.

But that said, if they are in good shape and when re-installed the end gaps are correct, I don't see why you couldn't re-use them.

I agree with all you've said. Replace them if you can, if not no sweat.

I'd soda blast the pistons, clean out the ring grooves and lands, and wouldn't hesitate to use the old rings if that's what you wanted to do.

We replace a lot of things on these old bikes just cuz it makes us feel good. (mea culpa)

Or we aspire to a "higher standard". But there comes a point when one can say, "for what?"

[Magpie]

Seems I've started a bit of a debate. I think I've often replaced parts, like cam and primary chains, just because. I was curious about this since the pistons are going back into the same cylinders they came in and the bores look good. Plus the leak down test was good. They are fairly cheap and a friend will do the hone so for once it's not necessarily about the money.
Good discussion guys.
Cliff.

[Gordon]

I'm tearing a CB750 motor down and wondering if, once the pistons have been removed from the cylinders, I must replace the rings with new ones and not just reinstall the pistons with the "old" rings. I had a leak down test done and the mechanic said it was loosing less than 10% air which was quite good. The bores look ok, one piston had a nasty top ring which broke when I tried to get it out. I cleaned up the ring groove and it all looks good.
Thanks in advance,
Cliff.

short answer; no.

Wrong.

Is it true that some people (especially bike shops and parts sellers who want to make as big a sale as possible) recommend honing the cylinders and replacing the rings anytime you take the jugs off?  Yes

Is there any good reason why you shouldn't skip the honing and continue using the current rings as long as they're still within spec and you're not having low compression or blow-by issues, aside from peace of mind that it's done and won't have to be done again for a long, long time? 
No

[TwoTired]

Agree with Gordon.
If the rings now fit nicely with both piston and cylinder.  And you don't damage them during dis-assembly/reassembly, they will work fine, as they have already worn themselves into a nice fit.

If you replace rings with new, you must hone for them to re-seat.  Each ring seating process removes more cylinder wall material.  Honing is abrasive and also removes cylinder wall material.  Every bit of wear gets you closer to requiring an overbore situation.  (New pistons/ new rings,and cylinders bores to fit them.)

Cheers,

[gnarlycharlie4u]

honda wants your money.  you only need new pistons if you are boring it.

yea I forgot to mention that I went in expecting a hone and left needing an 836 kit haha.

they said that because of water damage I need to bore out the cyls.

[bryanj]

Most cylinders are bored dure to wanting an "Upgrade"

2nd most common problem is water damage (but will still run just use a bit of oil)

Only ever bored one Honda due to wear, and that was a PC50 at 75,000 miles

[dave500]

ive pulled apart motors and just put it all back clean and so long as its within spec itll be ok,old rings can lose tension but so long as the grooves are clean and the rings are free its fine.

[fastbroshi]

Most cylinders are bored dure to wanting an "Upgrade"

2nd most common problem is water damage (but will still run just use a bit of oil)

Only ever bored one Honda due to wear, and that was a PC50 at 75,000 miles

  Honda does make amazingly tough cylinders/pistons.  I don't think I've ever run across a Honda motor, from a motorcycle or anything else (okay no 2 smokes), that needed a rebore because of wear.  Both 550 jugs I've run across measured almost new with both having covered over 20k miles.

[fmctm1sw]

as the grooves are clean and the rings are free its fine.

I'm hoping that's the only thing wrong with my #4 cylinder...

[dave500]

as the grooves are clean and the rings are free its fine.

I'm hoping that's the only thing wrong with my #4 cylinder...

thats a big difference,might be a valve?,dont pull the barrell untill your sure the heads fine.

[faux fiddy]

With posts of more experienced people above I could quote, and depending on you circumstance I say RUN IT!

Maybe scuff up the bores lightly with some  fine emory  cloth on a drill.

[Gordon]

Maybe scuff up the bores lightly with some  fine emory  cloth on a drill.

To promote faster wear of the rings?

[faux fiddy]

Maybe scuff up the bores lightly with some  fine emory  cloth on a drill.

To promote faster wear of the rings?

I thought it maybe help them seat again. Maybe I'm wrong, but if they had a shiny glaze on them I think I might do that.  Maybe  skip the drill part.

[TwoTired]

Maybe scuff up the bores lightly with some  fine emory  cloth on a drill.

To promote faster wear of the rings?

I thought it maybe help them seat again. Maybe I'm wrong, but if they had a shiny glaze on them I think I might do that.  Maybe  skip the drill part.

Used rings in the same bore they came from are shiny BECAUSE the are seated.  Forced re-seating just causes more metal wear.
New rings are NOT seated and a shiny, smooth bore may prevent them from doing so because there isn't enough friction to accomplish the seating task.

The seating event is a friction event where metal is worn off high spots, creating an eventual tight metal to metal seal (with an even thin oil film dividing the the components).

Cheers,

[camelman]

If your cylinders are not perfectly round, then re-using the rings will likely cause a poor seal.  This is because the rings will be worn into the oval form of the cylinder in one orientation.  If you take the pistons out, then the rings are going to rotate, and you'll never get them back to the exact position they were in prior to dismantling.  The result will be a square peg in a round hole issue, although not quite as noticeable. 

If your cylinders are perfectly round, then no issues and your rings will seat back in with a little honing.  If they are not perfectly round, then you might not get as good of a seal as you are hoping for, more blowby, and some degree of lower power.

Camelman

[TwoTired]

It is impossible to make any cylinder "perfectly" round.  It will never happen.  Humans cannot make anything "perfect".

As has already been noted, the Honda cylinders have excellent long wearing characteristics.  And, most notice little wear even after 75,000 miles.

I'm not sure how they would get significantly out of round under normal circumstances.  If something is damaged, it must be repaired, of course.

*IF* it were out of round, the rings can and usually do spin on the piston and eventually find its way back to the "out of round" position they were in before.

There is no point in honing a cylinder that already has mated with both piston and cylinder wall.   Honing removes metal and accelerates wear of the cylinder AND ring, unnecessarily shortening engine life.

[faux fiddy]

My concern would also  be with  the bike that comes apart and the rings are stuck in the grooves, and *perhaps* one breaks in getting them free. Do rings on one cylinder?

And I said  roughing it up with  emory cloth- maybe more like polish grit sand paper 2-3000 grit if you don't have the machine.

[midnightrider]

I agree with the short answer but, (don't tell anyone) several years ago when I was putting my K0 back together I was using new rings and while installing the cylinders I broke one.  (Don't even remember which one, probably oil ring).  I used the best looking one of my used ones instead and no apparent problems.  But I'm not proud of myself for doing it. 

i did the same thing! 

[Gordon]

And I said  roughing it up with emory emory cloth- maybe more like polish grit sand paper 2-3000 grit if you don't have the machine.

The point is there's no reason to do that.  The rings are already seated to the cylinders.  Using any kind of abrasive to roughen up the cylinder walls will only accomplish increasing the wear of the rings. 

[dave500]

if the bores are glazed and you can see clear reflections in them they need honing,may aswell fit new rings at the same time.

[somesuch]

ive pulled apart motors and just put it all back clean and so long as its within spec itll be ok,old rings can lose tension but so long as the grooves are clean and the rings are free its fine.

Old rings, especially Honda oil rings in my experience, can lose tension if the bike is allowed to get pretty hot. Easy to check though when you put just the rings in the bores to check the end gap.

On the other note,  what is the public opinion on the 10% leak down, I always thought it was approaching the end.....I know that the motor will run with much worse, just when putting a new motor together 2% should be more like it?

--Nick