while i have my motor tore down should i put new rings on all the pistons? it has 60 hrs on it. thanks chris

Yes and you will be doing new pistons as well correct? If not then you are only shooting yourself in the foot.

Just my $.02

You do not require new pistons to gain a benefit from installing new rings if: your rings are worn and the pistons are within spec


You can remove your rings from the pistons and insert them into each cylinder and measure the ring end gap when not on the piston.

This will tell you if your within factory spec on max/min ring end gap. Obviously if your out of spec (ring end gap beyond max tolerance)then you should replace the rings.

You can also measure the piston ring grooves and piston skirt to ensure that your pistons are within tolerances specified in the shop manual.

My opinion is that with only 60 hours of use on a stock engine, your pistons should be fine and your rings may be near max ring end gap if you've run alot of WOT for hours at a time.

You will also require adequate honing for new rings to seat properly which has some prompted several differnet opinions on the proper method of honing.

If you go with new pistons you most likely should add a new wrist pin, wrist pin bearing, wrist pin washers and new clips. You can also measure the wrist pin and compare to see if your out of tolerance for max wear.

Best to just review the manual and make the appropriate measurements to determine if your within tolerence. Sure beats all the opinions you get!!!

Never mix old pistons and new rings or new pistons and old rings.

The ring Leyland or ring groove in the piston is a place wears shows up in modern day chrome or 'Nikasil' (nickel composite coating) bore engine. Every time you’re on-off the throttle the rings flex up and down in the ring leylend. The piston is aluminum the rings are steel. What do you think will wear out first?
Measure the old piston groove to ring clearance by inserting the ring all the way in the groove, using a feeler gauge between piston and ring. Try it with old piston and new ring. Compare that to a NEW piston and NEW ring.
The wear starts deep in the groove first, because the ring uses the outer edge of the groove as a pivot when it flexes up and down. Measuring this "angled wear" is difficult with a feeler gauge but it will give you an idea of what’s up. Whatever you get on the feeler gauge is really a lot more, deeper in the groove.
If your ring to piston groove clearance is good and you just have to use your old pistons, to re-ring you MUST clean the ring groove completely. There are tools for this but an old ring broken in half will scrape out the groove fine. If the groove is not cleaned the deposits in the groove could hold the new ring out to far. Before measuring, clean the groove.

Will an engine run with sloppy ring groove clearance? Yes
Will it last as long? NO
Will the cylinder seal as well. NO...(Not cranking compression, cyl pressure at high rpm)
Will an engine with sloppy ring groove clearance have blow-by. YES
Can you win a race with sloppy ring groove clearance? YES

Just my opinion

Allcool,

The GPR rings are beveled on top to avoid the inner wear on the piston groove when on the combustion stroke?

I've installed new rings on mx'ers for years without piston replacment and have never had the issues you've mentioned.

How do you come to your conclusions when some are contradictory to the shop manaul?

Do you know what the wear tolerance is for the ring groove and what the tolerance is new?

I do agree with your suggestion on ensuring that the ring grooves are cleaned thoroughly before assembly.

MDKOCHE
Almost all rings are now beveled, that does not stop the ring groove from wearing.

What is contradictory to the shop manual?

The ring groove clearance is .001"-.002", one of the tightest tolerances you will find in a motor, think that over when you are re-ringing.
Some high rpm motors call for .0005"-.001", which helps prevent ring flutter.

Sorry Md I have to agree with Pat.Don't imagine I would like getting shot in the foot.

quote:

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Originally posted by allcool:
Never mix old pistons and new rings or new pistons and old rings.

The ring Leyland or ring groove in the piston is a place wears shows up in modern day chrome or 'Nikasil' (nickel composite coating) bore engine. Every time you’re on-off the throttle the rings flex up and down in the ring leylend. The piston is aluminum the rings are steel. What do you think will wear out first?
Measure the old piston groove to ring clearance by inserting the ring all the way in the groove, using a feeler gauge between piston and ring. Try it with old piston and new ring. Compare that to a NEW piston and NEW ring.
The wear starts deep in the groove first, because the ring uses the outer edge of the groove as a pivot when it flexes up and down. Measuring this "angled wear" is difficult with a feeler gauge but it will give you an idea of what’s up. Whatever you get on the feeler gauge is really a lot more, deeper in the groove.
If your ring to piston groove clearance is good and you just have to use your old pistons, to re-ring you MUST clean the ring groove completely. There are tools for this but an old ring broken in half will scrape out the groove fine. If the groove is not cleaned the deposits in the groove could hold the new ring out to far. Before measuring, clean the groove.

Will an engine run with sloppy ring groove clearance? Yes
Will it last as long? NO
Will the cylinder seal as well. NO...(Not cranking compression, cyl pressure at high rpm)
Will an engine with sloppy ring groove clearance have blow-by. YES
Can you win a race with sloppy ring groove clearance? YES

Just my opinion

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32racer

just so you measure the piston ring groove correctly make sure that you put the feeler guage on the BOTTOM SIDE of the ring for proper measurement. Allcool may have forget this very import part of ring groove measurement.

Also the top part of the ring groove in the piston is beveled to match the bevel on the top part of the ring. Thats why the rings have to be intalled with the beveled portion facing up and you measure your clearance on the bottom of the ring.

Another thing you don't want to do is take a broken in half ring and clean the ring groove with the broken ring upside down. Clearly a way to potentially damage the piston ring groove by forcing the non-beveled section of the ring into the beveled portion of the piston ring groove.


The shop manual indicates a side clearance of .001 ~ .002 in. Out of tolernace replace the piston and piston rings as a set. Measure from underneath the ring.


Another quote right from the manual
"measure ring end gap (as I mentioned above after removal from the piston or new ones before initial installation).
"Out of specification .018 ~ .024 in replace the piston rings as a set."


I repeat.. no where in the Yamaha shop manual does it indicate that you must replace the piston when replacing the piston rings.. Piston replacement is based entirely on measurement of ring groove clearance and piston skirt diameter (3.1456 ~ 3.1462 in)


Like I said...many opinions.. my statements are quotes from the manual.. wonder if its wrong?

quote:

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my statements are quotes from the manual.. wonder if its wrong?

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The manual is not wrong.
If all clearances are within tolerances and show no signs of wear.... go for it.


Never mix old pistons and new rings or new pistons and old rings.

What I am trying to say is that you will not often find a set of rings worn out and a piston not worn past its limits. They wear as a set.
To change a set of rings that are not worn does very little for you, especially considering the necessity to Diamond hone our cyl for a new set of rings to seat properly. If the rings and pistons are not worn and the cyl are in good shape put it back together again same piston in the same hole with the same rings.
If you do want to change the rings or pistons because of wear or damage or reliability do it as a set (pistons & rings) with all the other necessary parts in properly serviced cyls.

Just my opinion

[ 08-08-2002: Message edited by: allcool ]

If the pistons and cylinder show blowby [brown coloring on piston below rings and on cylinder walls] but pistons are clean with no scuff/score marks, then you can just use the ball hone [or diamond hone] just to break the glaze and restore the cross hatch patern in the cylinder. Then add your new rings. The boat wll take about 10-15 hr. to fully seat the new rings. If pistons are scored or otherwise damaged, replace the damaged ones. Definitly where you replace the piston, you need new bearing, piston pin and clips. Thrust washers are reuseable in my opinion. I have done four ring repalcements with this method and regained my 150lb on a riva pump gas head each time.
Where was your compression before you took the engine apart?

Don't need a diamond hone. ball hone to break glaze will do.

my compression was at 90lbs before teardown this is on a stock engine.

People who are running into the "spun ring" scenario have around 80 hours +/- on there pistons. Also, it could be argued that when you put the new rings on the old pistons you could actually push in the pin that holds the piston ring in place. This would go along with ALLCOOL's explantion of wear above. It happened to me and several others. Believe me, a spun ring will cost you more than the $80 you spent on the piston.

In talking to Harry @ GroupK and Glenn @ R&D, both of them highly recommended swapping out the old pistons when you have the engine apart and are near 80+/- hours.

Bottom Line: Better SAFE than SORRY.

[ 08-08-2002: Message edited by: stewart ]

For what it is worth, my GPR had 110 hrs when torndown for mods. Used Yamalube for the 1st 40 hours, then TCR2000. Ring end gaps were between .021 & .023"///Piston skirts had .002" colapse.///Cylinder wear was negligble @ only .0003" (3 ten thousandths inch)///Ring groove clearance exceeded the shop manual spec by .006 to .007", however cranking compression was still good @ 130 with a Swift Kit head. What concerned me the most, was that 2 of the pistons had either a loose ring locating pin, or ones that had moved. A loose or broken ring locating pin can cause the rings to catch on the exhaust port. I had one failure on my 97GP, which broke the cylinder sleeve in a ported cylinder. I believe that the shop manual specs and reusability guidelines are fine for the the average rebuild, however, most people on this forum are looking for "Performance". The shop manual is not written for performance enhancements. I'm not saying that others are wrong, but Allcool is on the performance track and I'm sure that he is a person who has had a lot of real life experience. He is just trying to prevent others from making mistakes. I have over 40 years experience in working with engines, and still don't know as much as I'd like to know.(Thats 40+ years of learning from my mistakes.)

It has become evident that many have experienced the piston ring locating pin either become loose, push in or fall out and cause the ring to turn.

In most instances it is the top ring and piston ring locating pin thats coming loose. This is very similar to the power valve pin coming loose and in my opinion and resultant from high compression, a minor amout of detonation which creates a hot piston crown and the expansion/contration that goes to work on the piston locating pin.

I've had the same problem on my 00 GPR.. piston ring locating pin pushed in, ring spun and caught the exhaust port..

Now comes the most interesting part.. THIS WAS AFTER A FACTORY YAMAHA REP examined the pistons and told me directly that they could be re-used with new rings without a problem. I had 1 hour after assembly before the ring spun.

Do the reps really know anything ????????????

[ 08-08-2002: Message edited by: MDKOCHE ]

MD, no they don't, to answer your question.

In speaking with Glenn @ R&D when my ring spun he said that it happened to Mike Fullmer (expert long course and offshore champion)twice. It happened to #2, they fixed #2 but did not address any other cylinder, and then within 1 hour #3 went. That is why I replaced all 3 pistons, right away, no questions asked! Again, Better Safe than Sorry.