I ride a 1986 Yamaha RX100. I replaced the bore set at 83500Kms and it has run 35000 odd kms since then. The question is do I need to replace the piston rings? Why am I asking-I just picked them up while shopping for seat cover, horn, etc recently. I get a FE of 30.5-34.5.

[praJEEP]

Do you feel any performance drop in these 35k kms if yes then please go ahead, if you are happy with its current performance then i see no piont in changing the current lot.

No, I am not experiencing any drop in performance. Infact, I am very happy about the performance. Just that 60+ speeds makes the engine feel rough. But thats bcoz, I have hardly done that speeds in recent times.

Can FE be affected because of piston rings? I guess, it cant affect just the FE and not the pick up/power right? coz faulty rings=loss of compression=loss of FE+POWER?

Right now acceleration/pick-up/power is very good. Just that FE seems very low. I know its an RX but it used to give me 35kmpl without caring to be too gentle.

[silver_shadow]

get a compression test done first. low FE could be because of many reasons.

[aaggoswami]

If you are not experiencing any power loss, then there is no problem in cylinder and you dont need to replace the piston rings.

If there are any traces of power loss or more than normal smoke, then piston rings will need replacement ( and other parts may also need the replacement ). Here as you have mentioned that there is not power loss, dont worry about this.

The low FE could be because of more than one reason.

[Sankar]

If you're happy with the performance leave it as it is. If you're worried about fuel efficiency get carb, plug, and airfilter cleaned and exhaust decarbed.

Changing the piston rings would do more harm than good, if there isn't any problem to begin with.

Originally Posted by aaggoswami

or more than normal smoke, then piston rings will need replacement

It's not applicable in the case of two strokes, since lube system is completely different.

[aaggoswami]

Originally Posted by Sankar

It's not applicable in the case of two strokes, since lube system is completely different.

What I meant is when there is more smoke coming out than normal, then its time for new rings. My Bajaj Spirit would always put out some amount of smoke as the engine and exhaust had heated up a bit. Its was nothing but the oil added in fuel. But when the smoke level increase even after regular cleaning, I had to overhaul the engine and I did not changed the block or head or even the piston, in my case only the rings did the job.

[ak916]

Originally Posted by Sankar

If you're happy with the performance leave it as it is. If you're worried about fuel efficiency get carb, plug, and airfilter cleaned and exhaust decarbed.

Changing the piston rings would do more harm than good, if there isn't any problem to begin with.



It's not applicable in the case of two strokes, since lube system is completely different.

Hi Sankar - Could you elaborate on that? I am contemplating changing the piston rings on my RX because I feel there is a loss in performance. However, If i had changed the rings when there was no loss in compression, what exactly would have gone wrong?

[audiophile]

Are u getting an vibration sounds from the block while riding or accelerating?
Loose or damaged piston rings would give you a vibrating sound. This would also depend on whether you bored the existing block or replaced the old block(cylinder) with a new one.

Mostly piston rings do not go bad very soon. I had my block bored and the piston and piston rings replaced 4 years ago.

Thanks guys for your views.
1. There is no loss in performance. But then I am not entirely sure of it either. Because I had meddled with sprocket (put a RX135) for higher FE and there was horrible loss of power After replacing it with the one that is meant to be for RX100 power is real good. But I am not sure this is all my bike can do or more. But the acceleration is smooth and I dont have to wring the throttle too much. Infact 1/4 throttle operation very easily takes me to 60kms/hr.

2. No vibrations felt from engine block.

So, my piston rings have done about 35000kms now. Do you think it needs replacement from usage point of view? Whats the average life of piston rings?

3. How will unwarranted replacement cause more harm? If you are really meaning it then I better not do anything about it!

Where in Hyderabad can I get the compression test done?

[SunnyBoi]

Average span of one set of rings is approx. 30000KMs. Get a change anyway, rings hardly cost 220-250 rupees. there wont be any unwarranted damage by just changing rings. The mechanic will tell you "saar, piston change karo, only 500 rupees saar" just ignore him and go for rings only.

[Sankar]

Originally Posted by ak916

Hi Sankar - Could you elaborate on that? I am contemplating changing the piston rings on my RX because I feel there is a loss in performance. However, If i had changed the rings when there was no loss in compression, what exactly would have gone wrong?

If the engine is performing well, it means that the piston rings and the bore has made a good seal between themselves.

When you put a new set of rings, it will take time for that rings to bed in with the liner. But keep in mind that the hone inside the barrel has been grinded down by the previous set of rings making a perfect mating surface between them. So the new set of rings wouldn't bed in as well as the old rings which were put in the bore along with a new rebore.

If the engine is performing bad, then you anyways change the piston rings, which will make it better. But not as good as with a new hone.

Do you see a good amount of blow-by beyond the piston rings? If yes, change the rings, it's time. If no, leave it as it is.

[praJEEP]

What compression ratio should an healthy RX engine have ? any idea !

@Sunnyboi: I already have the piston rings. Costed me Rs.390. Bought it from JC Road, Bengaluru. He told me its imported. Are you sure about 30k bit?

@praJEEP: I think its 9:1. I will refer the manual and let you know.

The only reason I am hesitating so much is, I dont trust these Hyderabad mechanics (service centers) to do a good job of it. No offense meant to anybody. I think, I will just let it be for the moment.