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Discussion Starter · #1 ·
Ok so i was about to change the gaskets of the engine of my zx750 j1, but when i opened the engine, my mechanic sayid its time to change the set of rigns from my pistons And "fix" the valves .


I dont have enought money to do both things so i suggested to just change the set of rings, but according to my mechanic that wouldnt worth it, beacue my bike was smoking a bit when cold, and he says if i change the set of rings the compression will be higher and damage the ruber on the valves wich will end in the same sjmoke or may be more!..

he says as im planning to sell the bike sooon, i have two choices 1.- or fix the set of rings and valves or 2 do nothing and sel it like that (of course changin the new gaskets).


Now my question comes because according to a friend he had the same problem and his mechanic todl him the same, but he changed Just the set of rings and the bike is very well, with no smoke and more power..

What do you think?.. was i clear? does any of what i sayd make sense for you guyz?? pls let me know! asap!
 

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The Cruising Gunsmith
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I don't know if your rings are bad or not.

How many miles on the engine and what kind of care has it been given?

In most cases, the engines need a valve job LONG before the rings go. It would not be unusual to need a valve job at 20,000 miles but it is likely the rings don't need to be replaced until maybe 50,000 miles or more.

If your bike is smoking cold, it is possible that it's the rings but it is more likely to be valve guide seals which would be fixed if you do a valve job. In most cases, if the rings are bad the bike will smoke whenever you open the throttle for hard acceleration. It will still smoke that way even when hot if the rings are leaking badly.

As for what he said:

1.- or fix the set of rings and valves or 2 do nothing and sel it like that (of course changin the new gaskets).
There is a third option:

leave the cylinder and rings alone and just do the valve job and, of course, install new valve guide seals when the valve job is done.

I do agree that putting in new rings alone is a waste of money. If the valves need to be done and the guides are leaking, the head must be done to get any improvement.

I think the rings might not need to be replaced, but I can't say for sure because I don't know how much wear is on your rings and pistons.
 

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Discussion Starter · #4 ·
wELL THE RINGS ARE BAD.

but the thing is its cheaper to change the set of rings that make the valve job.. thats why my options are only rings or nothing.

i would think that changing the rings might improve the bike because has more compresion and might be the smoke go also . no??
 

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Vintage bike addict
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Try door number 5 . Get the valves and rings done and ride it one more season before you sell.
 

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Patriot Guardian
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wELL THE RINGS ARE BAD.
Positive? Leaking valves will also impact a compression or leakdown test.

Do a leakdown test.

Now drop a spoon of oil into the cylinder, hand crank the engine twice. Repeat test.

If the leakdown holds, it's rings... if it doesn't, it's either valves or REALLY bad rings, but as said above, really bad rings will smoke whether cold or warm.


My money is on the valves unless you've really beaten the crap out of that engine... in which case, the bottom end is probably shot too.
Sell it as-is.
 

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The Cruising Gunsmith
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Positive? Leaking valves will also impact a compression or leakdown test.

Do a leakdown test.

Now drop a spoon of oil into the cylinder, hand crank the engine twice. Repeat test.

If the leakdown holds, it's rings... if it doesn't, it's either valves or REALLY bad rings, but as said above, really bad rings will smoke whether cold or warm.


My money is on the valves unless you've really beaten the crap out of that engine... in which case, the bottom end is probably shot too.
Sell it as-is.

If I understand the initial post, the engine is already torn down? If so, I guess you can't do any more compression tests.

The thing about rings: the rings are steel and the pistons are aluminum. The info I read is that most ring blowby occurs NOT at the ring-to-cylinder contact area, it is in the pistone gaps where the rings reside. The rings and pistons wear there and allows blowby.

FWIW, if the rings are to be changed, I would think the pistons would have more ewear and need replacing as well.

I still can't figure out how you wore out the rings... it took me 75000 miles to do that on my 750 and it was still holding full compression in the cylinder that had good valves.

You said you are sure the rings are bad? OK
 

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The thing about rings: the rings are steel and the pistons are aluminum. The info I read is that most ring blowby occurs NOT at the ring-to-cylinder contact area, it is in the pistone gaps where the rings reside. The rings and pistons wear there and allows blowby.
That would make sense as iron on aluminum would wear first before iron on iron contact would.
 

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The Cruising Gunsmith
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so he needs new pistons???
I can't say for sure without measuring the gap between the sides of the rings and the piston. In my manual that is a very tight spec and a critical spec. If that gap is still in spec, then the pistons and rings don't need to be replaced. The only way to know is to take the pistons out, remove the rings, clean all the crud out of the piston grooves and then install the rings and measure the gap.

I would think if there is blow-by, then the rings and pots should be replaced as a set, but that's just an opinion.

I was surprised at how loose the service limit is on the ring end gap in the manual: on mine, they allow up to about .030" (which is a spark plug gap).
 

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Positive? Leaking valves will also impact a compression or leakdown test.

Do a leakdown test.

Now drop a spoon of oil into the cylinder, hand crank the engine twice. Repeat test.

If the leakdown holds, it's rings... if it doesn't, it's either valves or REALLY bad rings, but as said above, really bad rings will smoke whether cold or warm.


My money is on the valves unless you've really beaten the crap out of that engine... in which case, the bottom end is probably shot too.
Sell it as-is.

There's the answer in my book. Put it back together if apart, and sell it telling the buyer that it could use a rebuild. No reason to put money into a bike that you won't get back out of it.
 

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Discussion Starter · #12 ·
Well first of all thanks all for your opinions.

Im completeley aware that the Best odpiotn woudl be change Piston, rings and valves job, but again the problem is money.

The changing of rings i can pay but not the valve job (i almost double).

So i figured if th engine is already down, it would be a waste to just put it all togheter and do nothing.

I was planning to change the rinngs and the the new buyer, ok the rings are changed u must do the valve job.

But according to my mech hes not fan of that option.. might be my ingonracne abput mechanics, but accordign to my firend is just my mechnic wants to make more money and i really can do that and it defenetaly worths it..

. . wha u think?
 

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Discussion Starter · #13 ·
If I understand the initial post, the engine is already torn down? If so, I guess you can't do any more compression tests.

The thing about rings: the rings are steel and the pistons are aluminum. The info I read is that most ring blowby occurs NOT at the ring-to-cylinder contact area, it is in the pistone gaps where the rings reside. The rings and pistons wear there and allows blowby.

FWIW, if the rings are to be changed, I would think the pistons would have more ewear and need replacing as well.

I still can't figure out how you wore out the rings... it took me 75000 miles to do that on my 750 and it was still holding full compression in the cylinder that had good valves.

You said you are sure the rings are bad? OK

Well just to add a note i Bought this bike Already Used and it was very cheap so i could imagine it wouldnt be in best condition.. the Real problem is i never had the chance to have a long ride really beacuse when i was ready to do it the gaskets blew =0. the Miles dont mark too much as i remember but defenetaly the last owner didnt treat the kawa very well.
 

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The Cruising Gunsmith
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Well just to add a note i Bought this bike Already Used and it was very cheap so i could imagine it wouldnt be in best condition.. the Real problem is i never had the chance to have a long ride really beacuse when i was ready to do it the gaskets blew =0. the Miles dont mark too much as i remember but defenetaly the last owner didnt treat the kawa very well.
OK, what we are saying is that unless the mechanic took the pistons and rings out, cleaned them and then made some measurements on the gap clearances, he doesn't know whether they need to be replaced or not. And we are saying it would be very unusual that they would need to be replaced and so the low compression or smoking is more likely valves and valve seals.

Your mechanic may be simply covering every possible cause because he isn't sure which one is the right one.
 

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The Cruising Gunsmith
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Well first of all thanks all for your opinions.

Im completeley aware that the Best odpiotn woudl be change Piston, rings and valves job, but again the problem is money.

The changing of rings i can pay but not the valve job (i almost double).

So i figured if th engine is already down, it would be a waste to just put it all togheter and do nothing.

I was planning to change the rinngs and the the new buyer, ok the rings are changed u must do the valve job.

But according to my mech hes not fan of that option.. might be my ingonracne abput mechanics, but accordign to my firend is just my mechnic wants to make more money and i really can do that and it defenetaly worths it..

. . wha u think?
Your mechanic is correct. The main cost of the job is the mechanic's labor, and getting it down to the pistons means pulling the head and camshafts then the cylinder. If he changes rings and puts together, that is probably at least ten hours shop labor (total). In this country, probably at least $500 just for labor cost alone plus parts are extra.

Then, to do the head later, you have to pull the head and camshafts and all so it is probably another $400 in labor to do the same labor again which was done before when the rings were changed.

That's why it might be smarter to only do the head and valves. I still can't believe the rings are gone unless the bike was severely abused. I also don't believe the mechanic has made the proper measurements to actually know the rings are bad, he is just quoting the whole job together.
 

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Discussion Starter · #16 ·
Your mechanic is correct. The main cost of the job is the mechanic's labor, and getting it down to the pistons means pulling the head and camshafts then the cylinder. If he changes rings and puts together, that is probably at least ten hours shop labor (total). In this country, probably at least $500 just for labor cost alone plus parts are extra.

Then, to do the head later, you have to pull the head and camshafts and all so it is probably another $400 in labor to do the same labor again which was done before when the rings were changed.

That's why it might be smarter to only do the head and valves. I still can't believe the rings are gone unless the bike was severely abused. I also don't believe the mechanic has made the proper measurements to actually know the rings are bad, he is just quoting the whole job together.
Ye well he didnt use any vacuometer or anything to really know about the state of the rings he just saw it and according to his experience he sayid that. but here the job of Rings are cheaper than the job of valves.

So as im understanding the valves use to be damaged First than the rings?.. so if the rings are bad, the valves must be really F%cked ? .

By the way my mechanic say i must get +25 rings, but on bike bandit i dont find any measurements just Set of Rings and set of OSL rings.. wich i dont understand.. what it means..
 

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Discussion Starter · #17 ·
Positive? Leaking valves will also impact a compression or leakdown test.

Do a leakdown test.

Now drop a spoon of oil into the cylinder, hand crank the engine twice. Repeat test.

If the leakdown holds, it's rings... if it doesn't, it's either valves or REALLY bad rings, but as said above, really bad rings will smoke whether cold or warm.


My money is on the valves unless you've really beaten the crap out of that engine... in which case, the bottom end is probably shot too.
Sell it as-is.
ye wel to make this Leakdown test is again money, i m pretty sure ot must be cause as first view my mechanic saw it and inmediately "he sayid rings should be changed , and if u had money some pistons, but u must do the valves for that also".


I cant really tell because i hadnt drivbe this bike i almost bought it and had parked for several months.


By the Way, Why this J1 has diferent system of valves than the L1? i made a valve job for the same bike zx750 L1 and according to my mechnic that was easier to do.. he says this bike has "shims" and its a total diferent process..
cant understand how kawasaki change so much between versions of the same bike!
 

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The Cruising Gunsmith
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but here the job of Rings are cheaper than the job of valves.
But the odds are very high that they won't fix your problem.

So as im understanding the valves use to be damaged First than the rings?..
I don't know if the valves are "damaged", but they load up with garbage and they don't seal well. They usually need to be cleaned and then have the seats lapped to get a good seal again. But, yes, valves usually need work a long time before rings do.

so if the rings are bad, the valves must be really F%cked ? .
I don't know, but if you have the head off the engine, you can look at the valves. You can also lay it upside down and pour thin oil into the cylinder and see how fast it leaks past the valve seats into the intake and exhaust passages. That will tell you if the valves are seating.

By the way my mechanic say i must get +25 rings, but on bike bandit i dont find any measurements just Set of Rings and set of OSL rings.. wich i dont understand.. what it means..
+25 is a "first over" oversized ring set. It's diameter is 0.25mm larger than stock.

"OSL" probably is an oversized ring set, I don't know the diameter.
 

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Discussion Starter · #19 ·
+25 is a "first over" oversized ring set. It's diameter is 0.25mm larger than stock.

"OSL" probably is an oversized ring set, I don't know the diameter.


but theres nothing like .25 in bikebandit.

can i just buy the osL (what the L mean) and fix it? my mechnic says that must be an standar OS that could be fixed for +25 or +50 .. otherwise where do you guyz get your .25 rings?
 

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The Cruising Gunsmith
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but theres nothing like .25 in bikebandit.

can i just buy the osL (what the L mean) and fix it? my mechnic says that must be an standar OS that could be fixed for +25 or +50 .. otherwise where do you guyz get your .25 rings?
When I shopped for rings, Kawasaki only supplied oversized rings in +0.50 and +1.00 sizes.

I think you have to shop for aftermarket (non Kawasaki) brands to get +0.25.

I still think this mechanic is blowing smoke up your rear end. The only way to know if the rings need replacing is to take a set of calipers and measure them. And also, he needs to use precision feeler gauges to check the gap at the ring edges to the piston grooves.

This guy is just telling you everthing that might be wrong with your bike, and you are picking the one item that is the cheapest. If you put rings in and don't fix the valves or oil seals, the thing is probably going to run like crap and smoke like a chimney.

AT LEAST DO THIS:

Take the head. lay it down on the ground upside down. get some motor oil and thin it down with some mineral spirits just to make the oil thinner. (make sure the spark plugs are installed in the head)

Pour the thinned oil into the cylinder areas and cover the valves. fill it with oil. Now, take a light and see if you can see oil leaking past the valves.

If you see oil going out by the valves, you need a valve job because they are not sealing at the seat. If you install new rings, it won't do anything because you will still have bad compression at every valve that leaks. You will still blow oil because the seals are probably bad.
 
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