pistons and rings

So I have done a compression test and I think I might need some rings, how often is it that the pistons will have to be replaced also or is it just a given to do it all, I have done a little looking in to it and it seems some of the parts might be hard to find or come by

It's always easier to get a usable response if people know what bike you have. As to your question, it is a little incomplete, did you perform the compression test with WOT? Do you own a factory service manual? What compression #'s did you get? Pistons need replacing only when something is wrong with them not just a s a matter of course

You are right I guess I overlooked that, the bike in question is a 1982 kz750 h3 or ltd, I do not have a factory service manual yet but looked through one online and unless I overlooked it I did not see a listing for numbers, Being that the carbs and exhaust are off the bike right now I had to do the test with the bike cold, I came up with right at about 90psi maybe a bit more on all 4 cylinders.

If you did the test with the engine cold the readings can be expected to be low. I would not make a decision based on a faulty test. Before you decide you need pistons and rings you should perform a valid compression test followed by a valid leak down test. Remember that pistons/rings are not the only possible cause of compression loss if a valid compression test shows low compression. How many miles are on the bike? Unless the mileage is quite high or unless someone was negligent in performing normal oil changes or ran the bike without an air cleaner generally speaking these bikes don't need pistons/rings to be replaced. My KZ650 has 56k+ miles and has plenty of pep and doesn't smoke, so considering your KZ750 four is based on the KZ650 I would run very careful tests before deciding it needed pistons/rings. Ed

DLP wrote: So I have done a compression test and I think I might need some rings, how often is it that the pistons will have to be replaced also or is it just a given to do it all, I have done a little looking in to it and it seems some of the parts might be hard to find or come by

I rebuilt my 750 at about 70k miles and it needed to be bored. At less mileage, maybe not? You have to measure the cylinder wall wear.

The bike has or is reading 41,000 and some change, I would like to try the test with a warm engine and see but the carbs are off right now and I pulled the exhaust off and a part of it broke, it was the little cross connect piece rusted through, I don't really know a lot about the history of the bike other than what I was told from the guy I bought it from, supposedly it sat for a few years and was actually about to get scraped when he got it, I think he said it had been abandoned in a garage or storage and then he had got it, the bike runs and was running when I bought it but was running pretty poorly, maybe I am jumping the gun on it but was just after some feedback. Trying to find out about some carb work and one of the people I talked to last night told me with the mileage and all that the rings and pistons where all gonna probably need to be replaced, I don't want throw money at something that don't need it but I want the thing to run good too.

If the numbers are all that close together Id take a chance with checking the valve clearances and throwing it back together and getting it running as is.
If its been sitting that long Id be willing to bet the oil is really funky which is not helping the rings seal any either.
Before you get it back together maybe throw a little sea foam in the oil and crank it over several times to get it run through the motor.
Then change the oil and filter to see what it looks like,Then put it back together and see if you can get it running.
Sea foam makes a really good carb cleaner also,just dump a big can in the tank and run the wheels off of it to see if it helps.

I have been considering that, putting it back together and see what I got, what actually started all this is I noticed some seeping and or build up of oil around the head gasket area and a little from around the valve cover end plug. I probably like recommended before get the carbs going, figure out something with the exhaust for now and try to run it and see how it is doing and do a hot compression test and all.

I think you are now on the right track......just get it running and after you've put a few miles on it then you can redo the leakdown and compression tests. There are quite a few things you can (and should) do before getting it started....as Plummen suggests check the valve clearances, this should be done on a stone cold motor which you have, only outlay is a set of feeler gauges (please get a metric set - mine was $12 from NAPA) This will also give you a chance to look at the oil seepage from the valve cover gasket you mentioned. Drain the old oil and put some fresh stuff in making sure it is a proper type.....see a thread named OIL on the same page as your post which will give you some valuable info. These are really cool and still quite powerful bikes, a lot of fun and satisfaction in getting them to run sweetly, have fun and welcome

Not sure if anybody is still watching this post but I got a few questions, I went ahead and pulled the valve cover to check the valve clearances, it is my first time doing this so please bear with me, I looked a few online post and went through the Haynes manual I got which was pretty vague, it just says pull cover then line up the t mark and check. Isn't the lobe supposed to point away from the bucket, what if it is pointing straight up, also how many should I be able to check at one time, I have read where it says 1 n 3 or 2 n 4 on intake when lined up with the t marks I seem to be able to check a cylinder at a time as far as ones where the lobe is pointing away, meaning I can check both intake n exhaust on cylinder one, rotate and then the next cylinder and so on, is this normal or is something out of whack

Almost forgot but the manual says range from .08-.18 mm is range but what if you are right on limit should it be changed or left alone, if I did this right this was my numbers cyl. 1= intake .10/exh .10 - cyl. 2=intake .10/exh . ? - cyl. 3 intake .13/exh .08 - cyl. 4= intake .10/ exh .10 , the question mark on on the one is because I couldn't even get my smallest gauge in to check which was a .04mm

For right now if theyre atleast in the shim range Id leave them in there,If theyre over or under on the range change them out.
As far as adjusting them I just check the ones pointing away from shim on both cams,spin it over with a wrench and check the others.
Keep a list of the clearances then if you can get the motor running/rings freed up you can always swap the shims if the rest of motor seems solid.