Piston Ring Replacement

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Hey all,
My name's Jeremy and I'm from Toronto.
I have an '82 XS400 Heritage Special.

I'm pretty sure I need to replace my piston rings. After fueling up and checking the oil in the middle of a long ride, I had a bit of freeway to cover. The bike held on for about 20 minutes, then lost power. It had burnt through a fair bit of oil. Now the little pig will barely start. And it'll only stay lit if I give it a bit of throttle.

Anyway, the bike has low compression in both cylinders when I test "dry". After a bit of oil is squirted into the spark plug holes, the compression comes back, but not enough.

dry test: right 56psi left 90psi
wet test: right 120psi left 140psi

So I think I need new piston rings. Right?

Here are the questions:

1. Has anyone on this board done their XS400 rings?
2. Do I need specialized tools?
3. Is this something a rookie can do himself?
4. I have a manual, but it details the entire motor teardown - not just a ring replacement. Does anyone know where to find a "how-to" for piston ring replacements? I've searched here and elsewhere, but most of the how-to's I've found are for cars.

Any help would be greatly appreciated.

Thanks guys.
 
your name reminds me of this, sorry...

8328.jeremyannoyinghorsegnomes.jpg




as for pston ring replacement;

carbs off

exhausts off

head off

barrel off

replace rings

new gaskets

reattach :D
 
In answer to your questions #2,3 no you do not need any specialized tools the only thing you could get if you wish is ring compressors to make it easier to get them back into the bores. When i did mine i didnt have any and used my fingers and it worked just fine and i would have to guess just as easy. Yes this is something a "rookie" can do himself, thats the beauty of these bikes they are fairly easy to work on compared to anything newer.
 
Hi Jeremy

Welcome. Your relaitively new here like me. I'm not far from you. I live in cambridge about an hour west of TO.

I'd say it will be rather easy, mines stripped down to nothing right now, I haven't got to putting it back together yet. Check out the bore while you have it apart. You shouldn't have a problem finding someone to rehone it locally while its off and I wouldn't think it would cost to much. I think sirius consolidated in cambridge has the gaskets. Just check them out on their website they will send right to you if you don't feel like picking them up.

Is your bike stock or a project you've been working on?
 
When you get the head off,get a set of feeler gauges and slip one down in between the piston and cylinder to see how much clearance you have. If there's too much,take it to a machine shop to get it bored and fitted with new pistons.It's not common for the rings to wear out all of a sudden. You may have cracked rings,but you'll have to wait until you break it down to know.Unless you have a bore gauge to measure the cylinder,you'll have to take it to a machine shop,depending of course on the miles on the motor.
 
dude. rings are STOOPID expensive. i got mine before there was a lot of hype for the 400, and it cost me $120 for the set! :0. fit perfect, but thats a lot of scratch for some flimsy metal. do you need a re-bore? if so, count on oversize pistons and rings, but youll end up paying the same for the pistons and rings combined anyway. because oversize rings and pistons are more common. just a thought
 
Thanks for the help and encouragement guys!

And Drewpy, thanks for that odd pic. Weirdo. =)
Congrats on the exif spread BTW. Yer bike looks awesome.

I'll get the thing pulled apart this weekend. I guess I'm just a bit chicken-shit. The only thing I've done to this bike is a carb re-jet.

So I can do the rings without pulling the motor, is that correct?

Volcom: Sure $120 is a lot, but it's worth more than that to have a motorbike instead of a driveway ornament.
 
I didn't try to scare you,just saying that you should be ready to do more than just re-ring.I hope that's all you have to do,but like I said,if it's got many miles,then it's more likely than not that there's more wear than just rings.If you're not accustomed to motor work,take the piston and jugs to a machine shop,and they'll tell you what to do.Look on ebay,and sometimes they come up,but make sure what size you need.Always get the lowest oversize possible,as there are only a few,and if you go over,the over-over by Wiseco are very expensive.I have a MX400 jug and head for my Dt400,but it's way out of the Yamaha range,so I'll have to pay $244.00 for a piston set or re-sleeve the jug to have a supercharged dirtbike. Good luck lha
 
Thanks lha.
I'm not worried about the need for a re-bore. If the motor is that bad I think I'll just part the rest of the bike out and buy something different.

This is my only bike. I want a runner.

The way it happened was very sudden, and I don't think I ran it for long enough to damage anything through wear. Cracked rings sounds right to me.

I guess I'll just have to open it up and see.

Shaun, Thanks for the tip on the gaskets - I'll check them out.
Motor-wise the bike is relatively stock. It has pod filters, non-stock exhaust, and a carb re-jet.

Here's a pic from last year:
 

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As Drewpy said,it is a cool looking bike,and maybe it'll run with a set of rings.Let's hope so. And you can scoot! lha
 
How much too big did you rejet it. Too large a jet and the excess gas can wash the cylinders clean of oil. This lack of oil greatly increases the wear on the rings and cylinders. Can go from ok to worn out in just a few high speed miles.
Leo
 
I agree about the jetting,you should only go up one size at a time.Replacing just the main jet is also not the way to do it,you must rejet the idle system,and the needle should be raised.Put the clip one groove down or put a couple of shim washers[Mikesx]under the needle if it's nonadjustable.By replacing just the main jet,which most people think is "rejetting"only changes the top 1/4 of the throttle,and doesn't address the other 3/4 of the range.I don't know if that's what you did,but many who aren't very experienced,and some that are do it that way. lha:banghead:
 
I think it was two jet sizes. I have pods and very free exhaust.
I also raised the needle by using one of those shim washers.
I suppose that could be a cause... I might reduce my jet size... split the difference. I wasn't happy with the MPG's I was getting after the re-jet anyway.

I've got the motor pulled now, and it's in my basement workshop.
I have to do the clutch too, so I figured I'd just take my time and do both jobs at the same time.

Thanks again for all your help everyone!
 
Two sizes shouldn't be too much,but you don't want it to run too rich,or you'll have performance problems and burn too much gas and like has already been said,the cylinders can get "washed out" by too much gas washing by the rings and diluting the oil film.The oil film is very important and is why the cylinders have a crosshatch pattern when new as there is an area for the oil to stay during operation.You may need two washers,as they take up the space of 1/2 clip position.I would however wait and see until you get it running,and start out with one step leaner on the main,one up from where you were.My$.02. lha
 

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