1981 XJ650 Piston Ring?

Hi all,

So I've put about 500 miles on my 81' xj650 that I'm just about finished building. And I noticed that theres a fair ammount of exhaust comming out of the tranny vent. More so when I'm stuck on the freeway in 100+ degree heat and the oil's nice and thin. I'm assuming that this is caused by Blow Back? Exhaust blowing past the piston rings and down into the transmission. If this is the case then I will need to replace the piston rings. I've been looking around and there are 4 sizes available. How do I tell which size I have in my engine? I would wager that no one has been into the engine yet so it's probably stock. The yamaha OEM part is 4H7-11610-00-00 for the standard size. On e-bay there's 1 ring kit for $40 with the 00 part number and many with the 10, 20, 30, 40 part number for less. I'd rather spend $40 and get rings for all cylinders instead of just one.

Does anyone have any insight into this?

Thanks in advance,

 

you should find a mark on the rings, if not you need to get the bores tested & if they are within original spec' so will the rings be.

 

So are the over sized ring kits from people boreing the pistons out or from years of wear and they gradually become larger? or somehting? The speedometer cable broke at 23,000 miles.

 

it's call engine blowby.

there's a tool. can't think of the name. and i think harborfreight even sells it. but it's a micrometer type tool where you slide up and down the cylinder wall. measure the number from the top and the number from the bottom. that will tell you cylinder wear.

the bigger rings would be for bigger pistons going into bored out cylinder walls. looking at the microfiche. i see piston sizes. but only one standard for the rings. the 00,10,20,30,40 numbers are for the ring sets. you have the standard set. first set, second set, third set, and fourth set. the picture looks like there are 4 rings on the piston. could be 5.

you might be able to just hone the cylinders and use replacement rings. there is also a material that is called ring expander. it's a real thin aluminum material that you put into the piston grooves. and put the rings over it. it helps to push the piston rings into the cylinder walls more so you get better compression.

the problem with your $40 set of rings. times that by 4 or 5 ring sets. and add the cylinder gaskets and whatever else you may end up needing. the job gets expensive really fast.

 

Thanks for your input. so the numbers 00,01,02,03,04 are for the sets of rings? or over sizes? Like 04 set comes with rings for all cylinders or something? It might be because I just woke up but I still don't get it....

I'm ok with the cost of doing this job I figure I can probably do it for around $300, everything here is for fun and a great break from my life as an IT Consultant ;-)

Anyway, it's looking more and more like I'm going to have to pull the engine apart before I order any part. Which means no riding for a while...gasp.....

 

that's the way the microfiche reads to me. i've never screwed around with an engine so your local dealer would know more. or others on this forum that have been down that road.

 

Oversize rings are for oversize pistons.

Rings/pistons have to be matched to the cylinders; the condition of the cylinders will tell you whether overboring is necessary.

If the engine turns out it needs to be re-bored, then you're looking at new pistons AND rings AND the cost of the machine shop work. Plus, since the head is off, you might as well do new valve stem seals and have the valves lapped-- at that mileage you may find a valve or two needs replacing, the seats cut, more shop time/labor.

The reason the oversize rings are so cheap is that finding oversize pistons is next to impossible.

Your $300 ring job will soon turn into a $900 upper end rebuild, IF you can even track down all the parts.

Which is why a lot of us consider these motors to be not worth rebuilding especially when there are so many low-mileage bikes being parted out.

Better to drop $100 or $150 and get a low mileage motor with good compression, and do a swap.

I'm not saying you CAN'T rebuild the motor; just that without expert knowledge going in, you're going to end up paying a lot of shop labor and may end up throwing good money after bad if the prognosis isn't positive.

Or just be sure the bike is 100% properly tuned, and ride it. A little excessive crankcase "ventage" on a hot day isn't necessarily a phophecy of doom.

 

it sounds to me like he doesn't have his crankcase breather tube hooked up to his air box for whatever reason. driving around the city sitting at a red light i wouldn't want that blowby rising from underneath so i could be breathing it either.

 

Have you done a compression tets???

 

I havn't done a compression test yet, the breather hose is not hooked up to the air box because I removed it and replaced it with an ammo can which is where all the electronics are now. On the vent I have a small air filter, kind of like a pod.

Thanks everyone for their input. I have a lot more to work with now that before. I'll keep an eye out for low mileage motors and the parts I need for this job.

 

I would first ask (what weight of oil are you using and what brand?) Second, how many miles do you go between oil changes? Next, if you do have to go with rings which only a machine shop can tell you that once you pull the cylinders I would highly recommend honing the cylinders with a butterball hone. This way you end up with a nice crosshatch hone which usually the rings seat in better. There are other things which can sometimes also affect blow by like the timing being off or a carb where the float is not adjusted properly which ends up pouring raw fuel into the burn cycle and thinning out the oil.
1. Start with a compression test, Do it again after squirting oil into the cylinder see if compression changes. Is she smoking out of either exhaust pipe? grunt007

 

Check this out, something like this might save you a ton of cash!

http://flint.craigslist.org/mcy/2247776558.html