total noob question while saying hello

[nicholauslee]

hello guys and gals (i'm assuming there's at least a girl or two),
new to this forum, I had what I thought might be a useful question and posted it on another forum and got reffered back to this one. I've known of this site, but haven't been on here much at all.

I got a 77 xs650 a few months back for dirt cheap, the problem was that it smoked like crazy. I figure it probably has to do with the valves or rings or something relatively fixable. So when I get it home I immediately start ripping into her. Mind you, this is my first bike I can call my own, although I was raised around motorcycles (mostly harleys).
Long story short, here's the question:

"My piston rings don't seem to match up quite right. My cylinder is marked 964, which as I understand means it's 74.964mm. My compression ring (top ring) is marked with RN with no numbers, which if I understand correctly means it should be a standard bore ring. However, my wiper (middle) ring is marked R with the numbers 25 on the opposite side of the split, meaning it's a first oversize, I think. the expansion rings don't appear to have any markings on them at all that I can see however.
Just wondering if I'm confused about this and it makes sense to you guys, but it seems to me that at least one of those rings can't be quite right? Shouldn't they both be marked the same?"

Now I've gotten my cylinders back today, they are marked 016. I assume someone just got an oversized ring set and tried to file down the gap, if I understand everything right it should be a stock bore piston and cylinder.

next question, does anyone know where I can buy a standard bore ring set? mikesxs appears to be out of stock, and I can't find them anywhere else yet.

 

[BigJimmyW13]

hello guys and gals (i'm assuming there's at least a girl or two),
new to this forum, I had what I thought might be a useful question and posted it on another forum and got reffered back to this one. I've known of this site, but haven't been on here much at all.

next question, does anyone know where I can buy a standard bore ring set? mikesxs appears to be out of stock, and I can't find them anywhere else yet.

First, welcome to the site. Also you can always check over at 650central.com and give MMM a call and see if he has any in stock.

 

[nicholauslee]

Thanks BigJimmyW13. I'll assume the 13 means inches. I was planning on giving 650central a call tomorrow, crossing my fingers until then.

also, here's a picture of what I'm sitting at right now.

 

[xscessivecompulsive]

Lemme know if you cant locate em over at 650 central, Ive got a brand new set sitting here that I never ended up using because they came with my replacement barrels and pistons I ordered from MikesXs! I doubt I'll ever use em so if you want em their yours!

XsC

 

[nicholauslee]

Man, been on this site for about 3 hours and I've already gotten more help than the couple of months on the other unammed site. Thanks guys, appreciate it.

 

[retiredgentleman]

nicholauslee;

If the piston has 964, yes its a stock piston @ 74.964mm.

You need to take some measurements or have an engine shop take some measurements, to check if the cylinder and piston are suitable for reuse.

Cylinder taper top to bottom should not exceed 0.002"
Cylinder wear limit is 2.9567"

With the piston at the bottom of the cylinder, should not be able to put a 0.004" gauge between the piston and cylinder on the thrust side.

Have a look at the Yamaha Service Manual at www.biker.net for all the engine specs.

If in spec then go with the existing piston/cylinder. If out of spec then need to go to first oversize piston and have the cylinder rebored to match the piston.

 

[XSLeo]

You have the right idea on the piston markings. 74.964 is the piston diameter. The 016 on the cylinders is the bore size. 75.016. Subtract the piston from the bore you get .052. Thats in the middle of the spec of .050-.055 clearance.
You say you "got your cylinders back today" Back from where?
As RG said take them to a machine shop to get them measured. If the clearance is too big even fitting first over rings won't help much.
Leo

 

[nicholauslee]

I got them back from the machine shop my dad actually brought them to. Not too sure how good the guy is though. He cleaned the walls up, and said there was a "slight taper to the cylinders but nothing that should be too much." With the calipers I have I got a reading of 75.01mm top and bottom, so I'm assuming it must be within a hundredth of a millimeter taper. I did end up buying the stock size piston rings off xscessivecompulsive and they should be here soon. Just have to wait until I get those and the gasket set I ordered, then time to put it back together.

The original problem when I got the bike was the ammount of smoke pouring out of the exhaust. It wasn't running very good either. When I pulled the plugs they were saturated in oil. I assumed it was the valves and rings and such. The valves looked terrible when I pulled them btw.

However, now that I know a little more about these bikes, I do know that it also had pod filters on the bike when I got it. I'm thinking maybe he pulled the filter box and never adjusted the carbs afterward, which might also lead to it's running rich (if I understand correctly). Guess I'll figure it all out over time.

 

[5twins]

Smoke could come from bad valve guides and/or guide seals as well. The numbers on the piston and bore were what these parts were new. The cylinder is probably a bit bigger and the piston a bit smaller now due to wear. Measure the diameter of the piston now, front to back about 1/2" up from the bottom. Subtract this new number from what's stamped on the bore.

 

[nicholauslee]

okay guys, question number two.
finally got everything back together, and after a couple wiring issues, think I got it all ready to start.
the only thing is, when I start kicking (starter doesn't work) all I can get is a loud backfire. flames shooting out the exhaust, the full nine yards.
I kept looking at everything, and from what I can see, it appears, that i'm firing on the wrong cylinder. Tried swapping the point leads, and all I get is compression kick back that almost threw me over the handlebars.
Any suggestions would be greatful. I assume it has to do with timing.

 

[retiredgentleman]

You need to carefully set the gap for each set of points first, and then do a static timing of the points using a VOM on resistance. The "right side" or large back plate is set before the left side ( half plate) when doing static timing. Take the plugs out when doing this, so you aren't fighting compression. Use a wrench on the alternator nut to rotate the engine CCW.

The "Search" function in the upper right corner can bring you tons of information. Type in something like............"timing points"

 

[nicholauslee]

Thanks. I have been using the search feature on this site, and you're right it has been very helpful. However, I still like to ask the original question even after I've read other peoples stuff, just to see if I get something particular about my situation that I might've missed in my stupidity. However....

A few things that initally worry me.
a. The engine cuts off when I turn the lights on. Maybe a bad battery?
b. Kind of sounds like it's knocking to me. Tapets? Oil not getting sent to the top? Maybe that's just how these motors are?
c. Seems to be idling a bit high. Adjustment on carbs? (the throttle adjustment screw is backed right off right now, gonna get new mufflers soon, so not planning on messing with it too much until I get those on.) Maybe just needs to get properly warmed up? (afraid to run it much until I figure out the knocking)

 

[shotgunjoe]

"The URL contained a malformed video ID."

 

[nicholauslee]

hmmm....
can't seem to figure this youtube button out on this forum, but here's the link all normal like.

 

[kopcicle]

hummm same thing happened to me ...

 

[nicholauslee]

see, there's that malformed video again...

 

[kopcicle]

well it runs ...

~kop

 

[XSLeo]

On your high idle, unhook the throttle cable and see how it idles. If the cable is to tight it won't let the throttle plates close.
On the stalling when you turn on the lights it sounds like a low battery and the charging system isn't doing it's thing.
Fully charge the battery then, try it again with the charger hooked up.
Leo

 

[nicholauslee]

thanks leo,

it turns out that the problem with the lights was actually just me being dumb. I moved all my electronics up and under the seat bump, except for the regulator, which is still hanging out on a bracket under the seat. but i have to plug that in seperately, which i forgot to do.

I also figured out the idle, i adjusted the fuel/air mixture and had it running like a dream. nice idle, great throttle response. not too rich, not to lean. I was actually really happy with it, except the knocking that was coming from the top end....

So I checked to make sure it was getting oil, and it was. and then checked the cam chain tensioner. tightened it a little. then she wouldn't start at all.

basically where i'm at now, I got it running again, but not very smoothly.
strange thing is, when i took out the tensioner to check to make sure everything was alright, the plunger doesn't come back past flush. according to the manual i have, you check the pressure of the spring by lining the plunger up flush with the adjuster screw. except, on this there's no way of going past flush, so I don't know if it's too tight or not.

I did have to replace the chain when i did the top end build. the PO had a bunch of washers in behind the spring to add tension to the chain, which was at least two links too long. now i'm starting to think he may have replaced the spring as well.

I'll be digging through here tomorrow to see what i can find using the search tool, but in the meantime, like usual, and suggestions would be helpful.

thanks again you guys, you've all been very helpful. awesome group of people in this forum.

 

[XSLeo]

If your plunger doesn't come out past flush when you have it out in your hand then something isn' right. I have several and the plunger comes out anout a 1/16 to 1/8 inch on them.
Some years used a copper washer as a damper betwee the adjuster screw and the plunger, some years it was a steeland rubber washer. If it has the rubber/steel washer and should have the copper washer this might be the trouble.
Here is a pic of a 75, top. An 82 lower. You can see the amount the plunger comes out.
Leo