79 xs650 Special - No Spark... But 12v. help?

[ippytattoo]

I don't what the prices are like in your area but when I had my jugs bored I took them with a set 3rd over pistons to a reputable machine shop and they did a bore and hone on both cylinders for right at $100. So to me $100 per hole seems a bit high.

 

[Pabeye]

Thanks Ippy!........newbie here so I have no idea of what stuff is "supposed" to cost.... I see you are in MS.... located, here in NY things tend to cost double of other places...LUCKY ME!..LOL.so maybe $100 per hole is about right LOL, LOL

 

[Pabeye]

Let's set the piston thing aside for a moment and move to another issue. Do you have any idea of how I should address the possibility of bits of piston from that hole that might have ended up in the crankcase? I have found some very small pieces caught in the oil strainer which I gently cleand out with a tooth brush. I guess there may be more in there! Suggestions........thanks!

 

[angus67]

when I rebuilt my motor, it had a piston pin that let go, scratching the crap outta the right cylinder, rod crammed the piston up against the head at an angle, then the piston got tore to pieces from being jack-hammered in there.
The guy I bought the motor from had gotten it a few years earlier, never ran it. He was told the kicker was locked up, but ran off the starter.
Yea...right.
So anyways, continuing my first rebuild journey, I had the same question about debris in the lower parts, obviously my piston was shattered, yours is just holed, you may have some fine pieces down there, But with mine, I tore the whole motor apart, and the oil in it was chunky with fine pieces of alum from the piston.
I used a full case of carb cleaner to clean it all out, Bought the (now unavailable) 6th oversize kit from mikesxs, it came with matched piston to cylinders, proper ryko rings.
Had a local shop clean up the head, I put in new valves put it all back together, fired rite up, runs great.
Mikesxs still sells those kits, but they stop at 4th over. If you want to go that route, it may be your best option, being your first rebuild. I learned a lot from this little motor.
You will too.

 

[Pabeye]

Thank you Angus......there is no major scoring in the cylinders, at least to my untrained eye. I just finished measuring the bores with equipment on loan from my jet mechanic friend......will post the numbers in my next post.

 

[Pabeye]

The old pistons are stamped 963......


The bore NUMBERS:

Right side....Top Left to right 75.08 front to back 75.01
Center " 75.0 " 75.01
Bottom " 74.98 " 75.0


Left side Top Left to right 75.0 front to back 75.00
Center " 75.0 " 75.01
Bottom " 74.99 " 74.99


Would this indicate just a new set of stock pistons?
Would this indicate just a new pair of stock pistons?

 

[retiredgentleman]

The old pistons are stamped 963......


The bore NUMBERS:

Right side....Top Left to right 75.08 front to back 75.01
Center " 75.0 " 75.01
Bottom " 74.98 " 75.0


Left side Top Left to right 75.0 front to back 75.00
Center " 75.0 " 75.01
Bottom " 74.99 " 74.99


Would this indicate just a new set of stock pistons?
Would this indicate just a new pair of stock pistons?

The right side 75.08 mm shows a cylinder taper of 0.004". The Yami Service manual says allowable taper is 0.002". Looks to me that you should buy the first oversize pistons, which are 0.010" larger. You would then take the oversize pistons to the machine shop, and they would bore the cylinders to match the pistons.

 

[TwoManyXS1Bs]

+1 on retiredgentleman's call.

Back in the day, working at the dealerships, any 'holed' piston mandated a full teardown and inspection...

 

[NONclow]

+1 on RG's call also. You're on the right track Pabeye

 

[Pabeye]

Thanks!........

 

[Pabeye]

Valve re install update: After lapping the valves and finding no leaks, it was time to put 'em back in. My method of removal was not working at all....However an ingenious design shared by a gentleman named Rich did the trick.....I bought a "C" clamp Harbor Freight and did the modifications to it he suggested.

Gotta say, it's still a tricky business...I cussed a few times and I still have t intake valves to go!

PS: rolled the valves they seem fine..also checked for leaks using the kerosene in the hole trick, all is good.

 

[XSLeo]

On any bits in the crank case I might split the cases and do a good job of cleaning.
At least set the cases so the place where the jugs sets is level. Fill with kerosene or diesel to almost full to the top of the case. You will have to have the right side cover on of course. Now spin the crank slowly so as to flush any stuff out of the bearings. Spin it long enough so the cleaning agent flows up out the place the oil feed line that goes to the head hooks. Drain and refill and repeat the crank spinning until the cleaner comes out clean.
Either way will be a messy job. I prefer the tear down.
Shop around. A lot of small engine places can rebore engines. I used a machine shop for car engines. Used by a lot of the local car racers. A lot of dirt tracks around here.
I got mine done 2nd over for $35 per hole.
Leo

 

[Pabeye]

thanks Leo.........I'll go with the fill with kerosene, spin and empty......I'm leaving the bores "as is" ......I guess my pockets are not as deep as yours...........

 

[ippytattoo]

Your right side cylinder is out of spec. Not only is it showing a taper to the bore but it is also showing that the cylinder is no longer round and if the pistons are not worn any (which they most likely are, your best bet is to measure them) the bore to piston clearance is questionable. If I recall correctly .005" is outside of tolerances .005"=.127mm and your measurements are showing .117 assuming there is no wear what so ever to the pistons. If you run it as-is you more than likely will have problems out of that cylinder. Could be as bad as poor compression or oil blow by and fouling of plugs. Just my

 

[Pabeye]

Thanks for your input Ippy........I do appreciate your expertise..........I'm not a perfectionist..........it it runs I'll be happy. BTW, the tolerances you are quoteing are beyond the accuracy of my measuring equipment...AND my eyes.........

 

[Pabeye]

Got the new pistons today .......and one set of rings.....still waiting for the other set.

I guess pretty soon (when I get the other set of rings) it will be time to see if I can get the beat back together......

 

[XSLeo]

On your cylinder sleeves where they stick out the bottom of your jugs, there was a three digit number. Do your sleeves still have this number?
With the stock pistons having a 963 on the top, this indicates the pistons were 74.963 mm in diameter. Most of the engines I have torn down have had the clearance right in the middle of the tolerance. That would be .052 or .053 mm If you add this to the stock piston size, 74.963 + .052 = 75.015. This 75.015 would be the bore size. The 015 would be the number on the sleeve.
The bore size is always 75.xxx, never 74.xxx.
If your 74.99 is right then your new pistons are too big. 74.99 - 74.96 = .03 is the correct way to determine the clearance. The minimum clearance is .050 mm that's about .02 mm bigger than your clearance.
Or 74.99 - .052 = 74.938, this would be the size for your pistons.
If your measuring tools or your eyesight aren't up to the task of getting accurate measurements, then I suggest taking your pistons and cylinders to a shop and get them measured.
Leo

 

[Pabeye]

Thanks for the education Leo. I double checked the #s........on the bore......everything is between 75.02 and 75.01.......using my handy dandy NEW Harbor Freight digital mic. The new pistons AND the old measure up (20 mm down from the bottom of the skirt) at 74.96 and 74.97 which happens to be the exact same #'s I got from the old ones! Amazing. BTW, the # printed on the side of the jugs is .016.alwasy wondered what that number meant! I believe the #s work out OK, unless I'm missing something......

 

[Pabeye]

Gasket question.........do ya put anything on these gaskets when ya install them? I'm pretty sure the one all the way on the bottom is out in with nothing, how about the rest?

 

[Pabeye]

Would ya believe I git this far with the project and then......

Had a bit of s setback yesterday. I was working on setting the ignition timing and something did not seem right. I went back to the "bible" ( the OEM Yamaha service manual" and started reading some stuff int the front about "adjustments" I stumbled onto the section that went into some detail about setting the cam timing. This was a paragraph that I had not seen before because previously I was reading the "disassembly " section...anyway I realized that I used the wrong mark on the cam sprocket when setting up the cam while the crank was at TDC. I was using the little dimple on the right side instead of larger "slot" on the left side. Well, I guess there it was a good thing because even though I had to take the nicely torqued rocker cover off again, and mess up the nicely set points and adjusted valves, and cam chain....at least now it's done right.