700SX top end rebuild (mr sled, turk, anyone)

[Tod]

sled back ground = 97 700SX with PSI pipes- stock head gasket- same jeting for 3000 miles - sled has 6200 miles on it.

I have been fouling plugs quite a bit and thought it just may be my coils or carbs. (new stator has 1000 miles on it) I have cleaned the carbs and tryed a different set of coils and still was fouling plugs. Thought it was a random thing but seemed to be consistant on the PTO cylinder. So on our way to ride as I already went through three plugs in five miles I decided to recheck the compression, rode on to the yammaha dealer and asked them if they had time to check compression - pull it around back- guy brings out gage and says pull three times. 80PSI on PTO 100PSI on other two. (three pulls WOT, plugs in other two holes)

OK so the 80 PSI explaines why I have been fouling on that cylinder.

After leaving that dealer I rode all day about 140 miles without any problem at all. The next day i fouled one time then it ran great the rest of the day.

Do we all agree that my plug fouling is do to low compression?? and how can this thing run so well on that low of compression other than the plug fouling?

Is it very likely that I can just re-ring all three and hone the cylinders. Or am I looking at new pistons, rings, pins, barings, and of course cir clips.

Have not had it apart yet as it runs so well after fouling a few plugs that I could live with it for the rest of the season then do it in the spring.

Thanks for reading my rambling and let me know what ya think.

Oh one more thing the sled does have 6200 miles on it and have not had any issue with the crank that I have heard about on the 97's. So when I do have it apart would I be follish to not redo the bottom end as well???

Tod

 

[kixx007]

Has the thing ever been rebuilt?! 6200 is alot of miles. Its best to do a top end every 3000 miles. of course you can go for alot more and never have a problem. I would overhaul the whole motor if it were mine. 6200 miles is alot if its never been rebuilt.

 

[Tod]

The motor has never been apart.

I did stop by my dealer and learned more about Piston colapse and how re-ringing a motor on a regular basis can really lengthen the life of the motor.

I will just redo the motor at the end of the season. I also picked up some "ring free" fuel additive made by yamaha, I guess Honda has even recomended it. I'll try some of it on the next ride as it may help me a bit.

Tod

 

[Turk]

A triple will still run OK with one weak cylinder. The low end will be a little soggy but it will be OK or seem OK at 1/2 to WOT. I put 1000 miles on my SRX last year with a totally demolished piston & cylinder but there was enuff left of the bottom ring to give me some compression at higher throttle. The low end was doggy & I fouled a lot of plugs but it was still drive able. A twin would not have even run!!!

 

[snowfoxsx]

i redid mine this year, 97 700sx 14000 km, never had trouble with the crank, or so i thought till i dug into it further and checked the bearings by splitting the case. found 4 bearings ready to let go so i just bought a whole lower end from a 2002 600sxr. it was cheaper. if i was you i would check the crank because it will be cheaper in the long run, instead of doing your motor twice it will be done once properly! glad i took the advice of a friend. i also found my pistons had collapsed skirts!

 

[800]

Check the jetting on your carbs. Single pipe 700's have Q-4's in the center and mag and a Q-8 in the PTO. That' s why stock they gurgle so much at low rpm. Anyway, most of the pipe manufacturers don't tell you to do anything with it when you go to triple pipes. Thats why you foul plugs. Its not why you failed a piston, if you did. If the piston if not failed, and just low on compression, when you lean out the pto, and put some heat in the cylinder, theres a slim chance that the compression will come up.