Heavy Smoke in Left Cylinder

[Grey_Ghost]

Howdy,

Started up the T500 yesterday after sitting about a week on the center stand and it smokes heavily from the left cylinder (The smoke started right upon starting). Ran it around town and down the highway for about 20 minutes to try to clear it out and it never went away. I may not be right on this, but it didn't seem to smell like two stroke oil and is more white in color than blue. Pulled the plug and it appeared to have a minor trace of oil on it, but not significant at all.

Is it possible there is a leak between the transmission and the crankcase that is allowing oil to enter? Any thoughts or experience with this?

Thanks!

[jabcb]

Did the bike run good? A weak battery can cause a weak spark for one of the cylinders.
Could also be time for a tuneup.


The center crank main bearing uses transmission oil. So a bad crank seal can cause transmission oil to leak into either cylinder.

Suzuki provided a transmission oil fill cap instead of a dipstick. Just a use a flashlight or screwdriver+ruler to keep track of the oil level. To be consistent, leave the bike on the center stand for a while before checking.

Suzuki modified the T500 transmission oil fill capacity because insufficient oil can damage some of the gears. So it’s good practice to keep an eye on the oil level.

[Grey_Ghost]

Did the bike run good? A weak battery can cause a weak spark for one of the cylinders.
Could also be time for a tuneup.


The center crank main bearing uses transmission oil. So a bad crank seal can cause transmission oil to leak into either cylinder.

Suzuki provided a transmission oil fill cap instead of a dipstick. Just a use a flashlight or screwdriver+ruler to keep track of the oil level. To be consistent, leave the bike on the center stand for a while before checking.

Suzuki modified the T500 transmission oil fill capacity because insufficient oil can damage some of the gears. So it’s good practice to keep an eye on the oil level.

Hi jabcb,

Ugh...I hope its not the center seal...Is there a way you can check/diagnose without pulling the motor apart?

We also keep the bike on the center stand religiously just to make sure we don't get random oil flowing into the crankcase. The bike has run very well since the rebuild was completed about 600 miles ago. We have checked the oil and it is fine (but that could also be because it hasn't leaked very much.) Might it also be the sealant between the case halves? Just trying to narrow sources before we dive in...

Thanks!

[Zunspec4]

Hi GG,

First off I would take the bike for a good run, also known as a good thrash . If it has not cleared itself out and continues to smoke excessively the first suspect is, I'm afraid, a leaking centre bearing seal. Assuming the cases were joined using Yamabond or Threebond 1104 it is very unlikely that you have a leak through the c/case joint itself.

Cheers Geoff

[karl pa]

I had the same issue with my 75 T500 last year,several years ago I had the same issue with my T250. Smoke out the pipes and after running awhile my transmission oil level began dropping, which is a sign of leaking crank seal. I put some blue devil seal repair in the transmission oil, they stopped smoking and dropping oil level in gearbox. sometimes you can get lucky and sometimes you don't.

[jabcb]

Since you just did a rebuild, I would suspect that the cylinders are imbalanced.

Check coil primary & secondary resistances. Check the points condition & timing. Is the left points in worse shape?
Make sure the carbs are balanced. Make sure the idle is balanced.

Had problems with the right plug cap on my gray GT750. After fixing it, that cylinder was a smoke signal generator until it had fully cleared out.

Had a smokey cylinder on a GT250. Installed new points+condensers & went trough the carbs. Not sure, but I might has also installed new coils. Smokiness is gone & it now starts easier.

[karl pa]

Sorry for what might be a dumb question, did you replace crank seals when you had cases apart? I reread your build thread but can't find mention of crank work.

[Grey_Ghost]

Sorry for what might be a dumb question, did you replace crank seals when you had cases apart? I reread your build thread but can't find mention of crank work.

Not a dumb question at all...As a matter of fact we did not replace the seals (I know, I know...we should have...I am ready for my beat down...).

When the bike runs, I don't think its an ignition problem as the left cylinder fires and runs just fine...It just cranks out smoke from the left side. Also, it has that distinct burnt motor oil smell. My best guess is it is coming from the center seal since I've read here the left side outer seals (because they are next to the ignition) aren't typically a source of oil.

I found the seals and have ordered them up and will pull the motor apart in the coming weeks and get the crank rebuilt...If I am missing anything, I'd love to hear y'all's suggestions.

[karl pa]

At least you know how it comes apart.
Like I said, Blue Devil seal repair in transmission oil helped mine. might be worth trying before you tear down.
Unless it is alot of smoke, then tear down is pretty much needed.

[Grey_Ghost]

At least you know how it comes apart.
Like I said, Blue Devil seal repair in transmission oil helped mine. might be worth trying before you tear down.
Unless it is alot of smoke, then tear down is pretty much needed.

Yeah, we're pretty proficient at disassembly at this point!

We pulled the motor out yesterday and in the process about a half cup of oil drained out of the left crank chamber and the counterweights were bathed in motor oil. Rebuild, here we come!

[quocle603]

sounds like you're going to need to place the center seals for the bearing. It is sucking in your gearbox oil into your left cylinder. Check your plug, it will be coated with oil.

[Grey_Ghost]

I picked up a new set of seals and sent the crank out for rebuild. We got it back about 2 weeks ago and during the process of re-assembly we noticed a few of the small cylinder head bolt holes were on the ragged edge of being stripped out. A couple holes were already stripped and had been repaired with a heli-coil by both myself and the PO. It seemed like only a matter of time before all of the holes would be compromised so we bit the bullet and sent the cylinders out for a full repair. The repair entails machining out the holes and installing a new threaded insert. Hopefully we get them back today or Monday. I never cease to be amazed at how expensive machine shop services are!

[Grey_Ghost]

Final update on the bike...Got the cylinder heads back from the machine shop with new time serts installed, re-assembled the bike and got it fired up yesterday. It looks like it was the crank seals as there was no smoke and it appears the problem is fixed. Thanks for everyone's help and suggestions!