XR100 White smoke


I could use some advice on fixing a smoking engine issue. I don't have the engine back together yet and want to cover all bases before I button things up.

The exhaust valve seal looked "OK", though I have replaced it already.Exhaust port deposits point toward oil leaking in the exhaust valve area.

There is corrosion marking and some pitting in the cylinder, indicating that the engine was sitting on the side-stand with water intrusion for a while sometime in the past. The engine runs (ran) well before taking it apart, so I'd like to avoid a re-bore and all that goes with it.

Does anyone have experience with heavy white smoke?

What are the chances that it needs to be re-ringed and possibly re-bored?

What are the chances that the exhaust valve seal will fix the heavy smoking issue?


Heavy smoking is never cured with new valve seals..........! Pitting in the bore ......... yep, would expect it to smoke! Oil scraper ring can't scrape oil off a pitted clinder wall, and it ends up being burned in the combustion chamber. Deposits in the exhaust port ........... yep, clear out to the end of the exhaust pipe! That's the path of the oil going out of the engine.

Old School Al

My 1998 burnt oil too. Picked up a TB Parts 120 BBK and a couple of jets for $190, including gaskets, cylinder, piston, rings and wrist pin.

Great power, can't beat the price.

Valve seals only do their job when the engine is cold. Many engines don't even run seals - they smoke a bit on startup, but then run clean. So, if the engine smokes after it's warmed up, seals are never the culprit.

Pitting in the cylinder - bore is your only option. Gotta get rid of the pitting so the rings have something to grab on to (like Al said)

I would also strongly recommend checking the valves themselves - or just replace them and have the seats re-ground to match the new valves.

There is nothing worse than doing a bore job, reassembling everything, and then finding out the thing still smokes bad enough to kill all the bugs in your county because of a leaky valve.

In the future, before you tear the engine down, do a compression test, then dribble a tiny bit (teaspoon) of oil in the spark plug hole and do another compression test. If the second number is higher than the first, your problem is in the cylinder - if the second number is the same as the first, then the problem is in the head.


OK - anyone know a GOOD place to take (or send) the jug and perhaps the head for work?

The service manual indicates the desired piston-to-cylinder gap to be

0.0004"-0.0016" with a service limit of 0.004"

I would not trust any ol' Bubba to meet those numbers, especially the lower limit of the desired gap, so a good shop is important.

OE Honda parts @ bikebandit.com ...

.50 over piston $45

.50 over rings $35

Top end gasket set $50

Cylinder bore .50 over and hone $75 - $90

= $205 - 220 + tax.

Wiseco .50 over piston kit $180.25 + bore and hone $75 - 90 = 255.25 - 270.25 + tax



TB big bore kit 169 + tax

Includes new cylinder, piston, rings, wrist pin, gasket kit (no valve seals)


Thanks! :smirk:

I ordered the TBolt big bore kit last night.

~$170 for the jug, piston, rings, piston pin, and gaskets is a WHOLE lot cheaper than OEM parts.

You won't be disappointed, the TB kit flat out rips!

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