XR400 Smoking under load - Plenty of power

[killerbanjo]

Hey all, I have just bought a 97 XR400R a week ago (my first "big" bike) and although the bike has plenty of power and pull its blows some under load when I am accelerating hard or popping a wheelie. I'm assuming its the valve seals as there seems to be no loss in power but I wanted to ask other peoples opinions first. Should I just order some valve seals and put some new rings in anyway? I need it for my commute so do not want it off the road for more than a day really...

I should add, I am doing about 30 miles a day on it and over about 2 days or 60~ miles its going from max oil level to just above the minimum oil level on the dip stick.

Thanks in advance

 

[xb33bsa]

its most likely a stuck or failed oil control rings you wont know if you need to bore it till you pull the engine down better find another form of transpo

 

[Powderfinger]

You can do a compression test prior to get a better idea of the cylinder, piston, rings condition.

I wouldn't count on doing that job in a day if you haven't done it before, some issue will most likely arise. Of course nowadays you can read and watch videos online that will minimize the unknowns.

 

[killerbanjo]

Thanks for the replies, I am confident doing the work myself and have done several full engine rebuilds before. But as I am commuting on this I wanted some opinions before opening the motor. I will purchase a compression tester as I have been meaning to get one for some time.

I think I will order some standard piston rings and valve seals, go for a rebuild and if the cylinder is not standard or is not in a good shape (same with piston) I will just put back the motor as is and then order the required parts.

 

[xb33bsa]

a compression tester will not always tell you if the oil control rings are bad in fact if they are bad then the extra oil can actually help comp numbers,by creating a better seal on failing rings..but it is still a good idea to do a comp test just be aware of the above.
there ios no good reason to rush the job buy a 100 doller pinto if you have to have a temp commuter

 

[killerbanjo]

Thats interesting, thanks. At least it will let me know roughly if the compression rings are in good condition. Assuming they are, I assume I am doing no damage to the motor by using it regularly assuming I keep on top of the oil levels?

And to be honest I still have my XL125 I could ride to work. I have only had the XR 5 days now so that is why I really don't want it off the road for too long! haha

 

[xb33bsa]

no to contrary the extra oil can mask the condition of the comp rings ,not always just a possability...you wont really hurt the motor until or if the carbon buildup gets bad enough to cause issues
if it is running good and starts easy (specially from cold)the comp probably isnt down a bunch
can you do a wheelie in third gear on throttle alone ?

 

[killerbanjo]

No way, my friends DRZ400 which has more power can't even do that! I can clutch it up in 3rd quite nicely though. If I go over a slight bump or hill I can yank the bars to keep the wheel up but not on the flat. My friend has a Bandit 600 and it easily kept up with him on the twistys on the way back from work last night (Sub 60mph anyway).

 

[xb33bsa]

haha

 

[barnett468]

.
its a waste of time and probably money to order the wrong parts . . take it apart and have the cylinder measured . . if it is out of spec it will need to be rebuilt.

if it is out of round by .0015 or tapered by .0015 its close to needing a bore . . if its out of spec by this amount in roundness and taper, its wasted and needs a bore.

have the valves, guides and seals checked.
.

 

[Powderfinger]

When you get your compression tester see about getting a valve spring compressor also if you don't have one.