1991 XR250R Smoking after Rebuild

[XR400RMan]

Hey everyone, Everything in my Top end is Brand knew, It has been rode maybe 1 1/2 hours since rebuild and has not been ridden hard by no means, It has a Supertrapp exhaust,K&N airfilter and Wiseco Piston, It is smoking badly and I know it can't be something wrong in the top end so is just probably the Piston Rings aren't sealing well yet and is letting some of the oil in the crankcase into the cylinder and burning it? Also I noticed today that where the Exhaust Pipe connects to the Muffler/Spark Arrester that there is oil leaking out and running down to pipe back toward the front of the bike, So my dad thinks that the muffler has oil in it and thats why it is leaking there. So what do you guys think? BTW my XR is an awesome bike. I don't think I would ever buy anything other than a Honda. Thanks again Matt

 

[tristan18au]

did you wear the bike in properly?
if not you have just done your top end again:D

 

[snaggleXR4]

Hey,
I'm no expert by any means, but, I've seen something like that before. A buddy of mine has a 2-stroke, he put in a new top end, and ended up blowing the seals in his tranny, allowing the tranny oil up into the cylinder. Granted, 2-stroke motors are totally different, but keep an eye on your oil level very carefully. Furthermore, with blown, or totally misadjusted valves could cause your bike to burn oil. It seems to me, on higher mileage/hour motors, changing one part, like the top end, puts added stress on the other already weakened parts. This often times causes failures in these other parts.

Did the smoking start first thing after the rebuild, or did you get a bit of normal riding in before the smoke poured out? If it started first thing, I would check your valves, and valve stem seals. If it ran fine, but then all of a sudden started smoking, then I'm guessing you have at least a blown seal in your tranny, allowing oil to be sucked up into the combustion chamber. Furthermore, if you did not hone your cylinder, then maybe your ring just can't seat.

Get it checked out ASAP. If you do insist on running it some more, then watch your oil level VERY carefully.

 

[Shaw520]

Dont worry about crank seals, four strokes dont have em.
Sounds to me like something went wrong in the rebuild. Who did it? There are several things it could be; Valve guides/stem/seals, ring alignment or installed upside down, incorrect ring gap, incorrect bore/piston clearance. These would be the most obvious.

 

[smb_racing]

you didn't happen to leave the oil ring out did you?
did you ensure that the piston was matched to the correct bore size? did the cylinder need a bored?

 

[SFO]

Shaws list of problems is correct!

You are not going to solve the smoking by speculation either.
Tke it back apart and check your guide seal installation, bore clearance, ring installation/end gap.
I know what a bummer it is but ya gotta know why it smokes.

 

[XR400RMan]

Thanks for the replys guys, No since the first time it has been started after the rebuild it has smoked, It didn't start just one day it has been doing it, The guy we had put the top end in it is a local guy but I forget his name, He is really good and knows what he is doing I think, He said that since the Wiseco Piston is in in that the Rings on the racing pistons are harder and it takes them longer to seat, Also since there is oil sitting in the bottom of the Muffler and when you stop the bike all that oil runs into the header pipe right, Could it be that the when the bike warms up the oil in the header pipe gets hot and smokes? Also yesterday when I shut the bike off there was still a little smoke coming out the end of the exhaust for like 5 minutes, Not much but some, is that normal? No I have the oil plug in it so that is the answer to the guy that suggested that(Forgot his screen name)No the bike has not been ridden hard at all, Not even close to be called riding hard, When the guy put the engine together he tried starting it and it would not start so he did a Compressoin test and it was way low so he said he made sure he had the valves adjusted and seated right and he did so he checked out the piston and the Factory didn't have one of the Rings on the piston seated right so he fixed it and that brung the Compression up where it was supposed to be, I will talk to my dad today and see what he says, I am going to go out in a little while and check to oil level, My manual says to put the bike on level ground and to let the bike idel for 2-3 minutes and then let the oil settle, My question is how long does it take the oil to settle? Thanks again for the help guys, I will update you when I get more information, Matt

 

[BigBore]

I'm not buying the "rings haven't seated yet" excuse. I've never seen a new motor smoke. Also, I'm wondering.....why is there oil in the muffler? I can see maybe a little sludge-like carbon build up if it has been buring a lot of oil.

Factory didn't have one of the Rings on the piston seated right

Ok, so the mechanic rebuilt the motor, tried starting it, but it had low compression. So he says that Wiseco didn't have a ring installed on the piston correctly? Rings don't come pre-installed on the piston. Hate to say it, but it sounds like something wasn't put together right.

 

[keith500r]

If the mechanic tried to start it with the ring incorrectly seated, wouldn't it have damaged the bore of the cylinder?? sounds like the shop goofed somewhere, I would try to get them to fix it correctly.

 

[XR400RMan]

What I mean't by the factory didn't put the rings on right, I should have said the dealer didn't do it right, See i had a Honda dealer bore to cylinder to fit the knew wiseco piston and They put the Rings on the Piston at the dealer, So when the mechanic I had put the Engine together saw that the dealer didn't have one seated right so he fixed, The dealer that bored the cylinder never took the Rings back off which was fine, Also when my dad went to pick up the new cylinder sleeve he saw a big scratch all the way down the sleeve that I guess Iron Horse motorcycles of Monroe was hoping he wouldn't see so my dad had them do it over again and it was no scratch the second time around. I don't know what's going on, I will try to get more info when my dad gets home, Matt

 

[smb_racing]

you wouldn't just have oil sitting around in your muffler, it had to get there somehow. Sounds to me like your valve seal on the exhaust side is leaking, allowing oil to get into the header pipe as well as the cylinder.

So when the mechanic I had put the Engine together saw that the dealer didn't have one seated right

The rings are seated after the piston is installed in the bore and the engine is assembled, this is basically a process of the rings conforming to the cylinder wall. You can't seat rings outside of the engine.

 

[BigBore]

Whoooaaaaa hold up. Sounds like you've got a real crack-pot dealer working with your cylinder!

Did the dealer who bored the cylinder put the rings on, then bore the cylinder to match the piston? Probably unlikely they did, but if so, that would be real bad! Also, that big scrath--its possible that they had to hone the cylinder so much to get rid of the scratch, that now the piston/cylinder wall clearence is too much.

 

[agent 86]

Matt talk to your dad get this fixed before you have to bring it to the late Sanford +Son Junk Yard! I'll putt my 2.50 cents in and say Big Bore is right! Where you go from here is up to you and your dad. Will the shop own up?

 

[XR400RMan]

I am with you guys on this one, I think there is something just a little off somewhere and it is letting oil into the cylinder. And Big-Bore I think they did have to hone the Cylinder to get past that big scratch, So I think that the Rings are sealed well at one spot on the cylinder and then as it moves there is a spot where the Cylinder is to wide and the Rings can't seal it, This is really confusing to me, Let me just say this, I checked the oil level today and all was good, I am going to get something done about this but what could happen if I left it this way and made sure the Engine oil level was correct before everyride what could get messed up in the engine or anywhere else? Thanks again everyone for your fast responses. Oh and one more thing my back yard is almost an acre big and I was riding around it in circles yesterday and when I first started it it only smoked a little bit but once the engine got good and hot I could not stand to ride anymore because my backyard was almost like someone was burning brush in it or something, So what I am saying is its not smoking a little but ALOT once it gets hot. Matt

 

[BigBore]

It'd be a real pain to keep riding it like this. You'd have to keep oil with you and check it constantly. I wouldn't advise it, though. You run the risk of letting the oil level drop too far.

The way I see it (somebody correct me if I'm wrong), its understandable that the bike will smoke more if its warm. When its cold, the oil is still a little thick, and it doesn't get around the rings as easily.

The best thing to do in this case is to tear it down (yeah it does suck), take the cylinder and piston to a different shop (if possible), and have them inspect the pison/cylinder clearence. Worst case scenario would involve purchasing a slightly larger piston kit (maybe .010" over) and have the cylinder bored to spec.

I dunno, like I said, it needs to be checked out first.

 

[XR400RMan]

Hey bigbore would boring the cylinder .010" over cut down Realiability on my little Thumper? I think I finally found a way to get it to start easily when its cold, Not that it was ever like a YZ250F or anything. Thanks again Matt

 

[XR400RMan]

Hey bigbore would boring the cylinder .010" over cut down Realiability on my little Thumper? I think I finally found a way to get it to start easily when its cold, Not that it was ever like a YZ250F or anything. Also when tearing it down to access the Piston and Cylinder would I have to take the Cam,Valves,Rocker arms all back out again? Thanks Matt

 

[BigBore]

Installing a .010" larger piston would not hurt reliability in the least bit. And no, you would not have to completely dissassemble the head. You'd just have to take the cam chain off the top sprocket, then unbolt the head and take it off.

 

[snaggleXR4]

Hey,
Bigbore is right. There are tons of guys that run like 277/280 kits in their 250's, it is proven to be quite reliable. In your case, the first overbore would not hurt reliability. It would help your power all over, especially bottom end.

It definitely sounds like your dealer messed up. I think I would yell in their face until they fix the cylider and put in another piston/rings that will fit. Good luck.

 

[XR400RMan]

I am back with a little more info, My dad ordered all the parts from Partsfish.com and ordered a OEM Piston and then he took it to Ironhorse so that they could bore the cylinder to fit the Piston and thats when they messed up the cylinder the first time, THats when they ordered the knew wiseco piston and then they bored it again to fit that piston, I think there is a low spot in the cylinder where the rings can't seal. Thanks for the replys everyone, Looks like I am gonna have to take the head off and check everything out, This thing smokes way worse than any 2-Stroke I have ever seen, Matt

 

[DualSportr]

Take it to a reputable Honda mechanic. Now.

The 'factory' does not install rings. The person doing the bore does.

Don't ride it any longer. The more you ride it while it's smoking, the more the bore will be glazed and the more it will smoke.

Remove the pipe, and clean it completely.

If the bike didn't smoke a bunch prior to the rebuild, the valves/head are probably not the problem (I say PROBABLY, they should be checked).

With that much smoke, it's not a bad bore, it's either a bad head, a broken ring, or the person installing the parts overlapped the corrugated oil ring - a typical mistake if the 'mechanic' is not used to dealing with four strokes.

If what you said was exactly what the installer told you regarding the installation problems (the factory installed the rings wrong), then they not qualified to work on this bike. Cut your losses and take it to a good mechanic.

 

[Rod Grove]

I rebuilt my own xr 250. put a 280 kit in it. The reason I rebiult it was because it was smoking really bad. I put it back together and it smoked just as bad. it ended up being valves and guides. If you have low compression make sure your decompression lever and cable are adjusted right and working correctly. Your oil in exhaust could be from worn valves and guides. I would take it apart and check that. since you will have it apart that far double check your piston and rings. I have a clymer manual for that bike if you want it ill sell it cheap since I no longer have the xr. GOOD LUCK! Rod

 

[XR400RMan]

Thanks Rod Gorve for the reply, Thanks for the offer on the clymer manual but I have one that covers the XR250R(Came with the bike). Me and my dad thought it might be oil in the exhaust burning but there is oil running down the cylinder head right underneath where the header pipes come out so it is burning oil bad enough to get past the o rings I guess, It isn't smoking as bad anymore I don't "THINK", Sometimes I will look over my shoulder and there is tons of smoke pouring out and other times it is "BARELY"visible. I will figure it out though, Thanks again Matt

p.s. I check my oil level everyday before each ride and add some if neccesary. Matt

 

[BigBore]

Just wondering.......lets say you run your bike on compression for a while. For instance, riding down a long hill in a low gear, without giving it any throttle. When you get back on the gas, does it smoke pretty bad? What you're describing kinda sounds like what my old 500 did. Didn't smoke all that bad most of the time, but after I ran it on compression for a few seconds, it would just roll smoke out the exhaust.

 

[XR400RMan]

Thanks for the reply Bigbore, How long would you call riding down a hill using compression braking? When I come up to a mud hole and say I am in 3rd gear I will put it in 2nd and then let out the clutch and the bike will slow down pretty fast but it doesn't do that but say a few seconds until the bike slows down enough to be able to ride in 2nd, When I get on the throttle real hard and then get where I need to coast through say an off-camber part of the trail I will just shut the throttle off and pull in the clutch and downshift a gear or two but keep the clutch pulled in until I almost get to the off-camber part then I will let the clutch out and let the compression slow me down, But when I coast for a while with the clutch pulled in I will rev the engine some and then continue coasting and then rev it again, I will look tomorrow if its not raining out and see if it does it alot after I use compression braking, You said your old 500 did this, What was the cause of the problem or did you find out? Thanks Matt