Motor rebuild problem, Please HELP

[Jared Coderre]

Hi Guys,

I just finished rebuilding my friends 400EX.

1. I installed a .20 Namura Piston 11:1 cylinder bored and honed
2. New Hot cams Stage 1
3. Replaced the cam chain w/ 450r chain recommended here by helpful poster from service honda
4. Re jetted the carb 165 main thorough cleaning while apart
5. New gaskets on all parts
6. Set intake valve lash to .013, exhaust to .015
7. Filled w/ 2.3 qts of 10w40 (dinosaur oil) verified the level on dipstick
8. I used a lot of assembly lube to prevent a dry start. Coated the clyinder wall with w/d 40
9. The cam chain tension was as expected for a new chain

It all went together normally and I did step by step per the service manual except the valve lashes (set to Hot Cams spec)

I started it up (started fine, idled fine) but it's smoking out the exhaust big time. The engine sounds fine. I hear no squealing, grinding, clicking or other weird dounds. I even started my stock 400 ex and listened, they sounded the same noise wise.

I ran it for about 15 minutes at about 3000rpm and shut if off per the hot cams intructions. I came in the house doubting I did everything right.

Is it normal for that much smoke? I am praying it's just the oil on the cyl wall burning off but I would have expected it to stop quickly.

Please offer any thoughts even things you think it shouldn't be.

[sixer3]

best guess is you installed your rings incorrectly, or you didnt lube the sleev and piston and the rings scratched the cyclinder as soon as you started it....but definately tear it down and inspect it, you'll be able to tell where the oil came from. also make sure its oil burning and not a differnt kind of smoke.

oil is usually blue-ish white, and will make the soot inside your exhaust wet

[exrider008]

Originally posted by sixer3
best guess is you installed your rings incorrectly, or you didnt lube the sleev and piston and the rings scratched the cyclinder as soon as you started it....but definately tear it down and inspect it, you'll be able to tell where the oil came from. also make sure its oil burning and not a differnt kind of smoke.

oil is usually blue-ish white, and will make the soot inside your exhaust wet


lets not jump to conclusions to fast. what color is the smoke.? my engines always smoke a little for a few min untill all the oils from you hands, grese, ect we need more info on the problem.

[Jared Coderre]

There was some external smoke coming from oily fingers and what not. this is oil coming out the pipe blue and white. Oill residue on pipe and plug.

Please more thoughts before I tear it down

[Wheelie]

Your valve clearances are way too loose. They should be .005 and .006 for the intake and exhaust, respectively.

[Jared Coderre]

Here is what they reccomended from the web site. If anything I may be to tight @ . 013 and .015


Intake
Intake lift (mm): 9.0
Intake lobe center (degrees): 106
Intake duration (degrees at 1mm): 246
Intake valve lash (mm): .13
Exhaust
Exhaust lift (mm): 9.0
Exhaust lobe center (degrees): 107
Exhaust duration (degrees at 1mm): 246
Exhaust valve lash (mm): .15
Note: Divide mm values by 25.4 for inches.


Would this be the cause of the smoking?

[Jared Coderre]

Wait, I was using the wrong settings. what's on the website is mm. I will reset now. But would this cause the smoking?

[Wheelie]

Blue smoke is oil, not good. Did you phase the rings right? After 15 minutes the smoke should've cleared.

Mine smoked very little after start up, and for only 2-3 minutes. I soaked the piston in oil and coated the cylinder as well.

Your case sounds excessive.

[Kaleigh]

The thing here.. is that he's trying to break in his cam and his piston.. thats not really good cause you have you ride it kinda hard to break in the rings.. and you have to take it easy to break in the cam.. btw.. are you using something to break it in.. like assembly lube or something.. mine smoked for awhile when I put my cam in... are you using synthetic.. and you coated your walls with WD-40.. you should used reg oil and coat the piston in reg oil.. does your machine still smoke..

[Jared Coderre]

I reset the valve lash and still the same smoke issue.

If it were the rings what should the compression be in PSI with a 11:1 piston and .020 over bore. I will buy a compression tester this should give me the diagnosis right? If I check dry and then a little marvel mystery oil in the cyl and if the compression changes I will know if it's the rings right?

To answer your questions Kaleigh & Wheelie:

I phased the rings @ 120 degrees
I used a liberal amount of assembly lube (no mass jokes about liberals, I am not one)
I am using dinosaur oil the $1.19 a quart stuff
The rings did not look like those pictured in the service manual ( per the manual one would have a beveled edge and the other would be sqaure as viewed from the side. I did size them correctly making sure the ring gap met spec.

Why would yours smoke from changing the cam? The oil would be isolated from the combustion chamber via the valve seals. I put new valve seals in and properly lapped the valves.

There's a lot of smart guys (including you 2) on here someone must have seen this before. I really would like some tests I could perform so I can isolate the problem and order some parts and get this fixed. I have built several Harley's and at least 20 top ends on two strokes and this problem has got me licked.

[Wheelie]

I prefer leakdown tests over compression tests personally.

Perhaps a broken ring?

Excessive blow-by--sucking the oil through the intake?

[lpmaster]

based on what you've explained, there is nothing wrong with your valves, when and if you rode it, did it seem to ride fine? as far as torque and power.

I know even with a completely gouged sleeve, my bike ran very hard, but it just smoked. (my circlip fell out)

your valves are working fine or you'd have a number of other problems....not just smoke, a compression test may or may not tell you a whole lot. you need to tear it down and find out for yourself exactly whats going on.

one mroe question, did the profuse smoking staart immediately after starting the bike for the first time?


also, check your oil for an excessive amount of metal flakes

[Kaleigh]

that the only thing with 400ex.. its hard to tell if something is really bad cause it runs no matter what you do to it..

but.. yea. i would check the oil.. see if there is metal shavings in it..

do one better and open it up.. see if there is anything wrong with the piston, cylinder or rings.. the circlip can be overlooked very easly.. check and see if that is on properly..

[Jared Coderre]

OK guys I found it. The cylinder was .037 out of round. I had a friend bore the cylinder and apparently his machining skills were not as he claimed them to be. A lesson has been learned. This sucks! Thankfully I didn't go more than .020 over bore I can at least save the sleeve. Looks like a bigger piston is my buddys future.

:grr:

[Wheelie]

.037 out of round!?:eek2:

Bummer.

[lpmaster]

hehe, that would do it

[Kaleigh]

Originally posted by Jared Coderre
OK guys I found it. The cylinder was .037 out of round. I had a friend bore the cylinder and apparently his machining skills were not as he claimed them to be. A lesson has been learned. This sucks! Thankfully I didn't go more than .020 over bore I can at least save the sleeve. Looks like a bigger piston is my buddys future.

:grr:

sucks but great to hear you found the problem.. ^_^... this is a good lesson for everyone though..