How easy is it to fix a smoking engine?

Question

Hello,

I am looking to buy a Honda SL 100 bike. It's only got 2000 miles, but apparently the engine smokes. It can run well, but then the smoke is pretty bad. Owner says it might need new rings?

How easy would this be to fix?

The bike is only $400, so if its an easy fix.. I'd like to do it.

Thanks!

Answer 1

my guess, blown head gaskets, my car does the same thing.  The gaskets are real cheap, probably ten, twenty bucks, but you have to strip the engine down to nothing to put them in.  So, that takes a lot of work, and you need to know what you are doing.  Also, the engine is probably bad if it has been like that for long.  I wouldnt buy it, but yet again i know almost nothing about bike engines, it might not be that hard.

Answer 2

For some that is easy for others it is not.  I would get someone to look at it first.  find a friend that has a compression tester to see if it seems to have low compression or leaks down bad.  You can also have the oil cap off and see if you feel air in the crank case from bypassing the cylinder ring.  all kinds of stuff can cause this from to much oil to valve seals.  Is it a 2 cycle?  If so can just be oil is mixed rich.  Get someone that knows to look at it.

rd

Answer 3

it is that hard, dont buy it. Its also a sign it wasnt taken care of

Answer 4

Stay away from it. Only 2000 miles on the engine and it smokes that badly? Something internal is wrong. It's probably been rebuilt incorrectly.

Answer 5

Don't buy it.  Chances are you will want to ride around before fixing it.  Smoking bike really attractive to cops and environmental people.

Answer 6

wow somebody beat the !#$^ outta that bike.

Answer 7

A smoking engine is usually from motor oil getting into the combustion chamber (where the air and fuel are burned), creating the smoke.  On your SL100 (a four stroke engine) there are two basic ways that the oil gets in there- either by seeping past the piston rings or leaking in through the valve guides.

If the engine smokes while power is being applied (constant stream of smoke out of the exhaust pipe as you ride down the street) this is a good indication of bad rings.  If it smokes on deceleration only (throttle closed as the bike slows down) then the culprit is likely the valve guides or seals.

In either case, you'll have to remove the cylinder head.  This is fairly straightforward mechanical disassembly (your just removing the proper bolts and pulling stuff off) but it also nvolves removing the cam.  The critical part here is that when you go to put the cam back in, it has to be timed properly with the crankshaft.  If you do not do this absolutely correct, you will end up with a bunch more engine damage (bent valves) and be in worse shape than when you started.

If the valve guides are bad (takes more disassembly and precision instruments to determine) you'll be best off simply replacing the cylinder head with a good used on, as replacing the guides gets expensive really quickly (parts and machine shop labor).

And this doesn't even get to the rings yet.  Once the head is off, you have to remove the cylinder (very easy) and determine what caused the smoking (requires some knowledge).  If the cylinder walls are scuffed up, the cylinder will neeed to be honed (about $20).  If the damage is deep, you'll be looking at boring the cylinder to a larger size, and then having to replace the piston and rings ($100+).

Piston rings don't normally wear out in 2,000 miles- they should last 10 or 20 times that long on a small bike like the SL100.  This tells me that the bike was probably abused, like run without enough oil or without an air filter.  Which also means there is likely other damage that you are not aware of.

I'd pass it by.  Unless you're an experienced mechanic, and happen to have a spare SL100 engine laying around, you'll likely end up spending more money than the bike is worth.