Motorcycle Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
Hi, I have a cbf125 2009 9k miles, it has always ran sweet as a nut besides the sart up. Ever since I bought it, it
never run for over 1 minute after its started it would just loose revs and then eventually die. But once its hot it
would never die and ran fine. So after searching for a few answers I found that the problem could be the tappets being
way to tight and not alowing cold air to come through? Anyway after much research I set out to adjuest the tappets.
The first time I did it it wasn't right but I found that out before I started the engine. The second time im fairly sure I
I have adjusted them pretty damn correctly. However now when I start the engine the is a small tapping noise (loose
tappet?) and an irregular 3 beat tap. Its hard to expain but basically the tappets are rattling I thing. The rattling
noise only ever happened after I atempted to adjust them. On the plus side the engine now doesn't cut out which is
what I set out to achieve so I guess something good came out of it. Im going to try and fix it with any suggestions
tomorrow and if not reluctantly take it to my local dealership to get it sorted. Thanks :) btw this is my first post so sorry for anything I have done wrong :p
 

·
Member Map
Joined
·
23,909 Posts
It is normal for the valve train to make some noise. I probably do 2-3 valve adjustments a day in the winter months, so the ear becomes tuned to hearing which ones are out of spec.

The only way to tell for sure is to adjust them to the factory specifications found in the service manual. Make sure the rockers are floating free (Top dead center is the most handy engine position) and double-check the clearance after everything is tightened down.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #3
I have adjusted the exhaust valve to 0.12mm and the second valve to 0.08mm. Which are the factory specs. Before I touched the valves my bike had no rattle or any weird engine noises and now after loosening the extremely tight valves that had no movement ( was in TDC as checked for the T mark and the o mark as specified by my manual ) Just cant figure out how adjusting them to exactly what the manual says would make them rattle loudly. Unless i've been stupid and done something very wrong haha. How much does a standard mechanic charge for sorting this out if worse comes to worse?
 

·
Member Map
Joined
·
23,909 Posts
Did you make sure you weren't 180 degrees off on the timing marks? To be sure, I usually remove the valve covers and turn until the exhaust valve opens and closes, followed by the intake valve, then give it a little more turn until the timing marks come into view.
 

·
Premium Member
Joined
·
7,622 Posts
Tappets

My first thought is you are adjusting them when the piston and camshaft are in the wrong position. There can be two top dead centers. One for when the plug fires, or the compression stroke, and one for the exhaust stroke.
Be careful not to get your thousanths of an inch, mixed up with fractions of a mm.

Unkle Crusty*
 

·
Registered
Joined
·
4 Posts
Discussion Starter #6
Dodsfall - I watch a video tutorial by someone with a cg 125 and seeing as the cbf is based from the cg I assumed the engines must be fairly similar (to an extent).

On the small sprocket with a chain on the inside of the engine there is a 'o' marked just above and left of the horizontal line that needs to be horizontal to the engine cover. I have read that the o can either be up and left of below and right of the horizontal line so im having trouble gauging which potion it should be in. Apparently it's to do with which way on it was assembled in the factory?

I have tried the screw driver in the spark plug hole 'techinque' and for some reason im stiff finding it hard to understand when its the compression stroke and the exhaust stroke. This is my first time doing any sort of mechanical work involving the top end of an engine and with the valves so sorry if I seem very bewildered by eveything :p

Unkle crusty I think I may be too. Before I started adjusting anything with the 'o' above the line and the T lined up with the groove (meaning it should be in TDC) the vavles were extremely tight and took a while to un do the little adjusting part. However when rotating it a further 180 degrees (so the 'o' is below the line which is not stated in the manual) the valves move a fairly large amount. Any ideas or is a video needed?
 

·
Premium Member
Joined
·
7,622 Posts
Valves

Piston going down, inlet valve opens letting in fuel and air. Piston goes to bottom dead center and starts coming up. The inlet valve closes sometime before TDC on this compression stroke. The plug fires moments before DTC.

Piston goes down on the power stroke and rises. The exhaust valve opens before the piston reaches TDC on the exhaust stroke and blows out the gases.

Digging into the memory banks here. There is likely quite a lot of overlap with this engine. As in both valves can be open a bit at the same time.

Be careful with the screwdriver in the hole, as the engine may turn faster than planned, and kick it out rather faster. i did it with a needle on my 650 BSA and it hit just above my eye. So turn the crank slowly.

I think you are going to get this thing figured. The valves / tappets should not have been much out of adjustment initially, so should not have required many turns on the adjusting screw. Sometimes when you tighten the locking nut, the clearance changes. It takes a bit of practice.

A couple of actual mechanics may have something to say as well.

Unkle Crusty*
 

·
Member Map
Joined
·
23,909 Posts
I have tried the screw driver in the spark plug hole 'techinque' and for some reason im stiff finding it hard to understand when its the compression stroke and the exhaust stroke.
Use the technique I explained above. It's pretty fool-proof.
 

·
Premium Member
Joined
·
5,476 Posts
Use the Dodsfall technique with the spark plug out, of course, or it will make the engine fight you, because of the compression.
 

·
Registered
Joined
·
3,162 Posts
http://www.dansmc.com/valveclearence.htm

So here is the Dodsfall way with a full explanation. The author also explains why a little loose is better than too tight.

Other types of valves are covered as well. Overall,dans is a really good reference site and is a good complement to a service manual and the good people here at motorcycleforum.
 

·
Member Map
Joined
·
23,909 Posts
I replaced the intake valves on 3 TW200's this week. The top of the valve stems were starting to mushroom. It's kind of a mystery as to why, beyond my suspicion that once they started to flatten out a little, it became a chain reaction increasing the damage. All of these were pretty noisy when test run beforehand.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #12
Hey guys thankyou for all the help. I rotated it 180 degrees from where I had been originally adjusting them (the place where my manual said to) and did it the opposite way to that. Just started my bike and she sounds nicer than ever. You can here a little tapping of the valves (where it was silent before) but its not obtrusive now. And it also solved the problem of it not idling whilst cold. Thanks to all the help from everyone :)
 
1 - 12 of 12 Posts
Top