Topic: Carbon deposit on pistons... is this normal?

[billdramp]

Hey folks,

I'm in the middle of my first engine build  on my 400four and when I took the head off... the pistons have what appears to be alot of carbon build up on the top of them... Is this normal?

Should I replace the piston because of this?

Any thoughts are appreciated.

Cheers,

Billy / PORTLAND

[kslrr]

Lots of carbon should be removed.  It can cause hot spots as well as raise the compression.  No need to replace pistons unless there is evidence that the pistons/cylinders are worn.  Use the end of a hack-saw blade to scrape off the carbon with the piston at Top-Dead-Center (TDC).

[paulages]

the pistons are already removed. you want more CR, right billy? 

[Gordon]

Clean the piston tops and clean the combustion chambers.  You'll be amazed at how much easier your bike starts when you're finished and how much better it idles. 

[75750SS]

Do it!  I noticed an improvement (idle and throttle).  Scrape what you can off the heads and pistons.  You can use ATF to soften the crud.  Permatex gasket remover works too.  I sprayed into the intake and exhaust ports.  It turns into a black slime, just blow out with carb cleaner.  To help clean out the exhaust ports, I bought a couple of copper brushes, the kind used to clean a gun bore (32 caliber and 12 gauge), which can attached to a drill. Used compressed air to blow out the dust.

[vintage_racer]

If jetting and ignition are right, a heavy buildup of carbon indicates a problem of some sort such as low compression. Inspect the bores and rings before putting the motor back together.

Dan

[BobbyR]

You can boil off most carbon in boiling water. Scub what is left over using one of the above methods.

[edbikerii]

I've found kerosene to work pretty well at dissolving carbon deposits too.

[aptech77]

Run some Seafoam to keep it under control.....

[sparty]

Hey folks,

I'm in the middle of my first engine build  on my 400four and when I took the head off... the pistons have what appears to be alot of carbon build up on the top of them... Is this normal?

Should I replace the piston because of this?

Any thoughts are appreciated.

Cheers,

Billy / PORTLAND

You bet! It is normal for a 30 year old bike to have carbon on the pistons.  After 30 years piston rings would be worn just from heat cycling alone.  You may have oil blow-by which caused the carbon build up.  It could also be too rich of a mixture.  If your bike is a "short tripper" carbon buildup will occur more easily.  Your bike most likely ran leaded fuel in the old days, so that could also cause the build up.  Today's gas is much cleaner to burn.

Clean the pistons, inspect for damage, install new rings, etc.

Sparty