De-coking heads and pistons intervals

[mimmo66]

The question of how often would you open up your engine for cleaning up the carbon deposits come to me when I had my heads off at 25k miles due to a valve recession.

I was surprised to see all the carbon deposits all over the head as well as on the piston, and comparing it  to my Jap bike of the earlier 90's I had in Italy with 60k miles on it when we opened her up  I have never seen anything like it before.

Perhaps these engines need more attention, or perhaps the gasoline
in North America just runs dirtier.

How often do you feel is a reasonable interval for cleaning heads, valves and pistons, and what do you think causes these large carbon deposits?

I use my engine in the 4/6 thousand rpm range most of the time with 91 octane gasoline; at 50k miles now I almost feel the need to do some deep cleaning!

Thank you,
Domenico

[Bob_Roller]

I had the heads off of my '81 in 1998 to have the valves and seats replaced due to valve recession, that was at around 45,000 miles .

Didn't do anything but a quick scraping of the piston crown with a plastic scraper, put it back together and haven't gotten concerned about doing it again .

The bike now has 84,000 miles on it .

The deposits are just combustion by-products, not much you can do about it .

I've tried fuel treatments, the only one that may have removed some of the deposits, is Regane manufactured by Gumout I believe .

[Semper Gumby]

I don't think you need be concerned by this.

But if it really bothers you -- you can connect some fish tank clear hose to the vacuum connection on the bottom of your carb and let it suck clean water out of a bottle while it runs.  This will soften the carbon  buildup in the heads and help blow it out when you rev the motor.  Other than that I wouldn't open a head unless it had other problems like -- valve recession, sticky/broken valve, low compression, and piston slap.  

I saw a mechanic doing this to a BMW 2002 back when I was in high school at the gas station I was working at in CT.

TTFN,

[mimmo66]

It's good to learn that the engine will not suffer from it, and that I should not be too much concerned.

I was comparing the carbon deposits between a vtwin Suzuki VX800
with circa 60k miles on it  to the Airhead which resembles more like a two stroke engine.

In the Jap bike, almost no deposits whatsoever, the Airhead at 25K miles was quite the opposite.

I've heard of people rerouting the crankcase oil breather from going into the carbs.
Perhaps this oil going through the carbs into the combustion chamber add up to these excessive build-up??

Just an hypothesis.

Domenico

[Barry]

In the Jap bike, almost no deposits whatsoever, the Airhead at 25K miles was quite the opposite.

While I agree with the view that the carbon is not a major concern I think you make avery good point in the comparison with the VX800.

The difference can only be down to accuracy of carburetion or burning oil.  The VX800 must have had very well set up carbs that didn't run  overly rich and didn't burn any oil. An Airhead probably runs richer at some point certainly when using the choke and is always going to burn some oil from the crankcase breather.

The only concern from carbon deposits is it's going to raise the compression a little and might cause pinging.  I know if mine is going to ping it will always do it on the left cylinder because I burn more oil on that side and have more deposits. Why is another story as I don't use the side stand.
 
I keep thinking about trying the water injection cleaning method and will do it one day.

[Crossrodes]

I don't believe my bike burns much oil however it certainly cokes up quickly in spite of tuning the carbs, timing etc.  Next time I think I'll try the water idea.