R90/6 Cylinder Clean Up

[pstanfo4]

Hi All!

I'm relatively new to motorcycle maintenance and am in the middle of replacing the push rod seals on my 1974 R90/6. Once I got down to the cylinder and cylinder head things started to look a bit carbonized (see attached pictures). Is this something that should be cleaned up? If so, are there any recommendations on how to go about doing it? Thanks!

 

[robsryder]

One of the airhead gurus, Oak (now deceased) recommended a product called HydroSeal II to remove carbon from airhead engine parts.

https://gunk.com/product/gunk-hydro-seal-ii-heavy-duty-parts-cleaner-hs3/

I obtained some of this an have used it with success. It took me several weeks of soaking and periodic brushing of the carbonized surfaces to restore the parts to a clean looking condition.

I have heard some mechanics, unwilling to spend the few weeks soaking in HydroSeal II, indicate that a carb cleaner with wire brush was used to remove carbon. YMMV...

I purchased my first batch of HydroSeal II from a local autoparts store. I see that one can order it from Walmart's online website ...

https://www.walmart.com/ip/RADIATOR...DUTY-PARTS-CLEANER-MODEL-NUMBER-HS3/357731744

 

[20774]

I used Hydroseal in the past on my /7 engine...the slower process seemed safer to me. Snowbum mentions Gunk as well as Simple Green on this page for decarboning:

https://bmwmotorcycletech.info/pistons.htm

 

[stevenrankin]

Why Bother?

I am assuming you had a good running bike, and a compression test showed good results?

You are only replacing push rod seals because they are leaking?

Then why bother with cleaning up the carbon? In a few weeks, it will be back again. Really, you didn't have to pull the pistons out of the jugs to change the seals.

OKAY, I get some people need to inspect things when they have an engine apart and like things squeaky clean, I do myself sometime depending upon the task at hand.

I am sorry if I come off like a jerk but you made a bit more work for yourself than you needed to. So, at this time, take the chance to measure out things before putting it all back together and if you need a bore job, pistons and rings, now is the time to do it. Otherwise put it all back together and ride it until it starts burning oil or the compression drops and it starts to loose power.

Spring, summer and fall are for riding, winter is the time for rebuilding, at least in my neck of the woods. Where do you live, I am always willing to lend a hand, tools and a lift. Plus I have an retirement airhead shop owner near by for what I can't do. St.

 

[52184]

Soak the piston (crown down) overnight in a shallow bath of WD-40. Screw a sparkplug back into the head and with the valves facing up fill the combustion chamber with liquid WD-40 and soak overnight. If the carbon is quite thick it may take a second soak after gently removing the first layer. The WD-40 will soften carbon enough to make it easily removable without harsh tools and risk of scratching.

You can buy refill containers of liquid WD-40 at NAPA. Gunk Hydroseal also works well but is sometimes more difficult to source.

Best,
DeVern

 

[manitou_commando]

Toxic Stuff is, Well, Toxic

A few years ago, I dismantled my 1988 R100 at 100,000 miles. Sent the heads off to Ted P. The pistons were rather crusty with carbon.
I soaked the pistons in Simple Green Soap for a couple of days. Didn't touch them with a brush. The Simple Green simply dissolved the carbon.
It's non-toxic and environmentally benign.