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.

 

[GTRider]

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.

 

[htwashere]

Hello airhead gurus, may I piggy back on this thread to ask for similar advice. I am doing the top end re-seal for the first time. Previously I have done a compression test and the pressure is good and the bike does not seem to consume oil excessively. So I am hoping to leave everything alone and just do the reseal. I would like to follow various tutorials on leaving the piston head in the cylinder for this job. After the head is pulled, I performed the gasoline leak test and my valves look leak-proof so it feels like I don't really have to remove the valves either at this phase.

Looking at valves and pistons, the carbon deposits are quite heavy, so I am so tempted to clean them up . I can clean the valves but I don't think I want to mess with the pistons as I plan to leave them in the cylinders. This is what I have done so far on one side:

With the valves, I had pretty good success using oven cleaner and engine degreaser. But there are some stubborn deposits that won't come off. After reading/watching Brook Reams' and Airhead Barn's tutorials, I decided to use a buffing sanding wheel to take them off. The result is much better. But as I am doing it, I feel like I might be damaging the finish by making scratch marks into heads. Anyways, here are my questions:

1) I hope noone is crying foul that I am using oven cleaner? It seems to work really well - it takes off over 75% off with just one overnight soaking. My only worry is if it will do any longer term damage to the aluminum? For the 2nd head, I may try the Simple Green option first.

2) Should I continue the buffing to get off the remaining carbon? I'm reading @stevenrankin's answer above and he may have talked me out of it. But you know how it is, not cleaning while it is open just seems like a missed-opportunity?

3) Any advice what I should do with the cylinder head carbon? they look terrible as well, but I do not plan to pull them out of the cylinder.

Thanks for your time!. Some pics are attached.

 

[20774]

In Oak Okleshen's top end manual, he recommended Hydro Seal to soak the pistons in. I did that a while back and could generally easily removed the built up carbon.

IMO I would not use anything aggressive to remove the carbon...you could indeed by doing damage to the original metal.

I'm of the opinion that you're going to need to remove the cylinders. You have disturbed the seal of the cylinder base against the engine case. Shouldn't that seal be cleaned and refreshed? Not easy to do that by just sliding the cylinder out. I think you're 75% of the way there, just go ahead and do things up so as to not create any problems in the future.

YMMV.

 

[htwashere]

In Oak Okleshen's top end manual, he recommended Hydro Seal to soak the pistons in. I did that a while back and could generally easily removed the built up carbon.

IMO I would not use anything aggressive to remove the carbon...you could indeed by doing damage to the original metal.

I'm of the opinion that you're going to need to remove the cylinders. You have disturbed the seal of the cylinder base against the engine case. Shouldn't that seal be cleaned and refreshed? Not easy to do that by just sliding the cylinder out. I think you're 75% of the way there, just go ahead and do things up so as to not create any problems in the future.

YMMV.

"...I'm of the opinion that you're going to need to remove the cylinders": I meant that I will pull the cylinder out with the piston head left inside the cylinder. This way I do not need to worry about compressing the rings and putting the piston head back. Since the piston head is inside the cylinder, I am nervous of doing anything there in case I may scratch up the cylinder wall. Do you mean pouring the Hydro Seal into the cylinder head so the liquid will sit on top of the piston head inside the cylinder?

 

[20774]

You said you did a compression check...did you go a leak down test? This can tell more info about valve seating and ring seating. Sounds like you're comfortable with the valves. I guess I don't see what bike this is on. How many miles on the engine? You didn't say why you were doing this. If you had say 25000 miles on the bike, I might do what you're doing. If you had say 75000 miles on the engine, one could consider doing it all now. Otherwise you might be back doing this again in 30K+ miles. You won't get any info on the cylinder wear, things like ovality and runout, or if the rings have worn to their limits.

I probably wouldn't use the Hydro Seal unless you removed the pistons. I poured a layer of the chemical into a plastic container and put the piston face down into it...I let it sit a week. If you can't do it that way, I wouldn't be sure you could successfully rinse the chemical out.

 

[htwashere]

You said you did a compression check...did you go a leak down test? This can tell more info about valve seating and ring seating. Sounds like you're comfortable with the valves. I guess I don't see what bike this is on. How many miles on the engine? You didn't say why you were doing this. If you had say 25000 miles on the bike, I might do what you're doing. If you had say 75000 miles on the engine, one could consider doing it all now. Otherwise you might be back doing this again in 30K+ miles. You won't get any info on the cylinder wear, things like ovality and runout, or if the rings have worn to their limits.

I probably wouldn't use the Hydro Seal unless you removed the pistons. I poured a layer of the chemical into a plastic container and put the piston face down into it...I let it sit a week. If you can't do it that way, I wouldn't be sure you could successfully rinse the chemical out.

Yes sir, I did the leak down test, it is leak-proof (I will test the 2nd one soon). My bike is a '71 R75/5. I bought from a long-time owner with 80000 miles. The bike runs very well for its age but it has all the general leaks and deterioration. I am a first-time airhead owner and hoping to learn-by-doing as much as possible. At this stage with my limited experience and tools, I hope to tackle things that I can understand based on research. I do realize a complete overhaul will be needed again in the future.

I won't touch the piston heads based on your advice. Thank you for such quick response!

 

[20774]

By leak-down test, I was referring to the test of bringing the piston to TDC and injecting a certain pressure into the spark plug hole to see how much air leaks by the rings.

No matter, if you have good results otherwise, I sure hope that things go back together well and you get to riding soon!!

 

[80092]

Since you went this far check the Piston ring end gap. If close to service limit replace and properly lightly ball hone the cylinders.
And if you want to inspect further measure your piston spec and cylinder taper. It will only cost you alot more money for the tools. Or have an engine builder measure the cylinder and piston.
How many miles on the /6?

 

[htwashere]

Since you went this far check the Piston ring end gap. If close to service limit replace and properly lightly ball hone the cylinders.
And if you want to inspect further measure your piston spec and cylinder taper. It will only cost you alot more money for the tools. Or have an engine builder measure the cylinder and piston.
How many miles on the /6?

Good morning. Since my last posted thread, I took out the 2nd cylinder and noticed the valves are leaking :-(. So I have decided to send them to an engine builder to have properly serviced. The bike is over 80,000 miles, I am not sure if previous owner had done anything here so I may as well give it a proper treatment. Thanks for your advice!

 

[stevenrankin]

Hello, yeah, 80K is about right for a rebuild of heads, and as you say, the previous owner's record of maintaining it has a lot to do with wear. St.