Is muriatic acid really safe on chrome cylinders? (and other newbie questions)

[Einsame Hirte]

Greetings! I've been searching the net for answers, and this seems to be the place for the chainsaw gurus.

I'm new to small engine work, and I'm learning on an old Shindaiwa 577 that was given to me because it won't start. Rebuilt the carb with no luck, then checked compression - 86 lbs dry and 134 wet. Pulled the exhaust and saw the piston was scored (I don't know enough to qualify how badly). Pulled the cylinder and found a bunch of transfer on the exhaust side. Intake side was pretty spotless, which apparently suggests it was running lean, so I guess I should vac test it later if I get that far.


(Image 1. Cylinder after only some light sanding with 320 grit and crocus cloth)

I did a bunch of research on how to clean the transfer off the cylinder, and a lot of sources (including a couple of posts here) say that muriatic acid works well and is safe on both nikosil and chrome plated cylinders. This one is chrome, so I gave it a shot, and it did remove most of the transfer except for a couple of stubborn spots. However, the swabs kept picking up a bright green color that wasn't described in the sources I found. This is the color of chromium chloride, and suggests that the acid is reacting with the cylinder lining in addition to the aluminum. A little more research found that muriatic (hydrocholoric) acid is actually used when deliberately removing chrome plating.

(Image 2. Cylinder after an hour or so of acid swabbing - only heated it with an air gun a couple times; I wanted to keep the reaction rate under control, especially when I realized it was etching the chrome).

(Image 3. View through a microscope at the chunk of transfer below the exhaust port)

The lining does definitely look etched, and it has a "silky" texture to on the finger, compared to a "glassy" texture on the (untreated) intake side.

So, the questions are basically:

1) Is the etching just a "cost of doing business" when using acid?
2) How badly damaged is it? Or does the etching even hurt it? ("maybe it even helps retain oil better?", he asks hopefully)
3) How should I proceed to get the rest of the transfer off? The acid is working, but slowly, and I don't know if I should risk etching the surrounding area more.
4) The chunk featured in the third photo above is very noticeable when rubbing it with a finger (or fingernail), but it is below the exhaust port so it shouldn't directly affect compression. Is there still a risk it will catch on a (new) ring and damage it?
5) The largest remaining streak above the port is only barely perceptible as a slight roughness under a fingernail. Just how clean does it need to be?

(Image 4. Piston after some sanding and polishing. The rings weren't completely welded, but the top one was a bit stuck, although I got it out without breaking. It's still obviously scored, but what concerns me the most is the nick above the top ring, which lines up with the streak above the port in image 2)

6) Is it correct that the piston itself doesn't contact the cylinder in normal operation? That is, the rings keep it spaced away from the walls? If so, then how critical is a little scoring, as long as it's sanded down and doesn't extend past the normal radius of the piston?
7) Given the condition of the cylinder, should I bother getting a new piston, or just new rings? An OEM piston is about $26 naked, which is worth it if it will make a difference and the cylinder is still good, but this is just a project saw and isn't likely to be run hard - we use late-model Stihls for most work clearing downed trees around the property, so this would be just a backup.

Thanks in advance for any input you guys have!

Edit: Typos

 

[tomalophicon]

Greetings! I've been searching the net for answers, and this seems to be the place for the chainsaw gurus.

I'm new to small engine work, and I'm learning on an old Shindaiwa 577 that was given to me because it won't start. Rebuilt the carb with no luck, then checked compression - 86 lbs dry and 134 wet. Pulled the exhaust and saw the piston was scored (I don't know enough to qualify how badly). Pulled the cylinder and found a bunch of transfer on the exhaust side. Intake side was pretty spotless, which apparently suggests it was running lean, so I guess I should vac test it later if I get that far.


View attachment 913750(Image 1. Cylinder after only some light sanding with 320 grit and crocus cloth)

I did a bunch of research on how to clean the transfer off the cylinder, and a lot of sources (including a couple of posts here) say that muriatic acid works well and is safe on both nikosil and chrome plated cylinders. This one is chrome, so I gave it a shot, and it did remove most of the transfer except for a couple of stubborn spots. However, the swabs kept picking up a bright green color that wasn't described in the sources I found. This is the color of chromium chloride, and suggests that the acid is reacting with the cylinder lining in addition to the aluminum. A little more research found that muriatic (hydrocholoric) acid is actually used when deliberately removing chrome plating.

View attachment 913751(Image 2. Cylinder after an hour or so of acid swabbing - only heated it with an air gun a couple times; I wanted to keep the reaction rate under control, especially when I realized it was etching the chrome).

View attachment 913756(Image 3. View through a microscope at the chunk of transfer below the exhaust port)

The lining does definitely look etched, and it has a "silky" texture to on the finger, compared to a "glassy" texture on the (untreated) intake side.

So, the questions are basically:

1) Is the etching just a "cost of doing business" when using acid?
2) How badly damaged is it? Or does the etching even hurt it? ("maybe it even helps retain oil better?", he asks hopefully)
3) How should I proceed to get the rest of the transfer off? The acid is working, but slowly, and I don't know if I should risk etching the surrounding area more.
4) The chunk featured in the third photo above is very noticeable when rubbing it with a finger (or fingernail), but it is below the exhaust port so it shouldn't directly affect compression. Is there still a risk it will catch on a (new) ring and damage it?
5) The largest remaining streak above the port is only barely perceptible as a slight roughness under a fingernail. Just how clean does it need to be?

View attachment 913757(Image 4. Piston after some sanding and polishing. The rings weren't completely welded, but the top one was a bit stuck, although I got it out without breaking. It's still obviously scored, but what concerns me the most is the nick above the top ring, which lines up with the streak above the port in image 2)

6) Is it correct that the piston itself doesn't contact the cylinder in normal operation? That is, the rings keep it spaced away from the walls? If so, then how critical is a little scoring, as long as it's sanded down and doesn't extend past the normal radius of the piston?
7) Given the condition of the cylinder, should I bother getting a new piston, or just new rings? An OEM piston is about $26 naked, which is worth it if it will make a difference and the cylinder is still good, but this is just a project saw and isn't likely to be run hard - we use late-model Stihls for most work clearing downed trees around the property, so this would be just a backup.

Thanks in advance for any input you guys have!

Edit: Typos

I don't know much about your questions but can say the 577s are definitely a very good saw and worth fixing up.
If I were in your shoes I'd get the cylinder as smooth as possible and pay the money for a new piston.
Tom.

 

[JOE.G]

Acid will eat the aluminum, after that do a light hone, the cylinder is plated I believe so be careful and use the correct hone. Cylinder needs to be clean and smooth. New rings and new piston are a must in my opinion.

 

[Vintage Engine Repairs]

1) Is the etching just a "cost of doing business" when using acid?
Never use acid. You don’t know if the cylinder plating is damaged under the ally transfer. That’s a sure fire way to damage a perfectly reusable cylinder

2) How badly damaged is it? Or does the etching even hurt it? ("maybe it even helps retain oil better?", he asks hopefully)
The cylinder transfer originally wasn’t bad, some green scotchbrite or 320 grit paper along with a healthy dose of patients is all that would have been needed.

3) How should I proceed to get the rest of the transfer off? The acid is working, but slowly, and I don't know if I should risk etching the surrounding area more.
As above, scotchbrite or 320 grit sic

4) The chunk featured in the third photo above is very noticeable when rubbing it with a finger (or fingernail), but it is below the exhaust port so it shouldn't directly affect compression. Is there still a risk it will catch on a (new) ring and damage it?
I have run a few saws with damaged plating, just make sure the transition / step isn’t noticeable. Use a dremel to carefully remove any step in the plating for a smooth transition

5) The largest remaining streak above the port is only barely perceptible as a slight roughness under a fingernail. Just how clean does it need to be?
If it’s transfer remove it, it needs to be gone.
(Image 4. Piston after some sanding and polishing. The rings weren't completely welded, but the top one was a bit stuck, although I got it out without breaking. It's still obviously scored, but what concerns me the most is the nick above the top ring, which lines up with the streak above the port in image 2)
Use a file to gently remove any burr or high spots

6) Is it correct that the piston itself doesn't contact the cylinder in normal operation? That is, the rings keep it spaced away from the walls? If so, then how critical is a little scoring, as long as it's sanded down and doesn't extend past the normal radius of the piston?
I have ran two saws with very noticeable scoring having carefully filed the high spots and cleaned the cylinder. It’s not ideal, but it won’t damage anything.

7) Given the condition of the cylinder, should I bother getting a new piston, or just new rings? An OEM piston is about $26 naked, which is worth it if it will make a difference and the cylinder is still good, but this is just a project saw and isn't likely to be run hard - we use late-model Stihls for most work clearing downed trees around the property, so this would be just a backup.
If your compression tester is accurate, that’s low. A new set of rings is worth a try. If the piston to wall clearance is within spec and there isn’t excessive skirt wear you may be able to reuse it.

 

[Woodslasher]

If a piston is $26, I'd say get a new one. If it was like the Hilti chop saw I just looked at and the piston was $176, I might try salvaging it but for $26 it just isn't worth it in my book.

 

[J D]

Take a bit of rod & cut a slot in the end of it, slot a strip of ~400 grit sand paper in it & put it in a drill so it winds it up & then use it in the drill to polish the inside of the cylinder. Can do the same with scotch pad you just need a wider slot.
After that, if it were mine I'd probably finish tidying up the piston, put it back together, measure squish & delete/replace gasket to get it down around .020. If that gives it decent compression pressure/vac test it & see how it goes. If it didn't run ok after a couple of tanks or lacked compression I'd put the new piston & a set of caber rings in it

 

[drf255]

Plating don’t look so hot. I use acid often, in combo with sanding. Nickel chloride is green also, and I get it on the qtip when I use acid. I spot treat with acid and neutralize quickly.

Acid isn’t quite as perilous as people make it out to be. It’s like any other tool if used correctly. Soak a rag in HCL and sticking it in a cylinder overnight probably wouldn’t work too well.

 

[J D]

If you prefer to use chemicals I use sodium hydroxide (aka caustic soda, aka lye).
Bung up the ports to protect the aluminium cylinder & use some foaming or gell oven cleaner to cover the area, let it sit for an hour or so then scrub with the scotch pad. Repeat untill clean.
WEAR GLASSES AND GLOVES! That stuff is just as corrosive as HCL to organics (like you)

 

[JOE.G]

This procedure is very common in the snowmobile world, I would not reuse that piston especially at $26 dollars and I would not re use the rings, Any time I pull a piston I use new rings unless I just put it together, At least check the ring gap .

 

[bwalker]

The problem with using a piston that's sanded on is you May open the piston to wall clearance enough to cause rocking in the bore, which will lead to skirt cracking with cast pistons.
I can't speak to Shindaiwa parts, but pistons are generally not to expensive.
As for using acid on the cylinder. I don't know the first thing about Chrome cylinders, but with nickle matrix plating I have done it safely more than a few times. As others have said just take easy and use as little acid for the shortest time possible.

 

[Einsame Hirte]

Thank you everyone for the advice, and especially Guadaost for the detailed answers. Tomalphicon's comment convinced me that it's a decent enough saw to spend some money on (most people I talk to IRL here have never even heard of Shindaiwa), and I went ahead and ordered a complete piston kit for $70. The bearing and pin look good, but it wasn't much more than the piston, rings and gasket individually.

I am concerned about the erosion on the lining, and the fact that it seemed to be eroding more than patches of transfer, which kept a shiny finish. Is it possible those are actually steel or some other alloy from the rings instead of aluminum? The one streak extends clear up to the top of the cylinder, right about where the upper ring would stop, I think. I got it smooth to the touch now with some extra sanding, although I couldn't get rid of the spots entirely; I'm really worried about doing more damage.

When I was trying to figure out how to deal with this, I kept finding competing arguments between sanding and using acid; a number of sources talked about the dangers of sanding. I ended up using the acid because it was allegedly wouldn't touch chrome, although now I don't think this is true, as the shot through the microscope shows. Nikosil might be more resistant, but just in case someone comes across this thread doing a similar search, I'd be very careful about using it on chrome. It does take the light transfer off pretty easily, but I think I may have overdone it and wish I'd spent more time sanding down the tough spots carefully. I was also thinking of using Oven Off (sodium hydroxide, as JD suggests), but apparently that is also used to remove chrome plating, so the same concerns would apply.

We'll see how it works out in a couple weeks, and I'll post an update. A new cylinder is $175 or so, and that probably isn't worth it.

BTW, can any Shindaiwa experts put an age estimate on this saw from the logo (see the profile pic)? Most of the 577s I've seen on the net have a logo without the sweeping curve between the name and the number; I assume that is a newer design. Oh, and that pic is from before I touched it - I did clean it up before I started working on it

 

[bwalker]

If you are really concerned you can always get the cylinder nicisiled.

 

[sean donato]

No offense, but if your unsure about the plating quality of the cylinder, I'd just replace it. $250.00 total to get a decent saw up and running is a drop in the bucket and less then half the cost of any new semi or pro level saw. Job done and having confidence that it will last is worth more then pinching a penny to save a questionable cylinder. Now mind you I have used some pretty nasty cylinders that ended up running just fine.

 

[bwalker]

If I had a a bad cylinder I would replace with nicisil in heart beat provided it was similar money. Nicisil is better than chrome plating.

 

[iowagold]

i guess we have always done the cyl and the piston and rod as a set if we are rebuilding a $1k or more valued saw.
as well as the bearings and seals as a kit.

you can get a lot of time in rebuilding what you have....
for us time is money....
down time is a big thing as well...

 

[J D]

I was also thinking of using Oven Off (sodium hydroxide, as JD suggests), but apparently that is also used to remove chrome plating, so the same concerns would apply.

Sodium hydroxide will react with the chrome extremely slowly, only concern would be the aluminium of the cylinder but you can cover that. When it is used to remove chrome it is done at temperature with a voltage applied or it would take forever

 

[82F100SWB]

Acid works in seconds if not minutes. For saws I use a qtip, sleds we would pour it on, but both are done with running water available and it gets removed almost immediately after application. You do not let it soak for extended periods of time.

 

[Bob Hedgecutter]

Acid works in seconds if not minutes. For saws I use a qtip, sleds we would pour it on, but both are done with running water available and it gets removed almost immediately after application. You do not let it soak for extended periods of time.

Most sensible answer yet!

 

[LogSawyer74]

Fill up a 5 gallon bucket with water. I only use acid on the heaviest parts of the transfer. Use a Q-tip to dap it on and let it bubble. Sometimes rub it in with the Q-tip. After 30 seconds, dunk it in the bucket to immediately stop the reaction. Do a little sanding, and hit the heavy spots with acid again if necessary. I tend to use the sanding for the thinner areas of transfer, and only acid for the thick spots to get it down enough to finish it off with sanding. Give the cylinder a thorough rinsing afterwards. Works good for me...

 

[Yotaismygame]

Plating don’t look so hot. I use acid often, in combo with sanding. Nickel chloride is green also, and I get it on the qtip when I use acid. I spot treat with acid and neutralize quickly.

Exactly how I do it. Takes maybe 20-30 minutes.