What is nu-chrome?

[Pedals2Paddles]

Reading a log book, it say "Cylinders nu-chromed by ACA" as part of the last major overhaul in 1991. What can ya'all tell me about nu-chrome?

 

[kgruber]

""""""NU-CHROME ®

The cylinder goes through the same process as channel chrome stopping at the point where the channels are created. At this time, the cylinder is removed from the chrome tank and honed. Silicon carbide is then mechanically induced onto the surface. This leaves the surface slightly abrasive, which results in a cylinder with lower oil consumption and faster break-in time."""""""

 

[Pedals2Paddles]

I read that. That doesn't tell me anything about it's long term purpose, pros, cons, etc.

 

[FORANE]

Dunno if Nu-chrome is the same as the chromed cylinders on my engine.
Disregard if this is not helpful...
My A&P advised cylinders are generally chromed when they no longer meet spec for simply honing. Chromed cylinders are more tolerant of infrequent operation as they are less prone to rust. They are more prone to blow by and perhaps the description for Nu-chrome purports to claim to be less so.

 

[flyingron]

To expound on what FORANE says, when your cylinders are worked they can be honed or even bored oversize to a point. If it is sufficiently warn you have to plate new metal on the interior surface. This is "chroming" because the alloys involved typically have a lot of chrome in them.

There are a number of brand name chroming processes such as Cermicrome, NU-Chrome,
etc... that add silicon-carbide additives to the process. This helps solve some problems straight chroming has. Good article here: http://www.avweb.com/news/reviews/182885-1.html?redirected=1

 

[Henning]

To expound on what FORANE says, when your cylinders are worked they can be honed or even bored oversize to a point. If it is sufficiently warn you have to plate new metal on the interior surface. This is "chroming" because the alloys involved typically have a lot of chrome in them.

There are a number of brand name chroming processes such as Cermicrome, NU-Chrome,
etc... that add silicon-carbide additives to the process. This helps solve some problems straight chroming has. Good article here: http://www.avweb.com/news/reviews/182885-1.html?redirected=1

Did they solve the problem of a weakened barrel and cracking at the Acme threads? That was the problem I saw 20 years ago with them, especially on TSIO-520s.

 

[Tom-D]

Chroming was a process that was used to return an old cylinder, that no longer could be bored over size and fitted with new over size pistons and rings.
We now have after market cylinders and both major engine builders manufacture new cylinders for the engine they still support. we need not used chromed anymore.

You can expect the chromed cylinders to either crack, or simply wear the rings out, and that should be the end of them.

IMHO they are junk.

 

[Henning]

Wearing the iron rings out on a hard chrome cylinder is actually the better option IMO than wearing the cylinder out with the chrome ring; pop of the jug, re-ring, reseat the new rings. Lots cheaper that way anyway. The problem I always saw was due to being bored to thin, not the surface.

 

[Pedals2Paddles]

So it sounds like this may be favorable if the engine spends or had spent a long time sitting without regular use since it can't rust. But of course does nothing to prevent the crank and camshaft from rusting...

 

[Henning]

So it sounds like this may be favorable if the engine spends or had spent a long time sitting without regular use since it can't rust. But of course does nothing to prevent the crank and camshaft from rusting...

Correct.

 

[Tom-D]

Wearing the iron rings out on a hard chrome cylinder is actually the better option IMO than wearing the cylinder out with the chrome ring; pop of the jug, re-ring, reseat the new rings. Lots cheaper that way anyway. The problem I always saw was due to being bored to thin, not the surface.

The big problem with chrome is the cylinders are old. old cylinders crack. Old cylinders that are chromed were at one time worn out, bored, then plated back to standard, to try to get one more run out of them. seldom happens with out problems.

In many cases the cylinder will not stop burning oil, we then pull it to see why, and fine the new rings worn out, several cycles thru this process maybe the cylinder will wear smooth and the rings will stop the oil usage. or not.
You never use a chrome compression rings in a chrome cylinder. the chrome to chrome wear will tear off the plating of both the ring and cylinder, and embed it into the bearing set, which will ruin the crank, and many of the gears in the engine.

You never use a stone in a chrome cylinder to smooth the chrome, it simply removes it. Take a hone stone to your bumper see what happens.

Try to imagine the cost of removing the cylinders and basically doing a top overhaul every 40-50 hours until you give up and buy new cylinders.

 

[Tom-D]

So it sounds like this may be favorable if the engine spends or had spent a long time sitting without regular use since it can't rust. But of course does nothing to prevent the crank and camshaft from rusting...

the ECI process "Nickel + Carbide" process does it better in new cylinders.

 

[FORANE]

The big problem with chrome is the cylinders are old. old cylinders crack. Old cylinders that are chromed were at one time worn out, bored, then plated back to standard, to try to get one more run out of them. seldom happens with out problems.

In many cases the cylinder will not stop burning oil, we then pull it to see why, and fine the new rings worn out, several cycles thru this process maybe the cylinder will wear smooth and the rings will stop the oil usage. or not.
You never use a chrome compression rings in a chrome cylinder. the chrome to chrome wear will tear off the plating of both the ring and cylinder, and embed it into the bearing set, which will ruin the crank, and many of the gears in the engine.

You never use a stone in a chrome cylinder to smooth the chrome, it simply removes it. Take a hone stone to your bumper see what happens.

Try to imagine the cost of removing the cylinders and basically doing a top overhaul every 40-50 hours until you give up and buy new cylinders.

I get the impression Tom does not like chromed cylinders. As someone who owns a plane that came with chromed cylinders, I agree with him. My O-320 with them is approaching 900 hours. I replaced one cylinder after it lost compression over WV. We put a new steel cylinder on. Oil consumption has remained high since new. Oil consumption got as high as 1 qt every 2 hour prior to the cylinder replacement. It currently uses about 1 qt every 6 hours. Given the choice I would not use chromed cylinders again.

 

[timwinters]

My engine (o-470) is all original, including the cylinders. They were chromed at the last overhaul and now have about 1,200 hours on them.

I "re-overhauled" one cylinder after about 100 hours due to a broken oil control ring. I'm pretty confident the overhaul shop screwed that one up when they installed that cylinder during overhaul.

I "re-overhauled" another at about 800 hours due to a worn exhaust valve guide.

I burn one quart every six to eight hours.

I'm happy with my engine.

The cylinder shop says these cylinders have one more run left in them. I'm not sure what I'll do when it's time to overhaul again. If it wasn't for the fact that they're original then I'd definitely go new but it's knda cool having a '58 that's all original.

At least I think it is.

 

[Pedals2Paddles]

This is one plane we're doing a pre-buy on right now. The nu-chrome was added in it's last overhaul (#2). I'm glad, since it had had a time of sitting around doing nothing. And understood that it won't help with the crank and cam. I do understand what the anti-chromers don't like it. I don't disagree either. But reviewing it, we'll probably need a major overhaul before the cylinders alone need work anyway.

 

[Tom-D]

two cylinders 7 hours apart, same engine same failure. this is not the head coming off, it is cracked in the barrel its self.

caused us to loose a crank, two rods, and a case.

 

[Tom-D]

For those who favor the chromed cylinders a question.

How do you know the steel barrel did not suffer hydrogen Embrittlement during the chroming process? and if it did was it removed?

 

[Pedals2Paddles]

Correct me if I'm wrong. The cylinder being old is what causes the failure. Not specifically the chrome. The chrome may allow someone to keep using a cylinder that would otherwise have been beyond rehabilitation. In which case, you may be on borrowed time.

 

[Tom-D]

The cylinder bore of a chromed cylinder,

 

[Tom-D]

Correct me if I'm wrong. The cylinder being old is what causes the failure.

That's the major concern, but not the only one.