Reworking Nikasil Cylinders

[earossi]

Inspection of my recently torn down P&C's found one cylinder that has a longitudinal score mark that is not only visual, but can be felt with my fingernail. Since my understanding is that it would be unacceptable to return this cylinder to service, I have been researching acceptable ways to rework the cylinder. There is a great deal of discussion in the archives about Nikasil and there are at least three companies out there that profess to have the skills necessary to rework these Mahle cylinders.

In particular, I have discussed the rework process with the folks at US Chrome who claim to have been in the business of reworking Nikasil cylinders for over 30 years. For this damaged cylinder, they will do a dimensional inspection of the cylinder to determine if it is still round and/or tapered. If out of spec, they would remove the Nikasil, restore the cylinder to its proper geometry and then replate the bore with a carbide coating (not sure if it is the same proprietary coating used by Mahle). Finally, they hone the finished cylinder to the proper diameter.

Research of past threads provided information that there may be an issue with the final roughness achieved from honing the finished bores of the reworked cylinder, in that the final finish may be overly rough which can lead to rapid premature wear of the new piston rings.

So, I would like to know what the history has been on this board of having premature ring wear due to such a rework and final finishing of cylinders that have been reworked and placed back in service.

My ultimate decision has got to be whether to just replace the cylinder with a new one or an in-spec used cylinder that simply only requires deglazing of the cylinder in order to accept new rings. What are your recommendations?

[Spenny_b]

Hi Ernie,

Can't, I'm afraid, offer any thoughts on the surface finish of the final hone process, but the whole subject of re-coating cylinders is unfortunately still a fresh wound for me.

I should add....I've not had a bad experience of the process itself - I never got that far, as the cylinders (Capricorn, not Mahle) I was sold by a supposedly reputable guy here in the UK, turned out to be great plant-pots/door stops/pen pots.

There's a company in the UK called Langcourts, and I believe they are either a franchise or a division of the parent company in the US. I was put in touch with the guy who runs the operation in the UK to assess these supposed good cylinders. Apparently he does something like 30k cylinders per year (lots of bike stuff), so definitely not something that's "off-piste" I would suggest.

You're right, they do absolutely measure for overall wear tolerance and ovality before doing anything. It was clear very quickly that mine were waaaay outside of spec, despite the vendor telling me he'd measured them and they were still well within spec.

My #6, I later found, had a 10mm long gouge towards the top of the stroke - ingress of something had wedged itself between piston and cylinder wall that the guy hadn't noticed (!). That was deemed fixable once the coating had been stripped. Unfortunately, mine had also suffered a "rucking" effect at the top 25mm of each bore, and the suspicion was that this wasn't just within the Nikasil but probably also damaged at the alloy level as well. With that and the ovality, there was too much machining deemed necessary to take a risk and re-work them.

I'm pretty sure that the guy I spoke with at Langcourts was very experienced in VW and Porsche stuff, in particular Mahle, so would be confident that they'd know what they're doing rather than giving me a nonchalant Gallic-shrug!

Cost would have been about £120 ($190) per cyl had we gone ahead....as it happens I also have another set of 97mm Mahles off of my 965 that were the original reason for the Capricorns being bought! Similar to you, had one with a very fine lateral scratch, and then was informed by "said reputable" engine guy that another cylinder had a couple of chips where the coating had come off...rather mysteriously....

Anecdotal and maybe not that useful, but if they were within serviceable limits, I more than likely would have gone ahead and done it....I may even have my 2 x Mahle cylinders re-done and then sell the set with pistons.

Cheers
Spencer.

[docrodg]

I asked a friend in near-senior management at Mahle here in the US about this before... he said that the Nikasil cylinders cannot reliably be reworked back to original. This was after he asked around. The pistons are still able to be done (I actually inspected the line that does Graphol coating), but the rework on the cylinders is a no-go.

[earossi]

Originally Posted by docrodg

I asked a friend in near-senior management at Mahle here in the US about this before... he said that the Nikasil cylinders cannot reliably be reworked back to original. This was after he asked around. The pistons are still able to be done (I actually inspected the line that does Graphol coating), but the rework on the cylinders is a no-go.

Not an unexpected statement from a company who has no vested interest in reworking old hardware. However, since there are at least three companies out there who claim to have reworked hard faced aluminum air cooled cylinders for a number of years, one woud expect that failures of their processes would have been well documented by now.

Specifically, US Chrome has been in business for over 30 years, and is now reclaiming plated cylinders for four cycle vehicles (cars, motorcycles, and outboard motors) and all types of two cycle apllications (motorcycles, snowmobiles and outboards).

Perhaps the Mahle executive could provide some reasoning to support his statement that reworks are not reliable. Or, can it be that the Mahle hardfacing is proprietary, and therefore unavailable to thrid parties? In which case, the hardfacing materials may, in fact, not be the original composition. There are hardfacings that may be a suitable replacement for the Mahle OEM coatings, which would validate the statement that the cylinders cannot be restored to "original".

Can someone else chime in here on this topic?

[TimT]

We use Millenium Technologies to bore and replate Nikasil cylinders and to have cylinders repaired.

[KTL]

Call Don over at EBS Racing and ask him his expereience with replating Mahle cylinders. I understand they've been providing this service for quite a while. Not sure if they do it themselves or sublet it to someone else.

I have a set of 98mm Mahle cylinders that came from my race car engine- 3.2 short stroke, 9.8 compression, Weber carbs. These cylinders have been in service for at least 6 years, as the engine was last rebuilt in 2005. The cyls are bored and replated 95mm SC cylinders. I believe that they are SC cylinders because they have the CE ring groove in them and are not cylinders that were 98mm from new. Steve Weiner has stated a number of times that the 98mm Mahles were never made with the CE groove in them. I can't imagine somebody would have put the CE groove in them, because the general consensus is that these rings really don't do anything anyway! But who knows.....

Anyway, my point of posting is that one of my cylinders had a 1 inch wide by 1/4 inch tall area of plating chipped off at the very top of the cylinder. I sent it to US Chrome last month and recently got it back. The cylinder was nicely reconditioned to my rather untrained eye. They stripped the cylinder and replated it, honed to spec. The original Mahle cylinders are honed too, if i'm not mistaken. Everybody selling their used cylinders always comments on the presence (or lack thereof) of honing marks still being visible

USC's order sheet asks you to specify the bore spec and also provide a piston to re-establish your desired piston-cylinder clearance. I did just that by measuring my cyls with a bore gauge to determine the existing bore diameter(s) and its ovality. Also measured my piston with a 3-4 in. micrometer to determine the existing P-C clearance. The cylinder I got back was exactly as I specified.

Since the rest of my cylinders would remain used and deglazed with a scotchbrite pad, I had the cyl. replated to the existing bore measurements.

Before
D1 @ dim a = 3.8592"
D1 @ dim b = 3.8587" ovality at upper area was 0.0005", well within 0.0016" allowance

D1 is meas'd 30mm below top edge of cylinder bore

dim a is diameter when looking directly into the cyl at its installed orientation (long fins down)

dim b is perpendicular to dim a

D2 @ dim a = 3.8589"
D2 @ dim b = 3.8592" ovality at lower cyl area was 0.0003"

D2 is meas'd at seat of cyl, where base gasket is installed.

After Replating by USC
D1 @ dim a = 3.8591"
D1 @ dim b = 3.8589" upper ovality = 0.0002" NICE

D2 @ dim a = 3.8592"
D2 @ dim b = 3.8588" lower ovality = 0.0004" Not bad.

So I got my cylinder back in the condition I wanted it- used/same wear dimensions as the rest of my cylinders and still well within spec. The cyls varied in dia. from 3.8586 to 3.8595 and max ovality at any one location was 0.0005" So they were in good used condition to begin with.

I don't have the ability to measure the surface roughness of the new plating. So i'll have to trust USC on this one. Do a search and you'll find a discussion on the use of different methods to re-hone a used cylinder. Henry and the guys did a nice job of describing the different methods they used and what their thoughts were on the resulting roughnesses. I recall that scotchbrite was a nice alternative to nothing at all, but not as good as proper Sunnen honing, and scotchbrite was MUCH better than subjecting the cylinder to the dreaded ball/grape hone.

Just my experience with one cylinder reconditioning. So take my results with a grain of salt, please.

[gregwils]

These guys are another option....Cylinder Repair, Head Repair, Cylinder Replating Services by Millennium Technologies

[earossi]

Originally Posted by KTL

Call Don over at EBS Racing and ask him his expereience with replating Mahle cylinders. I understand they've been providing this service for quite a while. Not sure if they do it themselves or sublet it to someone else.

I have a set of 98mm Mahle cylinders that came from my race car engine- 3.2 short stroke, 9.8 compression, Weber carbs. These cylinders have been in service for at least 6 years, as the engine was last rebuilt in 2005. The cyls are bored and replated 95mm SC cylinders. I believe that they are SC cylinders because they have the CE ring groove in them and are not cylinders that were 98mm from new. Steve Weiner has stated a number of times that the 98mm Mahles were never made with the CE groove in them. I can't imagine somebody would have put the CE groove in them, because the general consensus is that these rings really don't do anything anyway! But who knows.....

Anyway, my point of posting is that one of my cylinders had a 1 inch wide by 1/4 inch tall area of plating chipped off at the very top of the cylinder. I sent it to US Chrome last month and recently got it back. The cylinder was nicely reconditioned to my rather untrained eye. They stripped the cylinder and replated it, honed to spec. The original Mahle cylinders are honed too, if i'm not mistaken. Everybody selling their used cylinders always comments on the presence (or lack thereof) of honing marks still being visible

USC's order sheet asks you to specify the bore spec and also provide a piston to re-establish your desired piston-cylinder clearance. I did just that by measuring my cyls with a bore gauge to determine the existing bore diameter(s) and its ovality. Also measured my piston with a 3-4 in. micrometer to determine the existing P-C clearance. The cylinder I got back was exactly as I specified.

Since the rest of my cylinders would remain used and deglazed with a scotchbrite pad, I had the cyl. replated to the existing bore measurements.

Before
D1 @ dim a = 3.8592"
D1 @ dim b = 3.8587" ovality at upper area was 0.0005", well within 0.0016" allowance

D1 is meas'd 30mm below top edge of cylinder bore

dim a is diameter when looking directly into the cyl at its installed orientation (long fins down)

dim b is perpendicular to dim a

D2 @ dim a = 3.8589"
D2 @ dim b = 3.8592" ovality at lower cyl area was 0.0003"

D2 is meas'd at seat of cyl, where base gasket is installed.

After Replating by USC
D1 @ dim a = 3.8591"
D1 @ dim b = 3.8589" upper ovality = 0.0002" NICE

D2 @ dim a = 3.8592"
D2 @ dim b = 3.8588" lower ovality = 0.0004" Not bad.

So I got my cylinder back in the condition I wanted it- used/same wear dimensions as the rest of my cylinders and still well within spec. The cyls varied in dia. from 3.8586 to 3.8595 and max ovality at any one location was 0.0005" So they were in good used condition to begin with.

I don't have the ability to measure the surface roughness of the new plating. So i'll have to trust USC on this one. Do a search and you'll find a discussion on the use of different methods to re-hone a used cylinder. Henry and the guys did a nice job of describing the different methods they used and what their thoughts were on the resulting roughnesses. I recall that scotchbrite was a nice alternative to nothing at all, but not as good as proper Sunnen honing, and scotchbrite was MUCH better than subjecting the cylinder to the dreaded ball/grape hone.

Just my experience with one cylinder reconditioning. So take my results with a grain of salt, please.

Kevin,

Thanks so much for taking the time to put down the details of your experience with US Chrome. A good education for me and sets the expectations I should have.

One question, do you see any need to have had USC rework the remaining cylinders given that they appear to be within spec? I understand that you did not do it; however, I was wondering if by not doing all 6 barrels, will the "old" barrels age at a different rate than the reworked cylinder?

Also, did USC talk to you about coating the piston skirts? If they did, is there a reason you elected to not have them perform the work?

[Henry Schmidt]

We've been using Millennium Technologies for replating of cylinders without any issues.
We use them to plate both Nikasil and Alusil as well as Biral cylinders.
There are no new Mahle Biral cylinders available so restoring them became an imperative to maintain originally.
I don't give Mahle US much credit for having great answers to technical question.
Some years ago (3-4) I received a net set of Mahle 100s with one cylinder .004" out of round. I called Mahle Motorsport for their tolerance and to explain the situation.
Much to my surprise, his response was that they did not spec ovality simply interference measured by an air flow system.
When I explained that .004 was an unacceptable number by my way of thinking, his response was to "prang it". "PRANG IT ! WTF is that ?" He explained that I should whack it with a mallet. After the steam stopped coming out of my neck, I sent the set back with a request for a replacement set. They complied without hesitation and the replacement set was nearly perfect.

[tadd]

Another positive for millennium. I've had several awesome emails with a senior tech about the coating in response to alternative fuels. That they took the time speaks volumes. They have also coated two stroke motor bike cylinders for me that were not originally coated and did an amazing job.

Prang it... I love that. Gotta remember that one. Funny part is I can't tell you the number of highly specialized and expensive things that get 'final adjustment' with a hammer :-). Would you believe that the pit on a nuke is tweaked that way!

t

[AlfonsoR]

I don't have any experience with coating automobile type cylinders, but I have had some recip compressor cylinders coated. It actually doesn't work very well in that application, but my point is more about the process. The cylinder is first machined for optimizing adhession of the coating, then it is coated, then machined, then honed to the correct finish as required by the piston rings.

Henry is one of those guys that you can say has forgotten more than most of us will ever know. In this thread he gave some information regarding Mahle cylinder finishes. In post #40, bottom of page 2, Henry says that per Mahle literature, the finish is supposed to be 4.2 - 6.0 RA (roughness average). So this is my point, if you have the cylinders recoated, make sure the surface finish is correct.

do I need to hone this?

Incidentally, I tried to find the cost of a profilometer. Through MSC, you can buy a Mitutoyo for about $2,200. Or you can buy a Brown & Sharpe on e-bay for about $1,000.

[KTL]

Ernie,

I only did one cylinder because it had the plating chipped. Otherwise I would have reused the cylinders as-is w/out question. I did wonder about how the "new" cylinder would behave compared to the old ones. It's certainly plausible that the new cylinder will behave differently than the old ones.

That's why I decided to hit the old ones with a scotchbrite pad. I wanted to scuff them to increase the ability to seal the rings and also to try to mimic the same roughness as the new cylinder. I will scotchbrite the new cylinder as well. However, scotchbrite is only as effective as the base material. If the USC material is a notably different material than the Mahle material, then there's nothing I can do about that. We'll see

Regarding the piston coatings, I was lucky that my old pistons had already been coated on the skirts. I only have the experience with this one set, but it seems like the coating is worthwhile. I picked up a set of JE 10.5 pistons and i'm still debating if I should have the skirts coated...... The skirts on my old pistons seem to tell me that the stuff works. Hardly any wear on the coated areas, but easy to scrape off the coating. That tells me the coating does it's job when subjected to lubrication in the cylinder. This stuff must work because it has stayed in place for quite a long time. Again, I can easily scratch the coating off with light scraping pressure from a tool, like the anvils of my micrometer that rubbed off some of the coating when doing my measurements.

Alfonso,

Thanks for digging up that link. That is the discussion I was referring to in my previous post!

[docrodg]

Graphol coating is thin and put on like an ink. That is why it scrapes off easily.