pitted Nikasil coated cylinders

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Pits are not the same as ring gaps Jim, a ring gap is constant for the entire stroke, thus possibly allowing pressure loss. However, the rings will pass a pit SO fast that there will be no detectable pressure loss.

But as you say, it would of course be preferable not to have pits, and I’m sure John’s billet barrels will be totally pit free !
 
Fast Eddie said:
Pits are not the same as ring gaps Jim, a ring gap is constant for the entire stroke, thus possibly allowing pressure loss. However, the rings will pass a pit SO fast that there will be no detectable pressure loss.

But as you say, it would of course be preferable not to have pits, and I’m sure John’s billet barrels will be totally pit free !
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Agreed - a pit is not the same as a ring gap, but there are many many pits. People don't like them - even if the problem is only cosmetic.

I got involved in this because I was offered a set before I knew about the pits. And it was suggested that I could re-sell them. Then I saw the pits as shown on the Norton Commando FB page - the comments about the pits were totally negative. Now I wouldn't feel comfortable about selling them to someone else if they were as pitted as in the photos.
 
jseng1 said:
Agreed - a pit is not the same as a ring gap, but there are many many pits. People don't like them - even if the problem is only cosmetic.

I got involved in this because I was offered a set before I knew about the pits. And it was suggested that I could re-sell them. Then I saw the pits as shown on the Norton Commando FB page - the comments about the pits were totally negative. Now I wouldn't feel comfortable about selling them to someone else if they were as pitted as in the photos.
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Completely understandable.
 
I have had several Niksil coated alloy barrels go thro my fingers, the wose fault was the bore became worn, never saw any pits.
It seems to me that someone in manufacturing these didn't grind the bore prior to plating the bore, if they did the fault would have been obvious, so they plated it anyway.
 
As a TZ750 sidecar driver, for over 18 years now, we have found that you can only nikasil aluminium barrels 3 times, after that the coating, may or may not take. This is due to the nikasil process. This became such a problem, that we now use Fahrons Nikasil liners in our TZ barrels, after which, we have found we get twice the mileage before the barrels need re doing, than we did before when we just sent them to Lancourt for re nikasiling. After the experiences with the TZ,I would not entertain using Alloy barrels without liners in them,they are just not worth the potential hassle.
 
tonybsa said:
This became such a problem, that we now use Fahrons Nikasil liners in our TZ barrels, after which, we have found we get twice the mileage before the barrels need re doing, than we did before when we just sent them to Lancourt for re nikasiling. After the experiences with the TZ,I would not entertain using Alloy barrels without liners in them,they are just not worth the potential hassle.
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Where do you get those Fahrons liners?
 
I had pitting in an Audi bore from coolant leaking into the note and causing rust. The problem it had was oil burning, oil gets into the pits when the rings are at TDC and then this oil gets burnt during the combustion as the rings move down the note exposing the oil in the pits.
 
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Looking at this slightly differently, surely imperfections like the pitting shown, overtime could cause bigger problems such as failing of the coating?
Similar principle to a nick, say in a Conrad causing a potential weak point.
I certainly would have sent them back.
 
kommando said:
I had pitting in an Audi bore from coolant leaking into the note and causing rust. The problem it had was oil burning, oil gets into the pits when the rings are at TDC and then this oil gets burnt during the combustion as the rings move down the note exposing the oil in the pits.
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That makes sense - oil gets into the pits when the piston is up and is not scraped away by the rings when the piston desends - so the oil is burned along with the gasoline. Thousand of times per minute. This is something everyone should know about.
 
I wonder if carbon deposits may close pits in the TGA coated barrels eventually? It would be interesting to examine some of their barrels after say 3000 miles / 5000 km.

-Knut
 
tonybsa said:
As a TZ750 sidecar driver, for over 18 years now, we have found that you can only nikasil aluminium barrels 3 times, after that the coating, may or may not take. This is due to the nikasil process. This became such a problem, that we now use Fahrons Nikasil liners in our TZ barrels, after which, we have found we get twice the mileage before the barrels need re doing, than we did before when we just sent them to Lancourt for re nikasiling. After the experiences with the TZ,I would not entertain using Alloy barrels without liners in them,they are just not worth the potential hassle.
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Found that out on my RZ.
 
For some reason the original photo of the cylinders died. So here it is again. Another problem is that Andy's cylinders use odd threads. This locks the customer out of using available high strength US coarse thread reduced shank bolts that stretch (instead of loosening and pulling out alum cyl threads when the alum head expands/contracts over many heat cycles as well as brutal large displacement stress).

pitted Nikasil coated cylinders
 
Time Warp said:
I never did see (at the time) the manufacturer or a full picture of that cylinder so maybe like a lot of FB posts a pinch of salt is in order.

My Moto Guzzi has replacement Nikasil cylinders which are perfect and have sold by the thousands (Gilardoni)
They are cast so there must be a way.

View attachment 78573
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I bought a brand new pair of Gilardoni cylinders back in the 90's and one of them arrived with small pockets on the walls. It was the only time I've ever heard of it happening.
 
jseng1 said:
For some reason the original photo of the cylinders died. So here it is again. Another problem is that Andy's cylinders use odd threads. This locks the customer out of using available high strength US coarse thread reduced shank bolts that stretch (instead of loosening and pulling out alum cyl threads when the alum head expands/contracts over many heat cycles as well as brutal large displacement stress).

pitted Nikasil coated cylinders
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That seems to have been a common choice among alloy cylinder makers. Dunstall cylinders required the use of non-standard fasteners, although not changed to meteric. Later makers, including Robertson (whose cylinders I imported and sold for a number of years) and Maney used a combination of metric head bolts and British thread studs. They stuck with the original thread forms on the studs to be compatible with stock cylinder head threads. From what you've said, I'm guessing that Andy Molnar's cylinders are also using metric head bolts, right? The change is understandable. Most countries are on the metric standard, with high quality fasteners readily available pretty much everywhere. And in the case of the cylinder head bolts, the stock fine thread bolts would not be a good choice for use in the alloy cylinders.

Ken
 
lcrken said:
That seems to have been a common choice among alloy cylinder makers. Dunstall cylinders required the use of non-standard fasteners, although not changed to meteric. Later makers, including Robertson (whose cylinders I imported and sold for a number of years) and Maney used a combination of metric head bolts and British thread studs. They stuck with the original thread forms on the studs to be compatible with stock cylinder head threads. From what you've said, I'm guessing that Andy Molnar's cylinders are also using metric head bolts, right? The change is understandable. Most countries are on the metric standard, with high quality fasteners readily available pretty much everywhere. And in the case of the cylinder head bolts, the stock fine thread bolts would not be a good choice for use in the alloy cylinders.

Ken
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He chose some odd size - don't think it was metric. He should have stayed with what Maney was using - US coarse 3/8" x 16 tpi. I think he went with a finer thread to get more clamping pressure which makes no sense because stripping the threads is the problem and finer is more problematic. Sometimes a change is for the worse.
 
jseng1 said:
He chose some odd size - don't think it was metric. He should have stayed with what Maney was using - US coarse 3/8" x 16 tpi. I think he went with a finer thread to get more clamping pressure which makes no sense because stripping the threads is the problem and finer is more problematic. Sometimes a change is for the worse.
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You're right about Maney using 3/8"x16. My memory said they were metric, but I think I was confusing them with the Robertson cylinders, which used 10x1.5 mm socket head cap screws for head bolts. Sorry about that. I'm playing the age card as an excuse.

While I'm at it, I can't find my info on the Dunstall fasteners, I don't have any of his original head bolts, and the only cylinder of his that I have left has already had inserts fitted for 3/8"x16tpi fastesners. He did supply a complete fastener set with the kit, and I do recall that some of the studs were different in size from stock 750 fasteners. I also remember seeing several cases of stripped head bolt threads in his cylinders back in the day. He used a softer alloy for his cylinders than later suppliers like Robertson and Maney. Fitting inserts to the 810 cylinders was a little touchy because the threads on two of the holes are very closes to the liner, preventing the use of some of the larger inserts.

About Andy's heads. It's hard to tell from the pictures, but it looks like he might have just kept the standard Commando head bolt size, 3/8"x26 tpi. Have you measured the thread to see exactly what it is? Like you, I much prefer a coarser thread in aluminum cylinders, and if I had a set with 26 tpi threads, I'd put in inserts to change it.

Ken
 
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jseng1 said:
He chose some odd size - don't think it was metric. He should have stayed with what Maney was using - US coarse 3/8" x 16 tpi. I think he went with a finer thread to get more clamping pressure which makes no sense because stripping the threads is the problem and finer is more problematic. Sometimes a change is for the worse.
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Jim,
I have done some hand calculations and first results show there isn't much of a difference between 3/8 UNC-Coarse (16 tpi) and 3/8 BSF (20 tpi) as far as load transfer goes. The UNC thread offers a fatter thread profile than the BSF profile for obvious reasons which benefits the aluminum. On the other hand, the BSF has an edge in terms of fatigue performance. I will continue my investigation out of curiosity.
Real static load transfer simulation will require a finite element analysis as load transfer diminishes exponentially along the treaded interface.

-Knut
 
Hi all,

I have challenged Andy Molnar to show values for expected oil consumption after the run-in period. Pits may hold oil in the lower bore section causing no harm, but in the upper bore section accumulated oil will be washed out and burnt, increasing carbon deposits and pollution. Andy should acknowledge this if the effect is noticeable. As a prospective buyer this is essential information to me and probably to others.

-Knut
 
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