Re: ramblings on motorcycle stuff

[Godfrey DiGiorgi <ramarren@domain.elided>]

Motorcycle engines are a subject near and dear to my heart. They have 
often been far more radical in design then automotive engines, 
constraints of size and weight push them to more radical solutions harder 
than in automotive circles.

>RPM vs. HP
>
>If I recall during the hey day of Yamaha vs. Honda racing in the early
>1960's Honda had a 5 cylinder 50 cc GP bike.  Apparently it had more gears
>than most transmission have teeth but it only ran between 15,000 and 18,000
>rpm, (or was it between 20,000 and 22,000 RPM and had 18 gears, I just can't
>remember).  It was fast as stink but totally impractical for the road.  The
>rider would effectively stay within a very narrow power band and shift
>continuously.  So, what is the point I am trying to make?  No point, except
>that, like all cars, there are take-offs to be made.

Honda never had a 50cc 5 cylinder. They had a 50cc four-stroke DOHC twin 
with 4 valves per cylinder and did a 125cc 5 cylinder which was 
essentially 5 of those cylinders on a common crankcase with a common 
head. Power was from 18,000 to 22,000 rpm, and there were lots o' gears 
in the transmission, whether 16, 17 or 18 depended upon exactly which 
bike and which track. 

>[Moto Guzzi cylinders]
>The cylinders didn't have iron liners like most bikes at the time.
>Apparently
>they inserted a wire, probably with a very high chromium, in the cylinder
>and then ran a very high charge through the wire.  The wire would literally
>explode turning into plasma and evenly coating the cylinder walls.  It was
>reported to be far harder than any other liner and could take a lot of dust
>etc.  It also, apparently, transferred heat better than iron liners, at
>least that is what I remember the publicity brochure saying.  Of course, if
>the coating was every damaged, either an iron liner would have to be pressed
>in or a whole new barrel would have to be purchased.

You're mixing two types of cylinder platings here. Moto Guzzi's 
traditional single cylinder 250, 350 and 500 racing machines were fitted 
with a cylinder which was hard-plated with chromium, starting in the late 
'40s/early '50s. This was a traditional plating technique, not the 
hot-wire plasma bonding. The advantages were lighter weight, better 
cooling (virtually no thermal barrier between the cylinder lining and the 
cooling fins) and very long life span due to the hard chromium surface 
which resisted scratches. When Carcano designed the V7 road going twin in 
the early/middle '60s, he adopted the use of the chromium plated 
cylinders for all these same reasons in order to keep the top-end of the 
engine light and and the weight low. 

These cylinders were great but over time and the many many cold-hot-cold 
cyclings of a road-going motor it turns out that the chromium plating 
generally doesn't wear out through getting thin. What happens is that 
microscopic pinholes in the plating allow water condensates to get behind 
the plated surface and slowly fracture it. Also, chromium plating is so 
smooth that it's difficult for it to hold lubricating oil for the pistons 
and rings. As you state, the proper repair for a worn out or damaged 
cylinder is complete replacement, but after market fitting of iron liners 
has been done in the usually illusory search to fix a worn cylinder 
inexpensively. (I say "usually illusory" because fitting an iron liner 
typically means replacing the piston and rings anyway and costs around 
80% of the cost of replacing the entire cylinder and piston. But some 
people continue to do it to save the extra $40 out of $400 or so.)

Moto Guzzi only used iron liners in the V7 derivative motors in the 948cc 
engines made between '75 and '81, reason being there was insufficient 
cylinder wall thickness for stability in the older series engines. The 
exception to this was the 1975 and up 850 LeMans series, where they used 
cast iron cylinder liners because the bike was intended for use by club 
racers and it was more cost effective for club racing to provide up to 
three overbore piston sizes. 

Many motorcycle manufacturers were using the chromium plated cylinder 
technology for racing engines by the end of the '60s, Guzzi was alone in 
applying the technology to large-bore 4stroke road machines to the best 
of my recollection. Around about the mid-1970s, Kawasaki along with 
several other motorcycle makers began to use a new technique for cylinder 
plating, again seeking lighter weight. This was the hot-wire plating 
technique you mention, using a wire with a high nickel/silicon content. 
Thus the almost-generic name "Nikasil(tm)" for the process. This plating 
process achieves a much tighter bonding between the aluminum cylinder and 
the hard nickel-silicon plating material than chromium does, yet the NiSi 
plating is not as hard as the chromium. More importantly, it's not as 
smooth at a microscopic level and provides plenty of catch pockets for 
lubricating oil which makes it far more durable, and the tighter bonding 
effects a more complete seal between the plating and the cylinder so 
there is far less chance of water working its way between them and 
causing the micro-fracturing of the plating. Cylinders prepared with this 
process have proven to be extremely durable, light and cost effective. 
Piston rings do not have to be made of soft cast iron to seal properly, 
you can use a hardened compression ring, so you get longer ring life and 
can use narrower, lighter rings with less chance of flutter at high rpm. 

This process is so good that Moto Guzzi came up with their own version of 
it, trade-marked "Nigusil(tm)", and started fitting cylinders with this 
new specification in 1980/81 or so. All big bore Moto Guzzis since, 
Ducatis, and many other motorcycle marques, use this type of cylinder 
technology to great effect nowadays. Cylinder wear is negligible to 
extremely high mileages (often you will fit two or three sets of pistons 
to a cylinder over the course of 200,000 miles and can still measure 
little to no ovality in the cylinder afterwards), the resilient NiSi 
plating resists scratching well. It is more expensive, however, and more 
difficult to apply on multicylinder engines so adoption in the ubiquitous 
4 cylinder motorcycles on the market has been relatively slow (I think 
the Yamaha R1 is using them now). 

My apologies for the long ramble... :)

Godfrey

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