920 cc Conversion of Iron 850 Cylinders

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lcrken

lcrken

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While searching around for some parts today, I ran across an old 920 cylinder from which the liners had been removed. It shows the machining required for the sleeves, but also the extend to which the casting is bored through in several places. I think this is the worst case of daylight showing through that I have seen.

920 cc Conversion of Iron 850 Cylinders


920 cc Conversion of Iron 850 Cylinders


920 cc Conversion of Iron 850 Cylinders


920 cc Conversion of Iron 850 Cylinders


920 cc Conversion of Iron 850 Cylinders


Ken
 
Probably why it was found amongst the stuff you were searching through.
I have some "Well . . . I'll keep it in case . . . " parts like that.
If it was in my old stuff, I'd put it back, ya know, just in case, ya never know.
 
If anyone is interested, the liners used for these cylinders were made by LA Sleeve, and were 3.325" OD, with a 3.460" (plus or minus .005", hard to measure accurately) flange that is .100" thick. Total length was 5.5". The HPI conversions were done by Q&E machine shop in Anaheim, CA. They did an interesting technique at the top, with one sleeve machined at the flange to fit the other flange. Other folks who did similar conversions just milled matching flats on the flanges, or used smaller diameter flanges. This picture shows the technique.

920 cc Conversion of Iron 850 Cylinders


Ken
 
xbacksideslider said:
Probably why it was found amongst the stuff you were searching through.
I have some "Well . . . I'll keep it in case . . . " parts like that.
If it was in my old stuff, I'd put it back, ya know, just in case, ya never know.
Click to expand...

Yeah. I had some sleeves made up a while back, and thought about just putting them in this cylinder, but this one is too ventilated, and I thought better of it. I have a few other worn 850 cylinders that I saved just for the purpose, so I can probably find a better one, if I ever get around to it:).

Ken
 
With hindsight we can see how variable the castings were back then. Quality control was certainly less rigid. Read somewhere that
in the 1940s heavy castings were often a 50% success rate. Then the japs came along and changed the game.
 
Onder said:
With hindsight we can see how variable the castings were back then. Quality control was certainly less rigid. Read somewhere that
in the 1940s heavy castings were often a 50% success rate. Then the japs came along and changed the game.
Click to expand...


The “Japs”, as you refer to the Japanese, terminated the “Limey” motorcycle business in short order.
 
This thread is really off the rails.
But I can't resist: The "Japs" did not terminate the "Limey" motorcycle business in short order.
It took a really long time:
The first motorcycle appeared in Japan in 1896
Honda was founded in 1948.
The last Nortons (of an consequence) were made in 1975.

Besides, the death of the British motorcycle industry is well documented. They did it to themselves. A bit like harikari.

Stephen Hill
 
I said they changed the game. I was hardly slagging them. They produced a quality product, that alone probably would have put them in the lead but they went further and developed many new engines as well.
The still do.
Yes, old news.
 
Come on, let’s be honest here, the Japanese were thoroughly under hand, they just cheated, big time.

I mean, let’s just consider the evidence for a moment... they flooded the market, meaning they actually made the products people wanted in a quantity that they wanted so people could actually buy what they wanted. Whereas we Brits knew that the proper way to sell motorcycles was to not make enough and keep folk waiting.

The Japanese also cheated massively by making modern designs, on modern machinery. They made them faster, more sophisticated and more reliable. And to top it all off they made the f*cking things oil tight... I mean... come on... we Brits knew that THAT is no way to run a motorcycle business...
 
This is GREAT! Never heard it put quite like this. I remember the first bike I bought as a kid was a brand new Honda 400F (1976) did all the mods and could run it to 10,000 rpm quite often and never hurt it. Sorry Ken for the highjack.
 
Had same 400F. Flogged it right and proper. Ran like a top totally reliable.
No, it wasnt fast but sure was well made.
 
I would never bother to build a 920 motor. My 850 is over-bored a bit and is probably near 900cc. That extra 20cc might be like having a farting pigeon sitting on the back of your seat. One of my friends has been trying to build a 750cc motor out of a 650cc Triumph motor. Even though the carbs are rubber-mounted, it refuses to rev above 4000 rpm. If you gain a torque advantage with a 920cc Commando motor, you need the right gearbox to realise the potential advantage. Better to leave the capacity unmodified and play with other things ? A smaller capacity engine often spins up faster. The Commando problem is that revving it high to get more power is not wise. And fixing that problem is very expensive - however changing balance factor might help. My motor is rigidly mounted, but at 7000 rpm, it is completely smooth. Modified Commando valve gear should accommodate 8000 rpm easily. Heavier pistons would be a backward step.
 
When CB750 Hondas were introduced into Victoria, I was still racing my 500cc Triton. I can remember riding down the front straight at Calder Raceway, weaving in and out as I passed them. After they fitted the CB450 pistons, they were marginally better. These days they are 1100cc and methanol fuelled - my Seeley 850 is better. A bit later Z900 and H2 Kawasakis were the go. I once lowered the gearing on my Triton and led them all for a lap at Winton. Their big advantage was their gear box, NOT their larger capacity.
 
Hortons Norton said:
This is GREAT! Never heard it put quite like this. I remember the first bike I bought as a kid was a brand new Honda 400F (1976) did all the mods and could run it to 10,000 rpm quite often and never hurt it. Sorry Ken for the highjack.
Click to expand...
I got 11,000 out of mine with a French made Devil 4 into one Zorst fitted. It sounded like a Bassoon - very unique.
 
Onder said:
With hindsight we can see how variable the castings were back then. Quality control was certainly less rigid. Read somewhere that
in the 1940s heavy castings were often a 50% success rate. Then the japs came along and changed the game.
Click to expand...
Is it possible that they are all like that, and you only realize it once the liners are removed?
 
Fast Eddie said:
Yeah Al, that’s right mate, all down to the gearbox, nothing to do with their extra capacity, DOHC, bomb proof bottom ends etc, etc :rolleyes:
Click to expand...

On tight circuits such as Winton or Mount Gambier or Broadford, there is more at play than horsepower. A lot of that big stuff can be beaten. Some of those guys ride around bouncing off the ripple strips. A Z900 only has advantage towards the ends of the straights.
 
With that 920 cc cylinder, you might wonder at what point the bigger bore becomes less of a performance increase due to the liner not being able to stay round due to lack of support from the outer casting once things come up to temperature.
 
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