Norton 122 Model 88 500cc

pierodn

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Nov 10, 2012
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Hi.
Can i fit on this bottom end that has stock cranckshaft, Connecting Rods and cam, the cylinder and head (both spigotted) of an early 750 ?.
Thank you.
Piero
 
No.
Its not a straight bolt-on swap.
Or there would be lots of 608cc dommies (short stroke dommies) running around !?

The stud spacings for the cylinder onto the crankcase are slightly different.
So you'd have to machine them somehow to make things fit.

The 750cc cylinder is 5" tall, and the dommie 500 only 4".
The shorter stroke of the 500cc engine would leave the pistons an inch below the combustion chamber !
3:1 compression !!!

And I don't know what other difficulties there might be - the diam of the lower cylinder spigots
might be too large for the crankcase mouth, for example ??

Nice thought though - as many have contemplated before.
I'm sure it could be done, but you'd need to do some (serious) machining....
hopethishelps.
 
Hi Rohan,
thank you.
Do you think is possible to fit the atlas conrods on the 88 crankshaft?.
Piero
 
No !!!

You need to look at these things before asking these sorts of questions, Piero,
the 500 dommie rods are 1.5" diam and the 750 are 1.75" in the big ends.

Also, the dommie 500 rods are LONGER than the 750 rods, so you'd have 2:1 compression !
Cheers !
 
rohan, I think you need a new tape measure,according to mine 600,650, 750,barells are aprox 4.5 ins ,500 barells have one fin less and that doesn't equate to one inch.chris
 
I just went and checked.
Atlas cylinders are near enough 5" and dommie 500 cylinders are 4" tall. (ignoring spigots top and bottom)
Both utterly stock.
I can photo them side by side if you want.

Over to you.....
 
rohan,yes please do,ive just checked mine again this time with a digital caliper,600 barell comes out at 4.555 ins,650 barell comes out at 4.550 ins, and I believe these are standard ,750 atlas comes out at 4.490 ins but these are not standard because I had .60 thou machined off the top face because I was told atlas barells were that much taller than commando,i don't have a 500 barell to measure but as I said one fin less dosent equate to one inch,one ins is more like three fins, chris.
 
I've also measured a 500 cylinder on a built engine, it is near precisely 4" visible.
It has a stroke 17 mm less than a 750 engine, so that is ~3/4" already.
??
 
rohan,as I said I don't have a 500 cylinder to measure,4 ins sounds close,but 600,650,750 and maybe 850 are not 5 ins,and I don't believe the stroke has anything to do with the height of the barell. chris
 
chris plant said:
and I don't believe the stroke has anything to do with the height of the barell.
Click to expand...

???
So, a stroke of 72.6 mm and 89 mm have nothing to do with it ?? !!
I find that a little difficult to credit.
The extra length has to go somewhere...

Actually, Nortons used longer rods in the 500's than in the 650/750/850,
so could have made the 500 cylinder even shorter than that 4".
500 rods are 6" c-to-c.

As I said to Piero, if you put shorter (650/750/850) rods on a 500 crank (if you even could) and then used the longer cylinder, the piston would be well short of the deck height, and you'd have a compression of about 2 or 3 to 1.

I'll have to do a more controlled measurement of the Atlas cylinder, maybe a bit of parallax is coming into play.
 
rohan,you will find that the 600 has a stroke of 82mm the 650,750 has a stroke of 89mm,but the barell height is just about the same,that is why I said I don't believe the stroke has anything to do with the height of the barell, chris
 
Thats because the 600 used long conrods, and the 650 and 750 used short conrods.

Nortons obviously did that deliberately, to keep the cylinder heights not too different.
So that things like the exhaust pipes and carburettor location didn't need major changes,
can't have the carb lower parts banging into the magneto, or the exhaust pipes dragging ...
 
rohan,thats also true for the short stroke 750,the only things I thought were wrong in your posts was your height of the 750 barell and the fact that stroke dictates barell height,chris
 
Rohan said:
I just went and checked.
Atlas cylinders are near enough 5" and dommie 500 cylinders are 4" tall. (ignoring spigots top and bottom)
Both utterly stock.
I can photo them side by side if you want.

Over to you.....
Click to expand...

I have my Atlas barrels on the bench. From the base gasket surface to the head gasket surface, the measurement is 4.565"

Slick
 
Rohan said:
maybe a bit of parallax is coming into play.
Click to expand...

There was indeed a bit of parallax coming into play - lost a few 10ths....

This is a genuine 4", not so easy to do on an assembled engine,
Norton 122 Model 88 500cc

you guys are way too serious measuring to 0.005 accuracy !
Did you measure all sides though, Nortons were famous for not machining things square...
 
texasSlick said:
Rohan said:
I just went and checked.
Atlas cylinders are near enough 5" and dommie 500 cylinders are 4" tall. (ignoring spigots top and bottom)
Both utterly stock.
I can photo them side by side if you want.

Over to you.....
Click to expand...

I have my Atlas barrels on the bench. From the base gasket surface to the head gasket surface, the measurement is 4.565"

Slick
Click to expand...
and.........how do the barrel holes line up with a 500 crankcase, my I ask :?:
 
As was said (much) earlier in this thread, they don't.
And if they did, you'd have ~ 3:1 compression.

So bar the detail, much ado about nothing....
 
rohan, no I did,nt measure all sides ,the naked eye can see there is,nt a half ins difference. chris
 
Bernhard,as rohan said they don't,i think its the rear two studs that don't match up but its not by much,chris
 
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