750 cylinder barrell very flat top
- Thread starter pierodn
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The very flat top sounds odd to me. If I remember correctly there was a little bit of the cylinder block that stuck up above the top fin. You can use this barrel if you add a spacer between the crankcase and the base of the cylinder barrel. I think that you will have to assemble to top end, check the clearance between the valves and the piston, and then decide how thick the base spacer should be. I think the clearance between the valve and the piston is usually something like 0.030"-0.060", but I'm sure someone else who knows exactly what it needs to be will chime in.
Greg
Greg
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I think there is a translation issue here.
Pictures... Pierodn...Pictures. :roll:
CNN
Pictures... Pierodn...Pictures. :roll:
CNN
A
Anonymous
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Flat is good.
Pictures of your concern is worth a thousand words.
Ta.
Pictures of your concern is worth a thousand words.
Ta.
pierodn said:
I guess you're referring to an early Atlas barrel which has spigots (which have been discussed before here...). Norton went away from this design already during Atlas production time - IIRC 1966 - so there are only "flat" Commando barrels.
Tim
Hi Piero, I would say that what you are describing would be good for you to use in your commando application. As far as which size base gasket and head gasket you need, I think it kind of depends on what compression ratio you desire, how long your push rods are, wether or not you head has been skimmed or shaved and wether or not the barrels were possibly skimmed /shaved or milled to make true. But it sounds like it will work for the engine you are building. Can you try a trial fit to see how far the pistons travel at TDC ?
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I measured a few "unmolested" cylinders. Some of them have the top flange machined flush with the fins. The distance between the top flange and the bottom flange is 115,69 mm on all of them.
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DID you measure the height of the cylinder barrels?
The fact of them being a full machined top surface probably means they are "decked" or shortened.
A Dunstall type motor I own has been shortened and is still useable, but in my opinion not a good way to good engineering a motor. IMO it's value has been severely damaged. Useable but not desirable.
Any one who sells something like this built into an engine with out full disclosure is someone I would NOT want to do business with.
The fact of them being a full machined top surface probably means they are "decked" or shortened.
A Dunstall type motor I own has been shortened and is still useable, but in my opinion not a good way to good engineering a motor. IMO it's value has been severely damaged. Useable but not desirable.
Any one who sells something like this built into an engine with out full disclosure is someone I would NOT want to do business with.
dynodave said:
Hi,
I do not sell bikes, i am the owner, no businness.
If the barrell is usable, why dont use it!
I bought 30 years ago this bike that mounted this cylinder.
The seller, that i remember, remains a very good fellow even if the barrel was top flat.
Ciao
Piero
N
nortonspeed
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Just put a compression plate under the barrel to make up for the lost height, not a big deal :wink:
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Late Kenny Augustine of World's Straightest Commando 'WSC' fame on Tom Davenport's Phantom Oiler, found Norton factory machined barrels all have .003" out of square/flat top [sloped low rearward IIRC] so when I had Peel's bore honed the shop also corrected this unsquareness [also head bottom to head steady flat which was about spot on] - but they didn't have to remove metal down to fin level. If push rods adjusted for the whole stack height [include base plate & head gasket] - for centered rocker contact- then I can't think of any down side.
lcrken
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I think dynodave has the most likely answer. When I was racing I used to machine the top of the cylinders, both 750 and 850, to get higher compression ratio with stock pistons. I took from .060" to .080" off the cylinders. That was pretty common practice around here in the '70s. We machined the cylinders instead of the head, because the heads were usually ported and flowed at significant expense, and we didn't want to limit their future use, whereas cylinders were cheap and readily available (back then, not now!) I did have to do some machining to the valve cutouts in the pistons to get enough valve-to-piston clearance with race cams, and was careful to keep enough squish clearance.
There's no reason not to use them, but you will need either thick head gaskets or base spacers, or both. If you use them with standard thickness head gaskets, be sure and check that the head bolts are not bottoming in their holes. That can happen if a lot of material has been removed from the cylinder top. The cure is to use a thicker washer, or even double washers, under the head bolts.
Ken
There's no reason not to use them, but you will need either thick head gaskets or base spacers, or both. If you use them with standard thickness head gaskets, be sure and check that the head bolts are not bottoming in their holes. That can happen if a lot of material has been removed from the cylinder top. The cure is to use a thicker washer, or even double washers, under the head bolts.
Ken
lcrken said:
Hi and thank you.
I have measured the distance (of the flat barrells) between the top of the cylinder and the bottom flange where the base gasket goes: It is 115,69 mm.
Then, I have measured too two stock cylinder barrells, one of a early commando, another of a1972.
With great surprise the distance is both 115,53: the flat one is 0,16mm higher !!!!
In such circustance i think the flat barrells are more than good!
But, who built this barrells?.
Can I think they was not a skimmered barrells but a stock one.
What do you think about?
Ciao
Piero
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I measured a tall/regular barrel and get about 115.8 on one sample only. Based on your number I doubt they cut it down for increased compression. It should show 1 or 2 MM shorter if modified.
It may be strange looking, but if a good number is there.... then the barrel should function very close to original, though the origin may be interesting... but never known?
cheers
:mrgreen:
It may be strange looking, but if a good number is there.... then the barrel should function very close to original, though the origin may be interesting... but never known?
cheers
:mrgreen:
lcrken
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Pictures would really help. I've been assuming you're talking about an iron barrel, not aluminum, but I guess I should ask to be sure. There were some aftermarket iron barrels available some years back from people like Norvil/Fair Spares and Mick Hemmings, but I don't know who cast them, or if they were different on top. Could be one of those, maybe.
Ken
Ken
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