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Hi Mondster, OK, I see what you're after. A few thoughts. Take it as that. Dynamic balance crank. Even if balance factor is debatable, dynamic being off gives the butt burning vibration that stings the skin at high rpm. I can say that from personal experience.

What rods, pistons are you using? Is top of case deck lined up perfectly with crank?

How much durability are you looking for? Crank flex at higher RPM can cause problems long term. There is a difference in a real race bike only expected to last only a few races, a season at the longest compared to a road bike where you might expect at least 10k miles out of it.

According to David Gayllin's book, they replaced crank after ever race back in the day to prevent crank failure on the fastest flat track bikes.

Maybe give MAP cycles a call. Give Fanz & Grubb a call. These guys know how to build motors that run fast.

What fuel will you use? Race gas or pump gas? You must keep this in mind to prevent ping/detonation.

Light wheels & tires. Balance both wheels.


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I have to travel 95 miles to reach a road with a speed limit higher than 60mph and it has got harder to escape the speed traps in recent years.

Sometimes I chance 70-80 mph, if there are people ahead of me to take the flak.


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Originally Posted by triton thrasher
I have to travel 95 miles to reach a road with a speed limit higher than 60mph and it has got harder to escape the speed traps in recent years.

Sometimes I chance 70-80 mph, if there are people ahead of me to take the flak.

In the 1960s and 1970s, the A9 (main route N/S Scotland) was an awful road, mainly single carriageway, twists and turns through towns and villages, endless slow moving traffic. But then, in the 1980s, the new A9 was completed, a dual carriageway that bypassed towns and villages. 100mph for extended periods was possible, swopping up hills and down dale (although not on a Triumph twin). Halcyon days.

The same A9 is now infested with speed cameras and the threat of jail if you dare to travel over 100mph.

Dibnah #818053 07/30/20 4:14 pm
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Originally Posted by Dibnah
In the 1960s and 1970s, the A9 (main route N/S Scotland) was an awful road, mainly single carriageway, twists and turns through towns and villages, endless slow moving traffic. But then, in the 1980s, the new A9 was completed, a dual carriageway that bypassed towns and villages. 100mph for extended periods was possible, swopping up hills and down dale

http://a9road.info/route-informatio...%20predominately%20single%20carriageway.
Originally Posted by Automobile Association
Between Perth and Tore, to the north of Inverness, the A9 is a mix of single and dual carriageway sections. There are currently a total of nine dual carriageway sections which is approximately 32% of the overall distance, however those sections are relatively short and the route is predominately single carriageway.

Last edited by triton thrasher; 07/30/20 4:16 pm.

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Ok Mondster, back to your original query, and sorry for hijacking the thread for a while:

I did an upper-engine rebuild on a T140 for someone, and I got to test-ride it a couple of times. We made NO changes over stock, not even to the exhaust cam (and I don't think you meant a "Spitfire" cam, as BSA A65s are a single-cam engine). What we DID do, which was a dramatic improvement IMO, was to raise the gearing, went from a 45 to a 42-tooth wheel sprocket.

After the gearing change, the bike virtually "loped along" at 70 mph. On my last ride, I took it up to 95 mph, at which point it was still accelerating, and I got scared and backed off.


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The old A9 also used to run from Edinburgh to Perth as I recall, now the M90 (?) . Over 30 years since I last travelled those roads, I had an Opel Manta for one trip, Tarox brakes and pads, the only time they faded was on the then-new A9. Japanese 750 on the same roads in 1987(ish) was bonkers

I am planning to spend a summer on Orkney and other islands to escape the infernal heat of southern England, but I won't be travelling on mainland Scottish roads with the ridiculous risk of imprisonment for making good progress. 34C forecast for that London tomorrow, 16C forecast for Orkney, much more civilised.

https://movingimage.nls.uk/film/1962 4 minutes 50s is how I remember the old A9

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Been on that road today.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Inspiring, typical 60’s optimistic film.
I’ve never been there yet, is it still as good?
I’ve seen some similar era clips of the dawn of motorways and birth of new garden towns, the later evidence is less convincing.
Not sure what it has to do with our bikes, other than they have always burbled along those paths, and still do.
Many lovely roads to travel, as yet not ridden…

TR7RVMan #818108 07/30/20 10:52 pm
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Originally Posted by TR7RVMan
Hi Mondster, OK, I see what you're after. A few thoughts. Take it as that. Dynamic balance crank. Even if balance factor is debatable, dynamic being off gives the butt burning vibration that stings the skin at high rpm. I can say that from personal experience.

What rods, pistons are you using? Is top of case deck lined up perfectly with crank?

How much durability are you looking for? Crank flex at higher RPM can cause problems long term. There is a difference in a real race bike only expected to last only a few races, a season at the longest compared to a road bike where you might expect at least 10k miles out of it.

According to David Gayllin's book, they replaced crank after ever race back in the day to prevent crank failure on the fastest flat track bikes.

Maybe give MAP cycles a call. Give Fanz & Grubb a call. These guys know how to build motors that run fast.

What fuel will you use? Race gas or pump gas? You must keep this in mind to prevent ping/detonation.

Light wheels & tires. Balance both wheels.


I'm not really after build advice, I was just seeking out opinions on the crankcase vent. I think the vent in the primary for the late 650s and 750s is adequate, but I've also read some complaints of rusty primary components due to moisture buildup as a result of the breather. I figured I'd ask what everyone else thought and to my surprise the consensus seems to be siding with my assessment that it's fine. I do however still like the idea of a separate primary and I'll likely separate mine if I can find a 3 row crank sprocket that is machined for a crank seal. If I can't find one I'll probably put it together as is and worry about it later.

But since you asked about the build, it's a pretty simple one that is very similar to the 750 that Hillbilly Bike put together and occasionally writes about. 32mm Mikuni flat slide carburetors, 9.5:1 compression, stock intake cam and a 71-7017R exhaust. The rest is pretty standard and the parts I started with are all very low time. The bike has been lightened up with carbon fiber fenders and side panels, alloy wheels, etc. Brakes and suspension will be improved this winter. It's just a fun street bike, nothing more, and not really that exciting.

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Originally Posted by Mark Z
We made NO changes over stock, not even to the exhaust cam (and I don't think you meant a "Spitfire" cam, as BSA A65s are a single-cam engine).

I have no idea what most people call the 71-7017R exhaust cam that matches the intake profile but I've seen it referenced as a "spitfire cam" in numerous places. This is what I put in it.

https://montysclassicmotorcyclessho...-1970-83--t120-t140-bonneville-994-p.asp

Dibnah #818113 07/30/20 11:12 pm
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Originally Posted by Dibnah
The old A9 also used to run from Edinburgh to Perth as I recall, now the M90 (?) . Over 30 years since I last travelled those roads, I had an Opel Manta for one trip, Tarox brakes and pads, the only time they faded was on the then-new A9. Japanese 750 on the same roads in 1987(ish) was bonkers

I am planning to spend a summer on Orkney and other islands to escape the infernal heat of southern England, but I won't be travelling on mainland Scottish roads with the ridiculous risk of imprisonment for making good progress. 34C forecast for that London tomorrow, 16C forecast for Orkney, much more civilised.

https://movingimage.nls.uk/film/1962 4 minutes 50s is how I remember the old A9


16 deg,,,,,,,,,,, sod that!
It's midwinter here and 24 deg today. I seldom ride if it's below 20, i'm not into masochism.
I must admit though, once it's over around 32, i find riding can be a touch sticky unless you're
doing higher speeds.

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Is there a reason for preferring triplex drive?
IMHO it just introduces complications (the sprocket alignment should be more precise), it is wider (affecting the alternator), it is heavier, and it is plain unnecessary.
I know that all the twins of the 70's felt it important (more is better) but even the triples went back to duplex (enough is enough).
Just thoughts...

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Originally Posted by koan58
Is there a reason for preferring triplex drive?
IMHO it just introduces complications (the sprocket alignment should be more precise), it is wider (affecting the alternator), it is heavier, and it is plain unnecessary.
I know that all the twins of the 70's felt it important (more is better) but even the triples went back to duplex (enough is enough).
Just thoughts...

That's an interesting suggestion that I hadn't considered. I didn't realize that the triples had a duplex setup and I think all the 750 twins had the triplex setup so I assumed it was necessary. Maybe I'll collect the parts and switch it over this winter.

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Well its always possible I was talking out of the rear end as usual, but I think you will find a reasonable amount of truth in it.

A few like LAB will know all about duplex/triplex on Tridents and T140s. I only have experience of converting to duplex from single chain on a pre unit.
I would think that if a duplex chain is lubed and maintained properly, there is no reason to expect it to wear grossly prematurely

A triplex drive requires much more accurate alignment than a duplex (about 10 or even 20 thou may happen with a 2, don't even think about 10 with a 3).

I don't know why the twins went to triplex, I believe it's not the easiest chain to get these days. If you stay duplex I doubt you'll have any problems finding chains. Again refer to LAB.

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Originally Posted by koan58
Well its always possible I was talking out of the rear end as usual, but I think you will find a reasonable amount of truth in it.

A few like LAB will know all about duplex/triplex on Tridents and T140s. I only have experience of converting to duplex from single chain on a pre unit.
I would think that if a duplex chain is lubed and maintained properly, there is no reason to expect it to wear grossly prematurely

A triplex drive requires much more accurate alignment than a duplex (about 10 or even 20 thou may happen with a 2, don't even think about 10 with a 3).

I don't know why the twins went to triplex, I believe it's not the easiest chain to get these days. If you stay duplex I doubt you'll have any problems finding chains. Again refer to LAB.

+1
I used a duplex chain on my a65 race bike with better wear results than a triplex due to crank flex etc.
10 thou on a triplex is what you aim for but with a 3 spring clutch and whip in the end of the crank i
doubt it's that when being thrashed.

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"I didn't realize that the triples had a duplex setup" - the T160 used a duplex but it is 7/16" pitch, not the 3/8" of the R3 and T150. Impossible to get now as the T160 was the only thing using that pitch. Not a British Standard chain size. Conversions are available to go back to 3/8" triplex or 1/2" duplex.

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Originally Posted by mondtster
But since you asked about the build, it's a pretty simple one that is very similar to the 750 that Hillbilly Bike put together and occasionally writes about. 32mm Mikuni flat slide carburetors, 9.5:1 compression, stock intake cam and a 71-7017R exhaust. The rest is pretty standard and the parts I started with are all very low time. The bike has been lightened up with carbon fiber fenders and side panels, alloy wheels, etc. Brakes and suspension will be improved this winter. It's just a fun street bike, nothing more, and not really that exciting.
If you build it something like mine it will be well mannered, get good mileage, won't detonate on pump gas and other Triumphs ,Bsa's and even Nortons will be struggling to keep up... wink


Originally Posted by DMadigan
"I didn't realize that the triples had a duplex setup" - the T160 used a duplex but it is 7/16" pitch, not the 3/8" of the R3 and T150. Impossible to get now as the T160 was the only thing using that pitch. Not a British Standard chain size. Conversions are available to go back to 3/8" triplex or 1/2" duplex.

When I was building the double engine Triumphs I used 7/16 pitch two strand chain as engineering indicated 1/2 pitch is less tolerant of long term high rpm.....Don't Brit bikes use a chain that has larger diameter rollers than the typical roller chain of the same pitch?


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Hi Mondster, I would strongly recommend looking at Hilldilly’s build.
A lot of thought went into it. Pay attention to the squish band. That is the key factor. You’re going to have to deal with detonation some how.

Regarding rust in primary. I had no problems for first year. 15 miles to work one way.
Then I moved. 3 miles to work one way. I started noticing water in primary oil. I still did 50 mile joy ride once a month.
Rust was not bad, just some here & there.
Always change primary oil when you do engine oil.

Unless you plan on short trip riding, I doubt rust will be issue.

Hillbilly what are doing for breather?
Don

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a hundred bucks on twin plugging and you can run ten to one on kerosene.

best modification you can make to a triumph.


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Originally Posted by triton thrasher
I have to say the timing hole behind the barrel looks like a bad place to put a breather.

And you would be correct, because there was no end of bother. Their instructions recommended that though, and as a young 20 yr old I knew no better (probably still don't at 56 although nowadays I would ask on sites like this)

















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Originally Posted by kevin
a hundred bucks on twin plugging and you can run ten to one on kerosene.

best modification you can make to a triumph.
Well,a bit more than 100 bucks for a complete system......I seriously considered dual plugs when the engine was apart. But my experience was with tight squish so I went that direction to see how it would function on a street Triumph. I believe the best results would be using dual plugs and tight squish. This way the total timing might be ok at let's say 22 degrees. The engine would be ok with fixed timing perhaps...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Originally Posted by Hillbilly bike
Originally Posted by kevin
a hundred bucks on twin plugging and you can run ten to one on kerosene.

best modification you can make to a triumph.
Well,a bit more than 100 bucks for a complete system......I seriously considered dual plugs when the engine was apart. But my experience was with tight squish so I went that direction to see how it would function on a street Triumph. I believe the best results would be using dual plugs and tight squish. This way the total timing might be ok at let's say 22 degrees. The engine would be ok with fixed timing perhaps...

I’m headed in the right squish and dual plug direction. It will be interesting to see how it does.

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Not being an expert on this stuff, I spent a lot of time reading about tight squish/quench and also high velocity intake ports....much of the info came from tuners of Chevy wedge head V8's and Honda advanced work with 4 valve pentroof combustion chambers. The 1930's technology Triumph hemi head is not exactly the same but the principals are the same..High speed air flow with turbulence or tumble in the combustion chamber for the fastest burn.Current thinking says the ports should not cause too much turbulence... The faster the burn, the less overall timing and less time for detonation to occur. Dual plugs do speed up burn time but does not improve turbulence from the way I see it. Turbulence is important but I lack the experience speculate about it ....
Me and Koan here recently disagreed on the actual compression of my 750...But put it this way..with .020 8.6 compression rated stock original Triumph pistons, and reducing the cylinder height .032, the static compression should be higher than 9 to one..With the stock intake cam at 100 degrees lobe center, I cannot get this engine to ping on 90 octane non ethanol fuel. The bike can be at 2000 rpm in high gear on level ground and I can just slowly roll the grip wide open..the engine responds without a complaint pulls well...Not that I normally ride like,but just an example of the engines flexibility. This is with 32mm Mikuni flatslides jetted what appears to be leaner than most with a parallel port 79 head.I installed points to make it easier to adjust the advance curve. Right now the engine has about 20 degrees timing at a 900 rpm idle and full advance of 35 degrees at 2500 rpm. No kick back when starting.


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Originally Posted by Hillbilly bike
Originally Posted by kevin
a hundred bucks on twin plugging and you can run ten to one on kerosene.

best modification you can make to a triumph.
Well,a bit more than 100 bucks for a complete system......I seriously considered dual plugs when the engine was apart. But my experience was with tight squish so I went that direction to see how it would function on a street Triumph. I believe the best results would be using dual plugs and tight squish. This way the total timing might be ok at let's say 22 degrees. The engine would be ok with fixed timing perhaps...

squish accomplishez a similar thing without extra parts, and i suspect would be be a better solution by itself. dual plugs dont increase swirl, they just allow you to burn end gases before they detonate. but doing both would be the best way. i have to do it because the dome son my piztons get in the way of turbulence, and i went with the domes on the advice of the cam guy . . .

i run dual plugs on a T120 with an old Boyer, originally adding nothing more expensive than two six volt harley coils. worked fine for years. 30 btdc was best on that, retards for idle as normal. the easy thing about dual plugging iz that all you have to do is take off the head.

my LSR runs dual plugs with fixed timing at 30 btdc. it idles okay too, maybe a bit lumpy.


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Dual plugs can also be used with points. I had a a Shovelhead years ago using a dual point conversion and two double output Dyna coils. It always fouled the added on spark plugs. Looking back I think it was wired wrong. I dedicated a dual outlet coil per cylinder...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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