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Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #579947
01/08/15 4:53 pm
01/08/15 4:53 pm
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Posts: 10,158
Boston, Massachusetts
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John Healy Offline
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Quote:
are there modifications that one can do to a stock triumph T120 head that can significantly increase swirl? maybe my question includes increasing velocity in general, as it seems to me that one would help the other.


No, the 650 head, or the late 500 for that matter, does not lead itself to having a squish band without a lot of work, and expense. The 750 twin can be worked to have a squish, but requires different pistons and some work.

Increasing air velocity through the ports seems counter intuitive. Because drawing air into the cylinder is a timed event, air velocity is more than a consideration. In a lot of tuner's eys it is where a lot of the magic comes from. The common thought is to increase the port diameter, but in my experience with the 650 it is too big for a street engine to start with. For street work the early 9 bolt head with the small non-unit ports and valves makes for a more useable, easy to tune, and more rideable street bike with a good wide power range suitable for the standard 4 speed gearbox.

The same port as the late 650 works real well with the large bore of the short rod 750. Unless you know exactly what you are doing I would leave the ports alone, but concentrate your time and money to the area around the valve seat.


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Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #579951
01/08/15 5:15 pm
01/08/15 5:15 pm
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Posts: 10,158
Boston, Massachusetts
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John Healy Offline
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Quote:
JH,I saw that photo of yours recently and meant to ask...


They are blanks - you chuck them up and machine them to match the squish band in the head. The final shape, after some nibbling away the parts I don't need, is not unlike the ones the factory used in the T100 and Triple racers.

As the area under the dome is also not machined you can vary the top of the dome for improved flame propagation and final compression ratio. You need to put them in a piston vice and go at them in the Bridgeport. This also allows you to vary the piston weight to fine tune balance.


Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #579985
01/08/15 8:53 pm
01/08/15 8:53 pm
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Boston, Massachusetts
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John Healy Offline
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No, Nick no misunderstanding here. And they also have sensors to measure dynamic cylinder pressure under no-load and full-load. These can be used to predict abnormal cylinder pressures that can lead to detonation.


Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #579997
01/08/15 9:48 pm
01/08/15 9:48 pm
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ca, us
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DMadigan Offline
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I worked the squish in a different way. Instead of squishing around the edge of the piston into the centre, I put the squish opposite the spark plug so the charge is pushed around to the plug. No detonation problems with this on pump fuel.

Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #580012
01/08/15 11:56 pm
01/08/15 11:56 pm
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Posts: 10,158
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John Healy Offline
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Triton Because of the size of the valve cutaway on the intake side of this piston if the rings aren't set a bit lower than normal the valve pocket cuts right into the ring groove. Not ideal, but it seems to work out. Except for the valve pockets the whole dome of the piston above the ring grooves is solid when I get the pistons. The head is machined and measured and the dome cut to match. Then the inside is cut leaving a dome thickness in the range of .125". Do the same with the 750 we ran for years.

David - Nice "another way to skin the cat." KB pistons have been making a piston for sportsters with a similar dome configuration for quite a few years now. It is a whole new world when you find out you can get partially finished pistons and match the pistons dome to the head. SOme people create a trough across the top of the pistons in an effort to improve combustion. Still some small signs of detonation. It seems you exercised the throttle some, or were beginning to loose a valve spring, with that right cylinder exhaust valve kissing the piston - was it worth it? DId you win...


Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #580013
01/09/15 12:44 am
01/09/15 12:44 am
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DMadigan Offline
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That was probably when I was following an RG500 with my Wenco framed R3 racer on PCH coming back south from Laguna Seca. He could not out accelerate me coming out of the corners. If the throttle cable doesn't need adjustment periodically you're not turning hard enough, yes?

Last edited by DMadigan; 01/09/15 2:33 am.
Re: where do the coil wires go on dual plug heads? [Re: John Healy] #580089
01/09/15 2:17 pm
01/09/15 2:17 pm
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The T140D head with the parallel ports and the constant velocity carburetor. The T140D port design dramatically increased swirl improving combustion and lowered combustion temperatures to a point where it required running spark plugs 2 ranges hotter to prevent fouling.

hi John, very interesting info as ever.
But I still cannot understand how you can have "improved combustion" and lower temperature at the same time? Is it because they had a very lean carburation and very low CR?

Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #580111
01/09/15 4:32 pm
01/09/15 4:32 pm
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Posts: 10,158
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John Healy Offline
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Simply stated - the swirl from the incoming mixture seems to mix the air/fuel mixture better than the "splay port" resulting in a better burn or "improved combustion" = little or no detonation.

no-detonation = lower combustion chamber temperatures - and the "explosion" isn't pushing past (blowing away) the protective boundary layer that insulates the head from the heat of combustion.

With lower compression, which they had already done in previous years, you compress the incoming charge less. As a result the fuel air mixture does not heat up as much as it did with a higher compression. It is all a balance of controlling pressure in an effort to control heat. You want the fuel/air charge to burn and not explode.

The constant velocity carb prevents the rider from taking a handful of throttle at low rpm. Doing so, you can drive the dynamic cylinder pressure, and gas temperature with it, to the point that when the spark plug fires the additional pressure created by combustion pushes the end gas (un-burnt gas opposite flame front) to a point where it will self ignite. You have just created a case of severe detonation. In a CV carb the slide responds to manifold vacuum, and not just to throttle position and prevents the rider from causing the carburetor from delivering a big gulp of air when it cannot handle the dramatic increase in cylinder pressure it causes.

A good example of this is checking the cylinder pressure with a gauge. Leave the throttle closed and you get a very low reading - There is no air through the carburetor to compress. Open the throttle and the engine takes that big gulp and the needle jumps up over 100 pound and more. That is dynamic cylinder pressure - it changes with slide position.


Re: where do the coil wires go on dual plug heads? [Re: John Healy] #581391
01/17/15 2:57 pm
01/17/15 2:57 pm
Joined: Aug 2014
Posts: 375
New Jersey
Keane Lucas Offline

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Originally Posted By: John Healy
Simply stated - the swirl from the incoming mixture seems to mix the air/fuel mixture better than the "splay port" resulting in a better burn or "improved combustion" = little or no detonation.

no-detonation = lower combustion chamber temperatures - and the "explosion" isn't pushing past (blowing away) the protective boundary layer that insulates the head from the heat of combustion.

With lower compression, which they had already done in previous years, you compress the incoming charge less. As a result the fuel air mixture does not heat up as much as it did with a higher compression. It is all a balance of controlling pressure in an effort to control heat. You want the fuel/air charge to burn and not explode.

The constant velocity carb prevents the rider from taking a handful of throttle at low rpm. Doing so, you can drive the dynamic cylinder pressure, and gas temperature with it, to the point that when the spark plug fires the additional pressure created by combustion pushes the end gas (un-burnt gas opposite flame front) to a point where it will self ignite. You have just created a case of severe detonation. In a CV carb the slide responds to manifold vacuum, and not just to throttle position and prevents the rider from causing the carburetor from delivering a big gulp of air when it cannot handle the dramatic increase in cylinder pressure it causes.

A good example of this is checking the cylinder pressure with a gauge. Leave the throttle closed and you get a very low reading - There is no air through the carburetor to compress. Open the throttle and the engine takes that big gulp and the needle jumps up over 100 pound and more. That is dynamic cylinder pressure - it changes with slide position.
I get a great education when I examine some of these discussions. Taking this in a slightly different direction, It seems that most if not all the comments here apply to highly modified machines. I am no stranger to mixing fuels to reach necessary octane levels.My 1969 BSA owners handbook shows a minimum octane requirement of 98 ( I'm thinking RON) for a stock 9:1 A65. HB provided two good links,the Sunoco one I am familiar with. The other brought out something that seems to be lost on some people-that a slightly lower static compression ratio with a factory engineered timing curve is better than a retarded timing curve with high(er) compression ratios and is the better way to get our old -stock- iron to run on 91-93 octane pump premium.The article mentioned a 1 to 2% loss in torque with lowered compression. Didn't the majority of T140's have an advertised compression ratio of 7.9:1 in preparation for lower octane unleaded and the phasing out of super premium leaded fuel? With A65's or T120's I was never satisfied with the performance of retarded timing so as to operate on sub-standard fuel.The engine is so much happier with 100 octane and the factory settings and so am I.SO my question is, would quality forged pistons-not cheap- that provide a lowered 8:1 compression ratio for otherwise stock A65,T120,etc. machines be marketable, and if not why not? Hoping for a lot of feedback.


1969 BSA A65T w/A70 engine
1970 Royal Enfield Interceptor S ll
Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #581392
01/17/15 3:07 pm
01/17/15 3:07 pm
Joined: May 2005
Posts: 3,821
ohio
shel Offline
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ohio
My 76 T140V at 7.9/1 would run on lamp oil


When given the choice between two evils I picked the one I haven't tried before
Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #670447
10/08/16 9:26 am
10/08/16 9:26 am
Joined: Jul 2006
Posts: 108
Quebec, Canada
Transgarp Offline
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Quebec, Canada
Transgarp calling John Healy smile

I dismantling the engine of the T120R in May
According to this Web site, the wear of my conn-rod bearing confirms the detonation caused by a gasoline of too low octane or a too high C.R., here 9.5:1 with 750 Morgo kit
http://www.agkits.com/bearing-failure-analysis.aspx

My bearing wear:
http://transgarp.dyndns.org/motorcycle/0800/20160000/20160521_04.JPG

The last year 2015, I ride under this configuration :
750 Morgo kit CR 9.5:1
28 full-advance
21 teeth front sprocket, 46 rear
Detonation

In August 2016 I reassembled the engine with this configuration :
750 Routt kit CR 8.9:1
38 full advance
22 teeth front sprocket, 46 rear
No detonation

All my problems of detonation disappeared, while riding with the same super gasoline of Shell and more power all rpm smile

You surely wonder why I have enlarges the front sprocket.
Not the choice because of the necessary release of the chains to the top of the front of the swingarm considering which I installed the complete back suspension of a Honda XR650L on the frame of the T120R

http://transgarp.dyndns.org/motorcycle/2000/20161001/17.JPG

http://transgarp.dyndns.org/motorcycle/2000/20161001/08.JPG

Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #673622
11/06/16 2:32 pm
11/06/16 2:32 pm
Joined: Oct 2001
Posts: 241
Monclova
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Monclova
What do you know, I have an A65 that has the primary side rod brgs that look just like that. Spitting image. However, I have no information on the motor or how it ran when it was a complete bike. I know it had under 10,000 miles on it and the throws and bush are factory clearances. I assume it was all stock. It is a 1971 engine and everything else is specking out as should be. Maybe it had some bad spark knock hey? detonation? I don't know, but I have never seen a brg look like that except in books. I have seen automotive engines like a big block Chevy that was ran very hard at high speeds for several miles then shut down right afterwards and had a slight knock in the morning after cool off, when torn apart one rod or rather one rod with the bearings must have been to hot at shut off and stuck to crank, when it was disassembled it looked similar to what you have. No harm to rod or crank, could only figure one defective bearing that lost its integrity and stuck to crank. Reassembled and fine good to go. Sometimes you do even get defective parts from factory, I know this BSA engine has never been apart so maybe a bad one. Ive seen several bearing failures from vandervill in the past 25 years.

Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #675272
11/22/16 10:42 pm
11/22/16 10:42 pm
Joined: Mar 2011
Posts: 108
Alaska
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linker48x Offline
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Alaska
Not sure if the original post and original questions are still relevant. But to respond, my AHRMA road racer T140 engine has 11.5:1 pistons, has a twin plug head done many years ago at John Healy's suggestion by Dana Johnson at Import Machine Service in Mass., and uses a crank-driven twin plug ignition I got from Rex Caunt (modified PVL with little twin lead coils). When I first did this, I used a Boyer Powerbox, and John Healy suggested to me to place each of the two wires from each coil on opposite cylinders to get better spark, and I have continued to do that, it seems to work the best that way. To answer the other questions I saw above, I use 32 degree fork lead, and 110 race gas. The effect has been to make the engine run cooler and smoother and make more torque--the combustion chamber shape and flame front were obviously issues with a single plug and this very high compression. Runs great! Doubt twin-plugging is necessary on the street with 9:1 or so, though.

Re: where do the coil wires go on dual plug heads? [Re: kevin roberts] #678816
12/24/16 3:29 pm
12/24/16 3:29 pm
Joined: Dec 2013
Posts: 4,005
ohio, usa
kevin roberts Online content OP
fefsa
kevin roberts  Online Content OP
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ohio, usa
i twin-plugged my old street bike when all i could get was 89 unleaded. these days i use 110 leaded premium and run the timing back to 30 BTDC.

i'm running 11.75:1 now on another machine that is single-plugged at the moment, because i'm using an old ARD. but i'm using VP 108 C12 in it

http://www.racefuel.com/vp-c12-racing-fuel-108-octane/


i have no idea what i'm doing.
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