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Discussion Starter #1
There'a a lot of misunderstanding on vintage bikes forums about the effects of lower octane fuel and the potential problems it causes...I believe once you understand abnormal combustion ,you can deal with effectively one way or another.
This short video by Kevin Cameron is easily understood...Cameron is considered to be a leading motorcycle engineer and theorist..His many articles are worth reading



This is an article by Allen Kline who was the head General Motors emissions engineer.It's also fairly easy to follow and often quoted as an excellent expalnation

http://www.contactmagazine.com/Issue54/EngineBasics.html
 

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Discussion Starter #2
This is an example of detonation (pinging) damage on my dual Triumph engine land speed race bike.. Unknown to me the supposed fresh race gas was not fresh, the engine went into detonation at high rpm, the piston heated and seized quickly...This is an expensive forged piston, a stock cast piston may have failed causing catastrophic engine damage.



This is a 650 Triumph engine a friend wanted me to fix... A classic case of pre ignition punching a hole in the piston...it was caused by lugging the engine on year old gas....There is no pinging to alert the rider, it just happens in a second as mentioned by Kevin Cameron...

 

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Out of curiosity, I wish I knew why I don’t detect any ping under any circumstances. I know I ride fairly flat roads in my area compared to many parts of the country, but still, most people have a problem with it, don’t they ? Or am I over estimating the amount of people that have an issue. It’s not like my bike is in a super state of tune, it’s not. Gearing is higher than normal, that should make it worse. Stock points and advance mechanism ( new springs ) Modified air box with Uni filters, straight through short megaphones, Barnett clutch. I use 10% corn premium fuel of any brand available when I’m not near a station that sells corn free stuff. I use SeaFoam with every tank. I’ve had cars that pinged on these same roads. I’m not complaining, but I do wonder why I never have a problem with it.
 

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Discussion Starter #4
Cam timing is very important in regards to detonation....Stock T140 750 cam timing is more cause of detonation than in earlier 650 engines..
A sound Triumph can and will tolerate a brief period of light ping from time to time..I know this from experience over the years...Pre igniton will kill a Triumph in two seconds...
 

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Someday I’ll correct the cam timing. Though I’ve only owned the bike a few years the PO didn’t appear to be mechanically inclined and he’d owned the bike for many years. I’d be surprised if anything had been done to it at all.
 

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Discussion Starter #7
tony, how old was the gas on your double?

was it out of a sealed can?
It was in the original tightly capped can, about 3/4 full, but about 6 months old..I made a mistake ..Why one piston out of four had a problem despite all having the same clearance . timing and jetting is anyone's guess..My single engine bike was run on fuel opened a month before with no problems..
Jim the dyno guy I use has equipment to to test the RVP of gas and has found new sealed cans of race fuel do not met specifications sometimes...As you know there's more to a fuel's resistance to detonation than just octane rating..
Are you going to try and dyno the race bike this year?
 

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shoot, i'm having so much trouble getting wheels on the machine i don't know whether i'll have time to dyno it or not. i'm having to use outrigger plates for the front wheel bearings in order to fit a larger axle into the fork legs. still don't know whether i like that, but they're being machined right now.

i've got a couple of two-year old unopened cans of C12, but i'm just going to dribble that into the street bikes and use completely fresh stuff this summer.

would still like to get it on a dyno, though.
 

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Discussion Starter #9
K, On the various front end and wheel swaps, I make bushings to fit the axle to the fork or cut down the axle ends in the lathe..But your situation might be a bugger....
You would like the dyno shop owner. He's a friend of Kevin Cameron and is a hands on guy, you ride the machine on the dyno while he directs the action...
VP says their gas is good for three years in factory sealed cans.....
When you stop by my T140 will be available for flogging....You can experience a 9.2 compression Triumph running on 89-90 octane gas without sounding like a can full of marbles..
 

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my problem is that there are no bearings that fit the wheel with a 0.675 ID to match the conical sliders.

the 90 GSX 750 front wheels had little axles.
Can't you get some adaptors made up like these?
https://www.ebay.co.uk/itm/Triumph-Tiger-Cub-Stainless-Steel-Spindle-Sleeves-x2-W1649SS/162985786476?epid=1575205273&hash=item25f2b5bc6c:g:-tEAAOSw3YNXcSjL

On a tiger cub, the forks are flimsy and narrow. To fit C range forks, a wider spindle is needed, then it is sleeved up to fit into the 350/500 forks
 

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Cam timing is very important in regards to detonation....Stock T140 750 cam timing is more cause of detonation than in earlier 650 engines..
A sound Triumph can and will tolerate a brief period of light ping from time to time..I know this from experience over the years...Pre igniton will kill a Triumph in two seconds...
I found some info on T120RT ignition timing on Terry McDonalds site. In a Service Bulletin Road Coates recommended backing the ignition off to 34 degrees on the RT. They ran a 9.5:1 CR. He also advised changing the AAU springs, but doesn't say whether they were stronger or weaker. My guess would be stronger to move the advance point up a bit to combat detonation.
Triumph continued with 38 deg timing on the T140, but they ran only 8.6:1 on the early engines and 7.9:1 later.
 

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I’ve been playing around with the advance unit. I bought the new springs that were recommended. They do appear to be a little stronger, but they are so small it’s hard to say. I’ve been bending the spring tang to see what change that might make in how the advance works when you’re trying to start the bike. The most important thing I’ve found so far is that the felt lube strips prevent the advance from returning as it should . I’m going to try alternative materials , length, and contour.
 

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I’ve been playing around with the advance unit. I bought the new springs that were recommended. They do appear to be a little stronger, but they are so small it’s hard to say. I’ve been bending the spring tang to see what change that might make in how the advance works when you’re trying to start the bike. The most important thing I’ve found so far is that the felt lube strips prevent the advance from returning as it should . I’m going to try alternative materials , length, and contour.
I believe that @KADUTZ has done some useful experimenting with the AUU springs.
I am certain that I have seen a previous post by him on the subject.
 

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Can't you get some adaptors made up like these?
https://www.ebay.co.uk/itm/Triumph-Tiger-Cub-Stainless-Steel-Spindle-Sleeves-x2-W1649SS/162985786476?epid=1575205273&hash=item25f2b5bc6c:g:-tEAAOSw3YNXcSjL

On a tiger cub, the forks are flimsy and narrow. To fit C range forks, a wider spindle is needed, then it is sleeved up to fit into the 350/500 forks
didn't know such animals existed. the difference is only a millimeter, though, so if i go that route i'll switch back from conical to the larger disc brake axle, at 0.780, which i guess is 20mm. that would allow me to make collars 2mm thick.

the problem with the triumph forks is that the outer studs at the bottom of the sliders have a narrower distance between them, in order to capture the grooved axle without a nut on the end. whatever collar would fit the wider distance between the inner studs would have to be turned down to fit between the outer studs.

maybe there's room, maybe not.
 

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I believe that @KADUTZ has done some useful experimenting with the AUU springs.
I am certain that I have seen a previous post by him on the subject.
Peg


You are to kind. I have had a few sets lose tension due to age or heat in timing chest. There was one time 30years ago I had a problem with a new to me T140. Had a Club run the next day and springs were shot. Had an old set from a car laying around so I put them in. Worked fine for a couple of years til I got around to changing them.


As far as earlier comments dealing with the T120RT replacement springs the number shown was a stronger set of springs than stock.. I would also point out I supplied Terry Mc Donald with much of his information. Sent him a big envelope of stuff via Mick Duckworth after the Spring '92 article in Classic Bike. (For those that may not be believer's look in the June or July 92 issue where I was given credit.)


If I remember in the 70's some guys substituted springs for a 250 as they were lighter for faster advance. I wouldn't due it now due to the poor fuel.


To duc96cr if you felts are holding the weights open (In my opinion) either your springs are shot OR something is WAY out of adjustment.


As an aside since T120RT was brought up Pat Owens had his AA unit hard chromed to avoid wear and recommended H-D distributor cam lube.


Nuff for now


K
 

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What could be out of adjustment ? One question: when the advance is in the full retard position should the springs be loose , as in not snug to the posts on both ends ? It’s as if they are longer than they should be. I can’t find any specs for the springs, all I can tell you is that I bought a pair of the part number I’ve seen recommended on this forum. I’m playing around with the length and friction of the felt pads on the cam. Can anyone explain to me proper contact of the felt on the cam ? How many degrees before and after the cams highest point should the felt make Contact ?
 

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What could be out of adjustment? I don't know what
all has been fiddled with.
IF you have the AA unit fitted with springs and the weights are not FULLY retracted or if the springs are loose with no tension after fitting I suspect that is your problem. I don't know where you got the springs your supplier could have gotten a bad set or he could be selling crap.
As far as the felts they are there to apply lube. Don't think that takes a lot of pressure. Degrees of contact I have no idea.

K
 

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The springs retract the weights , they AAU snaps right back to full retard, with no felt pad mounted. But, the distance between the mounting points that the spring loops fit over does not result in zero play on the weights. You can move them ( and hence the cam) a small amount before the spring holds them back. The new springs check close to the same length as the ones I replaced, measured with digital calipers. I am 2000 miles from the bike or I’d give you exact measurements. What I’d like to know is : Should the springs have zero play when mounted ? Should they be in tension to hold the weights with no play ? Approximately how long ( how many degrees rotation ) does the felt ( when it is installed correctly) contact the cam ? You must realize that if the felt drags too much on the cam it can cause the AAU to not retract fully, meaning the timing will not be correct when you start the engine the next time. I can work this out for myself, I just thought someone might know. There are people on this forum whose knowledge of these engines far surpasses mine, so it’s easier to ask than go through the whole thing myself. For all I know this could be a common issue . It might be just a little piece of the puzzle as to why some bikes kick back, or don’t start well.
 
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