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#612417 - 08/11/15 12:16 pm T20 Tiger Cub: help with setting advance, please  
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take-it-slow Offline
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Hello to all. New member here. Hoping there are more Tiger Cub owners here than over on the Triumphrat.net site who can offer some experienced help.

Have a '65 T20 Tiger Cub (USA version) that I have just gotten back on the road after sitting in a fellows barn since 1975. She starts up first or second kick and runs well up to about 40 mph as checked with my GPS.

At that point opening the throttle more does not seem to produce more speed or more power... and on level ground.

Set up the advance using the Haynes book for this model/year using a dial gauge inserted into the spark plug hole. Set to 8 degrees BTDC which corresponds to .016" on the gauge.

Some confusion as to how the automatic advance unit comes into play here. Poster on the other forum has me way confused saying it needs to be fully extended (weights fully out) and that is contrary to the book.

Can anyone offer some real world guidance, please.

Thanks

More info: AMAL 32 carb fully cleaned, OEM style large round metal "donut" air cleaner, great compression... a bear to kick start. Smooth and strong at idle and when running at speed.





Last edited by take-it-slow; 08/11/15 1:02 pm.
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#612430 - 08/11/15 2:04 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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8 degrees BTDC would be the retarded position so the weights should be closed as for starting, but you should be timing it at the fully advanced position as if you get that wrong you get a holed piston and have a wrong retarded position is not as critical. What are the marking on the AAU, they can be 10 degree, 12 degree or 5 degree and that's before any previous owners modify them. 32mm carb sounds way too large for a cub, 26mm seems more like it, are you sure its 32 and not a Monobloc 376 or such.

#612431 - 08/11/15 2:07 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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I have never heard of fiddling with the advance mechanism when setting the timing.
The timing is given fully retarded, 8deg in your case - as you say .016in before TDC at the piston crown. I understand this equates to 32deg fully advanced - but that is only of academic interest.
I use the same method as you for setting the timing and it works fine. Your loss of power at the top end may be due to other factors or you may like to slightly advance and/or retard your ignition to see if you get better running - a lot of owners try this but it must be done with care.
You may not have seen the dedicated Cub Site, well worth a look:
http://cubsite.com/cubforum/index.php

#612436 - 08/11/15 2:32 pm Re: T20 Tiger Cub: help with setting advance, please [Re: kommando]  
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Originally Posted By kommando
8 degrees BTDC would be the retarded position so the weights should be closed as for starting, but you should be timing it at the fully advanced position as if you get that wrong you get a holed piston and have a wrong retarded position is not as critical. What are the marking on the AAU, they can be 10 degree, 12 degree or 5 degree and that's before any previous owners modify them. 32mm carb sounds way too large for a cub, 26mm seems more like it, are you sure its 32 and not a monobloc 376 or such.



AMAL Type 32:



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#612437 - 08/11/15 2:35 pm Re: T20 Tiger Cub: help with setting advance, please [Re: doug748]  
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I have to apologise to Kommando as it looks as if my post is directly contradicting his, not the case, we must have typed out our responses at the same time.

It might be worth checking you have the right jets in the carb. The figures I have are:

(AMAL 32/3 11/16in choke) Main Jet 110 (Home market model was 85), Pilot jet 15, Needle Jet 0.103 Needle pos 2, Slide 4.

#612438 - 08/11/15 2:42 pm Re: T20 Tiger Cub: help with setting advance, please [Re: doug748]  
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What komando said .
And

Is this a battery , normal DC coil , ignition ?
Or an ET ignition ? With the smaller AC coil

And what AAU is it using ?
The ET ignition needs to run the 5 AAU .
If the 5 AAU is used with , other normal , rectified current DC set ups .
The 5 AAU limits advance if timed at idle , so it can be set to idle nicely or rev well , but not both .

Set the bike using a full advance method , it may be harder to start , if the aau can not fully retard , but it will be more fun to ride

.

#612439 - 08/11/15 2:57 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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The simplest way to see if you've got the dreaded Energy Transfer (ET) ignition is to see how many wires come out of the alternator stator.

ET has five wires.


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#612441 - 08/11/15 3:11 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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Three wires out of the alternator. Has a 6 volt battery which it uses to start. Owners manual does speak of the ET in that it can be started if the battery was to fail. Set switch to the left. Have not really tried that as yet.

I have the AMAL 32 carb and it is factory stock for the 1965 US version T20. I have the sales catalog that clearly shows this and it is in the owners manual, parts book and repair manual for that year bike.

The advance unit is 10 degrees, also stock for this model T20 bike and I have the correct springs on there now according to the parts book for that year bike. My concern on these springs is they are very tight. Tighter than the ones that I replaced (which were clearly stretched) and tighter than the ones I have on the spare 12 degree advance unit I recently bought at a swap meet.

If they were limiting/preventing the unit from expanding would that possibly account for my "brick wall" issues?

If so, is it worth trying other springs... the ones from this 12 degree for instance... or will that damage the engine?

Last edited by take-it-slow; 08/11/15 3:25 pm.
#612445 - 08/11/15 3:47 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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Count your blessings, then forget anyone mentioned ET ignition.

The EMG (emergency) switch position is a feature of non-ET Triumphs.


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#612446 - 08/11/15 3:48 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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Weaker springs won't hurt anything. Could possibly make it kick back when starting and race a bit when it should be idling slowly.

Probably worth a try.


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#612459 - 08/11/15 5:01 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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If you had a 12 degree and now have a 10 degree then your revised retarded setting is 12 degrees btdc (aau degrees are cam degrees which are 1/2 crank degrees) to keep the 32 degree fully advanced figure.

#612460 - 08/11/15 5:12 pm Re: T20 Tiger Cub: help with setting advance, please [Re: triton thrasher]  
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Yes I see http://amalcarb.co.uk/carbspec/carburettor/spares/id/5829/
You have the stock carb for your year.
My 67 mountain cub came stock
with an AMAL 376/314 ...15/16in choke

Quote:
If they were limiting/preventing the unit from expanding would that possibly account for my "brick wall" issues?

Yes , your thinking is correct , the weights , the springs ,
how smoothly the aau rotates against any worn area and centrifugal force ,
all play a part in the advance curve .

If you time the ignition , using a full advance method ... at 32 ... with the aau locked @ full advance for static timing ... and using your softer springs ,
then the worse that can happen is the softer springs dont fully retard the aau
as rpms drop ... and you can experiment with spring strengths from there .
Put the heavier ones back on and see if it still revs as well .
I've read that aau springs can be cut for cheap from old oil-seal springs , but have never tried it .

#612462 - 08/11/15 5:19 pm Re: T20 Tiger Cub: help with setting advance, please [Re: kommando]  
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Originally Posted By kommando
If you had a 12 degree and now have a 10 degree...


No, sorry.

I said I found a 12 degree at a recent vintage motorcycle swap meet. I bought it for $5 as a potential spare, but I am not using it. I was thinking the softer springs it has might be worth a try on my 10 degree.

Some of the folks here seem to concur.

#612464 - 08/11/15 5:25 pm Re: T20 Tiger Cub: help with setting advance, please [Re: quinten]  
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Originally Posted By quinten
If you time the ignition, using a full advance method ... at 32 ... with the AAU locked @ full advance for static timing ... and using yoursofter springs...


Sorry, I'm a bit behind the curve on all this having had only bikes with CDI's up until now. This advance/retard has me confused.

You see how I have it set now. By the book at 8 degrees, the 10 degree stock AAU closed (retarded, correct?) using a dial gauge to get .016" BTDC.

Please explain, step by step, what you are suggesting I do?

Thanks!

BTW: What do you mean by "static timing"?

Last edited by take-it-slow; 08/11/15 5:27 pm.
#612531 - 08/12/15 3:38 am Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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Out There!
Two tips:
As you must know, the only way to properly time your engine is with a strobe with the engine running. If you cannot mount a degree wheel to the crank securely, you can attach it any old which way, use a piston stop to find TDC, then mark your drive sprocket or rotor for the proper amount of advance, and then strobe time it.
(A piston stop stops the piston somewhere before TDC, you then rotate the crank in the opposite direction until the piston stops again, and true TDC is at the exact midpoint. This is more accurate than using a dial because there is always a few degrees of no piston movement at TDC.)

Or, for the fast and dirty method, simply advance the timing incrementally until you get detonation or excessive kick-back on starting, and then retard it a bit. I've used this method on many of my bikes with only good results.


When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
#612616 - 08/12/15 3:13 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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Originally Posted By take-it-slow
Originally Posted By quinten
If you time the ignition, using a full advance method ... at 32 ... with the AAU locked @ full advance for static timing ... and using yoursofter springs...


Sorry, I'm a bit behind the curve on all this having had only bikes with CDI's up until now. This advance/retard has me confused.

You see how I have it set now. By the book at 8 degrees, the 10 degree stock AAU closed (retarded, correct?) using a dial gauge to get .016" BTDC.

Please explain, step by step, what you are suggesting I do?

Thanks!

BTW: What do you mean by "static timing"?

Static simplicity means not in motion .

What you have done is 'by the book' static timing 'at full retard '
With this method , If the aau is faulty ,, the aau may not fully advance and rotate
to 32 as the rpms increase .

the full advance method is similar , it is also stactic , but you are mimicking the piston and AAU plates position , as if the bike were running 'at full advance.'

find a way to temporality lock the aau at full advance (rotated),
Position the piston at 32 btdc on compression stroke . Position the 'locked 'aau so the points cam is just starting to force the points to break contact . Secure the aau in position and remove whatever you used to temporarily lock the aau at its fully rotated (advanced position)

Now,, unless the springs prevent the aau from rotating (advancing) , the bike is set to run best at full advance .

As you can see there is a potential 24 of error as the aau advances of retards .
Static timing at 8 allows any error to occur as the timing advances.
A static time at 32 mostly should only allow any error to occur as the rpms decrease .
From the pistons point of view , its better to work from 32

Strobing a cub , never done it .
On cubs , the stator is attached to the primary cover , strobing can be done ,, but its a pain ... the primary cover , stator and stator wire have to be , somehow , held out of the primary chain while the engine is running .... but not before a custom pointer is fitted . I have never bothered to strobe mine .
Get it static at 32 and go from there by sound .
Pinging is to advanced
Farty is too retarded

Disclosure: my bike came with a 5 ET AAU and 12 volt battery coil ?
The aau now lives in a box and I have fitted a Pazon sure-fire .
... static , then ear timed .

#612619 - 08/12/15 3:30 pm Re: T20 Tiger Cub: help with setting advance, please [Re: quinten]  
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Originally Posted By quinten
Find a way to temporarily lock the aau at full advance (rotated). Position the piston at 32 BTDC on compression stroke. Position the 'locked 'aau so the points cam is just starting to force the points to break contact. Secure the aau in position and remove whatever you used to temporarily lock the aau at its fully rotated (advanced position)


Most appreciated. I've been doing some reading so some of this is beginning to sink in.

Questions:

1) Why 32 degrees and how did you come up with that figure? If I have a factory stock 10 degree AAU and use 8 degrees for factory advance is that not 28 degrees total?

2) Is there a way to convert degrees to inches so I can use the dial gauge method. Seems to be way more accurate... in .001" increments in my case.

3) You say "secure the AAU in position" as the last step, but do you really mean the points disc?

As to running the bike with no alternator coil in place, apparently it can be done fairly easily using another 6 volt battery to supply current between the coil and ground.

Some suggest that this way you can use a timing light to "see" if the AAU is working and at what RPM (using an external tach of course). Also will allow you to check the spring tension to see if the AAU is not opening or opening too soon... before, say, 2500 rpm or ?? (not sure about the speed so please inform me) and if it is not closing correctly upon RPM drop.

This, based on paint markings for full advance and 0 degrees on the flywheel and using a pointer on the casing

All sounds easy but getting it to really work is another matter.

I will start your your method.

Last edited by take-it-slow; 08/12/15 3:48 pm.
#612674 - 08/12/15 9:42 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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Originally Posted By take-it-slow
Originally Posted By quinten
Find a way to temporarily lock the aau at full advance (rotated). Position the piston at 32 BTDC on compression stroke. Position the 'locked 'aau so the points cam is just starting to force the points to break contact. Secure the aau in position and remove whatever you used to temporarily lock the aau at its fully rotated (advanced position)


Most appreciated. I've been doing some reading so some of this is beginning to sink in.

Questions:

1) Why 32 degrees and how did you come up with that figure? If I have a factory stock 10 degree AAU and use 8 degrees for factory advance is that not 28 degrees total?

2) Is there a way to convert degrees to inches so I can use the dial gauge method. Seems to be way more accurate... in .001" increments in my case.

3) You say "secure the AAU in position" as the last step, but do you really mean the points disc?

As to running the bike with no alternator coil in place, apparently it can be done fairly easily using another 6 volt battery to supply current between the coil and ground.

Some suggest that this way you can use a timing light to "see" if the AAU is working and at what RPM (using an external tach of course). Also will allow you to check the spring tension to see if the AAU is not opening or opening too soon... before, say, 2500 rpm or ?? (not sure about the speed so please inform me) and if it is not closing correctly upon RPM drop.

This, based on paint markings for full advance and 0 degrees on the flywheel and using a pointer on the casing

All sounds easy but getting it to really work is another matter.

I will start your your method.

1... 32 is from " the tiger cub bible " it shows the 10 aau retard setting as 12
2... the book also lists 32 as equal to .238" btdc
The stroke is 64mm
The conrod center to center 123.825mm
An online calulator agrees http://www.dansmc.com/mc_software2.htm
3... yes , my description could have better , its been to 2 years since I tossed my aau in a box .
I dug it out and will update , when I have more time , one way , to lock the cam in the advanced position

Not sure if this book preview will post , but here's the tiger cub bible appendix with all the important stuff .
https://books.google.com/books?id=kgwAYJ...wIVxKoeCh3cLQQ0

#612702 - 08/13/15 5:26 am Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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1) Why 32 degrees and how did you come up with that figure? If I have a factory stock 10 degree AAU and use 8 degrees for factory advance is that not 28 degrees total?

The original AAU was a 12 degree unit not a 10 degree.

Your bike is 50 years old, at several points in its history spares were very hard to come by and wrong or different parts were fitted to keep it going, hence the reason for timing to fully advanced in my first post as you can never be sure what's really in there. In 1965 strobbing was just being introduced so the book says time to retarded, but within 2 years virtually all references were to fully advanced as the windows in the primary covers were added but the old manuals were not updated and the older bikes did not have the window for strobbing anyway.

#612729 - 08/13/15 10:27 am Re: T20 Tiger Cub: help with setting advance, please [Re: quinten]  
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Originally Posted By quinten
32 is from "the tiger cub bible" it shows the 10 AAU retard setting as 12 (and) the book also lists 32 as equal to .238" btdc


So that means the initial static 8 degrees now becomes 12 degrees. Then, add to that the 10 + 10 for the advanced setting to get the 32 total degrees for advanced.

Was not able to figure out how to use that computation site but going from .016" to .238" seems a drastic change. That means it is firing almost 1/4" before TDC, now.

Are we certain this is correct?

BTW: The index for that book does not show up on my screen. Says those pages are not available.

Last edited by take-it-slow; 08/13/15 1:07 pm.
#612759 - 08/13/15 1:14 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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Quote:
The index does not show up on my screen.

Try clearing your browsers cache or clear you RAM.
It a google book preview , sometimes I can pull up the page I want , quicker than looking at my digital copy of THE TIGER CUB BIBLE . sometimes google says 'I'm over my limit ' and will not show . the book is extremely comprehensive and worth the price just for the appendix . There is the usual number of different builds from the factory and/or afterwards , Cam profile/piston compression and carburetor differences . 32 seems is a safe place to start .
Try Search "triumph cub conrod length" , if you can get the book to preview , its at the bottom of page 170 .

The book shows 3 AAUs used in side points models .
A 10 unit , timed on various models advanded @ 32, 36 and 40 retarded = 12 ,16, 20
A12 unit , timed on various model advanced @ 32 and 40
And a 5 ET unit , advance timing = 32. retard = 22
.

#612898 - 08/14/15 11:11 am Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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Thanks.

So last night I played around with setting the timing using the advanced method you describe, here.

I made up a small wooden "doughnut" that allowed me to lock the AAU with the same bolt it uses to hold it on the shaft.

What I found was, setting the advanced timing of .238" was going to give me somewhere around .003" to .006" BTDC for the non-advanced (fully retarded) side of things.

Since that was much less than the original book value of .016" I am back asking if this all sounds correct?

Also, where do I need to be careful as far as dangerous engine pre-ignition/knocking? Is it more likely to come if the static timing is set too far advanced or too close to TDC?

Added: One thing we have not mentioned here is fuel octane. Are these settings from the Tiger Bub Bible taking into account using a higher than normal octane fuel or are they based on regular 87 octane?

The higher the octane the rating the more you can advance the timing before engine knocking will take place.

Thanks for your continued help on this. Want to get it right. Have a big British bike show this Sunday in East Hampton, CT and will be riding the Cub there to put in the show. Anxious to get some feedback from folks who can really appreciate this stuff.

Last edited by take-it-slow; 08/14/15 1:58 pm.
#612915 - 08/14/15 1:50 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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It is over advanced timing that commonly causes knocking.


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#612954 - 08/14/15 7:30 pm Re: T20 Tiger Cub: help with setting advance, please [Re: take-it-slow]  
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I'm no expert on the Cub models but most centrifugal type mechanical advances have the full advance in by 2500 rpm. So almost all of your riding time except for start up and idling at stops is going to be at the full advance. That's why most bikes with mechanical advances that you can strobe have only one mark at full advance and you check it at 2500 rpm. It's critical that you get the full advance correct because that is where the engine is doing all it's work. The retarded setting isn't even checked, though you do look to see if it retards and advances okay. The retarded setting is basically to help start the bike and on idle. If it does those things okay then it is probably close enough. Generally, if for starting it's too advanced it will let you know by kicking back.
As far as preignition or pinging or pinking, you need to be concerned at this full advanced figure because again that is where the bike is most of the time. You especially want to keep the revs up on these old bikes and downshift instead of opening the throttle under load.
I don't know why you would not want to buy the highest octane gas you can get. The cost on most hobby bikes isn't that significant. Give the bike every chance it can get to not ping.


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#612976 - 08/15/15 1:11 am Re: T20 Tiger Cub: help with setting advance, please [Re: htown]  
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quinten  Online Content
BritBike Forum member

Joined: Sep 2013
Posts: 1,580
Pacific northwest


How does the bike run now ?, fully advanced timed @ 32 ?

Thats the important thing . Not that the bike is 'by the numbers'

A little knock during tuning is not going to hurt the piston .
What your looking for , is the performance to engine longevity area ,
just short of pinging under load .
... with whatever fuel , and under the conditions in which the engine is expected to perform .

Yeah , your numbers dont add up .
What was your procedure for determining retarded-timing ... piston-position after
Setting from timing from the advanced side ?
Are your numbers right ?
Did the aau taper shaft slip ?
Gear lash error ?
Has the 10 slot in the aau backing plate been modified , by file or use ?
Is it really timed at 32 advanced ?

If the bike still runs like crap ,
Try Timing it again , and see if you get same numbers and performance ?

Most importantly , How does it run ? What was the original problem again ?





... for advanced static timing ,
if your points-cam-lock-tool 'doughnut' ... had a bite out of it ,( only 3 sided ) ,
You could slip it under the washer
Without having to fully remove the center bolt .
.

.

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