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ET: Engine (Twin) Black Shadow ATD

Dynamiteboss

Website User
VOC Member
Hi, Richard Gibson here, from Rockford, Illinois, USA. I’m new to the Vincent world, but have been wrenching for a considerable time; hot rods & motorcycles in the ‘50’s & 60’s, aircraft 70’s -> 2000, then British cars (Morgan’s) now a Vincent.

I purchased a 1951 Black Shadow, complete, assembled and unrestored at auction in October 2019. It has been in storage since 1991. I plan to clean it up and keep it in its original unrestored condition as much as reasonable.

While adjusting the valves, I discovered that the #2 (front) exhaust valve was not working properly, which led to opening up the timing chest and discovering a multitude of problems, which I have addressed and repaired. (hopefully) Basically, all moving parts in the timing chest are new, including the ATD.

While setting the ignition timing (using rear cylinder) for the rebuilt original Lucas mag, I discovered that the new ATD doesn’t have enough ”range” to allow me to use the ignition specs I got from the Rider‘s Handbook; retarded setting 4’ BTDC, max advance 38’ BTDC. The most range on my new ATD is 25’, so if I start at 4’ BTDC the new ATD will only advance to @ 29’ BTDC. (I’m actually working backwards from that, starting at 38’ full advance, but can only retard to 14’)

Compairing the new and old ATD’s I find that the new ATD has a rotational range of @ .225” measured at the outer ears, while the old ATD has @ .350”.

Something seems out of wack to me. Any suggestions? Any thoughts gratefully appreciated.

1st photo, bike as I bought it, 2nd, as it is now, 3rd, timing chest on initial opening
 

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vibrac

Well Known and Active Website User
VOC Member
First the ATD a half time pinion what does that mean well 38 degrees on the crank is 19 degrees on the ATD I should also read here where the general consensus is 34 dregrees is more appropriate with todays joke petrol
of course you measure on the crank (using the crank feed bolt hole) with the ATD held open
 

Dynamiteboss

Website User
VOC Member
First the ATD a half time pinion what does that mean well 38 degrees on the crank is 19 degrees on the ATD I should also read here where the general consensus is 34 dregrees is more appropriate with todays joke petrol
of course you measure on the crank (using the crank feed bolt hole) with the ATD held open
Yes, I understand that degrees on the ATD are 1/2 of crankshaft degrees. Everything I referenced above is in crankshaft degrees. If I do the math on the ATD movement, my new ATD is moving (rotating) @ 11 1/2 degrees. My old ATD rotates @ 17 degrees.

I agree about the petrol. Once I get everything sorted, I plan to use 35’ maximum advance.
 

LoneStar

Well Known and Active Website User
VOC Member
You may simply have the wrong model ATD. Lucas made them with several range specifications:

105.jpg

It does appear that all the 48-tooth ones have the correct range, but possibly a 48T gear has been installed on one of the other mechanisms.
 

timetraveller

Well Known and Active Website User
VOC Member
Just check what the total range in crank shaft degrees is. One needs to have firing at about 4 de BTDC for starting and about 34 - 35 degrees BTDC fully advanced for running. That is a range of, say,30 crank shaft degrees or 15 ATD degrees. It is possible that a new ATD has already been set up to give the reduced range needed with modern fuels.
 

Dynamiteboss

Website User
VOC Member
Just check what the total range in crank shaft degrees is. One needs to have firing at about 4 de BTDC for starting and about 34 - 35 degrees BTDC fully advanced for running. That is a range of, say,30 crank shaft degrees or 15 ATD degrees. It is possible that a new ATD has already been set up to give the reduced range needed with modern fuels.
That is exactly what I have been trying to do, but my new ATD will only allow @ 25’ range in crankshaft degrees.
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
Richard my handsome, please get rid of that aluminum idler before you reduce yourself to tears when it shreds itself, blocking oil filter and generally leaving your engine in a very sorry state. Although I did use one myself in my early years not being able to aford a steel idler.
One of the popular mods for economy is to fit twin plugs giving better acceleration, but the reduction of advance is about the 10 degree mark so requiring 4 BTDC retarded and about 25 to 28 BTDC advanced so you might need to build up (weld) ATD stoppers.
bananaman.
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
That is exactly what I have been trying to do, but my new ATD will only allow @ 25’ range in crankshaft degrees.
You can build up the ears with a little weld if you want to reduce the range so in your case you could file a little of the ears until you got the range you wanted.
 

davidd

Well Known and Active Website User
VOC Member
Richard,

If you can find a Vincent ATD I would endeavor to do so. That would save you some time even if the ATD that you have can be modified.

The aluminum gear seems to be in good shape, so I would be inclined to leave it alone for the time being.

There is some type of damage to the rear cam spindle or the timing cover. It would be nice if you could post a photo of the inside of your timing cover. There should be four Simmonds nuts and there are only three. There is a round disc in place of one of the correct nut on the rear cam. This nut controls the oil to the cam, so it may indicate that the cam has been damaged. I would rank this as "high priority," but everything may be fine, it is just something we rarely see. Each spindle that has a hole through it should have a Simmonds nut (like a Nyloc). The three that you have on there seem to have a red material inside them. It may just have been the lack of a Simmonds nut.

David
 

Dynamiteboss

Website User
VOC Member
Many thanks to all that have replied.

I believe Lone Star has found the problem; my newly purchased ATD has mismatched parts. I will return it to the vendor and get the proper one for my Vincent. Thanks much Lone Star. Others may want to look at the information (above) you sent me.

The view of my timing chest is as I found it originally. It had a multitude of problems; the front exhaust spindle had come loose, damaging the case, front cam, follower & timed breather, many missing nuts, washers & spacers, spindles rotating in the case, missing bits from the exhaust valve lifting system and more.

All moving parts in the timing chest have been replaced with latest updated new parts, including replacing the aluminum idler with a steel one.

Hopefully I can go for a start up this spring.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Interesting from Lone Star, There are only 2 Clockwise ones , And the other one has only 19 teeth ?.
I have never been a fan of the ATD, I prefer the "D" Distributor,
But it's what ever you have.
 

Dynamiteboss

Website User
VOC Member
Interesting from Lone Star, There are only 2 Clockwise ones , And the other one has only 19 teeth ?.
I have never been a fan of the ATD, I prefer the "D" Distributor,
But it's what ever you have.
I suspect that somehow, during assembly, that the mechanism from a 47553 unit got put onto a 48 tooth gear, and is now giving me grief. I did the math on the amount of rotation: my old ATD will give @ 33 degrees advance at the crankshaft. The new ATD will give @ 21.
 

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