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Late C fitted with monoblocs at factory?

gideonbok

Forum Website User
Non-VOC Member
Hi there.
I have a very late C shadow, made in 1955, engine number 10574, I believe, something like 11 engines before they made the full switch to the D series. When I got it it was fitted with monobloc carburettors, and I always assumed that someone switched from pre-monoblocs to the monoblocs. I'm starting to wonder if the machine might have been fitted with them, since they were soon going to be making the switch anyway. Anyone have any idea about this?
 

Len Matthews

Well Known and Active Forum Website User
VOC Member
Hi there.
I have a very late C shadow, made in 1955, engine number 10574, I believe, something like 11 engines before they made the full switch to the D series. When I got it it was fitted with monobloc carburettors, and I always assumed that someone switched from pre-monoblocs to the monoblocs. I'm starting to wonder if the machine might have been fitted with them, since they were soon going to be making the switch anyway. Anyone have any idea about this?

A Series C engine with factory fitted Monoblocs? Has this engine got two front heads? If not, a special adaptor would be needed for the rear cylinder and the battery carrier moved to the left. Even if it has two front heads a change of battey carrier position is still required.
 

gideonbok

Forum Website User
Non-VOC Member
It's got a front and a rear head, respectively. The battery carrier doesn't properly fit the standard battery with the monoblocs, you're right. It kind of fits, but it's very tight, and I've had to shave some of the top off the cover of the NOS battery that I've fitted into it. The previous owner had fashioned a modern style battery in an old exide box that he'd cut to fit.
 

hadronuk

Well Known and Active Forum Website User
VOC Member
A Series C engine with factory fitted Monoblocs? Has this engine got two front heads? If not, a special adaptor would be needed for the rear cylinder and the battery carrier moved to the left. Even if it has two front heads a change of battey carrier position is still required.


Stevens page 188 mentions that monoblocs can be fitted to a C series using adapter ET32/20 "without modification to the battery carrier". I think he neglected to mention that this is only possible if the rear monobloc is an opposite handed 689 model. I have 689 monobloc which was sold as "removed from the rear cylinder of a Shadow", but I have no knowledge whether it was original or a later conversion. It is stamped 689/003. It seems very little worn which suggests it was not an original fitting.
 

gideonbok

Forum Website User
Non-VOC Member
Thanks for the post. I tried to hit that I 'liked' the post, but for some reason it came out that I 'disliked' it. Then I 'liked' it, and now I can't undo what's been done. Though it may appear that I am, I'm not schizophrenic and neither am I.
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
I have a very late C shadow, made in 1955, ... Anyone have any idea about this?
If your bike was fitted with Monoblocs, Amal would have known about it. So, I checked Amal's "1955 Carburetter Settings List." That list shows the 1955 Black Shadow (as well as the 1955 Black Prince) was fitted with type 389/10 Monoblocs with 1-1/8" inlet bore. The Rapide and Black Knight are shown with 376/31 Monoblocs with 1-1/16" bore.
 

Spqreddie

Well Known and Active Forum Website User
VOC Member
If your bike was fitted with Monoblocs, Amal would have known about it. So, I checked Amal's "1955 Carburetter Settings List." That list shows the 1955 Black Shadow (as well as the 1955 Black Prince) was fitted with type 389/10 Monoblocs with 1-1/8" inlet bore. The Rapide and Black Knight are shown with 376/31 Monoblocs with 1-1/16" bore.

Thanks Magneto man,
This means that the other carburettor would be 689/10??
or was listed only the 389 as intended for two front heads?
if one would like to install two monobloc 1-1/8 for a normal set up (front and rear head) what should order now?
thanks!
Eddie
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
This means that the other carburettor would be 689/10??
or was listed only the 389 as intended for two front heads?
I'm in transit on the way back home, so I won't have the Amal list to refer to until late tonight. However, I'm 99% certain I would have quoted both L and R carburetors in my post if both were in the Amal list. This means that there's only a small chance the 689 was specified for the rear head, i.e. 389s would have been on both heads. I'll double-check this after I get home.
 

Magnetoman

Well Known and Active Forum Website User
VOC Member
I'm 99% certain...
I'm back from my trip, checked the Amal lists, and now am 100% certain. For 1955 only the one 389 Monobloc model (276 for the Rapide) is listed as being used on both cylinders.

I don't have time today to search through the entire Amal list to see if there are any machines that used it in 1955, but perhaps the 689 had not even been produced as yet(?), forcing Vincent to make do with what could be supplied. It was very early after the introduction of the Monobloc, so perhaps Amal hadn't yet started producing the left-handed version (I write this fully expecting someone to point out a very obvious example of a 1955 vertical twin that would have required a 689 in order that the float bowls not interfere -- although, even the smallest bore 689 is pretty large for any vertical twin of the time).
 
Last edited:

highbury731

Well Known and Active Forum Website User
VOC Member
So if you are fitting Monoblocs to a standard C with front and rear heads, do you use 389s (and not the 689) with the special rear manifold?
 
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