5b. Heads and Valve Gear
Heads
The two heads were both in good condition when I bought the bike. There
was a front head and a rear head supplied, which was fine by me as I was
going to build the bike to early Black Lightning specification. Later
Black Lightning's (from about 1950 onwards?) were fitted with two front
heads, as this casting was easier to bore out to 32mm without breaking
into the rocker tunnel.
The front heads are easily identifyable from the rear as the inlet tract
is slanted to the left. The rear heads are slanted to the right.
Less well known is that the 'C' heads were distinguishable from the early
'B' heads by having cast into them a small web, parallel with the spark
plug, between each cooling fin. I believe the purpose of the web was to
make the engine slightly quieter, the fins not resonating as much. I believe
my heads are early 'C' heads as the web is in place.
Early Series 'B' heads with no web.
Later Series 'C' head with web.
Pushrod tubes identify this as works head
The rear head looked to be in very good original condition, with the exhaust and spark plug threads almost perfect and the tolerance's of the rocker tunnels and upper valve guides still ok.
The front head looked to have had much remedial work already carried out on it to restore these common faults, but the good news was that the work looked to have been very professionally carried out.
This latter problem is quite common, it resulting from the aluminium rocker pin bearing moving in the tunnel when the head heats up. Once this movement starts, it does not take too long for the bore to wear to a point where the whole rocker is wobbling in the tunnel (note : to get round this, a later design of oil feed bolts can now be purchased that lock the rocker bearing in the tunnel).
Both heads had also had new valve seats inserted, again this work seemed to have been professionally carried out. It was fair to say then, that as bought both heads looked to be in good condition, ready for any tuning work I wanted to carry out.
Brass Exhaust thread insert can be seen here
on front head
( rusty look on parts is Copaslip grease)
Another brass thread insert on front head, this
one for valve cap
Next step was to have the inlet tracts bored out to 32mm and then the heads gas-flowed. In the past with Norton ES2's, I had found that opening the inlet tract had had the single most radical effect on power, allowing the engine to breath far better.
I did not know much about boring the inlet tracts of Vincent heads when I bought the bike, however, the previous owner told me that it was actually possible to bore a rear head out to 32mm, providing you were very careful!
I went out to meet Les at his home, where he had a small workshop at the back, from which he did all his work. I left the heads with him, in good company as sate around the shed was everything ranging from a Manx Norton head to a modern Kawasaki drag engine head.
Over the next year I visited him a number of times, finding him to be not only a brilliant head tuner but a real gentleman as well. He told me about some of his exploits in the second world war, in which amazingly enough he had participated as a horse mounted cavalryman in 1939, later moving on to Bren Carriers.
Both tracts were successfully bored out to 32mm, but unfortunately it turned out that on one of the heads, the inlet guide hole was slightly out of line, resulting in it being impossible to get a good valve seat cut.
Inlet Tracts after opening up - Big arent they!
Apart from the inlet tracts being opened up and polished, the other very noticeable part of Les's flowing was to relieve the combustion chambers around the valve seats. I believe the reason for this is to aid the passage of fuel into the chamber as the inlet valve opens. The whole job was beautifully done, finished off by the chambers and tracts being highly polished.
Just to show they are 32mm
If you look carefully you can just make out where the heads have been undercut around the valve seats
Both heads and barrels were in bare metal when I acquired them, which was fine while I was working on them. Once all the engineering work had been completed I wanted to finish them in a nice gloss black finish, giving them that famous look that was associated with their namesake. I know that some prefer the natural finish of a Rapide, but I have always thought the black version looks far more purposeful and imposing.
The dilema for me was more about what finish to use on the heads and barrels. I wanted something that would be both attractive and durable, but there are not many finishes that will withstand the heat given off by air cooled cylinder heads. In the past I had used brushed on 'Pot Black' which gives a reasonable satin finish and is able to cope with the heat, but unfortunately is not very durable. I felt that this restoration deserved something a bit better than that.
Bare heads after enamelling
Eventually I chickened out of doing it myself and passed it over to Bryan Dees at Deespray. Bryan is well known to Vincent Owners Club members, whose magazine he regularly advertises with, I had also heard first hand accounts complimenting his work.
Although it took Bryan some time to complete the work (I gather he is a one man band and has a lot of other work on) the results when they came back were excellent. It looks very much like a black gloss stove enamel and is a very high quality finish. Bryan also made an excellent job of masking off all the mating faces and orifices, which is very important as this can be very difficult to remove. Not only that but he delivered to my door, thanks Bryan!
When I originally bought the bike I understood that it was really the excellent main castings that I was buying, and that most of the internals would need refurbishment, including the valve gear. This was not really a problem, as in some ways it is easier to build the engine yourself with new parts, so you will know exactly what is in it.
It seems like a long time ago now (I think about 12 years), but buying the valve gear was the first large single expenditure I made after buying the bike. At that time I had been used to scrimping around at autojumbles to find new parts for my Norton's and it was nice to find such an established cottage industry in place for supplying Vincent parts.
Original valve gear looked tired
I rang Ron Kemp in South Wales and ordered everything I would need to refurbish the heads, this included the following new parts:
· Lower valve guides (ET41) and Upper valve guide Washers (ET40)
· Valve guide securing collars (screw into head to secure guides)
· Valve springs
· Upper valve spring caps (ET37) and collets (ET36/ET38)
· Valve Collars (ET35)
· Rocker Bearings (ET26). Three of the four bearings were special 'extended bearings', see below.
· Rocker Pins (ET28)
· Tappet Adjusters (ET27)
· Modified Rocker Feed Bolts (ET100). These include a lower retaining pad for securing the rocker bearings, see below.
· All washers and seals, including the large washers for the inspection caps
I also took the opportunity to buy some of the rocker oil feed pipes, as Ron had some available and the ones that had come with the bike were a bit tatty, having small dents in the pipes.
Once home, all the parts were then put in a large biscuit tin where (apart from occasional visits to trial fit a valve in the heads) they remained until I came to assemble the valve gear. Fast forward 12 years . . .
New Rocker Pipes (bottom)
By this time all work on the heads had been completed and the heads and barrels had been enameled. Given the amount of work that had been put into preparing the heads ready to accept the new valvegear, assembly was actually a bit of an anti-climax.
As part of having the seats cut, I had already fitted the lower guides. The guide arrangements for Vincent cylinder heads is very unusual, having a lower and an upper guide, which in theory, results in them running very true with little deflection. The rocker acts on a collar (ET35) that sits between the two guides. Because the lower guide has a relatively small contact patch with the cylinder head, these are retained by small screw in rings with slots in them. I had made a special tool to insert these slotted rings, which ensured that they were in fully tight, without slipping and ruining the slot. Before fitting the guides though, I had to machine the top off them, so that they would not protrude beyond the locking ring as the standard ones do. This is a necessary modification if using racing cams, else on full lift they will foul the collars (ET35).
Double ended jig on right allows guide locking
rings to be tightened fully.
Other jig helps ensure lower guide is inserted in line with top guide
I will see how I get on with just 2 sets to start with, as can only imagine this 3rd set being needed if holding sustained high revolutions near the rev limit. (Does anyone have any more information about these springs?).
Original Lightning Valve Springs.
Note 3rd spring
The rockers that came with the bike were in good condition, the feet not requiring any work other than a light stoning. Black Lightning (and Shadow) rockers I believe were supplied highly polished so I carried out the same treatment on these rockers.
I also removed any excess metal from the rockers, to make them as light as possible, without weakening them to the point of possible failure. This is a very useful exercise to carry out on any racing engine, as this is reciprocal weight and reducing it can result in higher rev's with less possibility of valve bounce. That said, the amount it is possible to reduce from these rockers I found to be relatively small.
Valve Rockers. Note difference between long eared rocker bearing and standard one in centre
To help alleviate this problem Ron Kemp supplies a special ET26, which had extended 'ears' so that more bearing metal will be in contact with the rocker tunnel. I purchased 3 of these bearings, there being little point in buying a fourth, as one of the tunnels had been re-sleeved only the length of a standard bearing. (see photograph).
The only problem with using these though, was that the threaded retaining plates had been made slightly oversize and would not fit between the bearings and rockers. Again, my lathe proved invaluable, and I was able to machine each plate to the correct size.
Final job was to insert the completed rocker/bearing assembly into the rocker tunnels. This, predictably, was a very fiddly job, taking considerable time and cussing to get them all in place. I'm sure the more experienced Vincent enthusiasts out there, on reading this will be laughing at my inaptitude at this task, but I still not sure if there is any way of completing this task without much use of four letter words!
Once the bearings were inserted I then screwed in the modified ET100 oil feed bolts, which completed the head assembly.
Completed rocker in head (with long eared bearing)
'Locking' oil feed bolt can also be seen
Finished Heads and Barrels
Valve Inspection Caps
A final cosmetic job was to fit the valve inspection caps. Early H.R.D
twins have caps with the words 'H.R.D' embossed on them, instead of the
later 'Vincent' caps. There was also an interim period when blank caps
were supplied, although I do not think these look as distinctive as the
embossed type.
When I purchased the bike, it came with a complete set of caps, but many
were of the plain variety or had seen better days. One of the caps though
was well worth using, this being a breather cap. Breather cap's allow
a breather pipe to be screwed into the top of the cap and I am told, will
greatly enhance the overall breathing of the engine. Not sure if there
is a best location to fit this particular cap, so if there is perhaps
someone out there could let me know.
Some years ago I rang the Vincent Owners Club about these inspection caps
and was lucky enough to purchase enough H.R.D. caps to make up a complete
set. It seems their pattern was slightly worn, so unfortunately the embossing
is not quite as fine as an unused original, but I was just pleased to
be able to purchase them at all. To their credit they were each supplied
highly polished and wrapped in individual tissue paper to protect them.
I have held off fitting these yet, simply because I would like to leave
the job until the end to give me something to look forward to!
Inspection Caps
Ones on far left from VOC. Second from left are original and unworn.
Top second from right is a breather inspection cap