KH primary chain alignment

[will_curry]

I took the finished twin out around my test route this afternoon.

What a transformation. I can open the throttle hard without any trace snatch and the
whole ride is so much smoother - as it should be.

[nevhunter]

How's the engine balance? Mine wasn't good even with the original (standard) pistons. They are NOT the worst bike on the road but never raced here AUSTRALIA to my knowledge. Mine sits waiting patiently for a rebalance and oil gallery clean out. Just not a high priority. Nev

[will_curry]

It's certainly no worse than I remember KHs and hopefully there will be no
need for me to strip the engine, at least until I've sorted my Mk1 engine out
with club rods.

Once the twin comes to pieces a trip to T and L for dynamic balancing is a must.
The benefits on my friends BSA twins was remarkable.

[nevhunter]

CAn you let me know when that is done and how it feels and what factor they used. My only advice so far is 65% and THAT bike was reportedly smooth. Being a 500 they are naturally better than the larger vertical twins. I've been balancing bike motors for ages but the FACTOR is good to know. Nev

[Roger Gwynn]

When I built my KH many years ago I experimented with various balance factors, changing 3 times I think and did not notice any difference between 65% and 75% but it was much worse at 80%. I tried head steadies, reaming engine tie stud holes as per Phil Irving and reducing the weight of the pistons but the only thing that made a noticeable difference was when I fitted electronic ignition. I have passed on the info about the FH engine sprockets to Draganfly, my apologies for any inconvenience caused I was sure that i used an FH sprocket on mine with only minor mods and I don't remember a problem with the spring, but rose tinted specs may be a factor.

[Simon.Gardiner]

Regarding the engine sprockets, here's a pic of what I've been running on the FH engine, note that the 'spigot' on the back is shallower than on the sprocket Will was given as an FH equivalent and in my case the sprocket sits further in towards the inner chaincase.

.
In the 1956 FH parts book the 21-tooth FH sprocket 10453-56 is also referenced with the number K98-48, which is the 21-tooth KH sprocket from 1948. (There's a '56 part number for the FH because 21-teeth wasn't an option for previous years, and the larger alternative sprocket retains its '54 part number.)
In the '56 KH parts book the 21-tooth engine sprocket has now been given the same number as the FH part (ie 10453-56) and the smaller sprocket also has a new number, it no longer has a 'K' prefix but now follows the FH format (as 10454-56).
So on this I'd say that from '56-on the FH and KH sprockets are the same. Maybe prior to '56 the KH sprockets will fit an FH but possibly the KH needs a narrower 'spigot' and a recess on the back face to allow clearance for the crankshaft oil seal arrangements (from what I can see in the books in '56 the KH gained a spacer and probably more clearance behind the engine sprocket.)
Oh what fun!
SG

[Roger Gwynn]

Oh I'm glad that someone else finds it fun! I had forgotten all this in the intervening years.

[robjameson]

This would make a huge amount of sense. I had been wondering what was done to account for the different mainshaft on the FERC models.

Could it be that the factory simply found that the FH sprocket fitted nicely, and no further work was required?

[will_curry]

I think the differences are more subtle than simply using the FH sprocket.

According to the parts list the spring, slider and sleeve are common to both configurations.

Used with an FH sprocket this configuration severely restricts the distance the slider can move and
thus the amount the sprocket can turn relative to the sleeve. With a 21t sprocket this rotation
is reduced to 'two and a bit teeth' compared to the 'nearly 8 teeth' with a 21 KH sprocket. An engine
with such a restricted action is exceedingly rough to ride. As soon as I rode mine I knew something
was seriously wrong.

Looking at the 1956 parts list and the extra parts listed I think that a spacer was provided to fit
on the mainshaft between the main bearing inner and the sleeve to move the sleeve the required
distance outboard. This spacer is, I think, "K261-56: Washer, distance piece bearing to slider".
"K168-56: Collar for sleeve" serves a similar purpose by moving the spring collar further out from
the end of the mainshaft. This achieves the desired chainline without compromising the ability of
the sprocket to rotate on the sleeve and the shock absorber remains as effective as before.

Moving the sprocket outboard however causes problems with the fit of the oil seal and this is the
purpose of "K263-56: Distance washer for oil seal".

Neither Waller nor the User's Guide provided me with any useful details and the club's collection
of drawings doesn't seem to include any of the parts concerned so it seems that the only other
source of information will be a late, unmolested KH.

[Roger Gwynn]

Ah Will, your comments lit a bulb in my tiny brain and I found this somewhat crude sketch that I did many years ago. Also there is amongst the works drawing an excellent sectioned engine drawing showing the early set up, extract below showing the early shock absorber.

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