classic motorcycle forum

"I'm just pondering the wisdom of splitting the crank up to check the big-end bearings..."

Yes it's a tricky one, perhaps depending on what you want to do with the bike. If you do pull it apart keep in mind that it is tricky to get it back together and running dead true. If you've not done it before best left to an expert? I've done it lots of times, and most often it's gone ok. Only once did it defeat me entirely (i.e. no better than a couple of thou run-out on the shafts after trying everything I know) and I had to pass it on to the expert who used appropriate (unknown to me) magic to get it running just so.

The epoxy is interesting. Often cases an an engine can be quite porous to oil and painting the inside with something (glyptal, expoxy of some kind) can keep the outside clean. Hopefully there's no major corrosion being covered up.

Leon

Yeah - I think I may have a contact with someone locally who runs a Cooper 500 car, so hopefully will have experience (or knows someone else) in doing that job.    Even though the bike is only a road-bike, and is running low compression (9:1 and petrol as opposed to 15:1 on dope), I'd like it to be "as good as I can get it".  Ideally I want to get into the cycle of "ride in summer / maintain in winter", however the learning experience of my first full strip down is taking longer than I had expected, mainly due to the unexpectedly poor condition of some components, and the lack of time I'm getting in the workshop.

As you remark Leon, placing trust in auction house puffery is moving on to shaky ground. Even the auction houses warn you against it.
So far as engine swaps are concerned a major virtue of Villiers engine was they didn’t change from year to year so you could safely exchange engines without worry plus of course for years Villiers powered bikes were so poorly regarded that it made more sense to replace a worn out engine with another less worn secondhand one than actually spend money refurbishing one. After donkeys years of these old bangers being mauled about its bizarre that we should expect the numbers to match up.
As you say, it’s only the ones with an established provenance that make sense. Provenance is all.

Villiers would add an extra letter to the engine prefix for various reasons, not all of which I yet know but no matter what the underlying engine remains the same.
I do know the extra ‘F’ refers to FIXED ignition. Previously Villiers had clamped the magneto backplate onto the protruding main bearing bush. Slackening off the clamping screw allowed moving the backing plate back and forth to get the ignition timing just so. Villiers even fitted an advance and retard lever to the backplate to facilitate this. It didn’t work. Getting the clamping force just right, loose enough to move but tight enough to stay put otherwise was nigh impossible. Some factories fitted some sort of device to hold the lever in place but these have mostly disappeared over the years.
The idea of slackening off the clamping screw to tweak the ignition just so remains a good one, just make sure you tighten it up again afterwards.
In the end Villiers not only dropped the idea but went further and mounted the backplate permanently in a fixed position, hence the additional ‘F’.
This came late in the XII-C’s life. The earliest engine number I have is GYF 10421, first registered in May 1939.

There seem to be a lot of GY-prefix engines used in little Francis Barnetts in the 1930s, like this one: https://cars.bonhams.com/auction/29728/lot/229/1933-francis-barnett-148cc-lapwing-27-frame-no-c27176-engine-no-gy-4934/

Some of them have a GYF prefix. What does the 'F' mean, and was there a serial number reset to go along with it?

Leon

... cont.



The scary part!!




Plonk!  (tinkle tinkle tinkle..... feck where did the pins go!)


There's 10 of the little buggers each side.


Output shaft:



Magnet to pull the pins out when they refuse to fall out by themselves.



Simple engines are great.



Timing side: ALL the pins fell straight out!


Timing side bearing liner is ok.



Output side not so much....

That patch feels rough as hell. New liner time.


I'm currently mentally debating the wisdom of breaking the crank down... looks simple enough... it's the reassembly that scares me!





Insides of the cases are epoxied to buggery.  I don't know if this is my Dad's doing... but it's likely.









Another view of that liner.



These "thimbles" screw into the cases and provide the base for the screw-down head rods


They're a git to get loose...


Paper gaskets infused with oil take heat well....


I'm reliably informed that the thimbles come out a lot easier if they're assembled with coppa-slip.  Luckily, I've got plenty!

The thimbles have these little pucks underneath to stop any galvanic reactions with the cases (or that's what I've been told - it could be just to provide a flat step for the thimble to wedge down onto).



Epoxy:


I'm glad to see that the drain plug hasn't been epoxied over....


Blue hylomar... my old friend!

You can sort of see the "lip" that JAP used to create a labyrinth seal on the cases here.

As said - I'm just pondering the wisdom of splitting the crank up to check the big-end bearings - they "feel" ok - but while I'm here it might be worth doing.  I'm just being cautious about that because bolting it back up "straight" is going to be paramount.

All that only took me about 90 minutes, and I managed to finally get down to the local "Classic vehicles" club night and join the club - they do a monthly meet only about 3 miles from me so it's dumb really that I've not joined before now.  Already hopefully got leads on a couple of hopefully useful contacts.


Just in case anyone is wondering: I'm using this thread mostly for myself to provide my thoughts and notes as I go, for reference to when I put it back together, or do it again!  Pretty sure there's no-one else on the forum with a JAP speedway engine to dismantle..   (happy to be proven wrong though! )