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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rex on April 06, 2026, 09:58:57 AM »
Those different tappet settings  when doing the valve timing is a Velocette foible too.
I assume (though I've never given it much thought) that it stops the valve spring operation from affecting the valve timing measurements.
Incidentally, when I was fannying around with the valve timing on my Venom (the timing marks were wrong- another long story) someone more experienced than me said to set the valve timing up just rocking at TDC on the exhaust stroke as a good start, and he was right. It was as near as..
Clearly not satisfactory on a Honda, but for something designed in the 1930s it was OK.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on April 05, 2026, 10:49:49 PM »
Aaaand I got into the workshop today as well! :D

I spent some time reading Fenner, Pitman, Irving and Greenwood... and while they don't disagree with each other completely.... there are some differences. :roll:

But - we'll get to that.

Back in the workshop I double checked the current setup:

This note tells me how the timing pinion on the crank-shaft was fitted prior to dismantling:


And that's how I fitted it:


The books had said that one trick was to fit the mag-platform/timing chest cover to check the backlash and to ensure that the gears weren't jumping about.

So I fitted the studs: using the double-nut trick to get the studs themselves nice and tight:


Timing chest cover in place (but not pushed fully home)
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This is what I was getting as backlash with both valves open.




2 degrees of backlash.  1 degree is what is mentioned in the books, so that's something to talk to the guru about... along with other things, but I'm not distubing him on Easter weekend!



I carried on regardless - it's all good practise.
You can't really see it here.... but the push rods are ever so slightly not straight.... which means they should be replaced.



I played with the timing wheel and piston tell-tale until I got the 0 degree mark right at TDC. 


The tappet clearance, according to one of the books should be 0.003" and 0.004", then reset to 0.002" once the timing is done: which seems a tad odd... but this comes from the Greenwood book - which is based, from my understanding, on racing experience.






Set both sides easily enough.

This is the timing numbers from the 4 books I've got....


I wanted to check the valve openings with the dial guages, so I dug out the ally bracketing I had found a few months ago and made a start on making up the 2 small brackets I needed.








Bit of heat to make the bend easier


Along with an assist from my number one, all time, favourite tool. :D


The holes for the small end are 1/4", and I ended up doing the other end 1/4" as well - turns out the dial guage lugs were exactly that size. :)


Guages fitted and aligned.



I lost count of how many times I spun this thing.
I marked the "correct" timings on the wheel in black, and the timings that I had, which were surprisingly close for a first go, in red. But I can't quite make sense of the offsets: I had expected that if they were "early" at one point, they'd be early all round.... but they're not... not quite... I am wondering if I've got a "sporty" cam here... but will be talking to the guru about it first.



One other thing I have seen a photo of, is a little handle on the timing wheel to make it easier to rotate, so I figured that might be worth adding.


I used an M5 bolt and a cork...  :D  It may get improve upon in the future!


So - I need to talk to the guru next week, and buy new push-rods, along with the ends (which come separate), a new oil-union for the rocker box, some new oil-nut fittings, a spanner to fit the buggers (if I can find the right one),

I have another job coming in which necessitated moving a few things about in the workshop... and while doing so I discovered that the right side fork is weeping oil... and there was oil under the gearbox, which I think "might" have been coming from the kickstart shaft.  Goldarn it! GAH! :(
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on April 05, 2026, 10:08:36 PM »
So - I got into the workshop for a lengthy session on Saturday... lots of photos!

First I turned the piston around... :roll:  The gudgeon pins are getting a little easier, but they're still gits to get into place properly.

Then confirmed that the ring gaps were in the right places:




Fitted the ring clamp


Then I fed some oil into the output side main bearing, to make sure it has some. Mainly because I still don't really see how oil gets into that tiny hole... just from splashing up??


I'd decided to use the RTV for the base gasket this time. (Once I'd cleared the dried out stuff in the nozzle.)


It's a lot more controllable than the 3Bond.


I put a layer on the top of the gasket too, once I'd got it in place over the piston.  I managed to not get too much goo in places it shouldn't be!


Cylinder back on. Wasn't too hard this time.


Prepped the head gasket again - both sides this time. Note to self... that mat is NOT fully heatproof... :D (I'm sure I took a picture of the somewhat heated newspaper the mat was sitting on...)


Before dunking it.


I wanted to redo the head gasket mainly because I'd only heated it up on one side previously and I didn't think it had "taken" properly.

Head gasket in place.



Once I'd spun the head rods up into the head I put the whole thing into the vice again to get things tight.


Fitted the timing wheel - mainly because it give me a decent grip for rotating the thing. :) (and marked a reminder....)


Stuck the tell-tale into the plug hole:


Fitted the lower valve covers.


Fitted the push rod guide fittings. (Only using the adjustable because they're rather large...)


Valve caps.


Fitted the rocker box


These two oil feed nuts are an absolute !"£%^% to get tight because you can't get a spanner on them.
I eventually (more later) managed to get them as tight as possible, but they need to be loose AS you fit the box in order to get the pipes into the feed holes in the head that feed the valve guides. I may need to find a split spanner or something to get them done up properly. (I'm also tempted to replace them because they're completly knackered).  I had the box on and off about 3 times trying to figure out how to fit the thing properly.


This is the point where I realised that the thread in the rocker box for the hole that holds the valve cover was $%^&&ed.


So the rocker box came off again!


I then spent quite a while trying to find larger screws that would be appropriate. I initially had the plan to drill out the hole to a larger diameter, then thread for a bigger screw.
After I'd started finding screws and had dug out some taps...
I realised that I should figure out what the original thread was...
It's a 1/4 BSF. 
And I've got a thread repair kit for that! :D

So I dug it out, drilled the hole out and tapped it for the repair:




All good!


Still got plenty of inserts left, but hopefully I won't need many more!


I also shortened the bolt that was in use slightly (it's not a match with the rest of the bolts in use here)


Always round off the end... ;) :D


And, even though I'd spun the nuts back off the bolt to clear the thread ends, I also span a die down the bolt too.


Now it's a matching length


Test fitting


So - time to start on this side of things....


Cam followers going in.


Timing pinion and cam-shaft into the chest.


Push rods in. Bit of a git to get in tbh, the exhaust especially, the camshaft has to come out to get the pushrod in between the rocker and follower.



aaaaand that's where Saturday's fun ended.  I needed to do some reading to remind myself of the process for timing the valves.  This is, again, where my existing knowledge is completely lacking, I've never done this before, but I'm very aware of the risks involved in getting it wrong!
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on April 03, 2026, 07:28:43 PM »
Quote from: Rex on April 03, 2026, 07:02:32 PM
If you ever have to (God forbid) centre the conrod in this way again, stick a piece of masking tape on the face of the rod and measure and mark the centre line using vernier calipers.

I was trying to do exactly that with the rule laid against the conrod sides but it was quite difficult to find a point on the cases that the caliper point would hook into reliably and consistently. Which is why I ended up simply using my Mk. 0.9 eyeball.

But making a centerline on the conrod to facilitate that would be an excellent idea, thank you.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rex on April 03, 2026, 07:02:32 PM »
If you ever have to (God forbid) centre the conrod in this way again, stick a piece of masking tape on the face of the rod and measure and mark the centre line using vernier calipers.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on April 03, 2026, 10:06:22 AM »
Quote from: murdo on April 02, 2026, 11:01:56 PM
Liking your work so far. My preference is for the Hylomar blue as have seen too much RTV stuck in oil galleries.

Yes, that's one of my concerns, not that there's many oil galleries in this thing! :D
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by murdo on April 02, 2026, 11:01:56 PM »
Liking your work so far. My preference is for the Hylomar blue as have seen too much RTV stuck in oil galleries.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on April 02, 2026, 11:55:37 AM »
So - yesterday I got the opportunity to dive into the workshop...

4 hours of facking about later....

In imperial...


and metric units:


9.3 kilos.... yeah - that's pretty hefty.

I pushed some oil through the big end to clear it out before proceeding:



Then left it to drain for a few minutes


Before starting the iterative process of finding the best mix of shims for an acceptable end-float and conrod centering:

Each trio of photos will be: the measured overall end-float, then conrod vs case centre-line with crank to LEFT, then crank to RIGHT.
one:




two:




three:




four:




six, no five! : ::)

(fecking guage)




That's acceptable and seemed to be as close as I was going to get with the shims I have.  Between 0.015 and 0.020 overall end float, and the conrod (allowing for the big-end float as well) is as centred as I can get it.

A sure sign of a troubled mind.....


I've ended up with a very thin shim on one side, and quite a thick combo on the other.

I believe the main reason for this is that the main bearing liners are of different vintages, and protrude into the cases by different amounts (which is the main reason for the adjustable shimming).  The old liner in the Timing side case is only slightly proud of the case it fits into (which is the side of the crank-wheel I had to grind down).  The new liner I fitted into the output side is much more proud of the case: ie, it has a thicker "brim" (think of it shaped like a top hat); so, to center the conrod, there is less "room" on the output side between the liner and the wheel.

I think I spent about 3 hours on that: each measurement above represents unbolting the cases, pulling out the wheels, pondering the next combo, then reassembling (making sure not to fling bearing pins everywhere), bolting up and resetting the guage.  The guage was a bugger to zero each time.

I then restarted the assembly process:
First get the mating faces clean:

Can you get high on meths fumes??


Stick the wheels in with the bearings and shims, then fetch the sealant.


Oh FFS!


Even with having squooged the stuff up and down the tube to try to get it mixed a bit better.. (metal tube - hence the leak above) it still came out very runny. In fact, it literally poured out of the tube (which is why I ended up with slightly more on there than I had planned.  ::) )




I cleaned it all up as best I could before it got too sticky




It does make quite a mess....


I can only hope that there isn't too much dribble inside the cases themselves.

Just for shits and giggles I checked the end-float again:

(fecking guage)


Satisfied with that, the end-float is still as I hoped and with luck, the 3Bond will go off properly.

I decided to carry on and fitted the piston again: naturally I scratched hell out of the piston getting the sodding gudgeon pin circlips in:




Then fitted the barrel rods:



To get a good "heft" on the barrel rod nuts I put the whole thing into the vice briefly:


So - we're back on track, if behind schedule slightly...


I left it there for the evening to let the 3Bond go off, and to ponder the next move:
Specifically: do I try the 3Bond on the base gasket again... or use something else: the immediately available options are Hylomar Blue, or silicon RTV.  I'm tempted to try the RTV to be frank, mainly because (from memory of last time I used it), it's much, much less runny than the 3Bond, and so easier to be exacting about where it's applied.  I don't really want too much of it dribbling into the cases.

So, I went back in and fed the cat:
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on April 02, 2026, 11:55:24 AM »
Quote from: cardan on April 02, 2026, 10:44:16 AM
Quote from: Rockburner on April 01, 2026, 11:04:30 AM
More grinding...

I think I'm getting a little pressured and starting to make stupid mistakes - so need to try to slow down a bit and be thorough.

Yes. What you're doing is not OK; I'm not sure why. Better get some help.

Leon

Care to be a tad more specific?  I did in fact forget the output bearing liner so I know I made that mistake - but have I made any more? This is still my first time doing this sort of work, and part of the reason for describing every step is to make sure that I'm not missing things, even if I have to go backwards again.

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British Bikes / Re: Troubleshooting a JAP Special
« Last post by cardan on April 02, 2026, 10:44:16 AM »
Quote from: Rockburner on April 01, 2026, 11:04:30 AM
More grinding...

I think I'm getting a little pressured and starting to make stupid mistakes - so need to try to slow down a bit and be thorough.

Yes. What you're doing is not OK; I'm not sure why. Better get some help.

Leon
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