Troubleshooting a JAP Special

[Rockburner]

Report from the weekend.

I snuck into the workshop late Saturday evening and did some more checking and tinkering.

I decided to try RTV-ing the rocker cover:


I also realised that the fuel line was very very close to the spark-plug cap, and then remembered that I'd seen a 90 degree fuel union somewhere... so dug it out and this is a lot neater (if needing a bit of a clean up)


I'd decided to forego the Ardningly bike-jumble in favour of actually getting the JAPton out and visiting the local classic meet.

So, Sunday morning I checked the oil:


4.6cm as a baseline.


Oh - and I added the finishing touch..




Made it to the meet alright (even though I went to the wrong location first..... D'oh!)


Got a fair bit of interest from everyone, mainly because it's 10x louder than everything else, so your arrival is noted....





On the way home I nearly had a KSI, I was coming up for the turning into my driveway, a right hand turn, so I stuck my arm out for at least 5 seconds (I learnt how to make VERY OBVIOUS hand signals a long time ago riding Dad's old bike collection), brought my hand back to make the turn, and the ABSOLUTE $%^ in the Merc CLK tailgating me OVERTOOK ME.

IF he'd been a microsecond less impatient,  he would have had me over his bonnet.

I was so enraged I chased him down with the horn blaring and gave him a piece of my mind (the only bit working, sadly).  Didn't really resolve anything, but I think I did get an apology out of him... (eventually, after I had to apologise for using bad words at him, wtf?? He was at least 30, has he not lived in the real world? :wtf: ).



Post-mortem of the ride:  The RTV on the rocker cover seems to have worked, but oil is still pouring out of the engine somewhere.  The most obvious  location would be the base of the push rods, and it's got me thinking: I reckon it needs a crankcase breather.

The engine, as designed, has a crankcase that is (essentially) open to atmosphere, so the down-stroke pressure wave has somewhere to go.  Now that my engine has the return pump blocking that exit route, and there is no longer a cable-operated decompression lever, there's no crank-case breather.  The De-comp system in the timing chest was cable-operated, so there WAS a route to atmosphere through that cable (not great, but there).

I'm going to talk to one or two people about it, but I'm pretty sure I need to put a breather tube into the crankcase/timing chest, luckily, there's a very obvious and handly location for one.

I also reduced the amount of oil flowing to the head, siply to reduce losses but if the fitment of the breather works well, I'll wind it up again to make sure the head gets enough (it doesn't want too much otherwise the oil overwhlems the valve-stem requirements and gets into the head).  I reduced it down to about 1 drop every 7 -10 seconds (it's difficult to get an accurate measure with the random tickover...)

[Rex]

Looking good though.
Where was the meet?

[Rockburner]

Looking good though.
Where was the meet?

Thanks! With the short-track tank it's a bit of a looker, it's different to most Featherbed specials (Tritons, Norvins) because they almost always use the big Manx tank (or something like it, Lyta etc) for the extra capacity (and almost all of them are silver or bare metal these days).

Down in Selsey, West Sussex, I think it was a bit quiet tbh, propbably because there was a lot of other meets going on along the South Coast (including the bike jumble at Ardingly which is popular)

[Rex]

Yep, there was the Old Fossils Run at Waterlooville, and another classic meet near Guildford on the same day.

[Rockburner]

Have been in and out so trying to keep up to date with everything....

Yesterday I spent an inordinate amount of time looking for anything that was 7/16" in diameter in order to make up a new breather insert for the timing case, then eventually I found the remains of the stud I used to make the grub screws for the holes in the cases. I thought I'd thrown it away, which is not like me, but eventually it turned up in the Imperial taps & dies toolbox!

I also found the remnants of the tubing I'd used for the push rods, which is 7/16s as well.

I first tried making fitting from the old push rod tube


But the die got away from me somewhat....

So I tried to make something up from the stud.
But I only got so far...


Unfortunately when I tried to drill the hole down the axis of the stud... The bloody drill bit snapped.


So that was plan B down the shitter.

I had another, more successful go at Plan A, with the other bit of tube from the new push rods


But to get to that stage... I had to get the grub screw out first.

Which was a struggle.

I used an impact driver, heat, a dugga dugga, more heat, the impact driver again, more heat, hammering one end of the slot with a screwdriver, more heat, more dugga dugga...

And EVENTUALLY the !"£%^% came loose!

I mildly mullered the thing, so today I started by cleaning up the grub screw in case I need it again, and cutting the slot a lot deeper!


Some more parts also arrived today.

These are extended adjuster screws for the Concentric.


Compare to the old ones


And fitted to the carb


The main benefit, as far as I'm concerned, is that I can tweak the screws without a screwdriver....

I then rummaged through the filthy bag of filthy hoses again and found something vaguely appropriate for the breather and fitted it.


It vents directly into the catch tank


Hopefully that will reduce the amount of oil being blown out of the push rod tubes, and if so, I'll have a go at sealing them with RTV, but I'm hoping to have time for a quick test ride tomorrow....

Maybe.

Because the other thing I did tonight was whip the Pilgrim pump off the timing case. Still not sure why I did that... But hopefully it was worth it.

Well, in wanted to see if the continued oil weeps that end up dripping off the bottom of the pump were actually coming from the pump.


This is a "spare" I have, which I got out to peruse and ruminate on, because I wasn't sure exactly which bolts were holding the pump on.


This is the driven side.


The pump is only held on by 2 bolts.

So I undid and drained all the hoses, and removed the fitted pump
The gasket came off easily with a sharp knife, it was shagged.


This is where the pump fits:
Top to bottom: fastening hole, drive aperture, fastening hole, oil feed oil.


(No wonder they leak...)

I was actually pressed for time, so I hurriedly made up a new paper gasket using the original as a pattern


Then got the 3bond out again and applied it "sparingly"


Placed the gasket


More 3bond on the outer face of the gasket, then refitted the pump, remembering, thankfully, to replace the drive thimble first!


The primary and secondary pumps are both held on by the 2 bolts... But nothing is holding them together. Well, I think there's some silicon sealant or something, but no visible bolts/screws or anything! I also have a nasty feeling that silicon bond might be compromised....


I did the bolts up "finger-tight" to let the silicon 3bond go off with a little bit of expansion, then I'll do them up properly tight tomorrow, and pray that the grey goop didn't get into the feed hole!

[Rockburner]

More Thursday afternoon Shenanigans!

Frist I tightened up the pumps, we'll see if that makes any difference whatsoever (I doubt it)


I checked the level in the oil, it was showing exactly 4cm (which is a bit odd because I could have sworn it was a 4.2cm when I returned from the  ride on Sunday, maybe the oil shrank in volume as it cooled? Either that or there's actually a leak somewhere.... which I doubt...)
I then added another 500ml... and the depth went up to 6cm.
So... 500ml is APPROXIMATELY (the tank isn't a uniform cubic shape...) 2cm...  Interesting.  6cm is roughly half-full.



I was then just going around the bike checking things and realised the bloody tank strap was coming apart.
So I pulled the thing off (easier said than done, natch...), punched a couple of new holes a bit futher in, and refitted the end piece


I moved the attachment point to the forward of the two holes and redid the pretty wire...


To be honest, I really don't like that tank fitting.... I am going to think about improving it somehow.  (more on the tank later....)

Tacho don't work.


(but the rest I think is reasonably accurate)

I pulled the plug which I hadn't done after the last ride on Sunday.


Black and sooty.... to be honest, I'm completely unsurprised.  The ride home was at snails pace and the engine was not happy at low throttle settings.


I gave the plug a quick Millyarding




And chucked it back in...
Note to self.. FIND A BETTER PLUG-SPANNER  I hate this cheap piece of tat.


I checked the engine was still running ok, fired it up and it was fine, so I tweaked the oil slightly, and the idle speed (REALLY easy to do that with the extended adjuster screws! )
Even just idling in the shed there was some oil coming out of the push-rod tubes, but the crank case breather was working well, and was surprisingly dry.


So, I took it out for a spin.
Selsey Beach.  I actually had an ulterior motive... I need to talk to the local JAP expert in Selsey about the engine so went down to see if he was around, he wasn't, so I took the opportunity to get a photo or two at Selsey Head.



I then fancied an ice-cream so wended my way slowly over to Bracklesham (the next village west along the coast).
Even taking the back roads I was baulked by traffic virtually everywhere...


I did assuage the frustration by overtaking a few cars and trucks though - maybe not much to brag about, but it felt good given the bike I was on.

The engine breather, I think, has actually helped the engine run a tiny tad better, it seemed a touch more eager today.

One thing it DEFINITELY does NOT like is pootling along.... it's quite positively happier at 3/4 to full throttle and when it's pulling.  It does NOT like trundling along at 30-40 on a constant throttle... I had to adopt a sort of "hyper-miling" technique of dropping back at idle, or with the clutch pulled, then letting the engine pull up to the car in front before dropping back again.  I'll have to look at the tuning guides and see which part of the carb is effective in that range - I "think" it's needle height, so that may need some fiddling with.

I then took a slightly longer route home (to avoid having to turn right into the driveway... :roll: ) and got a run through the local tight bends - the bike suspension may be somewhat hard and jarring, but it handles beautifully, holds a line and tracks very nicely, I can't wait to get it out on some open sweepers.

Oh yeah - I also tweaked the side-stand round a bit on the frame tube, and the bike sits up a bit straighter now, which I much prefer.

There's still a way to go yet though: things that need a good looking at:
- carb tuning
- oil leaking (hopefully some RTV on the push-rod tubes will contain most of it).  I have a nasty feeling there's a couple more areas though. The oil return feed line leaks where it goes into the tank, which confuses the hell out of me because there's absolutely no reason for it to do so - I even trimmed a cm off the end because it was looking a bit tired and it's made no difference. Hmm....
- the tank, yeah... it's rubbing against the steering head (well, the rhs downtube actually) and it doesn't sit centrally on the frame pads.  So - I need to make up a boss or something to hold it centrally... hmmm... I just remembered I have something that might do the trick... <makes mental note>
- LHS fork needs a new seal, and I may as well rebuild it (I hate rebuilding forks...),  On Sunday the seal seemed fine, but it was weeping today, it needs doing.
- Tacho - I suspect the speedo is just some old thing Dad bought at Kempton, so that may be a winter project to see why the Tacho isn't working.


It ain't over folks!

[Rex]

That bog at Bracklesham is a throw-back from the 1950s which is probably the last time it was deep-cleaned. How long can you hold your breath?
I like the bendy road back to the A27 though.

[Rockburner]

That bog at Bracklesham is a throw-back from the 1950s which is probably the last time it was deep-cleaned. How long can you hold your breath?
I like the bendy road back to the A27 though.

Not long enough... bleuuuurgh!

Too much traffic around these days, the bike doesn't like constant speeds (especially below 50), it wants to be ridden!

[Rockburner]

Another long session in the workshop this evening!

Just one thing first, after the ride on Thursday I measured the oil again...
If 2cm was 500ml... 0.6cm is around.... Errr.. 180ml, ish? That's a lot to lose over 23 miles....


Started by giving the plug another quick Milyarding


The shed was hot, but I didn't expect it to be this dry in there...


Then took a good look at the tank to fix the issue where it's not sitting correctly.


First I discovered that this jubilee on the oil return pipe was shagged, which it turns out was not the cause of that line weeping... More on that later...


(I have a few spare jubilees...)


There's a union nut that screws onto this, but it's obviously been forced up the tube because the two thread forms are different. FFS.


The tank was rubbing badly against the down tube.


It'll need a repaint at some point.



I found an old BMW part that I initially thought I could adapt, so I made a start on that work,


Always take the burrs off first....

(I'm sure I took more pictures...)

Then I realised that the rubber bungs could be used in a better way.
I cut one into half


Then simply cable-tied them to the down tubes, after cutting grooves for the ties


The new pads fit perfectly in the gap between the tank and the headstock


They'll keep the track nice and central.


So I pulled the tank off again, and in doing so the flaming oil tap caught the frame and dribbled everywhere!


D'oh!

I took the tank off because I wanted better access to the engine head while I tried to get the oil leaks sorted out.
I pulled off the breather and the rocker cover so I could redo the RTV.

I used the rocker clamp so I could remove the push rod and tube completely


Then tidied up the old RTV (which is really easy), before figuring out that hopefully the best way to apply the RTV was to fill the annulus at the bottom of the push rod tube with the stuff


Did the same to both tubes and refitted them


Spooge!


Refitted the breather with better loctite, the stuff I put on last time didn't do shit. I also tightened it up more with pliers.


I then spent some considerable time looking for a union nut that would thread properly onto the oil return tube. Eventually found one, but I needed to drill out the opening slightly to accommodate the suitably girthed hose attachment.


I think that because of the damaged threads, the previous union nut here hadn't sealed properly and that's why the feed line was weeping. Fingers crossed this one fits better! It certainly seems more solid.

I then took a look at the carb jets to see what needle jet was in there.
Hmmmmmm, that might explain things a bit....


So I fitted this one.


Oddly my needle jet collection are all 106s... But they're a different design:
The 3 on the left are 106s, but maybe for a different carb? The 4th is the 107 just removed, and the 106 I put in is of the same type where the entire jet tube is the measured bore, not just the bottom end.


We'll see how it runs on that, hopefully I'll get out on it this weekend.

[Rockburner]

So this carb stuff has been playing on my mind, so I blagged an hour today and nipped into the workshop.

First job was to fit the replacement jubilee on the oil return feed


I then reviewed the Amal Concentric rebuild guide, (which I've read a couple of times now...) and specifically looked for information and photos of the component parts, and there's a lot of information in there. https://amalcarb.co.uk/technical/rebuilding-mark-1-concentric-carburetter

First I wanted to reassure myself that the carb for a 4-stroke:
Confirmed!


Then stripped the jet block from the body.


And pulled the needle out.
It's the right length (near enough)


But, these two jets, are (according to the info in that link) for 2-strokes.
The 107 is the one I pulled out of the carb yesterday and (iirc) was the one it came with.


These 3 are correct 4-stroke needle jets (all 106)


I am rather confused as to how I've ended up with 2-stroke bits tbh.

So I replaced the needle jet with a correct 4-stroke 106 jet and kept the 206 main I'd already fitted.


The needle jet stays on the middle notch, but cross-refencing to the Amal information, it's the one with 2 grooves, which is the correct part.

Stuck the needle back into the slide (it's a 3.5), and refitted that into the body


Refitting the jet block, with the needle already in position it means there's no buggering about trying to fit the needle into the jet block of it's in situ.


The needle pulls to the right slightly at WFO, but it doesn't seem to affect slide movement.


All back together again.


As I was tidying up I found a brand new 260 main! But I want to change only one thing at a time, so that might be the next thing to try if there are issues at full throttle (which is the only part of the throttle range where the main jet has an effect)


I replaced the tank strap


Checked the oil again now it's cool, roughly the same as before


I then went to fire it up but fuel wasn't coming through, I poked about a bit then realised that the fuel tap was being fouled by the jubilee clip on the pipe!
Little details...


So I tweaked the tap because it had rotated a bit in the tank fitting


I refitted the 90 degree union and turned it away from the tap a bit.



THEN I could fire it up again!
I still can't believe how easy this thing is to start.
Everything seemed ok, and in the 5 minutes of idling there didn't seem to be any leakage from the push rod tubes.
The pump action is mesmerising...
https://youtu.be/zavcxQrl1vQ?is=NHoJ1tWF2tlLldTZ

Hopefully going to get out for another longer ride tomorrow.

[Rockburner]

There's always more to learn....

Last night I left a clean bit of newspaper under the bike after I'd run it up briefly.


This morning....


I'm pretty sure the culprit is the pump , which is not a surprise at all.


But it's only a dribble, it's livable with for now.

Today's plan was to get a few more miles on the bike, by visiting a Cars&Coffee about 20 miles away, then heading over to the Selsey RNLI charity event.
First I topped up the oil and petrol


And while I was at it I spread a little silicon into the Monza cap rubbers


Then set off, not without a little trepidation I have to admit!

But the bike is transformed! Fuelling at pretty much any throttle opening as pretty damned good!  :banana-wrench:  :banana-wrench:
So many thanks to the guys who pointed me in the right direction!  :obscene-drinkingcheers:

It does have a tendency to spit a touch after a prolonged period of constant small throttle opening (ie 30 zones and following dawdlers...), but once you get "on it" it's fine!

There's still a dribble of oil escaping from the push rod tube (inlet), but it was only a dribble.


On the way back towards Selsey, I even got lucky enough to get an empty bit of smooth tarmac and wound it right open!  :angelic-green:


Chin on tank..... The needle crept round the dial...

68...

69...

70…

..

71!


72!


...


73!


:lol:

Flat out is maybe 75 on the Smiths! :lol:


But the engine felt happy doing it!


Obviously though, by the time I got back towards the coast roads, the traffic built up and it was back to pootling along at 40....  :roll: yawn.

The vehicle gathering at Selsey was (tbh) a little quiet,



The ride home was more pootling, which the bike still doesn't like, letting me know with the occasional spit and hesitancy, so I decided to try and give it a bit more of a go by hitting the A27 just for a junction.

And got a bit of a shock.  I'd just wound it open again when the thing died on me! It felt like either fuel station or lack of spark, then it picked up, then died, then struggled on again....

By which time I'd reached the next roundabout and peeled off for home.

Very odd.

The engine was fine again at low speed, then I got lucky again and had a clear run to the house, so I opened it up for about 300 yards then cut the engine to roll into the driveway on a dead engine.

The result. Black, but dry, the insulator isn't completely black.


I need to review the plug condition photos, but I don't think it's that far off...
Just need to figure out if it's a tad rich, or a tad lean.

When I had it WFO previously I did try easing off a tad a couple of times, and the engine just seemed to roll off, rather than gaining or complaining.

More testing required methinks.

Note to self... Top up the oil on the side stand!

Obviously, the bike was parked on its side stand during the afternoon, and I think it started dribbling then, because the was a stain on the thigh of my trousers....

I also remembered that I had Sealey pressure testing kit, so took the opportunity to check the compression while the engine was hot.



Hmmmmm, that's actually a little lower than I was expecting...


I should have checked it the last time I took it out, to establish an early baseline.  I think I'm going do the compression ratio test soon, so we'll see.