31
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rex on February 10, 2026, 11:26:42 AM »Out the exhaust pipe?
Recent Posts
32
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on February 10, 2026, 10:47:40 AM »Nice.
I know nothing about these modern (!) JAP engines, but from 1914 JAP started using the "oil box" under the timing chest as part of the oiling system, which was powered by crankcase compression/vacuum. Are the four little round things flapper valves that power the oil circulation? How does the oil get to the big end?
The oiling system in veteran/vintage JAP engines works well, but I've seen more than one engine where owners have tried to "help" oiling by drilling extra holes that in fact stop the oiling system from working properly. Although the engines are "total loss", properly set up essentially no oil should end up on the road.
Leon
The oil is fed in fro mthe side of the timing case by a double Pilgrim pump (with another pump inboard of it, which is a return pump - long story), the feed from the Pilgrim that goes into the engine is (iirc) fed down timing-side crank shaft, and into the cases (whether it's fed direcly to the big end or not, I'm not sure, I'd have to refer to my Fenner). The other feed from the Pilgrim goes up to the rocker box where it's gravity fed onto the rocker-shafts and elsewhere.
Eventually all the oil end up in the sump where it's fed by piston pressure into the oil-trap chest and (as designed) out to atmosphere via the "flapper" valves in the photo (there's little metal discs inside those silvery circles that move freely (when clean....).
On this engine the oil that gets through the flapper discs is then routed into a return pump that feesd back up to the oil tank. I think this was a modification that came out of Formula 500 racing where the original design of the engine: total loss, wasn't really acceptable on tarmac race tracks (while being absolutely not a problem for shale). These engines were the best available for Formula 500 racing before the Manx Norton 500 single came along: good spread of torque, simple to work on, and reliable (or so I've read!)
If your older engines are total loss, but no oil is getting to the road.... where is it going?
33
British Bikes / Re: Igniton points cam oiler?
« Last post by ramwing7 on February 07, 2026, 04:04:45 PM »Thanks to all. I can certainly do that
34
British Bikes / Re: Igniton points cam oiler?
« Last post by Rex on February 07, 2026, 10:04:02 AM »Wicks don't always seem to be fitted to mags, same as the little felt effort that used to be in distributors years ago.
As the post above says, a tiny bit of grease on the face cam or cam ring is more than enough.
As the post above says, a tiny bit of grease on the face cam or cam ring is more than enough.
35
British Bikes / Re: Troubleshooting a JAP Special
« Last post by cardan on February 07, 2026, 12:35:44 AM »Nice.
I know nothing about these modern (!) JAP engines, but from 1914 JAP started using the "oil box" under the timing chest as part of the oiling system, which was powered by crankcase compression/vacuum. Are the four little round things flapper valves that power the oil circulation? How does the oil get to the big end?
The oiling system in veteran/vintage JAP engines works well, but I've seen more than one engine where owners have tried to "help" oiling by drilling extra holes that in fact stop the oiling system from working properly. Although the engines are "total loss", properly set up essentially no oil should end up on the road.
Leon
I know nothing about these modern (!) JAP engines, but from 1914 JAP started using the "oil box" under the timing chest as part of the oiling system, which was powered by crankcase compression/vacuum. Are the four little round things flapper valves that power the oil circulation? How does the oil get to the big end?
The oiling system in veteran/vintage JAP engines works well, but I've seen more than one engine where owners have tried to "help" oiling by drilling extra holes that in fact stop the oiling system from working properly. Although the engines are "total loss", properly set up essentially no oil should end up on the road.
Leon
36
British Bikes / Re: Igniton points cam oiler?
« Last post by cardan on February 07, 2026, 12:19:02 AM »Or the tiniest smear of grease on the cam. I mean a drop, smeared over the cam and more-or-less wiped off until there is nothing to see. Redo every ten years, unless you're desperate for something to do. Not sure which magneto you have - ring cam or face cam - but the fibre rubbing block does wear a bit over the years. If it's badly worn you can probably find a new one.
Leon
Leon
37
British Bikes / Re: Igniton points cam oiler?
« Last post by R on February 06, 2026, 10:08:45 PM »A quick spray with WD40 every blue moon goes a fair way to substituting for this !?
Keeps the moisture at bay too.
??
Keeps the moisture at bay too.
??
38
British Bikes / Igniton points cam oiler?
« Last post by ramwing7 on February 06, 2026, 09:03:28 PM »I recently picked up a 1949 BSA B31 in pretty much complete condition. I've been getting acquainted with it before I start any serious work.
I have a question concerning the magneto and how the ignition points cam is lubricated. The points spin around while the plate cam stays fixed. The mechanics manual gives directions for oiling a wick.
I can't find wick anywhere in the points compartment. The manual shows a picture of a fixing screw for the oil felt, but nothing resembling a felt.
Can anyone tell me where to look and what it might look like? A picture would be fantastic.
Thanks.
I have a question concerning the magneto and how the ignition points cam is lubricated. The points spin around while the plate cam stays fixed. The mechanics manual gives directions for oiling a wick.
I can't find wick anywhere in the points compartment. The manual shows a picture of a fixing screw for the oil felt, but nothing resembling a felt.
Can anyone tell me where to look and what it might look like? A picture would be fantastic.
Thanks.
39
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on February 06, 2026, 07:52:47 PM »Well, since I'd got my head down during the week, I figured I was owed an afternoon in the shed....
I've always liked the "exploded diagram" photos you see in some of the magazines... so I had a go myself.
Unfortunately I kinda ran out of room on the bench.... so there's a few items not shown. :roll:
After I tidied everything back up again, I got on with the things I had planned:
First wash the grease off the main crank bearings:
one bowl of petrol :
Aaaand about ten minutes later...
One bowl of R30 with all the pins in.
I figure they'll be safe in there until final assembly.
I also remembered that I wanted to check the valves properly, as discussed a lot further up the thread....
First I did a bit of cleaning up on the inlet manifold while I was there :
Much better.
Collected up all the valve bits.
Inlet valve went in first
Couple of Mica washers to slow down the heat transfer to the springs. I've already done all the work checking the spring-weights
The base cup and washer... and it's time to dig out the spring clamp!
This part always terrifies me..... it's like having a loaded gun with a hair trigger sitting on a jack in the box...
Especially when you realise you forgot to put the circlip on the stem. FFS.
Anyway - managed to fineagle it on without firing the springs into my face..
I actually did have to loosen it off because the springs were all leaning one way and I had to re-center the jaw of the clamp so I could get the collets on.
Note to self... put the circlip on FIRST.
(Well - after the valve goes in the guide... natch....)
Cocked and loaded.
Had to dig around for a plug, but found one.
NOT for drinking! (well - a last resort...)
Believe it or not... that's full.
Definitely full!
And NO DRIPS!!
I am SOOO $%^&&ing pleased with myself! I even did a little dance!
Waste not want not...
So - that's the head sorted!
Like I say - I am really happy that the valve seal, I spent a lot of time doing that and it's very very satisfying to see that it appears to have all gone right.
I put the head away but kept the Meths out...
The next job was cleaning up the cases.
I mainly wanted to get all the grease off the main bearing liners.
There's a feed oil that gravity feeds oil from the underside of the barrel, down to the liner...
Obviously there was grease in the feed hole.
Yeah - that got messy.... I pulled some meths into the syringe and blasted it into the top of the feed hole!
I blew air through the hole quite a few times, pretty sure it's 99% grease free now - anything left will just join the general gunkiness that is the end result of CastrolR getting hot. I used the meths to clean both cases up as best I could, including the main joining faces.
Then I started to look more closely at some of the peripheral bits of the cases.
This is the "sludge trap" which slows down the feed of oil out to atmosphere (these engines are designed to be total loss, and piss oil out onto the track - it's a speedway engien remenber!)
As in that photo, I have spare parts to replace those in the cases - but I'm not sure how to get them out, you can't really get a hammer inside the cases to knock them out from the inside, and I didn't want to get all Conan with a screwdriver....
So, while I pondered that... I spent an hour or so checking all the screws and threads for the peripherals.
These feckers are M5.
The dreaded silicon sealant....
If you look closely.... you may notice that yes, indeed, the black set-screws (for the sludge trap catchbox) are VERY closely aligned with the oval-headed screws for the oil-trap cover...
They actually interfere with each other!! But it's actually not a problem because the black set-screws are the right length for the catchbox. But it gave me pause for thought as I was cleaning everything out!
I cleaned up all the threads for the oil-trap cover as well - now there's plenty of thread to ensure the cover is held down tight.
And I found a nozzle in with one of the tubes of Blue Hylomar! that'll make life easier!
So - all the threads are clean, I've got the Hylomar all ready, the bearings are clean and soaking in oil (mainly so there's "something" to just about keep them in the cages when I assemble the cases), I've got the gaskets I need (I tried to make up some carboard templates last week, but had limited success).
I just want to get that sludge trap sorted out before I really get going on the full assembly. I've asked a question on a popular group on FB, so hopefully I'll get a response soon!
Oh - I also found that all the little parts that hold the rockers in place in their box - the washers and bearing liners had gone fecking rusty! I think my mistake was storing them all in sealed plastic boxes after I'd been fiddling with them repeatedly last year - a mix of trapped humid air and acidic finger grease.
So I gave them all a good brass-brushing and we'll see how they fare. The actual bearing surfaces seem to be fine - it's the rest (eg the outer surfaces of the liners) that had surface rust on them. my dumb mistake, but I doubt they'll be problematic.
So - progress and some mistakes, but, mostly progress!
I've always liked the "exploded diagram" photos you see in some of the magazines... so I had a go myself.
Unfortunately I kinda ran out of room on the bench.... so there's a few items not shown. :roll:
After I tidied everything back up again, I got on with the things I had planned:
First wash the grease off the main crank bearings:
one bowl of petrol :
Aaaand about ten minutes later...
One bowl of R30 with all the pins in.
I figure they'll be safe in there until final assembly.I also remembered that I wanted to check the valves properly, as discussed a lot further up the thread....
First I did a bit of cleaning up on the inlet manifold while I was there :
Much better.
Collected up all the valve bits.
Inlet valve went in first
Couple of Mica washers to slow down the heat transfer to the springs. I've already done all the work checking the spring-weights
The base cup and washer... and it's time to dig out the spring clamp!
This part always terrifies me..... it's like having a loaded gun with a hair trigger sitting on a jack in the box...
Especially when you realise you forgot to put the circlip on the stem. FFS.
Anyway - managed to fineagle it on without firing the springs into my face..
I actually did have to loosen it off because the springs were all leaning one way and I had to re-center the jaw of the clamp so I could get the collets on.
Note to self... put the circlip on FIRST.
(Well - after the valve goes in the guide... natch....)
Cocked and loaded.
Had to dig around for a plug, but found one.
NOT for drinking! (well - a last resort...)
Believe it or not... that's full.
Definitely full!
And NO DRIPS!!
I am SOOO $%^&&ing pleased with myself! I even did a little dance!
Waste not want not...
So - that's the head sorted!
Like I say - I am really happy that the valve seal, I spent a lot of time doing that and it's very very satisfying to see that it appears to have all gone right.
I put the head away but kept the Meths out...
The next job was cleaning up the cases.
I mainly wanted to get all the grease off the main bearing liners.
There's a feed oil that gravity feeds oil from the underside of the barrel, down to the liner...
Obviously there was grease in the feed hole.
Yeah - that got messy.... I pulled some meths into the syringe and blasted it into the top of the feed hole!
I blew air through the hole quite a few times, pretty sure it's 99% grease free now - anything left will just join the general gunkiness that is the end result of CastrolR getting hot.
I used the meths to clean both cases up as best I could, including the main joining faces.Then I started to look more closely at some of the peripheral bits of the cases.
This is the "sludge trap" which slows down the feed of oil out to atmosphere (these engines are designed to be total loss, and piss oil out onto the track - it's a speedway engien remenber!)
As in that photo, I have spare parts to replace those in the cases - but I'm not sure how to get them out, you can't really get a hammer inside the cases to knock them out from the inside, and I didn't want to get all Conan with a screwdriver....
So, while I pondered that... I spent an hour or so checking all the screws and threads for the peripherals.
These feckers are M5.
The dreaded silicon sealant....
If you look closely.... you may notice that yes, indeed, the black set-screws (for the sludge trap catchbox) are VERY closely aligned with the oval-headed screws for the oil-trap cover...
They actually interfere with each other!! But it's actually not a problem because the black set-screws are the right length for the catchbox. But it gave me pause for thought as I was cleaning everything out!
I cleaned up all the threads for the oil-trap cover as well - now there's plenty of thread to ensure the cover is held down tight.
And I found a nozzle in with one of the tubes of Blue Hylomar! that'll make life easier!
So - all the threads are clean, I've got the Hylomar all ready, the bearings are clean and soaking in oil (mainly so there's "something" to just about keep them in the cages when I assemble the cases), I've got the gaskets I need (I tried to make up some carboard templates last week, but had limited success).
I just want to get that sludge trap sorted out before I really get going on the full assembly. I've asked a question on a popular group on FB, so hopefully I'll get a response soon!
Oh - I also found that all the little parts that hold the rockers in place in their box - the washers and bearing liners had gone fecking rusty! I think my mistake was storing them all in sealed plastic boxes after I'd been fiddling with them repeatedly last year - a mix of trapped humid air and acidic finger grease.
So I gave them all a good brass-brushing and we'll see how they fare. The actual bearing surfaces seem to be fine - it's the rest (eg the outer surfaces of the liners) that had surface rust on them. my dumb mistake, but I doubt they'll be problematic.So - progress and some mistakes, but, mostly progress!
40
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on January 31, 2026, 09:56:13 AM »Good job Rockburner - it's a reminder of how much work goes into an engine rebuild. Pleased that you found someone knowledgeable to help with the big end and flywheels. An expert can make a tricky job look easy.
I have a couple of little worries.
I fear that not fitting a valve lifter will prove to be a mistake. Even if you keep the compression well down starting without one might be a problem. I guess you'll find out!
My other concern is about the grease in the roller bearings on the mains. Grease isn't a very good lubricant on rollers, and I fear it might stop the oil getting to the bearing. It might be worth chatting with your JAP expert about it.
Should be running again soon? Good luck!
Leon
Good points both.
The valve-lifter i removed has been broken for an unknown period, possibly years, and i was able to start the bike anyway, so I'll see how it goes. Now I'm much more familiar with the thing, refitting it is far less daunting if i decide I need it.
Yes I am aware of the dubiousness of using grease on the rollers. I'll be cleaning them off and soaking them in R40 before final fitment. Using the grease does help to keep the assembly together during the repeated assembly/disassembly process while getting the shims sorted out. Its all good.
Thank you though for pointing out those concerns, this is my first complete rebuild of anything, and the deepest I've ever gone into the bowels of any engine, so there's lots I know I don't know, and even more that I don't know I don't know.
But the list of things I know is growing, which is good!