1
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on Today at 11:37:07 AM »Squirt oil on the cam gears and see if the noise goes away.
Done that, no difference.
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Done that, no difference.
2
British Bikes / Re: Troubleshooting a JAP Special
« Last post by cardan on Today at 03:20:42 AM »Squirt oil on the cam gears and see if the noise goes away.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 11, 2026, 05:19:14 PM »Could it be the backlash in the cam gears when the torque on the cam is reversed as the follower goes over the peak ? This would be more noticeable when turning slowly.
The current thinking is that its something along those lines.
What's got me confused is that the guy who has done 100s of these engines has not experienced this noise before. If it was something expected like that backlash you'd think he'd have seen it at some point in his career.
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Vreagh on July 11, 2026, 10:36:58 AM »Could it be the backlash in the cam gears when the torque on the cam is reversed as the follower goes over the peak ? This would be more noticeable when turning slowly.
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British Bikes / Real women are waiting for you
« Last post by expatriot on July 10, 2026, 10:42:57 PM »6
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 10, 2026, 09:48:31 PM »Ok - so I had a call with the Guru and he offered some more suggestions for things to check: namely:
1: try rotating the engine with just one push-rod in, see if it's one or the other causing the issue.
2: check the play of the camshaft in it's bushes with no springs (ie whip the pushrods out)
3: measure the wear on the bearing parts of the camshaft spindle (ie where it sits in the bushes.
So - I did those.
1: Each "side" of the timing still has the click noises, but with only one valve in operation I was able to figure out exactly where in the rotation the clicks are happening. BOTH of them are about 5 degrees after peak cam lift. IE when the cam-follower has "just" passed the highest point of opening on the cam lobe.
2: there is f***-all play in the camshaft when the timing cover is in place, at all 4 cardinal points (TDC, TDC+90, BDC, BDC+90) whatever play there is, is identical. With a nadger of end-play. I think the bushes are fine.
3: I measured the cam spindle-ends with a metric vernier, then converted to imperial (see last photo in the post), to get the following:
crank end: 0.003071 under (nominal is 0.5", measurements avg to 0.496929")
mag end: 0.001969 under (nominal 0.5", measurements avg to 0.498031")
I also measured the mag-end bush inner diameter (the one in the timing cover): 0.497"
(I haven't got any means of measuring the crank-end bush without stripping the engine again, and even then I'd only be measuring the outer end of the bush, relative to the spindle).
So, If the bushes are fine, and even though there's a touch of end-play on the cam-followers, there's no other movement on that spindle (you need SOME play to prevent the followers binding on each other), ie both followers are not rattling on the spindle: we are both stumped.
Even the Guru is clutching at straws now: his last communique was an idea to check the actual cam-lobe for a slight dip at the point the click is happening. IE use a dial guage to measure each lobe as it rotates (preferably in a lathe, but I should be able to bodge up something reasonably solid....)
The really weird thing about this is that the click noise happens even when the crank is being rotated really slowly, so the thought that it's a "bounce" from the momentum of the parts in the system doesn't really add up.
My current thought is to say F**k it and just finish the build and see what happens! getting bored now...
(as an aside, replacing the camshaft bushes sounds like a right faff... the one in the timing cover needs to be machined after fitting to give the correct end play, and they need to be reamed to size "inline", ie both fitted in place when the engine is completely torn down. I'm quite glad I don't need to do that!)
1: try rotating the engine with just one push-rod in, see if it's one or the other causing the issue.
2: check the play of the camshaft in it's bushes with no springs (ie whip the pushrods out)
3: measure the wear on the bearing parts of the camshaft spindle (ie where it sits in the bushes.
So - I did those.
1: Each "side" of the timing still has the click noises, but with only one valve in operation I was able to figure out exactly where in the rotation the clicks are happening. BOTH of them are about 5 degrees after peak cam lift. IE when the cam-follower has "just" passed the highest point of opening on the cam lobe.
2: there is f***-all play in the camshaft when the timing cover is in place, at all 4 cardinal points (TDC, TDC+90, BDC, BDC+90) whatever play there is, is identical. With a nadger of end-play. I think the bushes are fine.
3: I measured the cam spindle-ends with a metric vernier, then converted to imperial (see last photo in the post), to get the following:
crank end: 0.003071 under (nominal is 0.5", measurements avg to 0.496929")
mag end: 0.001969 under (nominal 0.5", measurements avg to 0.498031")
I also measured the mag-end bush inner diameter (the one in the timing cover): 0.497"
(I haven't got any means of measuring the crank-end bush without stripping the engine again, and even then I'd only be measuring the outer end of the bush, relative to the spindle).
So, If the bushes are fine, and even though there's a touch of end-play on the cam-followers, there's no other movement on that spindle (you need SOME play to prevent the followers binding on each other), ie both followers are not rattling on the spindle: we are both stumped.
Even the Guru is clutching at straws now: his last communique was an idea to check the actual cam-lobe for a slight dip at the point the click is happening. IE use a dial guage to measure each lobe as it rotates (preferably in a lathe, but I should be able to bodge up something reasonably solid....)
The really weird thing about this is that the click noise happens even when the crank is being rotated really slowly, so the thought that it's a "bounce" from the momentum of the parts in the system doesn't really add up.
My current thought is to say F**k it and just finish the build and see what happens! getting bored now...
(as an aside, replacing the camshaft bushes sounds like a right faff... the one in the timing cover needs to be machined after fitting to give the correct end play, and they need to be reamed to size "inline", ie both fitted in place when the engine is completely torn down. I'm quite glad I don't need to do that!)
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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 10, 2026, 09:47:51 PM »More tinkering today....
I'm still trying to figure out where this clacking noise is coming from, and after a bit of fiddling about, it occurred to me to try rotating the engine within the timing cover off again. I was trying to figure out if there was a worn interaction in one of the ball joints (either end of the pushrods).
With the timing cover OFF, the clickety clack is NOT there. Whatever is causing this is only in effect when the Timing chest cover is fitted.
So - I continued trying to figure out what could possibly be happening.
I dug out a 1/2" length of rod so I could assemble the timing components in the cover, rather than the cases (to see if anything was interfereing)
First the rod needed a tad of tidying up. (No idea what it was originally)
It just needed to allow the cam-followers onto it, so rough was good enough.
I can confirm that there's nothing interfering due to the timing cover.
So - with more investigation... we get more information.
And here's a video explaining what I believe i have discovered.
https://youtu.be/HmQjgWlt1uA
So my choices are:
Order a new pair of bushes and in the meantime, strip the entire thing down again, with no guarantee (despite what I believe) that this is a solid fix;
Or:
Accept this slight looseness and carry on, knowing I'll need to strip the engine again at some point soon(ish) and accepting that there'll be a tad more wear happening in the current bushes. I don't know what that movement will do to the rest of the components: ie. what extra wear (above the usual) would be caused by carrying on.
Difficult decision. (I'm currently waiting to see if I can get a chat with the Guru to se what his opinion would be). Stripping the entire engine down would be somewhat demoralising at this point, even though I now know how simple it actually is. It's more the faff of stripping and cleaning the sealants and re-making gaskets etc that puts me off.
I'm still trying to figure out where this clacking noise is coming from, and after a bit of fiddling about, it occurred to me to try rotating the engine within the timing cover off again. I was trying to figure out if there was a worn interaction in one of the ball joints (either end of the pushrods).
With the timing cover OFF, the clickety clack is NOT there. Whatever is causing this is only in effect when the Timing chest cover is fitted.
So - I continued trying to figure out what could possibly be happening.
I dug out a 1/2" length of rod so I could assemble the timing components in the cover, rather than the cases (to see if anything was interfereing)
First the rod needed a tad of tidying up. (No idea what it was originally)
It just needed to allow the cam-followers onto it, so rough was good enough.
I can confirm that there's nothing interfering due to the timing cover.
So - with more investigation... we get more information.
And here's a video explaining what I believe i have discovered.
https://youtu.be/HmQjgWlt1uA
So my choices are:
Order a new pair of bushes and in the meantime, strip the entire thing down again, with no guarantee (despite what I believe) that this is a solid fix;
Or:
Accept this slight looseness and carry on, knowing I'll need to strip the engine again at some point soon(ish) and accepting that there'll be a tad more wear happening in the current bushes. I don't know what that movement will do to the rest of the components: ie. what extra wear (above the usual) would be caused by carrying on.
Difficult decision. (I'm currently waiting to see if I can get a chat with the Guru to se what his opinion would be). Stripping the entire engine down would be somewhat demoralising at this point, even though I now know how simple it actually is. It's more the faff of stripping and cleaning the sealants and re-making gaskets etc that puts me off.
8
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 10, 2026, 09:46:33 PM »I reckon your vice is as collectable as your bike will be.
What is the intended rolling chassis?
See page 1, it's motive power for a Featherbed special build.
The vice is certainly handy!
9
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rex on July 10, 2026, 04:55:45 PM »I reckon your vice is as collectable as your bike will be. 
What is the intended rolling chassis?
What is the intended rolling chassis?
10
British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on July 09, 2026, 09:20:25 PM »Soooo... a BONUS episode!
I had a bit more time in hand, so while I ponder the wisdom of just forging ahead, I took the chance to look at the push-rod tubes, and also modify my valve-lifter clamp
I read somewhere on FB the other day that the pushrod tubes have o-rings in....
and blow me.. they do!
Actually - that one had 4! Oddly the other one had only 2!
The modification to the valve-lifter clamp was because I realised that the offset of the forces was still causing me a lot of issues with it, so I err - bodged it to stop it falling off!
First I cut about 3mm from the underside of the clamp, to push the screw further over the top of the rocker box, then I bent a bit of old steel to make a hook to guarantee it wasn't going to pull itself off the box:
It works a treat!
I gave the inners of the pushrod tubes a clean:
O-rings? no, I can't say I've got more than a few....
( :wtf: where the hell did all these come from??? )
The o-rings are used to pad the bottom of the push rods so they fit neatly into the rocker-box at the top. Ideally they'd be a friction fit, and I've got that.... more or less...
Test fit:
So - if I don't get back into the house I have a nasty feeling my dinner will be served "au visage", so, until next time my oily brethren!
I had a bit more time in hand, so while I ponder the wisdom of just forging ahead, I took the chance to look at the push-rod tubes, and also modify my valve-lifter clamp
I read somewhere on FB the other day that the pushrod tubes have o-rings in....
and blow me.. they do!
Actually - that one had 4! Oddly the other one had only 2!
The modification to the valve-lifter clamp was because I realised that the offset of the forces was still causing me a lot of issues with it, so I err - bodged it to stop it falling off!
First I cut about 3mm from the underside of the clamp, to push the screw further over the top of the rocker box, then I bent a bit of old steel to make a hook to guarantee it wasn't going to pull itself off the box:
It works a treat!
I gave the inners of the pushrod tubes a clean:
O-rings? no, I can't say I've got more than a few....
( :wtf: where the hell did all these come from??? )
The o-rings are used to pad the bottom of the push rods so they fit neatly into the rocker-box at the top. Ideally they'd be a friction fit, and I've got that.... more or less...
Test fit:
So - if I don't get back into the house I have a nasty feeling my dinner will be served "au visage", so, until next time my oily brethren!