Troubleshooting a JAP Special

[Rex]

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.

[Rockburner]

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.

Yes - I'd imagine that closing up the tappets would reset the timing to be a tad earlier (a degree or two), and the opening period a tad longer than when measured with the more open clearances... very interesting.

So - that described timing method is essentially setting the exhaust open time exactly right... and trusting that the rest are inline?  Makes sense if you've got a single, one-piece cam shaft where the entire thing is ground from a solid blank: if the first movement is correct, then it's a reasonable assumption that the rest of the timing is right because it can't be wrong (with a solid cam-shaft & cams).  If the engine has multiple cams, or the cams are individual parts slotted onto the cam-shaft:  then there's the opportunity for non-synchronisation.

[Rockburner]

Had a nice video call with the Guru yesterday, and learnt a few more useful things. 

Like: when checking the backlash it's best to do this with the timing chest cover fitted and nipped up! 
So - I did that, and:



I'd say that's as close to 1 degree as you're going to get!

The backlash between the timing pinion and camshaft is fine!  We had a conversation about the various options for the timing pinion - they were made with allowances for the backlash (-6, standard, +6, +12, etc, he's seen a -20!) and mine is a -6.  He initially recommended going up to a "standard" if I could find one, but after rechecking (properly!), it's all good, which is a bit of a relief because these things are just not made any more! If I was to find a 2nd hand one, I'd have no idea how worn it might be (which is the same issue with pretty much all the parts for these engines).

I'm also going to make sure that when I'm doing the valve-timing from now on I'm going to have the timing chest cover fitted and nipped up to ensure things don't have too much play: it makes more of a difference than I realised!


Obviously the guru does this so often, he actually has a cut-down cover with the timing pinion exposed so he can adjust it without removing the cover! Very handy, but massively overkill for me, once I've done this and got it as best I can, it won't be getting changed again.  The ignition timing on the other hand....

The guru reminded me of something else: the "critical" valve timing to get right is the Inlet Opening position.  Get that right and everything else will follow : the cams and cam-shaft and gear are all one solid piece, so if it's right in one place, it can't be "wrong" anywhere else, so I'll work off that principle.

We also discussed the bent push-rods, it's just something that happens - they're tubes, not solid.  I need to find some replacements, and we discussed sources. 
This is the worst one: Dial at 0

Dial showing the runout:


FYI: that's the crappy dial, I've discovered that the needle is a little loose and will wander over time. ffs.  It's ok for one-off measurements though.

The other rod isn't as bad, but best to replace the pair while I'm here:




He told me that apparantly one of the main suppliers tried to sell ally push-rod tubes a while back, which wasn't a good idea as they all bent!  The people who'd bought them were (understandably) pretty pissed off and complained bitterly, but he doesn't know if the company still sells them, or what they're made of: I shall investigate!

The current preferred material for race engines, running full power, is chro-moly tubing, but he reckons that I will be fine with regular steel tubing: I need to take the ends off my current rods (the ends are soldered on), and check the wall thickness, then go find some steel tubing of similar (or thicker) wall and see about making some up; well; presuming I can't find some ready made replacements somewhere else.

hey ho... do a job, make a job (as my ex used to say...)


Oh yeah - I also discovered last night that the classic bike track-day that I was sort of attempting to have the bike ready for has been moved to June or July, from May: so that "deadline" is no longer looming as heavily, phew.  What with the discovery of the fork and gearbox leaks I was thinking it wasn't going to be ready, now I still have a vague chance if I still want to aim for it.

[Rex]

Re new pushrods, couldn't you do that old trick of repurposing rods from another engine? Shorten and refix ends as required?
At least you'd know that the material was good for the purpose.

[Rockburner]

Re new pushrods, couldn't you do that old trick of repurposing rods from another engine? Shorten and refix ends as required?
At least you'd know that the material was good for the purpose.

It's a possibility to look into.

[Rockburner]

Bit of a delay there... sorry about that.  Normal service will hopefully be resumed soon.....
(3 weeks of delay due to another project, and since then I've had health issues: currently working around a trapped nerve in my neck which is doing weird things to my left arm and hand).

However - I manage to struggle through a bit of workshop tinkering yesterday, after fixing the Flymo again (the choke butterfly had fallen off the pin, luckily the screw fell into the airbox instead of being ingested!)

I was trying to get the valve timing set correctly. 
After a bit of pissing about and accidentally completely $%^&&ing up the cam-wheel positioning while looking at the timing pinion I decided to be a bit more systematic about things.

Firstly I identified each keyway on the timing pinion

If you look closely at that photo, you'll see that what I id'd as "2", had a couple of punch-pin marks over it.  However, when I took the bike apart, it was set at position "1", so I can only assume that the pin punches marks were from a previous owner/build.

Just another photo of the camwheel.


The timing wheel again


The dial guages over the valves.


After MUCH tinkering:
- set timing pinion on key
- fit case
- tighten nut
- rotate and check valve-opening times
- repeat rotation
- remove nut
- carefully remove case to prevent cam-wheel jumping ship
and repeat....

I ended up with this information :


Moving the Camwheel one tooth forward or backward compared to the timing pinion gives an adjustment of approximately 17degrees, which I did on the 3rd and 5th keyways after seeing that the initial reading was quite a long way out. (Hence 2 sets of readings for those keyways)

Compared to the desired timings:


It looks like actually - position 5 gives the closest to the aggregated correct opening positions. : Exhaust somewhere between 70 and 65 before BDC, and inlet somewhere between 45 and 44 before TDC.

Once I'd found that "sweet spot".... I marked it!!


I then wanted to get the nut done up tight on the timing pinion, but was struggling to hold the crank while I did so.
So, I went furtling in the draw of odd tools.... and dug up this:


One of Dad's home-made contraptions.  an old primary drive chain cog with a bit of tube bolted loosely to it. It's far less usable than it looks....

So,  I set about improving it.
I figured it would work a lot better if the rod were fastened properly across the cog in 2 places, so set about drilling a new hole in the cog 180 degrees across from the original.

Explain this....



Making progress:


I went through a few of the smaller drills simple because the case-hardened cog was tough to get through with a cheap wood pillar drill!

Eventually I got to the point of drilling the second hole in the pipe - which went relatively smoothly.

Found some bolts (M6 coarse, from the box of metric oddments), and had a lot of fun (not) searching for a pair of nuts (I spent about 2 hours in all during the day furtling through the selection of metric nuts for different jobs).

The tool fitted - but the output shaft itself sticks out from the splines, so I needed to remove some material from the pipe where it crosses the cog.

I initially started drilling again, until the inevitable happened:


So I thought $%^&& it.


I don't like angle-grinders, but they are good for making a mess.

The finalised tool in situ:


Engagement of the splines is approx 90% - that's good enough for government work.


And the Timing pinion is TIGHT.
It's actually a left-hand thread as well, so theoretically, as long as the engine is "pushing", it should be doing itself up...



Next things are to re-adjust the valve clearances back to 0.002" and fully finish the timing chest fit-out. 
I think I left out a spacer on the cam-follower shaft, they're moving about too much and "clicking" as the crank rotates - I think it's just the missing spacer (friggin well hope so!), then properly fit the Timing case cover with it's gasket. I need to re-read my notes just to check the assembly.

I've decided to live with the slightly non-perfect push rods for now, but keep looking for replacements. They're relatively easy to replace and will just need the rocker-adjustments redoing to reset the clearances when replaced, ie it shouldn't affect the timing (I believe).

I'll probably also fit the other outer covers that need gaskets next, just so they're done, before mounting the Mag and setting the ignition timing.