Troubleshooting a JAP Special

[Rockburner]

Pride, as they say... Cometh before a fall.


I'd been quite chuffed with myself for the way things were going on the bike, so naturally it couldn't last.

Took it out for a longer ride to see how it behaved over 20 or 30 miles of continuous riding, not straying too far from home, riding around the local roads.   At first everything was tickty-boo, it loped along nicely, albeit the fuelling at low revs wasn't perfect: couple of backfires, but nothing worrying at all. Riding "at speed" was fine (tyre pressures were a tad low) but the engine felt good. Clutch and gearchanges were fine (even getting into first at standstill was a lot easier)

Then, while tazzing along nicely it suddenly just went "bleaerrrrrrrrrrrrrrrrrrrrrrrrrrr" and died.  I was on a quiet country road, and luckily a largeish driveway appeared so I rolled into that, safely off the road and stopped.

There was some swearing.

I pulled out the tools and checked the plug: Bit oily, but not overly so - running a tad rich I'd say. (and rolling off tests were indicating that too)


Yes there's sparks.  Yes there's petrol, yes the petrol is flowing into the carb.  Then when trying to kick it... I realised there was absolutely no compression whatsoever.  There is exactly the resistance on the kickstart that indicates the engine is turning over, (ie, it's not clutch slip) but no compression. In addition the head gasket wasn't "puffing" at all which would indicate failure of the gasket. (and there's no marking or blow-by staining to indicate gasket failure)

There was more swearing.

That's not a roadside fix.

I've broken down in worse places, and in worse conditions:




The fork weep is back...


Attempted artsy photo by headlight!




5 hours later:


Eventually got home at about midnight and threw the bike back in the workshop.

Mileage on the odo when I left:


Odo reading at breakdown:  It did nigh on exactly 30 miles!


Reference odo (from after approx 10-15 miles earlier this year)


so - it's done roughly 150 miles on this engine build...  :wtf: 

Still - more than I've done on either of the BMWs this year! :wtf:


Current thinking is the lack of compression is one of the following:
Burnt out valve - maybe that exhaust valve seat wasn't as ground in as well as possible?
Holed piston - messy
Failed piston ring  - that'll do the bore no end of good.
Valve-springs failure - outsider in terms of likelihood, but it would create the symptom.

I won't know until I get in there properly.   The "silver-lining" is that none of it is scary stuff any more and I feel more confident about figuring it out.

However - there's other projects that need to be done, so I'm going to park the JAPton for a month or so and get one or two other projects worked on.

Well - I needed something to keep me busy over winter....  :roll:

[cardan]

Bummer. Fingers crossed that it's something at the lesser end of bad: maybe a valve stuck in its guide, just off the seat. Good luck.

Leon

[Rex]

Good call. I've had a new valve guide pick up enough to grip the valve stem. Can you hear any chuff-chuff noises through the carb or silencer when it's kicked over?

[Rockburner]

Good call. I've had a new valve guide pick up enough to grip the valve stem. Can you hear any chuff-chuff noises through the carb or silencer when it's kicked over?

Not that I noticed. There's what i can only describe as a "springy" noise happening at some point in the rotation though. I'm assuming it'll be a fairly obvious issue when i uncover it.

[33d6]

Years ago had that issue with my 1926 Matchless. Took months to track down a sticky exhaust valve that would stop the engine as soon as it got faintly sticky then free up when cooled down.
You show a rather black and oily sparkplug so you may have a similar problem, particularly if you have bronze valve guides. Sorry I don't really follow four stroke threads so you may have already gone through this.
Cheers,

[Rockburner]

Years ago had that issue with my 1926 Matchless. Took months to track down a sticky exhaust valve that would stop the engine as soon as it got faintly sticky then free up when cooled down.
You show a rather black and oily sparkplug so you may have a similar problem, particularly if you have bronze valve guides. Sorry I don't really follow four stroke threads so you may have already gone through this.
Cheers,

All information is noted carefully and will be referred to, I can assure you of that!   Thanks! 

However I think this is something else (or possibly a follow on issue from maybe a sticky valve) - the engine cooled down nicely while I was waiting for recovery and there's still no compression.

[33d6]

Thank you for the response. I hope you diagnose the problem quickly.
I had a bit of a thing about lubrication of early valves and guides at one time and found it far more subtle than I expected. Looks simple but not so. The lubrication of inlet valves is entirely different from the exhaust. I'm talking single cylinder engines here.
A sticky inlet shows itself by ferociously sneezing back through the carb immediately before the engine stops as you've lost compression. Any lubricant introduced to solve the problem gets washed off by the incoming fuel so needs to be either continually applied (very messy with exposed valves) or be both a lubricant and fuel resistant (bloody nigh impossible). It took years to stumble upon high temperature silicone grease which combined with the basic design of my Matchless, (fixed head with valve caps and a simple penny in the slot valve cotter) made whipping out the valve for a quick grease every now and then an effortless doddle. Problem minimised if not entirely resolved.
The exhaust valve is different. As the engine has total loss lubrication via a Pilgrim pump and no oil control ring by design, (why do you need oil control when you keep pumping the stuff in anyway. An oil control ring doesn't help), you can appreciate that the exhaust valve has a constant light spray of oil coming past it. No lubrication worries there. Nevertheless I'd have these mysterious stoppages every now and then for which I could find no answer. By the time I rolled to a halt, got the bike off the road, took off my helmet, put it on its stand, blah, blah, blah it had cooled down enough to have compression back and start but immediately nip up again so the cycle repeated. It took a long time and repeatedly checking out possible fuel and ignition issues before the light finally dawned. A sticking exhaust valve. A quick clean of the valve stem and problem solved. And the occasional clean keeps it that way.

Same engine, same lubrication system, same valve set up, same everything but absolutely opposite problems. One valve hopelessly under lubricated and the other over lubricated.

No wonder I enjoy proper vintage motorcycles so much. So much challenge from such idiot simple components. They make you think.

   

[R]

Bronze valve guides are well known for causing sticky valve syndrome in the vintage bike world.
Far better to do them in cast iron, like the motorcycling gods commanded !

I bought an old Enfield, in 'good running condition'.
Unknown to me, it was fitted with a new bronze exhaust valve guide - just before the sale.
Ran fine on a few short runs.
On its 1st long run, on a warmish day, the compression suddenly disappeared.
While we were standing around looking at it, there was a huge CLONK.
I'd like to report it then ran fine again.
But it didn't.
Had shed a pushrod (ohv) and despite having a fair toolkit, wasn't sufficient to refit it.
Trailered back home to the workshop, and that elusive 1/8"W spanner was put to good use.
Bit of a ream out, and was good to go ...

[Rockburner]

Well - the JAPton is back on the ramp.

Still no idea what's happened to the compression as yet, but I've started stripping it down.

Head steady rotated out of the way and the carb off.


Just gaining access at this point.


Took the pipe off all in one go - the nut at the exhaust manifold was tight as f***.  I know I did it up "tight"... but not THAT tight!  Good thing I had an extension bar...  I also remembered to use some neoprene to protect the nut this time!


I was then going around the engine getting the engine bolts undone when I smacked my head on the sodding kick-start lever.  Which I decided was a good time to head in and enjoy the rest of the evening in peace...

More to come.

[Rockburner]

Time I actually did something about this bike.

I strolled over to the workshop with a certain amount of trepidation, there's a finickety facet of this bike, which I had a premonition would be awkward, and it proved to be so.

Well, there's 2 troublesome facets, but we'll get to the other in a moment.

I wanted to get the engine out, mainly because it's just easier to work on the thing, do timings, etc etc when it's out of the frame. It's not "hard" to undo 5 studs and pull the thing out... but this little git:
,
which is the stud that is tucked under the mag platform, decided to be a git and the nut on the hidden end stuck to the stud.  Which meant that there is no way to get the frigging thing out; without pulling the entire timing side of the engine off. FFS.

I tried to get the nut loose from the stud, but it wasn't having it.

The first thing to come off is the timing chain cover and pilgrim pump.  this joint isn't actually sealed in anyway, (but I've learnt a trick about this... let's see if I remember it when it comes to reassembly!)


While I was taking off the timing chain... I noticed something odd.
the Mag is supposed to have a notch on the shaft at the "bottom" when in the correct position (locked by a 6mm pin dropped through the shaft), but the "ding" in the end... with the shaft locked... is on the RIGHT?


That will need some investigation..., I tried calling BTH but I was too late in the day to catch them.

Once I'd got the mag off (later in the process) I checked the "primary" notch... and it's at the "bottom" when the shaft is locked


BUT that ding in the end... is definitely pointing right!

$%^&&ing weird.  I'll have to remember that.

Anyway... I carried on with the strip down of the engine in situ.
Removing the main sprocket nut.  did I mention I found some $%^&& off huge spanners?  They're Elora too! (I have a large collection of Elora now)


I still need to find a 2" and somethingth for the exhaust manifold.

Managed to get the primary timing cog off with the 2-arm bearing puller (which is a pain)


Custom tool number 342



You know I mentioned a second "$%^&& you" on the bike?
here it is:

This sodding head bolt is impossible to access with the Mag in place.  So every time you want to do anything in the head, the sodding timing has to be all stripped out and re-done. ffs.

Anyway, carried on with pulling nuts off studs... or winding studs out complete... (I hate studs, very very tempted to replace the 4 studs that hold the timing cover on with bolts)


I was wondering why the sodding cover wouldn't come off....
Then remembered something:

D'oh!

I also forgot that the sodding gear-change linkage gets in the way, so the camshaft popped out and nearly lost the oil-feed quirrel again.

got it off eventually though


We've been here before....


But this time I (sort of) know (well... ) kinda what I'm doing (making a mess of it as usual)
Oil feed quirrel after I picked it back up off the floor....


And it's out!


Actually - that wasn't that hard.  Right hand finger through the hole on the front plate, hold back of head, and the engine can be rotated backwards, then eased out to the right side of the bike.  Far less swearing than last time.

There's something missing here... I'm sure of it....



I continued with taking bits off,and took a few photos as I went.

Definitely think I should make slightly longer push rods....
This (minor) damage is caused by the adjuster nut on the rocker arm scraping the oil shelf. 


The other side:


But it's a lot better than it was when I first stripped it down.

The rocker box comes off as a unit, which is good. hopefully it can stay that way....



The naked head... (phnar)


The head tightening bolts are effing tight, so I utilised one of my vices.



I used the Wera Joker again to wind the head bolt down, still cannot recommend these enough. It's xmas soon, drop some hints to the missus.

And they're all loose.....



I decided to leave it there and ..


...



...




...


nah $%^&& it, here's the insides!















So - it's oil in there, and has obviously ben running rich, but I knew that.  The barrel looks ok, I can't see anything obviously wrong with the piston....



but the sodding valves piss white spirit (all I had) like a London Irish supporter at full time. BAH!

$%^&&sticks


After a bit of swearing I carried on and primed the explosive device

(Seriously, that always scares the shit out of me)

Lots of burnt oil around the stem, it had built up enough that I needed to sand it off before the valve would come through the guide. I actually needed to drift it through.








The seat is black... not sure that's good...












When the valve came out I confirmed a suspicion...


Yup... it's bent


And it's been hitting something...




I have the nasty suspicion that it's been catching the inlet valve, that would certainly explain the damage on the "inside" of the valve lip - the inlet valve would (I think) just catch it there.  I need to take the inlet out as well and see if it has any obvious marks as well.

Very odd though - that shouldn't be possible unless the cam is somewhat out of shape??  It's weird.

I'll whip out the other valve and take a look, then probably talk to some people far more knowledgeable than me!

I can't believe the sodding valve is bent again... it's exactly the same issue as last time.