Troubleshooting a JAP Special

[Rockburner]

I guess I should also state that I don't want to be grinding material off the crank itself; I could grind down that nut and the crank-pin shaft end to get more clearance; because I don't want to mess with the crank's balance: I've no idea how well balanced it is.... but I don't want to mess with it!

[cardan]

"I fitted the 0.060 thrust washers on the timing side, and a 0.023 on the output side..."

I guess this is part of the mis-matched engine thing. It would be nice if there were no shims between the face of the crank and the bearing inner. Usually this is accomplished by shimming the bearing outer in the crankcase. As it stands, your shims are pretty large and heavy, and there could be quite a "hula hoop" effect as they spin around the main shafts (or the shafts spin inside them), which could cause damage to the shafts and/or the shims. In reality, if you're not going racing, it will probably be ok. But it would worry me. Maybe check with your JAP man?

You mention there is not much end thrust when the engine is vertical: true provided the piston is square and centred. You might be amazed to see the inside of an engine that has been running with a bent con rod!

Leon

[Rockburner]

"I fitted the 0.060 thrust washers on the timing side, and a 0.023 on the output side..."

I guess this is part of the mis-matched engine thing. It would be nice if there were no shims between the face of the crank and the bearing inner. Usually this is accomplished by shimming the bearing outer in the crankcase. As it stands, your shims are pretty large and heavy, and there could be quite a "hula hoop" effect as they spin around the main shafts (or the shafts spin inside them), which could cause damage to the shafts and/or the shims. In reality, if you're not going racing, it will probably be ok. But it would worry me. Maybe check with your JAP man?

You mention there is not much end thrust when the engine is vertical: true provided the piston is square and centred. You might be amazed to see the inside of an engine that has been running with a bent con rod!

Leon

I took a 0.050 and a 0.040 thrust washers out of the engine when I stripped it, and the internals seemed ok. The engine is pretty unstressed and won't be used for racing or anything.

The thrust washers are part of the design on the engine, it's not possible to adjust the main bearing liners, they're pressed into the cases, and the thrust washers/shims allow for the end first to be adjusted. This IS a 1930's design....

But you're right that a call to the expert is in order.

[Rockburner]

In regards to the issue of the crank-pin nut contacting the bearing liner screw......




I've had a word with the JAP Guru... and his advice was to simply take an angle-grinder to the crank-nut and make clearance!

Apparantly it's a common thing, the cases are "not" exactly precision made, and there's a lot that were cast by jobbing engineering firms after JAP stopped production, so exact fitting is not always going to happen. His advice was to figure out the desired shims on the crank (to get the piston and con-rod as central as possible), then see if the nut is striking the liner screw (and the casing), and then get the grinder out! 

He also suggested that if I wanted to confirm the clearance I've created, I can fit slightly narrower shims (eg ten-thou thinner), and see if there's contact.  If not, then I should be good for the lifetime of the engine.  Sounds like a plan to me.

He also pointed out; when I mentioned my concern about affecting the overall balance of the crank; that shaving a 1/16th off 1/3rd of the crank nut would be akin to taking a piss before a weigh-in... totally irrelevant! Which was reassuring.

So - that'll be the next thing on the list!  GRINDING!

[Rockburner]

So, last night I started out by making up the new base gasket :


I have made myself a set of templates out of some thicker carboard and used that.  I've trimmed the inner circle to be slightly larger, so hopefully there won't be a capillary path from the cylinder base straight out under the gasket this time.

I also made up a quick Mag-pinion cover gasket from the excess paper to avoid wasting it.


I then tidied all that away and got down to the main job of the evening.  I finished stripping down the crankcases again and experimented a bit with the shims just to confirm the crank-touching-the-cases issue.

I'm sure I took more photos over the course of the evening, but it looks like the phone camera didn't actually save them, which is odd....

Anyway: here's a few shots of the same modification that was done to the Output side of the assembly at some time before:



This is, essentially, what I need to emulate on the other side.
Interestingly.... the output side is the nut that was removed when we replaced the big-end bearings: in this photo you can see that the nut has been done up slightly tighter this time than it had been before: you can just see the threads on the crank-pin becuase the nut has been rotated on the pin about 5 degrees more this time.


I decided that the grinding would have to be done.
So I cleaned up the wheels as best I could, wrapped a tea-towel around the bigend to prevent too much grit getting to it:


Protected the timing-shaft oilway:


Experimenting with the best way to clamp up the wheels so they don't wander about.


Then remembered I have a little B&Q trestle that would make life a bit easier, clamped it to that and did some taping to protect other gaps and holes:


I also marked up the approximate area that needed work:


In addition I wrapped some duct tape around the shaft just in case the grinder got away from me!

Work in progress:






I did the majority of the grinding outside (to avoid any conflagrations...!) with a 115mm Ryobi, and it worked very well - nice and controllable.  The light was just enough that I could see what I was doing, but more would have been preferable.




And for some reason, that's where I stopped taking photos. (soz!)

I got to a point where all the marker had been eradicated, then, as the light was fading, I took the trestle back into the workshop and get the Dremel out to tidy up and polish.  I used the Dremel grinding wheel to make the ground-away area slightly concave and to take off the rough edges, then wire-brushed and polished it a bit.

I then cleaned it all up, using meths and paper to try to get rid of as much grit as possible, before removing all the protective stuff and unclamping the wheels.

I tried the wheel in the cases with a 0.023 shim (which is the minimal it would need I think.. I stil need to figure out exactly the best shims to use - more on that later*.

The $%^&&er is still scraping. GAH!

So - I need to take a bit more off - I suspect I just need to "round-off" the ground area so that it clears the head of the bearing-line-fixing-screw.

It's sooooo close!! 


* Something from the conversation I had with the Guru:  Although the recommended end-float in the Greenway book (which is the Speedway "Bible") is 0.012" - 0.015" : The Guru recommends letting it be a little looser : 0.015"-0.020"... and the engine will rev more freely.  Given that my engine is "square" (bore = stroke) and will be wanting to rev more easily due to that: I am taking that advice and giving it strong consideration.  The flip-side is that the Guru tends to be building up engines for actual racing... ie, they'll get stripped down again after a season, and a season is not really that many miles.   So: my thinking is to compromise on this and aim for an end float that takes into account the hopefully longer mileage that the engine will do before it's next strip down:  I'm going to aim for around 0.015", or slightly higher, end float: ie the looser end of the Greenway figures, and the tighter end of the Guru's advice.  The aim is to have the engine in good fettle for a few years of riding around on the road with the occasional classic "parade" track-day.  It's unlikely to get utterly thrashed, but I would rather not be rebuilding it every winter!

[Rockburner]

More grinding...



(forgot to block off the timing shaft oil feed... oops )

Progress:


Checking with a 1/2" wide rule


Checking with a 1" wide rule


The cleared area needs to be around 4/5" from the shaft - approximately.

Almost done....



After all that I stuffed the wheels back into the timing side case... and it's STILL "just" touching that odd ovoid shape in the cases with no shim in place - and it's just the outer parts of the ground area (there's a distinct double touch I can feel).

However - there WILL be a shim in there and when there's a shim, there's no touching. So that's gone relatively well I think.

I buttoned up the cases dry again and without any shims to check the end float, and conrod centrality, with the intention of fitting shims not just for good end-float, but also to get the conrod as central as possible.

Overall end float with no shims :


Using the case joining line as the "centre-line" for adjusting the conrod centering. There's nothing else on the cases that is machined in any way so that it could be used for an accurate measurement for centre-ing the conrod: ie, there's no matching face or point on either side that I can use to measure the offset to the conrod and get a balanced measurement with any accurary.
This is with the wheels as far "left" as they will go:


This is with the wheels as far "right" as they will go (the rule hasn't moved).


So - need to play with this a bit more, figure out the shims and tinker, then rebuild again.

Over night I also had a nasty though that I may have put the output side case on without the main bearing pins and carrier... D'OH!  So I'll be checking that end-float again!

I think I'm getting a little pressured and starting to make stupid mistakes - so need to try to slow down a bit and be thorough.

[cardan]

More grinding...

I think I'm getting a little pressured and starting to make stupid mistakes - so need to try to slow down a bit and be thorough.

Yes. What you're doing is not OK; I'm not sure why. Better get some help.

Leon

[Rockburner]

More grinding...

I think I'm getting a little pressured and starting to make stupid mistakes - so need to try to slow down a bit and be thorough.

Yes. What you're doing is not OK; I'm not sure why. Better get some help.

Leon

Care to be a tad more specific?  I did in fact forget the output bearing liner so I know I made that mistake - but have I made any more? This is still my first time doing this sort of work, and part of the reason for describing every step is to make sure that I'm not missing things, even if I have to go backwards again.

[Rockburner]

So - yesterday I got the opportunity to dive into the workshop...

4 hours of facking about later....

In imperial...


and metric units:


9.3 kilos.... yeah - that's pretty hefty.

I pushed some oil through the big end to clear it out before proceeding:



Then left it to drain for a few minutes


Before starting the iterative process of finding the best mix of shims for an acceptable end-float and conrod centering:

Each trio of photos will be: the measured overall end-float, then conrod vs case centre-line with crank to LEFT, then crank to RIGHT.
one:




two:




three:




four:




six, no five! :

(fecking guage)




That's acceptable and seemed to be as close as I was going to get with the shims I have.  Between 0.015 and 0.020 overall end float, and the conrod (allowing for the big-end float as well) is as centred as I can get it.

A sure sign of a troubled mind.....


I've ended up with a very thin shim on one side, and quite a thick combo on the other.

I believe the main reason for this is that the main bearing liners are of different vintages, and protrude into the cases by different amounts (which is the main reason for the adjustable shimming).  The old liner in the Timing side case is only slightly proud of the case it fits into (which is the side of the crank-wheel I had to grind down).  The new liner I fitted into the output side is much more proud of the case: ie, it has a thicker "brim" (think of it shaped like a top hat); so, to center the conrod, there is less "room" on the output side between the liner and the wheel.

I think I spent about 3 hours on that: each measurement above represents unbolting the cases, pulling out the wheels, pondering the next combo, then reassembling (making sure not to fling bearing pins everywhere), bolting up and resetting the guage.  The guage was a bugger to zero each time.

I then restarted the assembly process:
First get the mating faces clean:

Can you get high on meths fumes??


Stick the wheels in with the bearings and shims, then fetch the sealant.


Oh FFS!


Even with having squooged the stuff up and down the tube to try to get it mixed a bit better.. (metal tube - hence the leak above) it still came out very runny. In fact, it literally poured out of the tube (which is why I ended up with slightly more on there than I had planned.  )




I cleaned it all up as best I could before it got too sticky




It does make quite a mess....


I can only hope that there isn't too much dribble inside the cases themselves.

Just for shits and giggles I checked the end-float again:

(fecking guage)


Satisfied with that, the end-float is still as I hoped and with luck, the 3Bond will go off properly.

I decided to carry on and fitted the piston again: naturally I scratched hell out of the piston getting the sodding gudgeon pin circlips in:




Then fitted the barrel rods:



To get a good "heft" on the barrel rod nuts I put the whole thing into the vice briefly:


So - we're back on track, if behind schedule slightly...


I left it there for the evening to let the 3Bond go off, and to ponder the next move:
Specifically: do I try the 3Bond on the base gasket again... or use something else: the immediately available options are Hylomar Blue, or silicon RTV.  I'm tempted to try the RTV to be frank, mainly because (from memory of last time I used it), it's much, much less runny than the 3Bond, and so easier to be exacting about where it's applied.  I don't really want too much of it dribbling into the cases.

So, I went back in and fed the cat: