classic motorcycle forum

"I'm just pondering the wisdom of splitting the crank up to check the big-end bearings..."

Yes it's a tricky one, perhaps depending on what you want to do with the bike. If you do pull it apart keep in mind that it is tricky to get it back together and running dead true. If you've not done it before best left to an expert? I've done it lots of times, and most often it's gone ok. Only once did it defeat me entirely (i.e. no better than a couple of thou run-out on the shafts after trying everything I know) and I had to pass it on to the expert who used appropriate (unknown to me) magic to get it running just so.

The epoxy is interesting. Often cases an an engine can be quite porous to oil and painting the inside with something (glyptal, expoxy of some kind) can keep the outside clean. Hopefully there's no major corrosion being covered up.

Leon

Yeah - I think I may have a contact with someone locally who runs a Cooper 500 car, so hopefully will have experience (or knows someone else) in doing that job.    Even though the bike is only a road-bike, and is running low compression (9:1 and petrol as opposed to 15:1 on dope), I'd like it to be "as good as I can get it".  Ideally I want to get into the cycle of "ride in summer / maintain in winter", however the learning experience of my first full strip down is taking longer than I had expected, mainly due to the unexpectedly poor condition of some components, and the lack of time I'm getting in the workshop.

... cont.



The scary part!!




Plonk!  (tinkle tinkle tinkle..... feck where did the pins go!)


There's 10 of the little buggers each side.


Output shaft:



Magnet to pull the pins out when they refuse to fall out by themselves.



Simple engines are great.



Timing side: ALL the pins fell straight out!


Timing side bearing liner is ok.



Output side not so much....

That patch feels rough as hell. New liner time.


I'm currently mentally debating the wisdom of breaking the crank down... looks simple enough... it's the reassembly that scares me!





Insides of the cases are epoxied to buggery.  I don't know if this is my Dad's doing... but it's likely.









Another view of that liner.



These "thimbles" screw into the cases and provide the base for the screw-down head rods


They're a git to get loose...


Paper gaskets infused with oil take heat well....


I'm reliably informed that the thimbles come out a lot easier if they're assembled with coppa-slip.  Luckily, I've got plenty!

The thimbles have these little pucks underneath to stop any galvanic reactions with the cases (or that's what I've been told - it could be just to provide a flat step for the thimble to wedge down onto).



Epoxy:


I'm glad to see that the drain plug hasn't been epoxied over....


Blue hylomar... my old friend!

You can sort of see the "lip" that JAP used to create a labyrinth seal on the cases here.

As said - I'm just pondering the wisdom of splitting the crank up to check the big-end bearings - they "feel" ok - but while I'm here it might be worth doing.  I'm just being cautious about that because bolting it back up "straight" is going to be paramount.

All that only took me about 90 minutes, and I managed to finally get down to the local "Classic vehicles" club night and join the club - they do a monthly meet only about 3 miles from me so it's dumb really that I've not joined before now.  Already hopefully got leads on a couple of hopefully useful contacts.


Just in case anyone is wondering: I'm using this thread mostly for myself to provide my thoughts and notes as I go, for reference to when I put it back together, or do it again!  Pretty sure there's no-one else on the forum with a JAP speedway engine to dismantle..   (happy to be proven wrong though! )

Hi RB
On some J.A.P ohv's the rockers are held in place by cast on "pip's" on the outer cover.  In your photos I can see the protrusions on the rockers that would sit against the cover pips.
It looks wrong when you take the cover off and the rockers can push /pull , but is fine when the outer cover is fitted

John

Yeah - it'll be something to be checked thoroughly when I reassemble the box.  Which won't be happening until I get that damaged oil gallery fixed.

In the meantime: while I'm not rushing, I've not been idle either:

The following is a conglomeration of progress:

When you think you have a large spanner....


But you still end up needing something larger!


That nut came undone far more easily then I was expecting, but the threads cleaned up nicely. The exhaust is nicely patinated with spilt Castrol R, so I'm not going to polish it, just clean it up.

Next job is either to get the head off, or pull the engine out of the bike, just not sure which to do first.

pulled the head off :









This was most of the oil that had overflowed into the fins on the head.






These scores look nasty, but tbh, I think they're actually just superficial.


So i thought I'd pull the barrel as well.


Nice polished con rod there...


Nasty lump taken out of the barrel skirt though.
Funnily enough, I have the oddest feeling I've seen this before... Maybe in a photo or something. I need to see if there's any photos of this in the paperwork I have.




Next job is to fit a plug, or bolt into the head, then fill it with water to check the valve seals.

Oh, and see if that barrel is useable....


Oh yeah - I took a quick video of the movement on the big-end.

https://youtu.be/3hB3lH5znKU?feature=shared

Not the steadiest of shots I'll admit - but hopefully you can see the movement left to right of the conrod.

This seems a lot to me..... but is it a lot for a an engine designed in the 1930s?






Concerning this damage to the barrel skirt.....

I've chatted to one or two mates of my Dad today, and although no-one remembers anything about this.... we sort of agree that:

a) IF this damage had happened during the current "build" of the engine... then that damage would be apparent elsewhere: ie, the conrod would be dis-attached to the piston and in several pieces itself: it's not.  and;

b) Using this barrel would be exactly the sort of thing my Dad would do, if he considered that the piston is unlikely to be affected and the barrel wasn't going to start cracking up any further.

I've got a boroscope (ish) somewhere around, so I'll have a poke around in the cases, but I think that the barrel will be useable, and the damage was from a previous useage: ie some racer (possible a Formula 500 car) blew the engine, caused the damage, but then discarded the barrel to scrap/sale.  The damage is likely 50 years old.....


any road - next jobs are to continue stripping the engine, and figuring out how the hell to mount the timing disc onto the drive-side of the crankshaft so I can attempt to check the timing on the thing.  I also want to get the drive sprocket off - but can't figure out how to lock the crank in one position (tbh - I'm not even sure if the drive-sprocket nut is right- or left-hand threaded....)



I figured out how to get the nut off the engine sprocket...





The jaws on this clamp fitted into the sprocket carrier splines perfectly.


The nut came off with a LOT of torque required... because the $%^&&er was loc-tited.

Tidied up the edge on that barrel liner skirt. It's usable because the piston is on a short stroke length.



I also had a long call with a lovely old feller who is a bit of a guru with these engines, and he definitely have me some good advice and warned me about some things I wasn't aware of. 
It turns out the conrod in the engine is most likely an aluminium one, which is not as strong as the steel ones (obviously), and they haven't been made since the '70s, however, given that the engine is setup as a 400cc, running 9:1, on regular petrol, instead of 15:1 on meth... We reckon it should be okay for road use.

He also gave me some directions on the rocker box rebuild, and described how to do the valve timing using "split timing". Apparently he's never seen a JAP cam that was actually manufactured to the exact correct shape!


Oh yeah, and the valves need lapping...

https://youtu.be/qFme0sPGCp0?feature=shared

Especially the exhaust!



Stripped the valves out of the head tonight.







The inlet valve had a good seal. You can see the shiny ring around the head of the valve, that's indicative of a clean seal to the seat.
The odd broken/tired rings are the mica washer(s) that sit under the spring cup. I'm not sure about these. I don't know if this is multiple washers, or one washer that has delaminated. I know nothing about the material mica.



The exhaust needed a little... "persuasion" ... to separate the collets from the spring cap.



You can see that the exhaust seat isn't shiny like the inlet.



Lots of crud around the valve stem tube fitting on the exhaust side



Needs a clean



And, guess what.....

There's a video too!
https://youtu.be/h3auMMXjmrQ?feature=shared
(please pardon the language....)

Obviously I now have to decide if I need to get that inlet stem tube replaced, (They're pressed into the head, so I need to find someone to do it for me), or if I live with it. The exhaust side looks a lot newer than the inlet one.

I'm going to hold off on lapping the valves in until I make that decision.

Still pondering the best way to clean the burnt on carbon from the inside of the head and barrel (and piston), without damaging any of the surfaces.

Well - I finally got back into the forum after lots of trying. (Many thanks Admin!)


The JAPton is being stripped down because the magneto ran out of sparks, and the head decided to give up retaining compression.

Issues found so far :

Timing chain was a bit loose...


I wonder why....


Rocker arm end-float was somewhat wide....


They were both like that
This is roughly where it should be :


And the amount of movement has caused this damage to the oil galleries in the rocker box:



The engine sprocket was a git to get off.



The barrel skirt is damaged... but given the complete lack of damage to the piston/conrod, and the age/history of the barrel, we've concluded that this is old damage (I'm going to split the cases anyway).


Exhaust valve seat was knackered - you could see daylight through it!




errrrr.


Ah.


Well - that explains the highly unimpressive performance of the valve-lifter.



Cam follower probably needs replacing:


Next series of steps will be to continue the strip down so as to be able to check the main bearings (I'm not expecting issues, but I've been advised it's worth doing).  I'm not sure I'm brave enough to split the crank itself though.

Need to find an engineering workshop to weld some ally to that rocker box and tidy up the oil gallery so the exhaust rocker actually gets oil.

Then buy a few parts (hopefully), if not try to find them in auto-jumbles ( ), and reassemble.

Might be time to file the slot on the kickstarter a little wider enabling the bolt to clamp more.

I've done that already - the slot physically can't close up.

Quote from: Rex on August 28, 2023, 10:09:27 AM

Quote from: R on August 27, 2023, 11:46:01 PM

There is some chat about viton tipped fuel needles, or not, in monoblocs.

Yep, some claim that the Viton needles are prone to sticking "up" and shutting the supply of juice off.
Re the pit bike Choagy carbs, an old boy I know paid £14 for one off Ebay, and stuck it on his reluctant Tiger Cub. Apparently it started second kick and even ticks over fresh out the box.

I've heard this myself which is why I'm considering it. Ebay also has sets of main & idle jets for a couple of quid or so. I've never had the experience if viton needles sticking despite using them for decades.

Got any links for the jets?

Well, I've still not figured out what's wrong with the JAPton. Did some checks last week and fuel flow is good ( more than half a litre per minute, which ought to be fine).

Raised the needle by one because i thought it might be a bit weak, and tried starting it up and although it started easily enough, its still spitting back and backfiring.

I'm beginning to think the ignition timing has slipped, so i took a cover over the magneto drive sprocket to check it.
Seemed fine so went to put the little cover back on, and bugger me if the sodding thread didn't strip.

GAH!

So I'm going to put the JAPton aside for a bit and concentrate on the other projects i need to get done before winter, and will very likely spend the winter stripping the thing down and learning more of its foibles.

last week I "fixed" the hole in the JAPtons crank cases (timing chest actually).

I did stick an endoscope down it, but there wasn't a lot to see!

I cut down the new bolt so that it was roughly the length required to fill the cases, with a crush washer on top:



Then fitted it in with a good amount of Soudall Fix-All smeared into the threads and around the crushwasher and head.  With any luck that will act as a seal and thread-lock even though the bolt isn't done up that tight.  I tried very hard NOT to strip the threads so only did it up as tight as I dared....



Obviously will be keeping an eye on it, but I can't move it with my fingers... so it's an improvement

I had an idea that the issue with the carb tickler might have been the paper gasket between the jet block and the main body (the surfaces this gasket mates to are not the smoothest....).  So I stripped the carb down and put a small amount of blue-hylomar on each face of the gasket and reassembled it.

No difference.  Whatever is preventing the tickler working correctly is still evading me.  Next attempt will mean going into the float bowl itself and seeing there's something odd about the interface between the tickler and the float.  I've been doing some reading up and it seems that the new nylon floats sometimes cause minor problems so it's worth taking a look.




Took the JAPton out for a spin round the block this evening.

It might run ok at less than 1/4 throttle, but any more than that and it starts bogging down, won't fire at all, then after 2 or 3 deafening explosions from the exhaust it'll pick up and run well for about 10 seconds before it starts bogging down again.

Rinse and repeat again and again if I try to ride it anything more than 1/4 throttle (ish).

And obviously it's still pissing oil....




So... Back to to the tuning leaflets....