J.A.P. 4/3

Picked this up yesterday.  Oh No - it's air cooled    What was I thinking








Seems to mainly all there. Obvious at first sight are missing magneto points cover and starting handle - anyone got either lurking in spares box? Also as you will see from picture 1 part of the flywheel cover is missing so I'll need to find a local metal basher.

Was seized at first but I whipped off the head and sprayed some GT 87 down the bore and got it moving in a few minutes.
Bore, valves and piston look OK at first sight - it came off a allotment rotovator so probably only did a few hours work a year.
Magneto HT winding reads approx 7K so that's promising.  Removing the tin-work revealed a collection of different nuts,  bolts and studs had been used over it's previous life. Bottom of the cowl is shot so, again, I need to find someone to plate it up.

First job is to clean most of the gunk off and get a spark at the plug.

Can't beat a good old (air cooled!) JAP, especially a larger variant. My 4/2 doesn't have that cowling removable section to access the points - the whole cowling has to come off! It seems quite common I've found to have a variety of fixing types as long as the tapped holes are intact it's easily rectified.
Also found unused magneto points seem to grow a fungus type of deposit, easily cleaned off. I've also found the condensers to be serviceable but worth checking if you still can't get a spark.
A good clean up makes things far more pleasurable!

Alan

What's this little jigger on the inlet manifold do? According the the manual it's a 'Release Tap'
Can't see what it releases.

Not seen one of those before.

Alan

Having removed the tank bracket I found this.  No mention in manual - over engineered breather ?

Certainly looks like an engine breather. Don't know about over engineered but seems to be in good order with the oil mist keeping any rust at bay. I'm guessing the two slotted screws are holding the disc valves in place, if so it will allow them to be removed for easy cleaning.

Seems to be an interesting engine, I have no idea what the release valve is for, hopefully someone will be able to come up with the answer.

Neil.

Well, lack of spark was easily diagnosed - plug lead was open circuit. Took a fly lead from HT and placed near body spun it over and got a big fat spark. Happy bunny.

According to the manual...
 
"No adjustment is provided for timing the magneto, which is unnecessary, as the magneto is correctly set before leaving the works ...."

I can understand that the retarded impulse timing is fixed for starting but surely there should be some adjusting for 'running' timing (25° before TDC). Or am I missing something?

As far as I'm aware the only timing adjustment available is by releasing the 2 screws that locate the 'points plate' which will then give (very) limited adjustment.

Alan

I have WIPAC mag and it has 'slotted' mountings so will allow a little adjustment. We shall see.

The release tap, may be to allow petrol vapour to be vented.
If petrol lies in the bottom of the induction pipe when the engine is stopped; this will, on a hot engine, vapourise and hang up at the highest point. This vapour lock may make the hot engine very hard to restart.
I think that may be what it is for.

Breather is standard JAP, the 2A/2S models have the same. Tap is to release excess vapour, again a standard JAP fitment, timing will be fixed like many engines with impulse mags such as Coborn, Wisconsin etc.

Pete.

Thanks gents.

Looks like the project has hit the buffers.
Took the exhaust off to find that one of the mounting holes was snapped. Breaking for parts I guess.

Shame to break it just for that.

If it were mine I think I'd be looking into sleeving the port and exhaust and just using the one stud to locate the exhaust

If you know anyone that does TIG welding they could build that up again for you drill and tap a new hole.

Robotstar5 wrote:If you know anyone that does TIG welding they could build that up again for you drill and tap a new hole.

 Welding cast iron ?? My ignorance astounds me!

As  everyone on the forum is aware my welding and machining skills are nil so I'm happy to take advice. A bit of internet research seem to suggest oxy-acetylene or brazing might be preferable too keep temperature lower. Any thoughts / comments Stuart.

mattblack wrote:Shame to break it just for that.

If it were mine I think I'd be looking into sleeving the port and exhaust and just using the one stud to locate the exhaust

Will have a look into that idea, Cheers.

Woodsman wrote:

Robotstar5 wrote:If you know anyone that does TIG welding they could build that up again for you drill and tap a new hole.

 Welding cast iron ?? My ignorance astounds me!

As  everyone on the forum is aware my welding and machining skills are nil so I'm happy to take advice. A bit of internet research seem to suggest oxy-acetylene or brazing might be preferable too keep temperature lower. Any thoughts / comments Stuart.

Send some pics to john@doubleboost.video if anyone can sort it John can, he's Newcastle area so it may need posting?.

Paul,

What ever method you use to weld or bronze you need some serious brownie points to accrue with your better half as the item to be welded etc needs to be preheated, usually in the oven , as cast iron suffers from stress cracking next to the welded repair.

Maryalice

Just picked up my bored out starter boss from David. Works a treat - many thanks to David. Always a pleasure to step into his shed and admire some of the lovely model engines he makes. Note also the magneto cover I got off fleabay - it's the right way round now.
Once I've replaced the duff HT lead I'll give it a spin to see if it will fire.

Good to see it back on the engine, only to glad to help, cheers David

Agree what you say about David`s shed when I was at his a while ago collecting an engine it was excellent to look at his workmanship, Hello again David had the model 72 from you if you remember. Don

Back to the cracked exhaust mounting.  What do we think about a biggish blob of JB Weld reinforced with some steel. Ugly maybe, but would it work?

If your going to reinforce it with steel why don't you just use steel, braze in on then re drill the hole, I'm sure somebody local to you can make the repair, another way would be to braze a large blob and re shape it by hand.

Maryalice