350 cc side valve JAP engine parts needed

[33d6]

Hi David,
Do you think we could have a few photos of the whole bike? So far we are running on imagination and good look at it all would be terrific.
Personally I think you have the beginnings of a really fun special. One which could keep you entertained for years and be good enough to ride all over the country should you wish.
Any chance of a photo or two?
Cheers,

[iansoady]

Come on chaps, it's not that hard. I made this for the Sunbeam using thick walled tube:



Used a Chinese 3,5" lathe. Admittedly getting the thread right was tricky but my turning is hardly expert standard. The slots were cut with hacksaw and file.

[chaterlea25]

Hi All,

I have a couple of sv JAP engines, one in a little OK Supreme 285cc on that engine the exhaust threads
had mostly rusted away, I had to make a new exhaust pipe anyway as the original was missing
I just made a sleeve that was a push fit up over the stub and welded this to the pipe, a little sealer and all is fine
The second JAP is on a Howard Rotovator  600cc,  that also now relies on a pipe clamped over the stub 
So for a "ratty" special there's no need to spend €99 on an exhaust nut thats too big anyway

John

[33d6]

I suppose it depends on your intent. Just a bit of fun or something you want to show off a little. All options are reasonable but in the end it's what the owner wants isn't it. I confess something about this particular combination of engine and bike appeals to my inner idiot but I've no idea why.
Cheers,

[Mobike]

Hi all,
Thanks for your input,as I mentioned previously my late father always spoke fondly of JAP engines he had owned.
I was offered a beautiful 're built 500cc Ohv engine complete with mag and carb several years back,but it's owner insisted he wanted £500( well worth the money)for it.Sadly at that time work was slow and my slightly lesser offer (400)was nt accepted,he said a " friend " was going to get him his 500 pounds.
Next time I spoke to him the " friend" Had told him  he only got 350 pounds for it.....
Hence years later my purchase of this as a project,it is a JAP engine albeit not the one I would have liked,but it is giving me something to play with!
I will post a few pics on here when it's looking a bit more presentable,as so far I 've just been getting it running better and checking the motor out.
The existing exhaust/stub? Is currently just pushed into the exhaust port and retained by a bracket welded to the pipe fixing to an engine mount bolt.It does seem to work so for now at least I 'll live with it.
I am hoping to get a straight inlet to replace the curved one and a stub fit 1"  Amal to suit,I have a few Amal carbs but they are bolt on and I don't have welding gear to alter the inlet to take them.
The other similar JAP engines I 've seen ,have a long induction tube to take the carb clear of fouling the mag.
Just another thought,would a different mag make any difference ?
Obviously the one fitted is I believe from when the engine was possibly  originally from an Atco 20" deluxe mower ?
Would a different mag (as used on motorcycles with JAP engines)make any difference?
It keeps me occupied and there is always a c11 side valve motor option,or a c11 Ohv bored out to 290cc using a Hillman imp piston....should keep my interest going for awhile!
Cheers

[chaterlea25]

Hi Mobike,
A manual advance magneto would give better performance than the fixed wico
Lawnmower engines tend to be run at one speed so fixed ignition works
A rotating coil mag would be better running at half engine speed too, high revs can damage them
Be careful trying to unscrew the inlet pipe, the one on my sv and others I have seen are Left hand thread
I do not know why this is ? and cannot see a reason why???

John

[john.k]

Unfortunately ,ebay has inflated magneto prices beyond reason.........you used to be able to get BTH and Lucas mags from engines like Listers and Petters for $2 each at swaps once ,now everyone is asking $200 each for dud mags,than never been within 100 yds of a motorbike...........same with JAP sidevalves .....used to get them with scrap machines ....Ive got a couple of very nice 500 and 600 sv s used as starting engines on Rustons and Dormans.....pure bike engines used to rotate big diesels to start............then there the Autotruck 750 twins ........and the Autorail 1000s...........I remeber when the Messageries Martimes wharf next to the customs house closed ,the autorails were just run off the wharf into the river for laughs.

[Mobike]

Hi all,
Yes the price of mags is pretty high ,I do however have a spare mag for my B31...
I will look it out tomorrow and look at it with " new " eyes! Unsure of the rotation on both so need to check that first.
Thanks for the warning about the thread on the inlet  manifold John,,I m always wary of disturbing anything that has potentially not been disturbed for a long time!
Might not have spotted that one as it's tightened well into the head!
I have removed both turrets from the head and also the plug/bolt on the left side,which all came free fairly easily,so perhaps been off in recent times.
The plug/bolt on the left side of the head was presumably for a decompressor in another use?
As mine has one on the crank case obviously that position isn't required.
Another interesting thing I turned up on the net,apparently JAP moved the plug position to the rear of the head and it improved performance and top speed performance.I think it was for a T.T. race.
I really enjoy sifting through all the information out there!
The head on mine has a "flat " area at the same position but it has nt been machined.
My aim is to just get it rideable and see how it feels before I start throwing any money at it.
If the engine performs reasonably well,I have a 1946 girder fork / rigid rear it would look very good in.....(dont panic!not altering it in any way as i may one day restore it to standard!)
On the subject of fitting a different engine in a motorcycle as in Bsa frame /JAP engine how does that work with DVLA?
Do you just make an application and they take it for what it is, or is it more messy?
Thanks again for your help and interest.
Cheers David

[Rex]

The DVLA aren't too bad, the problem will be getting some sort of acceptable dating certificate for it. If the person doing the dating cert makes a big deal of it being non-standard and a recent build then the DVLA can get funny.
Forget the VMCC for a dating cert. When they request pics of the forks, gearbox, hubs etc you know you're knackered from the start..

[Mobike]

Thanks Rex,it did come with a dating letter from the BSA owners club dating back to 2015.
But it must have had a standard engine fitted back then as it is a  different number?
I ll have to look into that in more detail,
Thanks David

[Mark M]

Our Dating Officer for the REOC tells me Dating Certs are now only good for one year. Although l can’t see why, if a thing is identified one day why would it be different the next? Anyway, beware!
REgards, Mark

[Mobike]

Yes it does seem a bit picky!
Still I guess it keeps the system going!
I have contact details of someone that deals with such matters so will have to have a chat !
Cheers David

[Mobike]

For the curious !

[john.k]

You wont be allowed to have an exposed chain  drive like that.....it contravenes the machinery guarding laws,let alone MOT.......I know its exempt MOT,but still an unsafe machine,no matter how old...........i suspect you will have to organize a mag drive from the LHS engine primary sprocket........which many vintage bikes did have............being a tin chaincase ,it will be easy to organize.

[iansoady]

It could be quite fun but at the end of the day I wouldn't spend the time and effort necessary. But each to their own.