JAP 55 petrol/paraffin

This one has been on the backburner for a few years, as it for some odd reason had 3 broken teeth in the camgear and I've been trying to source a donor engine for it. It's an otherwise very good object from the estate of some smallholder up north in the valley here. Good tins, no corrosion to speak of, and seemingly low mileage on it. The debris from the broken teeth did no damage to the internals, except that some shavings embedded themselves in the adjacent big end shell. No damage to the crank, just the bearing. Here it is, missing teeth at 12 and 8 o'clock.



A few model 55's have followed me home since I restored my grandfathers trusty old woodcutting engine 15-16 years ago, but none of them have been fully restored yet. I just tinkered a little with a few of them to get them up and running again. At first I thought it too bad to cannibalise a good object to get the dual-fuel unit back online, but by now I have decided to take the plunge and simply move the paraffin parts over to another good block. When time permits I intend to try to braze that camgear with silicon bronze and my TIG-welder. And if it seems to stick and looks like it can be machined, I have a local shop that can help me to cut new teeth in it again. Which will both serve as a little experiment, and give me an opportunity to put an engine together from the parts that are in the poorest shape from my little hoard of 55's.

I never took too many pictures, which I sometimes regret, so all I have of it now is taken recently. The one below is of the engine partially assembled on a donor block of the same construction. There are 2 main castings of the model 55, and this particular paraffin unit was built on the early, crude, and square block castings. Here it is as of now, somewhat cleaned, lapped, and with a restored and hot magneto. Ready to be put together for a little test run before dismantling and paint. Complete with a rebuilt mounting ear on the left side of the base, as it had been broken off at some point. It actually welded up pretty decent, after some initial sputtering and grinding to lift some of the worst contaminants out of the surface material.



The designers were obviously afraid of cylinder wall lubrication issues running the somewhat dry paraffin, so the cylinders have a spiralling groove cut in them to hold extra oil. I've never seen anyting like it before, here's a picture of it after a careful honing, as the STD pistons got a new set of rings:



I can't promise a fast progress with this restoration as I have a few other projects going too. But at the least I aim to get it to run on both fuels in the not too distant future.

Why not weld and sit for few hours with files, cheaper and effective.

Maryalice

maryalice wrote:Why not weld and sit for few hours with files, cheaper and effective.

Maryalice

Thank you. How would you go about welding it? It seems to be made of a high carbon, grey, hard and brittle cast iron. Which might be why it broke off a tooth in the first place. I also seem to see some slight chipping in this gear in some of the other JAP's I have. So it might almost seem like the material perhaps is a little too hard and brittle for the application.

From the little research I did, some of the guys I found seemed to prefer to braze it with silicon bronze, using the TIG welder to apply the heat in a process very much like TIG welding itself. Reason being that the silicon bronze had wear and hardness properties comparable to that of the cast iron gear. And that the TIG-brazing process put less heat into the gear, and thus created lesser issues regarding stress and hardening, than traditional brazing methods.

But I have barely looked into it, and decided to use a good undamaged block of the same variety instead, before I started to mess around with the camgear. I'd still like to try to repair the cam though, it would save an engine if it could be made as a lasting repair. So if you have some experiences to share I'm all ears, as this will be my first attempt at something like this.

Progress was a little slow on this one as I got distracted with other things. But I managed to clean and buff and straighten the heat exchange manifold a little, and send it through the sandblasting and paint department.




Before it went in the sandblasting cabinet I used some machinist dye on the flanges, to print "templates" for making gaskets later.



And here's the finished result before being put in the oven for a heat induced hardening process.



The spray can paint I'm using for this is actually affordable, extremely durable, and highly recommended. After being slowly brought up to around 200 degrees C in the oven it gets impervious to thinner, and forms a scratch resistant layer that really stands up to the heat. Here on the aluminium manifold I used it without primer on the sandblasted surface, but on cylinders, heads and manifolds I use a good high zink 2k primer as a base, that can also withstand a great deal of heat. And the combination actually works and has served me well. Here's the can: