JAP OHV 350cc vintage motorcycle engine with Royal Enfield cover – SOLD

JAP OHV 350cc vintage motorcycle engine with Royal Enfield cover – SOLD


JAP OHV 350cc vintage motorcycle engine with Royal Enfield cover.

This is an interesting OHV JAP 350. The engine number is IO/E 8700 / CR.

I say “interesting” because I am wondering if someone has used and Enfield cover on a slightly earlier engine.

Royal Enfield definitely used JAP as an engine supplier. In late 1923 Royal Enfield used a JAP 350cc engine apparently. However, the engine number is for either 1922 or 1942, as JAP used the same sequence of letters twice. (I didn’t think JAP offered OHV engines in 1922. I thought they were all Side Valve). I suppose it’s possible that the engine was made in 1922 and supplied in 1923.

In 1924 – 1926 Royal Enfield definitely used the 350cc OHV JAP motor in the Sports Model 351.

As I’m neither a JAP engine expert, nor a Royal Enfield expert, I will stick to the engine condition. Either way, this has the makings of a great little engine and would play its part in a vintage project.

The other unusual thing is the marking “OK” cast into the head. I know JAP supplied for the OK Supreme.

According to my information the numbers read as follows:

I – 350cc

O – Overhead Valve

E – 1922 or 1942

8700 = sequential number

C = Crank case with inclined mag platform

R = Cylinder type number 3


Overall good condition, with a very good bore, good fins and threads and what appears to be a new piston.

Cylinder head: The fins are good. It has “OK” cast in the top. The spark plug threads are fine and the plug is included in the sale. As you can see, there is only one cylinder head stud and one spacer for the rocker box. The underside of the head is nice and the mixing chamber is in good condition. The valve guides appear to be new. There are no valves or springs. Cylinder looks like the cast number is 12972 on the underside.

Rocker box: Seemingly complete. Please see the images. Cast number is 9670/?

Cylinder barrel & piston: I haven’t removed the barrel. The engine turns nicely and I have shown the piston in the raised and lowered positions. The bore is good. The piston is a Royal Enfield one (as shown in the images). The cylinder barrel will need some nuts to bolt up to the main casings. Piston has “Enfield” and “15” on the top.

Main engine cases: Good. They have marks from use but no obvious cracks, chips, or damage to things like the engine mount holes. The engine number is very clear and has not been tampered with. The crank and connecting rod is fitted and the cams etc are as shown in the images. There are no connecting rods.

The Royal Enfield cover: My opinion? I think this would be a correct part for say, a 1924 engine, but I think someone has used it on a slightly earlier engine to suit their racy Royal Enfield. The outer colour doesn’t match enough for it to be original with the engine. Having said this, the valve lifter all seems to work fine and is in the correct location. The number on the inside of the outer cover is 704? Birmal.

There you have it. A JAP OHV 350cc vintage motorcycle engine with Royal Enfield cover needing very little.

International shipping available. Please ask. Shipping is charged separately from the item. 

Combined shipping available if you buy more items at the same time. 

Viewing: Please come and check it over before you buy. It is at PE28, near St Ives in Cambridgeshire.

Shipping: I usually ship to most destinations. If you don’t see a price, please ask. Thanks. International shipping available.

Collection: If you don’t want it shipped, I have plenty of space. If you can’t collect for a while, it’s not a problem. However, I will need to be paid very soon after the sale. Thanks.

Payment: Good old fashioned money on collection is preferred. I can accept payment through PayPal or by bank transfer as well.

Import Taxes: Please note that IMPORT DUTIES are not something I can control. If you are buying from outside the UK, there is a chance that you will have to pay import taxes. Import taxes vary from country to country. If there are charges to pay, it is the buyer’s responsibility to research the cost and pay the duties. The price that you see on my advert is for the item and not the item plus whatever taxes might be due.













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