I have noticed the difference in cylinders too. I even put photographs of the two models in my Welbike book. No written source material found on the subject of Villiers engines for Excelsior Welbikes, at least not by me. By the looks of my 'Welbike register' with app. 150 surviving Welbikes, most surviving Welbikes come with the proper XXE pre-fixed Villiers JDL engine.
At Excelsior's engines were not put in sequential order so that lowest Welbike chassis would get the lowest Villiers numbered JDL engine. The is a variation of app. 250 between frame and engine numbers.
As there are no factory ledgers left, we may never know more specifically what was done at the works.
I have not looked into which barrel would originally be fitted by Villiers for their output to Excelsior's for the Welbikes. I only assume that extra power is not needed, but rather a slightly larger bore (tolerance wise that is), as to minimalise the effect of running on petrol without the two-stroke oil.
The tuned engine story is mentioned, but that IMHO could indicate this de-tuned measure?
I have app. 150 surviving Welbikes listed, but regrettably just app. 20 e-mail addresses. If I can find time, I can approach these to find out casting numbers on the barrels, and possibly get some indication on which is which.
In the meantine, Welbike owners could contact me on rpa@robvanmeel.nl and give me details like engine and frame numbers, and a photograph showing the casting numebrs of the barrel?
Thanks for the reply Lex, so Welbike engines don't have the extra letters and numbers cast onto the barrel? and do they have the larger ports shown in the first post?
Ok, I had my post removed by the admin's, thanks for that! I had my complete email address on there, and got bombarded by spam!!! really thousands of emails, not nice! so here the message again, without my complete address.
OK, Ron prompted me to answer here, so this is what I know, all my original Welbikes, and engines have the barrel with the B5764 casting number (no additional numbers under there). there are ways to determine if an engine is altered, for example with a different side cover, that has the engine number stamped in it, email me if you are in doubt.
Have over 200 numbers in my database, and adding every month, so can always check numbers, I think the difference in frame and engine numbers is due too MKI's seizing with first use, as the troops were not informed of the running in procedure, and then the bigger bore clearance was used as countermeasure, and since replacement engines were needed for the army, the numbers got very disrupted, between 170 and 750, but as Rob says on average about 200-250 higher than the frame numbers.
Please send me your numbers to: welbike and the rest, I can also give you the correct C number for on the petrol tanks, and have much additional info on US and Australian numbers.
The extra numbers and letters are only on one side of the barrel, I suppose if they were facing downwards you may not be able to see them in a Welbike.
No one yet has mentioned noticing any other differences in Welbike versus Autocycle engine spec so it appears there are only 3 differences.
1. Larger ports in the barrel
2. Greater clearance in the bore
3, Letter E rather than A stamped on the outer crank case cover
The larger ports in the barrel would result in better gas flow, and potentially a larger space and therefore a greater quantity of fuel below the compression chamber which could mean a slightly increased compression ratio?
Greater clearance in the barrel may slightly reduce compression?
Which just leaves the letter E which in the case of this item on ebay seems to be quite valuable.
For future reference this is a seized JDL bottom end, no barrel, piston or head with the engine number XXE 493, and an unconfirmed story about where they were found.
"They came from the workshop where Colonel Dolphin carried out the building of the prototype Welbikes. Sadly the old airfield sheds have all gone now"
Hopefully in time more info about these engines will come to light, meanwhile I will build my engine with the parts I have knowing its more or less correct.
I just looked at the underside of mine with a mirror and torch Rob. No extra numbers, it's the same as the top side.
And just for anyone who might be interested. This is the predecessor to the Villiers Junior Deluxe engine, known simply as the Villiers Junior. This one is from my 1939 Autocycle. They have no cylinder head and a dome top "Deflector" piston. Ron
Rob, the A prefix is for Autocycle, the E is for Excelsior (Welbike) wish someone found the Villiers company archives!!. Not had the time yet, to look at the barrels on my engines to build, all packed away, and ready to assemble, but will get to it an a couple of months.
re villiers history of office records back in the early 90s i had scrap men find me out in my shop the villiers factory was around 10 miles from my shop they were clearing out one of the villiers factory's i bought a load of early engine parts sadly all gone now they also had loads of small film rolls of engine parts on film i just took a handful put one in my modern parts protector and it melted they told me all the paperwork of the works were just scattered all around the rooms unless someone picked them up I'm I'm afraid they are lost.
I took my Welbike to Castle Drogo show on the edge of Dartmoor a few years ago and a man introduced himself as Colonel Dolphins godson, he knew about the Welbike connection but he couldn't add anymore, and he didn't think there were any family members left who may have had surviving documents.
Although of little importance, I do have this letter, from somebody who worked with Colonel Dolphin, interesting that he mentions a Dolphin logo on the first Welbikes (prototypes ?), this letter was part of an archive of material from the 1984 BBC tv series SOE, after a chance find at the local carboot sale of a a folder with paperwork to the BBC series, the seller told me had done a house clearance and there was another four boxes at his stores, so a deal was done so to speak.
Welbike ( frame #3088 )
xxe3442 Engine #
My cylinder also has large ports.
In looking at any engine, regardless of motorcycle, two stroke ,four stroke etc power is increased in several different ways.
1. Compression , it can be increased by piston, cylinder head , piston cylinder , length of rod. I have not been able to check the deck height of the cylinder barrel( shorter barrel length = increased compression ) or the cylinder head ( smaller combustion chamber also would = higher compression) these modifications would certainly have been very easy to do at the factory before assembly , and perhaps the least obvious modification. Only comparing them with non Welbike factory parts would indicate if these machining operations would have been done.
Obviously piston height would have an effect on compression as well.
2. having an engine over square I.e. the bore is larger than the stroke, even if only slightly that engine will rev higher and produce more power. If they machined the cylinder bore larger to have a more " sloppy " fit , this may account for some of it as well.
cc = (0.7854 x Bore x Bore (mm) x Stroke (mm) x Number of Cylinders) ÷ 1,000.
so Using the above formula and using roughly .040 oversize (52mm) it yields a 106.19 cc engine, so now you have increased the cc of the engine as well.
3. airflow, an engine is nothing more than an air pump, the quicker and more efficiently you can move air through it, the more power you can make, the cylinder ports are definitely one modification that can be used to improve performance as well.
4.Ignition timing , I am aware of what the factory settings are for the " normal" JDL engine is , and I know that many run just fine that way, however were any of the Welbikes advanced in their timing by a few degrees ?
Please keep in mind these are all theoretical as to what may or may have not happened when The Welbike was being produced.
To truly do a proper investigation you would need to compare a welbike engine to a non welbike JDL and be able to do a side by side comparison.
I know of many manufacturers who on occasion tweak an automobile a little here and there to make it it run slightly better than the rest of the production line units, whats to say that the good people building the Welbike maybe hot rodded some or all of them ?
This is just my two cents and I am by no means an expert on the Welbike engine, I have however been building hotrods and fun cars for 40 years and am a Master automotive technician.