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.

Mark

email (option): myakovi2@hotmail.com