Converting a 197cc Hawkstone (Villiers) engine to a 250cc

[kayjay283]

Hi. I have a 200cc Hawkstone and was looking to change it to a 250cc. Is it a case of just replacing the barrel and piston?

[johnrunnacles]

It can be, Kayleigh, that was all I had to do with mine BUT you do need to make sure that the new barrel is compatible because the standard 200 conrod is shorter than the one on the normal 250 crank.

If you're talking iron barrel, some people overcome this by having metal shaved off the bolt-down bottom flange of the standard 250 barrel, but it can weaken the structure. Better to find a more squat, straight 250 conversion, in my opinion.

On an alloy barrel with through bolts, I guess you would have to have metal turned off the bottom of a 250 barrel.........not a situation I am familiar with, having only made the conversion with an iron barrel.

Hope this helps, and I'm sure that others will chip in on this one (?)

John R

[Stuart Baskill]

Hi. I have a 200cc Hawkstone and was looking to change it to a 250cc. Is it a case of just replacing the barrel and piston?

I believe that a 31A barrel will fit on a 9E as the con rod is 5 1/4 inch long but 32-37A use a 5 1/2 inch long con rod.I,ve not tried it .

[Buzzer]

I have built one using a 31A cylinder on a 9E bottom end. The cylinder is identifiable by the number "C11588" cast into the base flange.

[kayjay283]

It can be, Kayleigh, that was all I had to do with mine BUT you do need to make sure that the new barrel is compatible because the standard 200 conrod is shorter than the one on the normal 250 crank.

If you're talking iron barrel, some people overcome this by having metal shaved off the bolt-down bottom flange of the standard 250 barrel, but it can weaken the structure. Better to find a more squat, straight 250 conversion, in my opinion.

On an alloy barrel with through bolts, I guess you would have to have metal turned off the bottom of a 250 barrel.........not a situation I am familiar with, having only made the conversion with an iron barrel.

Hope this helps, and I'm sure that others will chip in on this one (?)

John R

Thanks John. I do have an iron barrel do you know anyone that has a 250cc conversion for sale?

[Colin Sparrow]

A 250 crank (complete with longer conrod) will go straight into the 9E cases. I've done it...

[kayjay283]

I would prefer to use my crank and conrod assembly if possible. Does anyone know if there is a benefit to keeping the shorter stroke 197cc bottom end and taking the capacity up to 250cc and if it is practical. I assume the 197cc barrell won't "bore out" to 250cc!!!???

[John-Boy]

The original 250 upgrade was the Vale-Onslow conversion, barrel, piston and cylinder head, which bolted straight on. They are pretty rare but Adrian runs one and Simon Bateman has had one or two.
The claimed output was 18 BHP compared with the 197 SAS of 13 BHP or the standard 197 of 7.9 BHP.
I think boring out a 197 to 250 is not feasible.

[John Wakefield]

I believe that a 31A barrel will fit on a 9E as the con rod is 5 1/4 inch long but 32-37A use a 5 1/2 inch long con rod.I,ve not tried it .

The 31A barrel is trials/roadster based so wont have enough power for scrambles. You would need a 34A barrel & turn 1/4 inch of the bottom, quite ok to do but destroys a original which are now getting rare & expensive like all Villiers bits.

[Brian Catt]

Adrian's one goes very well, it might be worth chasing that avenue.

[johnrunnacles]

I've got one that I might sell, Kayleigh. Unfortunately, it comes with the rest of the bike! Otherwise, have a word with Simon B.

Best of luck.

John R