engine/gearbox options

[cheekychapy]

my trekker looks great but hell its not running right. The engine is not holding compression and the gearbox cogs in third gear hate each other having a battle every time its selected.
I have a 1200cc engine and reduction boxes and if i have to change the engine i'm wondering what my options could be. the reduction gearing confuses me. so maybe someone could help?
if i increase the engine size am i restricted by the gearbox?
and if i change both the engine and gearbox what are the limitations of the axle and reduction gearing?
can someone suggest a configuration that keeps the reduction boxes but gives moer power than the 1200cc?
cheers

[cubist]

1500 single port or any 1300, 1600 twinport. The reduction boxes are strong enough to take the 1600 and give 70mph on a run in my experience. I had an 1835 in my '68 with reduction boxes but that was bloody noisy!

[cheekychapy]

thanks for the info. i always thought that the gearbox prevented uprating the size of the engine. from what you say i can mate a 1600 to the 1200 gearbox i have now? i don't mind taking my time on the highway, just want a bit of umpf uphills and around town.
there was on ebay local but been withdrawn!
cheers

[cubist]

Not quite! You'll need a flap wheel to grind the 1200 gearbox case out 7mm on the inner face diameter to get the larger 1600 flywheel in there. It's a bit trial and error the first time but a doddle then. Be careful with the grinding around the bottom engine bolt studs and there'll be plenty material left for strength. It's not the ideal way - swapping the gearbox is a whole lot better - but it's effective and i've never had any problems with cracking or splitting. Good luck

[nijyboy]

Check your gearbox code first, you may still have a Trekker gearbox in place and a 1200 engine retro fitted?

[cubist]

Seems more likely... certainly easier to fit a bigger lump if you have the genuine gearbox

[cheekychapy]

thanks for info, final confirmation needed!! i've got hold of a twin port 1600 AD engine and now i know my gearbox code is AK which i think is for a 181 1500/1600cc.
stupid question is before i take the 1200 out and fit the 1600, it is going to fit insn't it? thats a 1600 TP to a AK gearbox?

and if this gearbox is for a 1500/1600 then maybe thats why the 1200 don't like to mesh with it?? ...wonder where the 1200 came from...anyone want one??

[cubist]

Your 1600 tp will fit the 1500/1600 box without mods - and I do want your 1200...

parts@kubel.co.uk