Help - Big engine in smallframe


Can anyone help (with tips and photos) in assembling a Sprint 150 engine in a small frame? Is there a subframe for the job?



in other words dont do it

This post is from anearlier discussion re: t5/p2 motor in a 50 special . Your specific measurements will be different but the the theory remains the same.

ps. say goodbye too good handling tho’

Step 1: Drill out the holes in the frame that the engine bolt goes through to the diameter of the large frame engine bolt.

Step 2: Cut off the engine side panel, if you don’t the engine won’t fit.

Step 3: Inside the 50 special engine bay, next to where the carb manifold goes through, there is a piece of metal that has to be flattened out, do that or you won’t have clearance for the cylinder head.

Step 4: Now in the engine bay you can more or less see the shape of the small frame motor cylinder. In that hole drill 3 hole side by side, first for the throttle cable, second for the electrics, thrid for the fuel pipe. you can’t put the fuel pipe through the hole where the carb manifold used to be as it will not gravity feed if you do.

Step 5: The rear shocker has to be made more upright so that it doesn’t hit off the clutch casing and so as to raise the angle of the engine so that there is clearance for the carb box lid. This is easily done by taking flat bar of tempered steel about 4mm thick and 25mm wide. it has to be about 75mm long. once you have it cut to length, drill two holes in it, the centre of each one being around 15mm from the edge of the bar at either end. bolt this to the top of you shocker and then bolt it into the frame. thats the shocker done.

Step 6: Carefully measure and mark the main engine mount for cutting, you have to cut between 8 and 9mm off either end of the main mount.

Step 7: Slot your engine in and connect it up.

thats it!! as simple as that. good luck!!

you will love it, i had one with a t5 motor and it was very fast!! not quite as good as my 210 that i have now though, it’s in a 50 special as well.

Polini 130,

In your 50 special, did you fit a 10’’ (sprint, rally) fork?

If so, is it hard?



Polini 130,

You rule!

I will send you some photos during assembly and when ready.

Thanks a lot.


no used pk forks, remember your sprint engine dimension may be slightly different so don’t take the measurements qouted literally