ANOTHER TV200 ENGINE REBUILD – CLOCKING THEM UP NOW
This Lambretta came in with the customer saying it doesn’t pull top end, can I have a look at it.
First job, on the dyno to check it out. GT240 70mm Piston x 62mm crank – showed only 19bhp! Now I wouldn’t let anything like that go out of the building and saying it was professionally built there was nothing for it but, engine out and check what was done!
Sure enough, not what I would have fitted or used. Port timings were miles out, but nothing really could be done to improve it. The crank runs with no crank shims, I’ve not used cranks like that since the 1980’s – why? They go wrong! The con rod can move to one side as theres nothing keeping it central, when it moves over it creates heat and the big will melt! You need shims on either side of the con rod, especially if the top of the con rod isn’t kept in line by the piston, which this engine wasn’t.
The rest of the engine was not up to our standards either. I’d welded the engine lug at one point but more inferior repairs had been done after that, so it was agreed a full strip, repair, clean up, bead and aqua blasted ready for the new MB package rebuild.
Same as the last one – the full MB RT Reed package. 70 x 60mm Touring Reed tuned, bgm crank, Vape already fitted but modified and rewired, MB5 gearbox, MB5 clutch, gearing sorted to work all the time, and of course the usual MB parts, top and bottom slippers, bearings, seals, gaskets and fasteners. Rear wheel and cowlings re fitted.
On the dyno the new motor keeps its low down power even though it’s got shorter stroke. The exhaust was as it came in an old MBgm V1-2 the new engine now lifts power at 4500rpm and starts to increase power to gain another 5 horse, with more power higher up reviving to 8500rpm.
With our new Clubman with a tweak I lifted power even more across the rev range from 4500rpm and gives a super smooth power graph!
I also tested his old MBgm V1-2 against the Avanti Ex box – down on power! SIP Clubman even more down on power! And I also tested 2 common expansions and they were both down on power apart from a bit of peak. Hey but no one listens.
All in a days work!
Any comments email mark@mbscooters.co.uk
