Scooterotica

I’ve had an Mb shorty reed fitted to my rapido 225 race. Also had a 58-115 crank made, using a DT250 piston. Looking for advise on what packers I need.


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Who did the work? They'd usually be the first target for questions - the rest of us are guessing...

That said my guess - your stroke is standard but the rod is 8mm longer than standard so a packer at the base of 8mm would put your port timings in the same place, unless you're using a piston with a different compression height.

Coincidentally, I am using the same piston in a rebuild of a TS1 but with a 60 mm stroke.

In your case, though, as the variation between the Lambretta & Yamaha DT250 compression heights is 6 mm (39 - 33) you will need a packer of 2 mm. In theory, that is.....

What I have decided to do in order to gain more blow down & tame the timings a tad, is to use a different packer to what I should.

In my case, I should have a 3 mm packer (accounting for the extra 1 mm radius of the crankpin) but I am using only a 2 mm packer.

(It does make for extra work but this is certainly not the first time that I have juggled port timings. I know that it really is worth thinking about as I run a piston ported Rapido 70.5 x 61 mm with a TS250 piston that pulls the exact equivalent of TV200 top gear via a Pacemaker ‘box, unfussily from less than 30 mph.)

As I simply refuse to use head gaskets & am very fussy about ensuring the correct squish & centralising the bore to the head, it’s a good job that the owner is very patient

Fortunately, I now have a Myford lathe. So, the cylinder head centralising recess & extra depth due to increased stroke was not too difficult once I had made a jig using a faceplate. Unfortunately, the same jig cannot be used with reed valve cylinders owing to the swing, but I managed to spigot the top by making a bung to fit the bore & fitting it extremely close to the headstock.

ask Harry Barlow mate, he did the work.