Scooterotica

just rebuilding my imola with a 60/110 crank .
to get the port timings correct ive had to use one gasket at base of the barrel but this leaves the piston crown poking out the barrel at tdc by approx 0.5-1mm. therefore I need to use a packer/gasket between head an barrel to obtain correct squish. the head is the type that has a 1.2mm lip that usually drops into the bore but obviously cant due to piston position at tdc. are thicker types of gasket/packers available for this situation and if so where from.

As you've added to the stroke by 2 mm, 1mm at each end, and are using a 3mm longer than standard rod this isn't surprising.
I'd look for a selection of base gaskets or packers around 2.5 - 4mm thick to try till you get the squish you want.
Most of the well known tuners should be able to supply these. AF, MB, Scooterotica, etc.


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Thanks rosscla ive ordered a selection of base packers of different thickness and some head gaskets to ,im just concerned the piston will end up too far below the ports at bdc.

Rosscla ive just rebuilt using a 2mm packer with base gasket each side and in conjunction with a 1mm head gasket which just allows the head to sit into the bore by a little I get a squish reading of 1.04 to 1.07mm . the piston is still below the edge of the exhaust and transfers by about 1.5mm. this is as close as I can get it by trying different packers etc. not sure what to do to rectify this other than a different piston crown height perhaps ??

I think you'll struggle to find a piston like that and if you can add crown height to level the top of the piston to the bottom of the ports then it'll be out the top again.

It's probably a bit better to have the piston below the ports at BDC rather than above.

What are the timings like now?

cheers for your reply rosscla I appreciate it.
im going to go in garage this aft and see if I can find out what the timings are at mo. cheers.

Bazza,

I think you need to stop worrying about the squish for a moment, and have a check of your port timings.

With your piston below the transfers at BDC, what is the transfer port timing/duration. You risk running too much transfer timing, which will be more detrimental than a poor squish.

You might be fine, but you need to check. Report back in the morning...

In order to get the piston in the right place at the bottom I had to pack out 3 different thicknesses CH gaskets to get the right squish, not ideal but it works.

thanks fellas il report back when I have some news on timings.

ok ive use a digital vernier to measure from top of barrel to top of tranfers & exhaust ports . im also using a 0.7 packer and gaskets either side which puts the piston slightly below bottom edge of ports at bdc . the piston crown edge is level with top of bore at tdc so I put this in to calculator as 0.00 (is this correct ?) . the results are :- exhaust 181.72 transfers 122.00.
Advice on this will me greatly appreciated.