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I am trying to check port timings on an RT195 kit but there are large discrepancies between my measured timings and the calculated ones, so I'm doing something wrong, just not sure what,
Measured using a timing disk and a 0.1mm feeler gauge to stop the piston
From exhaust port opening to exhaust port closing 171degrees,
From transfer port opening to transfer port closing 120 degrees
Calculated using lambretta images
1.9mm above the barrel, using gaskets as packers and a strong back, when the piston kisses the strong back measure the gaskets 1.9mm
Set the piston at the top of the exhaust port (using the feeler gauge) and measure down using a digital vernier and correct for gauge thickness, 40.1mm gives 164.25 degrees
Set the piston at the top of the transfer port (using a feeler gauge) measure down using a digital vernier and correct for feeler gauge thickness, 51.7, gives 111 degrees transfer timing.
I was expecting around 125 degrees transfer and 170 exhaust and the readings to be within a few degrees of each other.
can anyone help o advise what I'm doing wrong?

i have a standard rt195 kit here in my workshop , i will do the measurments using the port timing calculator and see if i get the same as you, im going to put in 60/110 for the crank

That would be helpful as it's the same set up as mine if the piston top is set to match up with the transfer ports.
my set up with a 0.5mm gasket and 3mm packer , Head gasket is 0.9+0.5 giving a squish of 1.35mm
Thanks

put your calculations in again apart from your packers/gaskets just to see if cylinder comes out the same .

Not sure what you mean?
This is how I applied it
Stroke 60
Conrod length 110
Piston crown to top of barrel at TDC 1.9mm (With base gasket and packer fitted)
Top of cylinder (no gaskets) to top of port 40.1'mm

Meds wrote:Not sure what you mean?
This is how I applied it
Stroke 60
Conrod length 110
Piston crown to top of barrel at TDC 1.9mm (With base gasket and packer fitted)
Top of cylinder (no gaskets) to top of port 40.1'mm

as i mean, just to see if cylinder is the same as mine.

I think I have worked out the issue.
I have measured to the top of the dome an not the crown height.
So I need to work out the difference between crown height and the top of the dome.

i was thinking that or that you didnt allow for the recessed head. i dont have the cylinder on the case and i geustamated at 2mm for piston at tdc in my calculations. anyway glad you have sorted it

Every day is a school day.
I recon a bit more than 2, possibly 3-4
I stuck the numbers in wit a 1.5mm the other direction and got a much more sensible answer, although it's not going to make a lot of difference in this case as I have rebuilt exactly as it came apart.