compression height and conrod length choice. headache.

[olliewtf]

Right. 146 is the magic number.
So as far as i understand, in order for the piston to be somewhere near the top of the cylinder at TDC to make most port timings useable, the conrod length and piston compression height should equal 146.
Here's my problem. I want to use a ts185 piston on my sr barrel, and thought i could just use a 60x110 crank, as in my naivety i figured longer rod, long length overall therefore i can play with packers. i didnt consider that the ts piston has a compression height of 32mm, so, 110 add 32 = 142.
I assume this would mean that the piston would sit roughly 4mm below the top of the barrel.
The reason this such an issue for me is my transfer timing. using this crank, my transfer timing would be 135 if the piston sat 1mm below the cylinder. in order to get my timing to where i want it be, (around the high 120s), id need the cylinder to protrude 1mm from top of barrel,which i imagine can only be achieved by shaving 2mm off the base of the barrel. so then i need to consider the impact on my inlet.
now the transfer timing might not be that dramatic after the rebore as all i did was put a stupid chamfer on it which raised it 1mm, but didnt really open up the port. so hopefully itll come back at 47mm from top of barrel rather than 46mm.
Either way that doesnt solve the crank piston mismatch. Am i right in thinking, to use this combo, the only solution is to shave off the bottom of the barrel?

failing that, i can go 115 rod. this then equates to 1mm too long, which is fine as it allows the use of gaskets on the base to get the transfer as i want it. the only issue here is that i had my heart set on a 60mm crank, a mec one as im scootering on a budget (i know), and 60 115 doesnt seem to be that common. AF do a 62 115 but its a bit more than i wanted to spend and may require too much fettling for me, i dont mind grinding a bit of a channel, but i have heard some need casings welded.

So. can anyone clarify my findings, as ive only just understood all of this, and maybe throw some crank options into the mix?

all help is much appreciated!

[corrado]

I'd ring AF Rayspeed [between 5pm and 6pm is best] as I'm sure they do the 18 roller big end bearing cranks in more sizes than shown on their website. I'd be surprised if they haven't got 60 x 116.

[olliewtf]

that sounds like a plan. i assume that ive got my facts straight with regard to matching of piston and crank?
out of interest, would a 62mm require extensive casing work, ie extra welding, or can my dremel suffice making a small passage for the big end? or is it more pot luck?
cheers!

[corrado]

You may get differing opinions on that. The guy I trust with work that I haven't got the required skills for has the cases machined then rewelded for added strength when using 62mm cranks.

[olliewtf]

Yeah i may leave it and go for 60mm, at least that will only require a small amount of work with the dremel (i hope!).
the most important thing for me atm is keeping costs down, i wasnt even intending to rebore until i saw the scoring. but oh well thats lambrettas! at least i now get to play with a new set up. cheers mate!