Crankshaft question

[drunkmunkey6969]

If i use this in an engine I guess I will have to use a three mm packer plate? If I do, what is the likely effect on the engine regarding performance?

If your current crank is 107 and you fit a 110 then you must fit a 3mm base packer to account for the difference, and then your port timings will be ALMOST identical to the 107 rod. Any microscopic changes will be negligible.

However, one of the additional benefits of a long rod is that you can actually vary the size of the base packer to alter the port timings. So for example a 2.5mm packer would lower them and give the engine a bit more torque, a 3mm packer keeps everything roughly as it was with a 107 rod, and a 3.5mm packer raises the port timings and gives a tad more peak power.

But in any of the above examples, no matter what you do with the rod and base packer combo....you must make sure the squish is correct. Usually via varying thickness of head gaskets.

[drunkmunkey6969]

By changing the length of the rod, the the position of the piston in the cylinder has now moved (in this case up by 3mm) for any given point in the crank rotation. Just plug the numbers into the port timing calc and see for yourself. Change the rod length from 107 to 110 to 116 and watch the numbers move.

http://lambretta-images.com/archive/porttiming.php

but you're jacking the cylinder up by using a packer plate so in theory you're not affecting port timings

the port timings change because the piston is now in a different part of the stroke (as in going from BDC to TDC) depending on the length of the rod. In other words, if the piston is at BDC on a crank with a 110 rod, that piston will be sitting 3mm higher than one with a 107mm rod.

Go to the link, plug in the numbers and hit calc. You will see what I am talking about.

If you change only your rod then and it's now 3mm longer then yes, your port timings change........but your top end wouldn't even fit back together again?

One of the assumptions when fitting a long rod is that you fit an accompanying base packer. The difference between a 58mm stroke with a 107 rod and a 58mm stroke with a 110 rod + 3mm base packer is about 0.5 of a degree. So if you had en exhaust port with a 180.8 duration on a 107 rod, with a 110 rod + 3mm packer it's now 180.3 duration......negligible on your average road going scooter.

[drunkmunkey6969]

110mm rod,possibly a Piaggio 'ape',rod,using larger small end Bearing to suit the 'Suzuki' 225 conversion,with the 'TS250 piston.

Most 110 rods are Yamaha and and use the same size Lambretta little end pin/bearing and standard Lambretta piston when used with a base packer.

[coaster]

By changing the length of the rod, the the position of the piston in the cylinder has now moved (in this case up by 3mm) for any given point in the crank rotation. Just plug the numbers into the port timing calc and see for yourself. Change the rod length from 107 to 110 to 116 and watch the numbers move.

http://lambretta-images.com/archive/porttiming.php

but you're jacking the cylinder up by using a packer plate so in theory you're not affecting port timings

the port timings change because the piston is now in a different part of the stroke (as in going from BDC to TDC) depending on the length of the rod. In other words, if the piston is at BDC on a crank with a 110 rod, that piston will be sitting 3mm higher than one with a 107mm rod.

Go to the link, plug in the numbers and hit calc. You will see what I am talking about.

You are both right to a point, if you fit a 3mm packer then the port timing will be unaffected. However, you have the opportunity to fit say a 2.5mm packer and a thicker head gasket which will have the effect of slightly de-tuning for better low down torque (depending on the top end in question. It's a bit of a balancing act though and you might end up having to have the head machined to get the desired squish but all good fun

[Daggs]

If i use this in an engine I guess I will have to use a three mm packer plate? If I do, what is the likely effect on the engine regarding performance?

If your current crank is 107 and you fit a 110 then you must fit a 3mm base packer to account for the difference, and then your port timings will be ALMOST identical to the 107 rod. Any microscopic changes will be negligible.

However, one of the additional benefits of a long rod is that you can actually vary the size of the base packer to alter the port timings. So for example a 2.5mm packer would lower them and give the engine a bit more torque, a 3mm packer keeps everything roughly as it was with a 107 rod, and a 3.5mm packer raises the port timings and gives a tad more peak power.

But in any of the above examples, no matter what you do with the rod and base packer combo....you must make sure the squish is correct. Usually via varying thickness of head gaskets.

Thanks for that 'drunky' That was the sort of info i was looking for.

[Grumpy225]

If i use this in an engine I guess I will have to use a three mm packer plate? If I do, what is the likely effect on the engine regarding performance?

If your current crank is 107 and you fit a 110 then you must fit a 3mm base packer to account for the difference, and then your port timings will be ALMOST identical to the 107 rod. Any microscopic changes will be negligible.

However, one of the additional benefits of a long rod is that you can actually vary the size of the base packer to alter the port timings. So for example a 2.5mm packer would lower them and give the engine a bit more torque, a 3mm packer keeps everything roughly as it was with a 107 rod, and a 3.5mm packer raises the port timings and gives a tad more peak power.

But in any of the above examples, no matter what you do with the rod and base packer combo....you must make sure the squish is correct. Usually via varying thickness of head gaskets.

You are correct, I should have said it gives you some flexibility with the port timings and packing plates.