Conrod choice help

[Mannyroad]

Hi,
I have a pair of crankcases and barrels off a bike that has been used. The barrels have been bored out and lined for a pair of Suzuki SP pistons that came with the barrels. There were no conrods supplied. The barrel bore suggests the cc will be about 840cc. My problem is, how do I check the pistons to tell which conrods will work? I recall reading a post that, as I understood it, suggested you need to measure the piston pin bore and measure from the little end pin to the top of the piston, to know which conrod type will work. Can someone clarify?

 

[Mannyroad]

These are the barrels. Would the crankcase number help?

 

[Signal]

Have a look here for conrod info.
https://www.heidentuning.com/xs650-shop/engine/crankshaft-rods-bearings.htm

What size gudgeon pin do the pistons you have take?

 

[Signal]

Post #24 has a possible answer.https://www.xs650.com/threads/want-a-860cc-xs.13477/page-2

 

[Miker Vee]

These are the barrels. Would the crankcase number help?

When using a standard stroke crankshaft, SP370 pistons need the 533 type conrods.
They will give you the correct deck/compression height.

The piston pins are 20mm and fit the 533's small end bores.

The pistons need to be machined for correct clearance in the squish zone. Yours look to be done.
I've also seen the valve pockets enlarged; something I can't immediately recognize in your picture.
It may be wise to check valve to piston clearances during assembly.

 

[Mannyroad]

When using a standard stroke crankshaft, SP370 pistons need the 533 type conrods.
They will give you the correct deck/compression height.

The piston pins are 20mm and fit the 533's small end bores.

The pistons need to be machined for correct clearance in the squish zone. Yours look to be done.
I've also seen the valve pockets enlarged; something I can't immediately recognize in your picture.
It may be wise to check valve to piston clearances during assembly.

That's great information, thanks. Yes, gudgeon pin is 20mm. So 447 rods are too short then, must be 533's, yes?

 

[Mannyroad]

When using a standard stroke crankshaft, SP370 pistons need the 533 type conrods.
They will give you the correct deck/compression height.

The piston pins are 20mm and fit the 533's small end bores.

The pistons need to be machined for correct clearance in the squish zone. Yours look to be done.
I've also seen the valve pockets enlarged; something I can't immediately recognize in your picture.
It may be wise to check valve to piston clearances during assembly.

That's great information, thanks. Yes, gudgeon pin is 20mm. So 447 rods are too short then, must be 533's, yes?

Post #24 has a possible answer.https://www.xs650.com/threads/want-a-860cc-xs.13477/page-2

So the bike these crankcases, barrels and pistons came off may have been a Halco conversion. Seems possible, and the pistons do look to have been modded, so looking very possible. So a std crank with 533 rods would work??

 

[Mannyroad]

Just checked the crankcases. The number is 3L1-021783, so that would also suggest it will require 533 rods. Correct?

 

[Miker Vee]

So a std crank with 533 rods would work?

Yes but please note, the 533 rods have larger diameter big end pins.
So you need a complete 533 crankshaft.
Don't try to put 533 rods on 447 flywheels.

 

[Miker Vee]

Just checked the crankcases. The number is 3L1-021783, so that would also suggest it will require 533 rods. Correct?

AFAIK all crankcases have the same dimensions around the crankshaft, so any crankshaft would fit if you wanted.
Between crankcases, there are some differences in the big end bearing oil jets, but I don't believe that makes any difference.

 

[Mannyroad]

Yes but please note, the 533 rods have larger diameter big end pins.
So you need a complete 533 crankshaft.
Don't try to put 533 rods on 447 flywheels.

OK, understood, and thanks again for your help.

 

[Mannyroad]

AFAIK all crankcases have the same dimensions around the crankshaft, so any crankshaft would fit if you wanted.
Between crankcases, there are some differences in the big end bearing oil jets, but I don't believe that makes any difference.

Got it

 

[Mannyroad]

Post #24 has a possible answer.https://www.xs650.com/threads/want-a-860cc-xs.13477/page-2

Thanks. Checked it out.

 

[Signal]

Yes a 533 crank will swap into cases fitted with 447 crank at factory.