Topic: cb650 pistons

[cafe75-550]

Does anyone have a set (or just one actually) of cb650 pistons laying around? I'd like to know some dimensions, primarily the compression height, or the distance from the pin (center or top, whatever is easier for you) to the top of the dome. Bonus would also be the distance from the pin to the shoulder (minus the dome off the last measurement). Thanks in advance! 

[cb650]

Last week I took a 650 engine to scrap that had the pistons exposed.   I should have one laying around somewhere.   PM me or I forget.




                                      Terry

[cafe75-550]

Pm sent! It might also be good to know the "squish" distance, if someone has a cylinder block laying around...whatever distance is left at the top of the cylinder at TDC...

[cb650]

The top of the pistons actually come above the cyls.  If you had asked month ago could have looked more closely.  Will post measurements in morning when beer wears off.





                     Terry

[cb650]

Center of pin to top of dome  1.045".    center of pin to shoulder .885"




                     Terry

[cafe75-550]

Thanks Terry, that's really helpful. As I've posted elsewhere, I'm trying to put together a 550 hybrid running 750 sleeves and 64-65 mm pistons, it turns out to be a little more difficult than just putting in 836 pistons since the 750's had offset valves, and none of the SOHC's had much in the way of valve clearance. So the domes of the 650 pistons actually come above the cylinders? I would guess the the shoulders are slightly below, but even still that would mean almost zero squish...can anyone else confirm this?

[Pinhead]

I believe the 650's pistons have something that "resembles" squish around the outer edge of the pistons since the dome does extend past the block into the chamber.

[cafe75-550]

Yeah, that would make sense. I just reassembled enough of my spare 550 engine to note that the squish on the 550 is about 1 mm, probably less when everything is all torqued down, I was under the mistaken impression that it was ~5mm from looking at the cylinder walls, but if I'd thought about it I would have realized thats the distance to the 1st ring + the squish, and the distance to the first ring is ~4mm so....

[cafe75-550]

here's a picture of what I was talking about, can see a slight shadow that is ~1mm of space between the top of the piston and the top of the cylinder, would make perfect sense for the domed piston to "stick out". Now if I could get a picture like this of the 650...

[Pinhead]

I'm pretty sure the pistons on the 650 "pop up" past the top of the cyllinders. I just don't know by how much. I haven't torn my engine down yet...

[cafe75-550]

Are you planning on tearing your engine down? If and when you do, it would be great to see some pictures and have some measurements...

[Pinhead]

Yeah, eventually I'll have it tore down, but it won't be for at least next winter (unless it breaks down...).

[cafe75-550]

Thanks anyway! My plans are for this winter, and with the data on the pistons above I can probably figure out everything I need anyway, would be nice to have a picture just for visual reference though. Hopefully nothing happens that makes you speed up your project (unless its winning the lotto maybe), I hate it when that stuff happens.