Topic: I need specs for a 550 bigbore piston

[Flying J]

Talking to a guy about doing a small run of big bore pistons for the 550. I am still new at this part of bikes so im looking for a little help. What is the CC of the head, and also what is the compression height? I know that most of the kits have been 61mm but can you go bigger on the 550? Would it be safe to bump up to 62? I would like to do something like dynomans hot street but for a few hundred less.
Also what is the thickness of the 750 piston rings?

[Tintop]

looking forward to seeing what comes of this.

[classic bike tuner]

62 mm is to much in a stock 550 liner  wall thicknes with 62 mm wil be 1,75mm

try fitting 750 liners  need to be shortend and maybe to thick [69,5mm]

volume of scamber dont  now exectly  about  12cc

for pistons
63,5mm    http://www.petrolscooter.co.uk/catalog/product/view/id/7518/s/piston-kit-63-5mm-15mm-cg-200cc-engine/

there are more pistons but dont go to high on compression ratio on a road bike

[Flying J]

Measuring off my 750 piston i got 2.8mm for the oil ring and 1.5 on the other two rings. Can anybody confirm these numbers?

[bwaller]

The 500/550 combustion chamber is exactly 13cc's. The compression height of a 550 piston is 23mm. 750 rings thickness-1.48mm compression rings, 2.8mm for the oil ring. These are 61mm rings.

cbt is correct a stock 550 sleeve can be bored safely to 61mm, but no more. At that diameter, there is no room for an overbore, one time deal.

It is time consuming designing the piston crown considering dome height, valve relief depth, compression height, etc. etc. Of course it can be done. Who are you talking to?

I believe Dynomans pistons are CP... very good quality. I talked to Buzz two years ago and he was only thinking about these. I went my own direction, but by the time I was done adjusting all the dimensions mentioned above, that $600 price including rings is worth it. 

[Flying J]

Thank Bwaller. Im sure dynomans pistons are worth it but just through discussion I was put in contact with this guy and if things work out his price per piston is less. So I will investigate and see if it pans out. I will be dealing with UEM.
http://www.kb-silvolite.com/

[q2418130103p]

The dynoman pistons are from J&E, I've got a box of them right here.  Very perdy.

[Flying J]

What is the rod length on the 550?

[Tintop]

I can check one tomorrow, there are in storage right now.  You want C to C right?

[Flying J]

yes please.
 And also wan to verify that the piston deck sit flush with the top of the jugs.

[Tintop]

yes please.
 And also wan to verify that the piston deck sit flush with the top of the jugs.

can't help there the engine is in pieces.  LOL

[fastbroshi]

I just did a real quick check, the center to center is right around 99.5mm.

[bwaller]

yes please.
And also wan to verify that the piston deck sit flush with the top of the jugs.

If you are talking about a stock 550 engine, then the last couple I had apart the pistons were below deck +-0.016".

[turboguzzi]

I just did a real quick check, the center to center is right around 99.5mm.

no way, 500/550's are 105 or 106mm center to center (from memory) certainly not under 100mm.... take your time when measuring

[Flying J]

yes please.
And also wan to verify that the piston deck sit flush with the top of the jugs.

If you are talking about a stock 550 engine, then the last couple I had apart the pistons were below deck +-0.016".

I set the jugs back on my motor and spun it and it look like .025 below. Could that be because they were not bolted down tight?

[Tintop]

Hey ffj, went over to check that rod, their still on the crank.   Will need to try again, as I didn't have the right tools handy.

The barrel would need to be torqued down to get a true reading.