Have a Chinese S/T C/L .51 (new) that I would like to remove the ring, check the gap (& fix if needed) and reinstall, perhaps without destroying the ring. Then proceed to break it in.

So, couple of questions......

1) Procedure for removing it and replacing it?
2) Proper gap for the original ring, and best method for increasing gap if required?

Cheers,

David

Dennis has it right. The #1 rule for piston rings is to replace them if you have to remove them from the piston. If you decide you need to, get a Frank Bowman ring (or two), or just send the P&L to him to fit the ring. Or Tom Lay. He's busy, but he is shipping engines. My G.51 and .46 came in today's mail.   Steve

Randy has a neat suggestion for a simple check on the ring gap....which is to move the piston and ring so that gap can be seen and estimated through the port.  If a sheet of paper (assume 20#) will fit the gap is OK as it represents .002 to .003.  And he indicated the gap has been acceptable on most of the s/t 51's out of the factory.  Says it is the break-in that usually causes the ring problems.

Things leaned...........

David

David,
Did Randy specify what type of breakin problems he was referring to (i.e. wrong fuel, wrong size prop, wrong rpm, etc.)?
Thanks.
DennisV

Hi Dennis

I told him that I have seen many rings ruined by improper breakin, If you get the engine too lean or too hot during it's first few runs the ring will expand too much forcing the ends to touch, at that point the brand new properly gapped ring is toast, it will either break or wear a flat spot on the ring. neither is good.
When you break these in with a tight gap, you need to ALWAY do it on the ground, preferably on a bench so that you can control the breakin process. If you try to fly it and it goes lean all you can do is watch it kill the new ring.
The best way to break in a new  ST 51 is with the engine running very sloppy rich, then lean it out till it runs a very fast 4 cycle, pinch the tubing so that it will just burst into a 2 cycle for a couple of seconds, Do this for the first 3 tanks of fuel. After the 2 cycle go back to a very rich 4 cycle then up into a very fast 4 cycle..repeat process..
I use 4 ounces at a time.  After the first 3 or 4 runs you can put the motor in a 4 fast cycle, then into a 2 cycle for a couple of seconds then back to a nice rich 4 cycle.,
I break these in with SIG Champion with 2 ounces of AERO-1 added to it,and an additional 2 ounces of Castor.
I use Sig fuel to run these by mixing the Champion (half syn half castor 20%) with the 25% all castor SIG, and add 1 ounce of Aero-1,  You can substitute either castor or syn oil for the Aero-1 if wanted. They seem to like to run 24% oil total part castor and  either  5 or 10 nitro. The nitro percent will not matter on breakin

Regards
Randy

Regards
Randy

Greetings Randy,
Many thanks for the information. I know a couple of people who have had problems  with their new Chinese ST .51 engines (i.e. low compression, broken rings, erratic runs, etc.) so I was interested in any information that would help break in the engines properly.
Best regards,
DennisV

HI Dennis

I have built 100s of the ST 51s for people and have found not really many more problems with the China 51 than I did with the Italian 51s. If you have one that is low on compression, it has a problem no matter which version it is. either a bad ring ,broken ring, or a out of round sleeve, and  needs  attention to correct the problem. I have also had a lot of people ship me their 51s that do not run well , both versions and I have found flat spotted rings and broken rings.
The sleeves for the most parts have had little problems.

Regards
Randy