Greetings,

Picked up a used Supertigre 61 some time ago and have never run it. Took it apart for a anti-freeze bath and noticed that the top of the piston was pitted on the top edge on the exhaust side. Also, the ring was broken in the same spot. Can anyone tell me what could have caused this. Would detonation be a possible cause? Thanks for any advice.

That's it. You guessed right. The ST 61 (I have 4 of them) are the only engines that I have that show these pits. The two S61K's that I have were acquired used and were both pitted.

You should get your ring from Frank Bowman. You could let him install it maybe? You should ask him? There has been too many variations in them from Super Tiger as to roundness and ring gap. This is a pinned ring. Usuallly the pin is at the left front but if the piston is in backwards, it would be in the right rear.

There may be some other damage if it was run that lean that long? Look to see if the piston is scored on the sides. Look at the inside of the sleeve for scratches? Where that ring broke, there should be big scratch on the sleeve. You will have to get a brake cylinder hone to clear this up.

Good luck

Jim

Jim

Thanks for the advice. I guess this is the reason why I don't like to buy used engines from someone that I do not know. I was looking around today and I can get a new piston, rings and a liner for about $75.00. I am not familiar with Frank Bowman. Can you please tell me about him and how I can get in touch with him. These engines are $119.00 from Tower new. I also feel that I am close to the point where it'n doesn't make sense to repair it.

Thanks again,

Chuck

This is from Ann Marie Cross at Great Planes -- Jim

Those old engines which we know we have parts for are listed in the parts listings at:

http://www.osengines.com/parts/discontinued.html
http://www.supertigre.com/parts/index.html

If your engine is not listed here, we have little or no information available to assist you.

These gentlemen rebuild old motors and stock large quantities of older engine parts. Either of them may be able to assist you:


1) Preferred means of contact: PetesRC @ aol.com.
Pete's Hobbies
1814 Nelson SE
Grand Rapids MI 49507
Fax- 616-245-3106
Phone calls will be greeted with an answering machine. Please leave Name, Ph No. and, preferably, what you are looking for:
PH 616-243-9149
(Please note that there may be as much as a one week delay in response time due to extensive travel to shows, swap meets, and FLYING TIME! Lucky them! :-)

2) Model Airplane Engines- Antique to current, to use, to get out of production parts off of, or general purpose. 1200 Engines on My list - Buy- sell-Trade! send 33 cent stamp to get list or write to:
Contact: Bob Boumstein/ HWC PO Box 94 Boystown NE. 68010
E-mail : [email protected]
Fax 24hours : 402-334-4173
Phone: WEEKENDS ONLY 402-334-8688 (messages returned on Sunday only!) No
calls before 9AM CSTor after 9PM CST


3) Gene Steinkamp
8773 Russet Drive
Cincinnati, OH 45239

4) PISTON RINGS ONLY:
For discontinued piston rings, try contacting Frank Bowman. He manufactures repro and current piston rings for our modeling needs. He can make standard and Dykes type rings. If he doesn't have the ring you need in stock, you send the piston and cylinder and he will make it then. prices are $7.50 up to $9.50. His work is of the finest quality.

Frank can be reached at [email protected] or 1-505-327-0696 ( 6pm to 9pm mst. weekdays) and the following address:
Frank Bowman

Jim,


Thank you very much for the information you were very helpful.

Chuck

Sounds like a bad case of detonation.
Try using a smaller propeller to reduce the load.

I'd bet on detonation as almost a sure thing. After you get it fixed, add a head shim or run lower nitro fuel.

Hello!
I doubt the pitted piston crown was subjected to just "detonation" (wrong ignition point).
I have experienced these pitted pistons many times before in F3D pylonracing when we ran Rossi and MVVS 6,5cc engines and the pitted pistoncrowns was allways caused by running our engines too lean so that the glowplug filament melted and burnt small holes in the top of the piston crown and sometimes scoring the sides of the piston.
So if you experience such a piston ...be very carefull and look for any scoring marks on the piston and on the cylinderliner.
Look also for a combustioncamber that is totally sandblasted from small glowfilament remains!! And look out for glowfilament remains inside the ballbearings.......

Regards!
Jan K
Sweden

Jaka, thank you very much for the resonse. I also want to mention that the ring was broken on the side of the piston where the pitting occurred.

there is another possibility- a broken bearing. if the rear bearing has a metal retainer, when the retainer breaks, the metal fragments get ingested- they blow up the bypass and into the cylinder, where they bounce around and ding up the piston crown and the combustion chamber. if they get lodged in the port, they will damage the side of the piston and the ring and maybe the liner too. i have never seen detonation cause this kind of damage, though i suppose it is possible, but i have had damage like this caused by bearing failure several times! be sure to check your bearing- pieces of the retainer can break off and you cannot really tell from outside the engine, it still turns over smoothly! if your retainer is broken, you have your culprit, if the bearing looks new, it was probably replaced by the previous owner. if you need to replace your bearing, consider one with a phenolic retainer, they do not have this failure mode, but they are more expensive. one other thing- on a ringed engine, the squishing of the piston caused by the bearing schrapnel can cause the ring groove on the piston to be squeezed shut, clamping the ring tight in the groove and then the ring cannot move properly to seal against the cylinder. since your ring broke, be sure to check the piston to be sure the new ring has clearance to the ring groove.