RunRyder RC
WATCH
 1 page 740 views Post Reply
HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › Changed cylinder and ring. Still no compression
09-05-2006 10:23 PM  14 years ago
Topic Vote0Post 1
gkoutsis

rrKey Veteran

Athens Greece

MyPosts All Forum Topic
Changed cylinder and ring. Still no compression
Changed cylinder and ring. Still no compression

So, my old OS 50 needed a new ring.

It was flying just fine but I had almost NO compression when cold. Power was ok but not that great compared to other OS 50s.

Got a new ring and cylinder, installed them carefully, broke the engine in for 3 tanks.

Still no compression. Its much better than before but still not enough to justify a new ring and new cylinder.

My OS37 on 10 gallons has twice as much compression.

The head is tight as hell, same for the backplate.

The big question is, should I chang the piston? I've been reading here and everybody says that its the ring that creates the compression not the piston. Thats why I didn't change it.

Oddly enough, the bearings are in top condition (More than 30 gallons through the engine).

George
George
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
09-05-2006 11:36 PM  14 years ago
SteveH

rrProfessor

Texas

MyPosts All Forum Topic
It's been my experience that happens when you only change the ring, and not the piston and the ring. The thing is, the ring and piston wear in together and actually make a sealed surface on the bottom of the ring/top of the piston ring groove, and I don't think it ever seals as good when you change only the ring.

If you take an engine apart that is running good, you can see a shiny surface on the bottom of the ring where it has worn in with the piston. Additionally, if you reassemble the engine and install the ring upside down, it will have reduced compression. Go ahead, ask me how I know.
The government cannot give you anything without first taking it from someone else.
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
09-06-2006 12:02 AM  14 years ago
gkoutsis

rrKey Veteran

Athens Greece

MyPosts All Forum Topic
So, a piston is needed.....George
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
09-06-2006 01:08 AM  14 years ago
dkshema

rrMaster

Cedar Rapids, IA

MyPosts All Forum Topic
The ring's where the compression comes from. The piston is a "loose" fit in a ringed engine. Take the ring off and see how poor your compression will be. In an ABC or ABN engine, the sleeve is tapered and the piston is a relatively tight fit at the top of its stroke.

Perhaps you need to check the head and/or head gasket to make sure they are sealing.

Dave
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
09-06-2006 01:12 AM  14 years ago
gkoutsis

rrKey Veteran

Athens Greece

MyPosts All Forum Topic
I'll get some pics in a few days. I plan on cleaning the engine thoroughly.George
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
09-06-2006 01:20 AM  14 years ago
Doug

rrElite Veteran

Port Saint Luice Florida....

MyPosts All Forum Topic
The ring and piston provide the seal ( the high pressure delta "P" between the upper and lower side of the ring provides the force to expand the ring and provides the seal). The OS-50 does not have a lot of ring tension and a a result the "flip" compression is never that good. It is possible that the lower land of the ring grove is damage providing a leakage path. The cylinder never needs to be change unless it is damaged. However the piston ring land does wear. As for your bearings I would bet that they are "Junk" Take the rear bearing apart and inspect the races and report back (easy to do and easy to reassemble).
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
WATCH
 1 page 740 views Post Reply
HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › Changed cylinder and ring. Still no compression
Print TOPIC

 2  Topic Subscribe

Saturday, November 28 - 2:08 am - Copyright © 2000-2020 RunRyder   EMAILEnable Cookies

Login Here
 New Subscriptions 
 Buddies Online