RunRyder RC
WATCH
 1 page 840 views POST REPLY
HomeRC & PowerAircraftHelicopterEngines Plugs Mufflers Fuel › Connecting Rod to Crankpin fit.
02-07-2010 03:35 AM  8 years agoPost 1
Mikerobe

rrVeteran

Green Turtle Cay,Abaco, Bahamas.

My Posts: All  Forum  Topic

When using the cooling fan to rotate my OS.70 back and forth, I can feel and hear clearance between the piston movement and the crankshaft. How much clearance/noise should there be before this becomes a repair issue?

The lot I got is not a lot, but I thank God a lot for the lot I got!

PM  EMAIL  GALLERY  Attn:RR  Quote
02-07-2010 03:38 AM  8 years agoPost 2
Dr.Ben

rrMaster

Richmond, VA, USA

My Posts: All  Forum  Topic

Unless your engine has a TON of time on it or has been abused, the sound your hear and play you feel is normal.

I little freeplay is desired on the crank end to ensure adequate lubrication, even with the librication holes in the rod.

I wish I could tell you how much is too much, but you kinda gotta have the engine in hand to know. I will tell you this. It has been AGES since I've needed to replace an OS con rod d/t wear issues. They last a LONG time.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

PM  EMAIL  GALLERY  Attn:RR  Quote
02-07-2010 04:25 AM  8 years agoPost 3
Mikerobe

rrVeteran

Green Turtle Cay,Abaco, Bahamas.

My Posts: All  Forum  Topic

Hi Dr Ben,
Thanks for the response!

When the motor is at TDC it feels and sounds worse, however, this is probably just because of the stroke change. The engine does not have a lot of time and has only been leaned for short periods during initial tuning setup.
I may just be to finicky about nothing, if you know what I mean!

The lot I got is not a lot, but I thank God a lot for the lot I got!

PM  EMAIL  GALLERY  Attn:RR  Quote
02-07-2010 06:53 AM  8 years agoPost 4
steve9534

rrKey Veteran

yakima, wa.

My Posts: All  Forum  Topic

Rod clearance
This question comes up periodically and deserves a thoughtful response. Dr. Ben is correct as usual in that the OS rods just don't seem to wear out, but there's more to the story. The rod clearance needs to be sufficient to allow oil to enter and lubricate the big end bearing just as Ben has stated. More clearance is generally better in a two stroke motor. The thing most folks don't think about is that a two stroke when running is only loaded on the top or piston side of the big end bushing and would run just fine even if the lower half of the rod were removed. You'll normally feel some play in the crankpin/big end bushing as you turn the motor over and you may hear a clicking from the rod when starting, but when the motor is running, the free play doesn't really matter and shouldn't be a problem. Obviously, it is possible to wear out the big end bushing on the rod. As a practical matter, I've never seen that happen on an OS rod, including some that are close to 20 years old. Hope this helps. steve.

PM  EMAIL  GALLERY  Attn:RR  Quote
02-07-2010 04:40 PM  8 years agoPost 5
Dr.Ben

rrMaster

Richmond, VA, USA

My Posts: All  Forum  Topic

Steve,Mike,

Interesting story for you. I recall reading an article about 10 or 15 years ago in Radio Control Modeler by Col. Bob Johnson about how he and at least a few other guys were actually relieving the ID of the crank pin end of the rods in their OS91 ducted fan engines to get a bit more clearance for lube. For a while they couldn't ifgure out why the Rossi 91's were holding together while the OS's were throwing rods when both engines had good quality machining. Finally he measured the con rod clearances and discovered the Rossi's were set up with a statistically greater clearance on the pin end of their rods versus the OS, presumably for more lubrication passge. After they relieved the bushing in the OS's just a little, they stopped having rod failures.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

PM  EMAIL  GALLERY  Attn:RR  Quote
02-08-2010 12:20 AM  8 years agoPost 6
steve9534

rrKey Veteran

yakima, wa.

My Posts: All  Forum  Topic

Ben
Interesting that I read that same article and was thinking about it as I submitted my earlier reply. Thanks for the kind reply. steve.

PM  EMAIL  GALLERY  Attn:RR  Quote
02-08-2010 01:27 AM  8 years agoPost 7
Mikerobe

rrVeteran

Green Turtle Cay,Abaco, Bahamas.

My Posts: All  Forum  Topic

Ben, Steve,
Interesting info, the piston skirt is acting as a pressure and vacuum pump, however, I don't have enough knowledge about how the pressure of combustion compared to crankcase induction pressure being created at the same time. Obviously there is resistence here as enough pressure must be created in the crankcase to both provide a fresh charge of fuel and air as well as scavenging out spent gases.
Anyhow, most interesting thinking about what's going on in such a short time.

The lot I got is not a lot, but I thank God a lot for the lot I got!

PM  EMAIL  GALLERY  Attn:RR  Quote
02-08-2010 11:37 AM  8 years agoPost 8
airdodger

rrElite Veteran

Johnston USA

My Posts: All  Forum  Topic

The piston skirt does not contribute to the seal in the engine, other than keeping the ring from rocking. The pressure is dependant on the ring seal both ways.

Chris

PM  EMAIL  GALLERY  Attn:RR  Quote
WATCH
 1 page 840 views POST REPLY
HomeRC & PowerAircraftHelicopterEngines Plugs Mufflers Fuel › Connecting Rod to Crankpin fit.
 Print TOPIC  Make Suggestion 

 2  Topic Subscribe

Saturday, September 22 - 2:12 pm - Copyright © 2000-2018 RunRyder   EMAILEnable Cookies

The RC discussion world needs to consolidate. RR is now one choice for that. Its software is cutting edge. It hosts on-topic advertising. Help RR increase traffic buy making suggestions, posting in RR's new areas (sites) and by spreading the word.

The RunRyder Difference

• Category system to allow Rep/Vendor postings.
• Classifieds with sold (hidden) category.
• Classifieds with separate view new.
• Answer PMs offsite via email reply.
• Member gallery photos with advanced scripting.
• Gallery photo viewer integrated into postings.
• Highly refined search with advanced back end.
• Hosts its own high end fast response servers.
• Hosts thousands of HD event coverage videos.
• Rewrote entire code base with latest technology.
• No off-topic (annoying) click bait advertising.
Login Here
 New Subscriptions 
 Buddies Online