Cox Engines Forum
You are not logged in! Please login or register.

Logged in members see NO ADVERTISEMENTS!


Piston to Cylinder -  what's a good fit, what's bad? Cox_ba12




Piston to Cylinder -  what's a good fit, what's bad? Pixel

Log in

I forgot my password

Search
 
 

Display results as :
 


Rechercher Advanced Search

Latest topics
» Cox .049 Tee Dee engines back in stock (limited availablility)
by Cox International Today at 2:54 pm

» Very off-topic.........Time passes and not always for the best......
by rsv1cox Today at 2:47 pm

» Scientific "Zipper" Build...Zipper Flys!.
by akjgardner Today at 12:59 pm

» Golden Bee basic running problem
by 944_Jim Today at 12:44 pm

» Simple Gliders
by rdw777 Today at 9:48 am

» Roddie-Rigger.. a 2005 original design
by roddie Yesterday at 11:48 pm

» Jim Walker Bonanza etc.
by rsv1cox Yesterday at 6:30 pm

» Throttles for Cox Tee Dee .049 / .020 / .010 engines --- videos
by sosam117 Yesterday at 8:54 am

» Introducing our Cox .049 TD Engines
by Admin Tue Jul 23, 2024 2:00 am

» Project Cox .049 r/c & Citabrian Champion
by getback Mon Jul 22, 2024 4:14 pm

» So to the rescue of an EZ BEE .049 r/c
by MauricioB Mon Jul 22, 2024 10:01 am

» Sturdi Built?
by rsv1cox Sun Jul 21, 2024 6:58 pm

Cox Engine of The Month
July-2024
robot797's

"ULTIMITE COX 010: it has a clutch, E starter, throttle, exhaust, aluminum tank, aluminum venturi, gearbox with forward and reverse, and now its on a custom drawn and printed stand"



PAST WINNERS
CEF Traveling Engine

Win This Engine!
Gallery


Piston to Cylinder -  what's a good fit, what's bad? Empty
Live on Patrol


Piston to Cylinder - what's a good fit, what's bad?

Go down

Piston to Cylinder -  what's a good fit, what's bad? Empty Piston to Cylinder - what's a good fit, what's bad?

Post  mike in SC Fri May 10, 2024 2:32 pm

New here to the forum, appreciate all the good info and experience...
I did search to see if this topic has been covered, certainly has, but must be buried inside some topics, so here's my question:

I've bought several "Thimble Drome" stamped 049, must be original Baby Bee?  All of them were stuck, but soaking in "Marvel Mystery Oil" for at least 24hr, then use of Kroil or PB Blaster penetrating oils gradually loosens them up just fine.  (careful, Marvel Mystery Oil appears to dissolve the rubber venturi gaskets...)  (also use 91% Isopropyl to dissolve out gum after free them up)

Latest motor was locked up, but appeared to have little time on it: piston-rod had very little play.  But when trying to re-assemble, the piston would not easily slide up into the cylinder (I don't force things): the top of the piston would slide up even with the top of the exhaust port slots, then super snug. I didn't see any rust or gum inside the cylinder or on the piston, they appear clean.

Not being certain if it is piston or cylinder, I moved this cylinder to an engine that had poor compression (no "pop" at all, and wouldn't complete a rotation on its own) and now this engine has great compression!  Very good smooth feel and "pop", and completes rotation!  

However the "Loose" cylinder on the "tight" piston will rotate through, but still gets very snug when the top of the piston is even with the top of the exhaust slot.  Now I can make a rotation, but it's too tight to "pop", and just drags around.  Based on the simple swap test, the piston must be the problem, as it's still too tight with the loose cylinder.

Instecting the piston, I don't see or feel scratches.  I don't know any history of this engine, but as tight as the parts are I'm surprised the motor ran... could something somehow have damaged the piston?    Is there anything I can measure or check? Anything else I can do to salvage?

Experience appreciated, and if there's already an answer please direct me to it!! Or is this where I decide if I just send Bernie $19.95?

mike in SC
mike in SC
mike in SC
Moderate Poster
Moderate Poster

Posts : 25
Join date : 2024-04-24
Age : 67
Location : Columbia SC

Back to top Go down

Piston to Cylinder -  what's a good fit, what's bad? Empty Re: Piston to Cylinder - what's a good fit, what's bad?

Post  gkamysz Fri May 10, 2024 2:59 pm

Cox thin wall cylinders are easily damaged. The most common problem is someone used the wrench in the exhaust slots and deformed the cylinder in that area. This can happen either from being tight in the crankcase on removal or over-torquing on install. It could be bent from crash damage, which won't be obvious to the eye. In both cases the crank/piston will typically be free a the low end of travel near bottom dead center.

I have one engine that appears to have no time on it, but is tight when the piston is just above the exhaust port. Inspection with a loupe showed a bright spot on the bore where there is a bump. On the exterior of the cylinder in the corresponding location there is a small dent. I can only assume it was hit with something either very early in it's life or left the factory this way. One day I'll lap the bore back to life.

Below the top of exhaust port, the surface is not extremely critical and can be touched up with small files and/or some fine sand paper. Use magnification to see what you're doing it's fine work. People have straightened bent cylinders.
gkamysz
gkamysz
Gold Member
Gold Member

Posts : 390
Join date : 2018-02-22
Location : Chicagoland

Back to top Go down

Piston to Cylinder -  what's a good fit, what's bad? Empty Re: Piston to Cylinder - what's a good fit, what's bad?

Post  balogh Fri May 10, 2024 3:10 pm

Mike, all old stock thin wall cylinders No 1 and 2, and TeeDee thin wall and most stepped wall cylinders Nos 4 and 5 have tapered bore, that causes the piston to stick near the top dead center..these tapered bore cylinders were made to the highest precision in the heyday of COX till around 1972..taper bore became less frequent until it was applied only with specialty motors like Venom and early Killer Bees in the mid 1990-s. Later engines had no taper bore.

My experience with taper bore cylinders is that they maintain good compression for hundreds (yes, hundreds) of runtime hours..
balogh
balogh
Top Poster
Top Poster

2022 Supporter

2023 Supporter

Posts : 4803
Join date : 2011-11-06
Age : 65
Location : Budapest Hungary

Back to top Go down

Piston to Cylinder -  what's a good fit, what's bad? Empty Re: Piston to Cylinder - what's a good fit, what's bad?

Post  mike in SC Fri May 10, 2024 7:42 pm

@gkamysz: I didn't think of deformation of the cylinder... there's not a lot of material at that point (this one has two ports one each side), that makes sense. I put some torque on this cyclinder myself(2 wrenches) so I need to watch that. Fortunately this cylinder works on the other engine with poor compression... Thanks for that info! That will help me.

Is there anything to watch with the pistons? can they get damaged or distorted?

@balogh: so if cylinders were tapered at top, it makes sense, I tried to see if the piston would fit down from the top: no go. I was thinking it was like a car engine, that develops a ridge at the top so piston won't fit, but taper makes sense. I'll watch for those.

Good Info, I've learned something about cylinders... I'll definitely treat them a little more gently!

thanks, mike in SC
mike in SC
mike in SC
Moderate Poster
Moderate Poster

Posts : 25
Join date : 2024-04-24
Age : 67
Location : Columbia SC

Back to top Go down

Piston to Cylinder -  what's a good fit, what's bad? Empty Re: Piston to Cylinder - what's a good fit, what's bad?

Post  Sponsored content


Sponsored content


Back to top Go down

Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum