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Piston "jamming" in cylinder liner Options
Yatto
#1 Posted : 27 June 2014 13:18:30

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Hi Everyone :)
Yatto (Dave)in Oz here.
Help!!!
Has anyone had problems with the piston "jamming" (getting caught)at the top of the cylinder liner when the liner is in fully in place (down as far it will go). The piston will not move down freely.
The piston moves up and down freely without any problem before inserting the liner.
Is it me??........have I done something wrong?......lol.
Warthog
#2 Posted : 27 June 2014 13:53:30

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Hi Dave BigGrin you've done nothing wrong as the piston is meant to have a tight fit..later when you fit the pull cord you will then be able to simulate the starting of the engine and will notice that the piston will become free from the tight fit as you will have more leverage rather than trying to turn the shaft with fingers and thumbs.. Just make sure you have lubricated the parts with after run oil before attempting to simulate the piston movement.

Regards

Spencer
Tomick
#3 Posted : 27 June 2014 14:07:38
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The cylinder liner has a fine taper to it, which seals the compression, and is because the piston does not incorporate a piston ring.
A few drops of after run oil will ease its movement, and will ease further after a few start-ups.
Supaheli
#4 Posted : 28 June 2014 05:33:48

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What do you do if there are scratch marks on the outside of the liner ???
Supaheli
Warthog
#5 Posted : 28 June 2014 08:31:57

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The outside of the cylinder liner has no major tolerances to contend with and any scratches are there due to the manufacturing process so will not effect the movement and performance of the piston.

Regards

Spencer
kenjara
#6 Posted : 29 June 2014 20:12:25

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An engines piston is supposed to be tight at top dead center. Even more so for new engines.
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karl1113
#7 Posted : 29 June 2014 22:45:10

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a very small lecture is required here, from memory of my r/c flying days many moons ago, this type of engine was known as an abc engine,the abc meaning alloy bronze liner. and as others have said there is a fine taper up the lining,and made to a very fine tolerance,this helps keep the compression high,but because of the material of the liner,it expands when hot, thus freeing the piston slightly and allowing very fine particles of oil to lubricate the liner,as it has no compression rings or oil rings to do the job. this type of engine was considered high performance and long lasting. Blink BigGrin
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Warthog
#8 Posted : 29 June 2014 23:22:15

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Some more info here about Abc engines etc


http://www.mecoa.com/faq/abc/abc.htm


Spencer
Supaheli
#9 Posted : 30 June 2014 11:33:28

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Warthog wrote:


Some more info here about Abc engines etc


http://www.mecoa.com/faq/abc/abc.htm


Spencer
interesting information...learned something new
Supaheli
Senorita87
#10 Posted : 16 July 2014 04:31:19

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Tomick wrote:
The cylinder liner has a fine taper to it, which seals the compression, and is because the piston does not incorporate a piston ring.
A few drops of after run oil will ease its movement, and will ease further after a few start-ups.


Where would you get after run oil from? And will this definitely fix it? As I'm having the same problem mine gets stuck and won't even turn do a full circle on goes up but don't all the way around
rowdy85
#11 Posted : 16 July 2014 05:20:31

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You can pick up some afterrun oil from a local hobby shop or maybe even a Mr Toys store if they have a Radio Control section. The after run is really just to keep things lubricated and protect the bearings from corrosion while the motor is sitting. A brand new nitro engine will be really tight when new and even after some running in, so at this stage it would be near impossible to turn the motor over via the crank shaft and that's fine 'cuz that's how it should be.
Gary O
#12 Posted : 16 July 2014 12:57:00

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Marvel Mystery Oil works.
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#13 Posted : 16 July 2014 13:20:36

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As previously mentioned people here are jumping the gun.

It is not a problem and you should not be looking for a fix. That said after run oil will be essential to keeping your engine well maintained so it would be advisable to get some.

When its time to break in your engine it will get lubricated when you first run your fuel mixture through it.

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Senorita87
#14 Posted : 09 August 2014 08:46:36

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Ok so I'm still having problems with the piston I know people are saying this is normal but when I have put the recoil kit on it the piston gets stuck so which means the cord just hangs out and doesn't retract
Can someone from admin comment on this please as I would like to know how would I go about getting a replacement piston book 66 as I get mine from the new agency as i can't do anymore
Thanks
Warthog
#15 Posted : 09 August 2014 09:23:02

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Hi Senorita87


First of all double check the assembly of the crank arm and that it is in the correct position and in line with the cylinder lining. Make sure you have added the after run oil before attempting to recoil the piston, make sure you are giving it a good pull as you would starting a petrol engined lawn mower etc so that the piston does a few good rotations when pulling. Once or twice is enough and further pulling of the recoil cord should be avoided until your RB7 is ready to run.

If you still think you have a genuine fault with the recoil kit then there are contact details on the magazine that come with your parts. Either give them a call or email customer services.

You could also request another copy from your news agents where you get your copies from but you will have to pay for this but it will at least allow you to continue your build.

Any faulty parts may/will have to be returned.


Regards

Spencer
Supaheli
#16 Posted : 09 August 2014 12:17:06

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Make sure you have the 1 way bearing on the correct way...
Supaheli
Tomick
#17 Posted : 10 August 2014 10:14:04
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Remove the glow plug, which should allow the cord to recoil with a slight tug of the cord.
If it won't recoil, then it's possible that the cord has been over-pulled and damaged the recoil, in which case you'll need a new recoil unit.
pwormald
#18 Posted : 25 August 2015 10:25:10

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Hi, I have just assembled my engine and was also initially concerned with the piston being tight at top dead centre. I have used after run oil during assembly.(I had not read these posts until now). I am now more re-assured that this is not going to be a problem. I would just like to check one thing re the grooves on the conrod. Could someone please confirm that the grooves on the conrod are facing the crankshat counterweight when properly fitted. I fitted mine looking at picture 06 on page 312 of step by step instructions. I have now re read step 05 on page 311 and am 99% sure I am right but just want to re-assure myself.
thanks phil.
Tomick
#19 Posted : 26 August 2015 08:45:10
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The groove should indeed face towards the counterbalance/towards the inside of the engine, and also not visible when you remove the pull-start/engine back plate. Otherwise the conrod/piston will jam at the bottom stroke.
pwormald
#20 Posted : 26 August 2015 10:38:29

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Many thanks Mr T. Build going very well and looking good. Phil
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