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how to dismatle a 4 stroke engine

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Daniel Cardona01/10/2009 23:21:03
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hi i'm looking for a tread or website, anything that could explain how to open a 4 stroke engine and showing how dissamble it as it should be. for example how to get the timing good in case nothing was marked, how to remove valves, what to take care before removing, and what are the most important parts to inspect and how to  install everything.
 
any help!
 
regards
Daniel
Doug Ireland02/10/2009 01:26:34
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Hi Daniel, do you have a specific reason why you need to strip the engine?
00102/10/2009 09:03:02
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Daniel, if you must dismantle I would suggest a book. 'A guide to O.S. model four strokes' Published by Radio Control Modeler Magazine in the U.S. $7.95. Which could save making an expensive mistake.
 
Even if your engine is not an O.S. most commonly used Chinese 4 strokes are a similar design or layout.
If the engine is a Saito there is a book for that also. 
ken anderson.02/10/2009 09:11:39
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my brother like's to take thing's to bit's to see how they work...........he has a vast collection of thing's that don't when he is finished..........
 
 
              ken anderson.........
Daniel Cardona02/10/2009 09:20:52
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yes doug i have a SC 30 four stroke and engine bearings dont sound that they are in good condition also there is a little play. so with a good book as richard sad and with little patience i think i can make it. any other suggestions ??
 
regards
daniel
ken anderson.02/10/2009 09:36:42
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hello daniel-the first time i took apart a 4st(OS)91 to replace the front bearing was under the watchfull eye of some one who had done it-i would suggest if your not 100% you take some photo's as you go......the taking off of the backplate and stuff is easy-the awkward bit for you will be the cam and the timing....the best way is to put it back together with the piston at tdc...the cam drive cog will have a mark on which will line up with a mark on the engine...as long as that is lined up ok and the tappet clearence's are done you should have no prob....i would take off  the cam cover and take some photo's to refer to when you rebuild it........sound's daunting task the 1st time- but you will be ok with a bit of TLC............ ..
 
          ken anderson
 
 ps-the lad who kept me right had a saying..."their only nut's and bolt's".....also-i think you'll find there will be timing mark's on the various bit's......if not-scratch some on yourself for reference.......

Edited By ken anderson. on 02/10/2009 09:38:59

Daniel Cardona02/10/2009 09:47:17
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170 forum posts
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yes KEN the timing part is the one that i'm a little worried, i have an old OS 26 SURPASS and i noticed that it has a mark T on the prop backplate. T for top dead centre i assume. but it's not the same on the SC and ASP engine. definitly i'm not going to open the OS to learn on it's dear to me and a museum piece. i think i might order that book.
if anyone knows about a good website post it here guys.
 
regards
Daniel
Former Member03/10/2009 08:56:34

[This posting has been removed]

Peter Miller03/10/2009 09:43:16
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The timing mark for OS engines and OS clones is as follows.
 
On the side of camshaft gear there is a dot. With the engine at top dead centre this dot must be lined up with the pushrods.  i.e  pointing up the smae line as the push rods.
 
Because the gear is a skew gear you will have to start sliding it in out of position. Just make sure that when it is fully home it lines up as mentioned.
 
There will be no need to take the head and valve gear to pieces so just leave that in one piece.
 
Keep the push rods and tappets separate so they go back in their original positions.
 
Work carefully in a clean area, mark things with a spirit marker pen so you know which way round they were and take note of what you do.
 
They are not really complicated so have a go.
thomas oliver 103/10/2009 23:09:24
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23 photos
A good way to check that you have got the timing correct is to check that there is "overlap" at the end of the exhaust stroke and beginning of the induction stroke.  To see this, turn the crank and watch the rockers.  The inlet rocker will begin to open the inlet valve before the exhaust valve rocker has allowed the exhuast valve to fully close. Wiggle the crankshaft back and forth and the two rockers will rock together.  This is to allow for the inertia ( reluctance to start moving) of the mixture  and it ensures more complete filling of the cylinder and hence more power.  The same sort of thing happens in the spark timing of a petrol engine -- the spark occurs before top dead centre to start the combustion early and allow the "flame front" to spread and get the expansion of the burning gas to begin as early as possible.  You should be able to see the piston crown at the top of the stroke when  this is happening by checking through the plughole.

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