OzVMX Forum
Marque Remarks => CZ => Topic started by: shakeyCZ on November 14, 2010, 11:31:50 am
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Hey all just abit unsure is BTDC taken from the highest point of the piston? as I just want to makesure so I can setup my points, and get the gap set. Also TDC is when the piston is at its highest point and about to change direction ? is this correct?
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TDC is the top of the piston travel -- only way to be ecact is to use a dil indicator -- but beware angled spark plug holes -- they can make the reading a little difficult -- and then you must set the "timing" for BTDC or Before TDC and that will be in degrees, you will need a degree wheel to put on the crankshaft and read from that -- but for most engines there will be a mark to tell you where TDC is and where the required BTDC is -- usually shown and explained in the relevant workshop manual wchich for CZ's is available on line -- google "CZ Madness" and you will see a lot of info there.
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Does it really make a difference?
Top dead centre is top dead centre. Whether it is taken at the centre or the lower side of the piston it's where the that particular area isn't going to travel any further up. It's all downhill from there (A bit like turning 40)...... ;)
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There are a few old tried and tested methods of finding top dead centre. if there is no mark on the flywheel for instance.
The approved best method is to remove the cylinder head [easier on a 2/ ] and find T.D.C. with a dial indicator. If this is done with a 4/ it is important to make certain that the cylinder barrel is locked down securely to the crankcase. [Is it through bolted]?
The bubble method. Set up a timing disk and pointer, get the piston as near as you can guess to T.D.C. Then get a cake of wet soap, rub your finger on the soap, then over the vacant spark plug hole to form a bubble, slowly rock the flywheel to and fro to form the highest bubble. This is T.D.C.
Of course a 4/ motor must be on the top of the compression stroke. I have frequently used this method successfully.
An accurate method I have used when setting up a timing disk especially when building a motor with different cams etc where I need to check numerous figures is as follows.
Set up a timing disc and flexible pointer such as a piece of wire mounted to a convenient screw into the crankcase so the end pointing to the timing disc can be adjusted.
with the cyl. head bolted on find a bolt with the same thread as the spark plug hole or in some cases a long reach plug with the side electrode removed,screw this into the plug hole with the piston well down the stroke.
Next slowly rotate the flywheel 'till the piston contacts the end of the bolt.
Bend the pointer to a convenient mark on the timing disc and note the reading.
Rotate the flywheel in the other direction 'till it again contacts the stopper bolt.
Remove the stopper bolt and turn the flywheel to a point exactly half way between the two previous points. This is Top Dead Centre.
These techniques as described in the late great Phil Irving's bibles.
cheers pancho.
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hmmm Okay Im putting back together my CZ 250 and I don't have a timing wheel, I have my manuals but I dont understand when they say 3.00mm should be BTDS, and the points gap should be 0.05, so where do I take the 3.00mm from? I have the head off, from the top crown of the piston? ??? ???
(http://sphotos.ak.fbcdn.net/hphotos-ak-ash2/hs589.ash2/154163_10150320184565361_706830360_15569013_5980393_n.jpg)
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shakey
12 thou at tdc points gap
use a tally ho paper and adjust points so when the paper can just move(points opening) approx 3.00 mmbtdc depending which cz you have
http://www.czmadness.net/specs/cz250.html
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Sounds like, Step 1 set points to .05.
Step 2. move the piston to the top of its travel.
Step 3 Set up a dial indicator to confirm that a point on top of the piston is actually at the top of the stroke[by rotating the flywheel slightly in each direction]
Step 4. rotate flywheel BACKWARDS 3.00 mm.
At this point the contact points must just make/break contact. If this is not the case the mounting plate of the points should be moved to achieve this.
If like my RT1 the points mounting can not be moved the points setting [of 0.05]
may need to be varied to achieve the 3.00 mm Before Top Dead Centre.
Recheck the setting and re-adjust if necessary.
cheers pancho.
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As Pancho says & try to get the "x" on the flywheel lined up with the nicks on the edge of the stator plate at the same time, points gap at TDC isn't as important as this because these marks are where spaek is strongest
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Did you have any joy in sourcing the points locally & if so which ones?
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Nah no points yet, had to get a new rear carb boot so I got some from the UK, now just working on the getting the timing set, Got a PM and I will ring jim and hope he can give me some guideance.
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Lucky for me I was able to grab a piece of intercooler hose from supercheap which fits perfectly over the carb & airbox, had enough that I've now got a spare. Not sure on what size carb you're running but the 36mm on mine almost touches the airbox
If you have a look at the czmadness manuals & find the one with the yellow tanker standing up on the front look for the section called tuning for power, my copy explains how to time the bike quite well on pages 85 & 86 including the part about phasing.
When I timed mine I took the head off as that makes things more accurate, set the gap then set the timing at 2.8-3mm BTDC- hopefully the marks line up. If they don't it's probably better to get the phasing & timing right rather than worrying too much about the gap
Hopefully thats clear as mud & you shouldn't find it too hard
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To get 3mm BTDC you will need a dail indicator that can be fixed into your spark plug hole while the head is on.
http://commons.wikimedia.org/wiki/File:Dial_Indicator_Gauge.jpg#
as your piston rises and comes in contact with the needle at the bottom of the indicator, the hand on the face moves around the dial, as the piston reaches TDC the needle will stop, as the piston moves back down the stroke the hand starts to drop back down again.
You will need to first find TDC (the very top of the stroke) make note of the number the hand reaches at this point (these numbers are indicating mm's of piston travel) then rotate the crank backwards until the indicator reads 3mm less than the TDC number.
Set your points to the right gap while piston fixed in this position.
Good luck.....make sure you hold your tounge right. ;)
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well I can't find any marks on my flywheel not even an X on it,
hey Tony27 did you set your points from TDC then set the timing from 2.8-3mm BTDC
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hmmm Okay Im putting back together my CZ 250 and I don't have a timing wheel, I have my manuals but I dont understand when they say 3.00mm should be BTDS, and the points gap should be 0.05, so where do I take the 3.00mm from? I have the head off, from the top crown of the piston? ??? ???
(http://sphotos.ak.fbcdn.net/hphotos-ak-ash2/hs589.ash2/154163_10150320184565361_706830360_15569013_5980393_n.jpg)
You will need to put your head back on.
Find 3mm BTDC with the dial gauge as outlined above and set your points gap at .05mm with piston at 3mm BTDC.
Done and Dusted.
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From memory I sent the gap, then found TDC with a dial test indicator, found it much easier with the off as you get the plunger going in line with the bore instead of tipped over in the head. Adjusted everything so that phasing & firing happen together for a really strong spark
The X is on the magnet that will be visible at the firing point, I'll take a photo of the flywheel I robbed the centre from for the ts185 ignition conversion I'm working on
My bike is a 380 so the timing is around 3.5mm
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The X isn't as obvious as I'd hoped due to lighting but hopefully this helps
(http://i788.photobucket.com/albums/yy166/tony27_photo/003.jpg)
(http://i788.photobucket.com/albums/yy166/tony27_photo/002.jpg)
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I found my X on the flywheel after I steel wooled it, so I guess when I put the flywheel back on the crank I was surpose to line it up some how, should I have done this? so should the piston be at TDC when I installed the flywheel? As I found no info on this in any of my books for my CZ.
And thanks to all for your help Its been great and I will keep trying till I get it right. ;D ;D
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the flywheel can only go on 1 way as it is held in place by the keyway.set it all up to run points gap is 12 thou at top dead centre.must be done first.
using dial inticator zero tdc then move flywheel to 3.02 mm btdc .02 is for the plug on side.set points to be just cracked.check this with tally hos or with a test light.tighten then recheck
jim
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HI,
couldn't help but notice the photo shows the Ignition flywheel has been dismantled (unrivetted)from the centre boss , the standard procedure to remove the ignition flywheel undoing the lefthanded nut and use the CZ flywheel puller to remove it intact.
Do you have a complete flywheel or photo of one, they can only be located on the crankshaft taper one way , on the keyway,
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jikov
the guy is making a cdi for cz using the center of th flywheel in earlyer posts i think grafting a ts185
jim
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Jimg1au is correct there, I bought that flywheel in from the states for about $35 to get the centre for fitting to a ts flywheel
Only complete flywheel I have not in the bike is for the sidepipe engines & they have quite a few more letters stamped around the outside of them.
I'm still using points as I haven't drilled the stator plate yet but that should happen in the next week or so seeing as I just dropped the bike into work for fitting of a low level rear brake arm & to make a new stand as the shock mounts won't be usable for the stand with the brake rod running under them. Also in the middle of making some copies of the #1 products fork kits for Ian Pike & my bikes to try out at Taupo
Think the next couple of weeks will be really busy ::)
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my flywheel has no keyway slot nore dose my crank on that side, its just pressed on, is this no good?
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well i have changed my mind he still sux, as he told me it died because he forgot to put oil in the fuel as he was going on 70 years old, but it turns out that the key must have gave way and the flywheel moved around the crank, maybe he did put oil in, and the flywheel cause the timing to slide out enough to detonate, ive just got to figure out a way to get the bit of the key out of the crank, i hope I dont have to split the engine again >:( >:( will post a photo soon of the key slot
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The key is only for a reference it does not nor ever has held the flywheel in place. Try this lapp the flywheel onto the crank with valve grinding paste, freeze the taper with freeze spray and lay the flywheel in the hot sun for an hour do up with a rattle gun. It will not move and go off with a loud bang when taken off.
The firing point will be in the same spot relative to the stator.
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well I put the flywheel back on and lined it up where is should go now I will on the weekend have another go at setting the timing, I have all the tools now so hope I can do it.
Yet again thanks for all you help everyone and I will let you no how I go ;D ;D