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Old 02-12-2010, 08:56 PM
landspeed landspeed is offline
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Tecumseh TVS 600 2-stroke kickback - not flywheel key

Hi! I'm new to this site, and trying to repair my lawnmower engine - it is a Tecumseh TVS-600 (this is stamped on the side). A good parts diagram for the engine is shown here: (the ignition system is very basic, with just a coil and a magnet on the flywheel which goes past the coil, and a HT lead to the sparkplug, and a single wire that goes to the on/off/engine speed selector)

http://www.partstree.com/parts/?lc=t...S6001661-25-EN

It had some problems, where it would become difficult to start when it had been used for a while, unless it was left to cool down, but otherwise, it ran smoothly, and started easily.

It was used by someone (not myself), and it made a funny noise, so they stopped using it. It turned out the blade had half-loosened, such that it would have spun around 180 degrees before the crankshaft caught up with it again - this would have caused sudden changes in the speed of the engine for sure.

I then tightened the blade, tried to start it, and it kicked back very badly, pulling the starter cord out of my hand. It kept doing that every time I tried to start it (in fact, it would run backwards for a while, by doing the kick-back, and then turning backwards slowly, but just fast enough, so it would keep running (barely) backwards.

I have done the following tests / investigation to find out what might be wrong:

(1) I noted that, when it did the running backwards thing, even if I switched the speed setting to 'Off', it would still keep running backwards, for 10-20 seconds, slowly.
(2) Checked crankshaft (the blades side of the crankshaft) and it isn't bent at all when spinning it. Also, it spins freely when sparkplug is out, no catching / resistance etc.
(3) Removed flywheel and checked flywheel key - it is in one piece, and hasn't shifted. It is very, very slightly worn, but I don't think this would be causing the current problem or the issue in (4) below
(4) Removed sparkplug and checked where TDC is using a screwdriver to detect the piston movement. Rotating the engine slowly using the flywheel, the magnet passes the coil when the compression stroke is *just* starting (a few degrees of compression has occured). Actual TDC occurs about 88 degrees *after* the magnet has passed the coil.
(5) Checked compression - this is good (no compression tester, but at least as good as any other working lawnmower engine / other small engine I have used in the past, and probably better)

Any ideas on how to proceed next, or what might be wrong? I was wondering if the crank was twisted, but, it is quite a short crankshaft, (see the diagram in the link above) and it is quite thick; I can't imagine it could twist 90 degrees without damaging the flywheel key, and without any bending of the crankshaft occuring at all?

Thanks for your advice - will keep looking at the engine and see if I can figure it out but would be grateful if anyone could help me with this!

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Old 02-12-2010, 09:32 PM
landspeed landspeed is offline
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Point (1) is incorrect - actually, when in the 'off' position, it does stop, but, when in the 'start' or any position except off, it kicks back on the first pull / first turn of the engine (it does have good compression / spark etc!)

Any ideas anyone?
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Old 02-12-2010, 10:22 PM
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dutch1 dutch1 is offline
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The engine is an old points and condensor ignition--unless someone has chipped it. Since there is no valve/camshaft train for timing, about the only two things that can effect the timing is the flywheel key and the points. It's difficult to imagine that it could be 88 degrees out of time due to the points being excessively worn/out of adjustment. The points are in a case under the flywheel. Honestly, I'd replace the points and condensor. Adjust the points to .020" with the arm of the point set on the highest point of the lobe on the crankshaft. When you pull the cover off the case containing the points, rotate the crank until the lobe of the crank opens the points to its maximum and if it differs greatly from the figure above, that is most likely the problem.

If you are not already aware, Tecumseh is out of business and OEM parts are getting hard to come by. I just looked at my NAPA small engine catalog and it would appear you can obtain parts from them. Points part #7-01024, condensor part #7-01324. Hope this helps.
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Old 02-13-2010, 12:55 AM
landspeed landspeed is offline
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OK! I hadn't looked underneath the metal plate under the flywheel (Item 258 on that parts diagram 'Blower Cover Housing', but I can do that. Are you sure it is a points and condensor system? (the reason I ask is, it has a plastic box which seems to have a coil in it, and a large magnet attached to the flywheel, which when it goes past the plastic box, generates a spark. The plastic box has 1 wire which goes to the on/off/motor speed controller, and a HT cable which goes to the spark plug.

The black box is part number 100 on the parts diagram, and it is called 'Solid State Ignition'. It looks like it is under the flywheel on the diagram, but actually it is in line with the flywheel, on the top of the engine (so the flywheel magnet goes past it and generates a current).

Should I go ahead and dismantle the engine to look underneath the blower cover housing, or could there be something else wrong with then engine?

Thanks for your help so far!
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Old 02-13-2010, 01:46 AM
topsites topsites is offline
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Quote:
Originally Posted by landspeed
it is a Tecumseh
Yup, there's the problem.

Quote:
Originally Posted by landspeed View Post
Are you sure it is a points and condensor system?
That's what you said it was...
Not sure on that engine but on my older Kohlers the points and condenser is accessible by removing a small cover,
it's held on either by a screw or two or maybe it just clicks into place, either way once that cover is out of the way
anyone can clearly see the one or two individual parts the points / condenser system consists of.
A coil is usually an all-in-one dohickey, no covers or anything, just one piece that consists of coil and spark plug wire and the leads.
So, chances are if there is no cover to be removed...
But I have no way of telling for sure, without looking at it.

Did you get the blade on nice and good?

Last edited by topsites; 02-13-2010 at 01:52 AM.
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Old 02-13-2010, 02:29 AM
landspeed landspeed is offline
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Everything is fitted together tightly - no problems there.

Looking at my lawnmower, but also at the link I posted in the first post, the ignition system of the lawnmower is as follows:

A black box sits next to the flywheel. The box is called the 'Solid State Ignition'. A magnet is attached to the flywheel - when this magnet goes past the 'Solid State Ignition' (it moves 1mm away from it), a spark is generated in the spark plug.

The black box has a HT lead which goes to the spark plug, and a single wire which goes to the engine on/off switch - and there are no other electrical connections.

I was wondering, from the problems noted in my first post, and the tests I have already done, and the fact that it has a solid state ignition, what my next line of investigation should be, to figure out what has gone wrong to put the timing out by 90 degrees?

Thanks!
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Old 02-13-2010, 08:21 AM
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dutch1 dutch1 is offline
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The black box you're referring to is the ignition coil although it is not a solid state type of ignition system since it has points and condensor unless as I said earlier someone has previously chipped it. There is no need to remove the part 258 as the points are contained in the little oblong case. Remove the clip(437) and the cover(438). Inside the case you will find the points(440) and condensor(447). Part 441 is the plastic lobe that slips over the crankshaft and is what opens and closes the pointsl Check it for wear as well. If there are no wires running to the case then it could have had an ignition chip installed. If there are wires running from the case and points/condenser are present, do as I told you to do in my original post.

You describe the air gap between the coil and flywheel as 1mm. By my recollection of metrics this is getting close to .040". By spec you will find that the air gap should be .010-.012" This is excessive and could be the at least a part of your problem.

Dutch
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Old 02-13-2010, 10:56 AM
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FIXDISS FIXDISS is offline
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I just pulled out an old AV520 and looked at it. Like you described there is only one wire (kill wire) other than the plug wire on it. In this application there are no points and condenser. I removed the plug and checked for flywheel position at TDC. The magnet on the flywheel was just past the coil to the point where the first fin on flywheel was centered on the coil (solid state ignition module). I also noted that looking underneath the flywheel without removing it ,the flywheel key in the crankshaft was also inline or centered on the "SSIM". If your flywheel is not at the above position at TDC then the key must be sheared. If the key is not sheared then look at the key-way in the crankshaft.If it is not at TDC as described then you must have a broken crankshaft journal .
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Old 02-13-2010, 06:28 PM
landspeed landspeed is offline
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The key is intact (I have removed the flywheel and taken the key off and put it on again). The key on mine is odd, in that the crankshaft keyway is at TDC in the position you described, but the flywheel key is such that the crankshaft keyway and the flywheel keyway are kept 90 degrees apart from eachother (e.g. offset from eachother). If I had a different flywheel key then I could get the timing to be correct again, but there is no way that the flywheel key has been damaged to get to the alignment it is currently in - it was manufactured like that.

I guess it sounds like the crankshaft is damaged then (which is odd because it isn't bent at all and turns without resistance), so it must have somehow reshaped internally to be exactly 90 degrees out of sync, but still have appropriate compression and have TDC at the same height, but 90 degrees out of sync). If I get a differently aligned flywheel key it will probably just break the crankshaft after a second or two of running

I will have to strip the engine and look at the crankshaft - does anyone know if the gaskets can be replaced with universal instant-gasket if it turns out the crank is OK? (if the crank is not OK, then the engine is a write-off as you can't get cranks any more).

Also, does anyone know if the Honda GXV120-160 series engines would fit in place of a Tecumseh engine (similiar compatiability with screwholes etc)? If so, I might just get one of those - as my lawnmower at home has one, and has lasted over 17 years, and was secondhand from a hire place when we got it (and has also chopped stones, tree roots, and so on, with never any problem like this)

Thanks for your help so far!
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Old 02-13-2010, 07:22 PM
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FIXDISS FIXDISS is offline
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Man this is bugging me. Ok I just pulled the flywheel off the av520 to find what I think is your problem. When you remove the flywheel there is a tapered bushing insert that acts as the shear key. There is a depression inside the bushing that aligns on the key-way of the crank . The flywheel actually fits onto the tapered bushing which has a raised key-way. Look carefully at the tapered bushing and you will probably find the inner part is sheared smooth.The open part of the tapered bushing is not a factor.It just helps to lock the fly-wheel and crank in place kinda like a clamping action.
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