Author Topic: Terrot MT 1, 100cc 2 stroke: non-starter!  (Read 56156 times)

Offline The Artful Bodger

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #135 on: March 27, 2018, 11:17:37 AM »
Not unusual for a piston port two stroke to spit a little fuel back through the carb. as the name suggests the piston acts as the valves and doesn't do a perfect job. Rotary or reed valves are more efficient and tend to prevent this.
  Many small engine two stroke carbs don't have a pilot circuit on the carbs, tick over was maintained by holding the throttle open a little. Killing the engine was by shutting the throttle off. If your carb doesn't have a throttle stop screw (a screw, usually with a spring on it,  going up at an angle to hold the throttle slide up) then it's not meant to tick over. D 1 Bantam carbs are like this, I've drilled and tapped one of mine so it now has a throttle stop screw.
  If your timing mark on the flywheel is near the firing point you will get a magnetic "surge" when playing with the flywheel. Don't think of a magneto generating a constant charge for the ignition circuit, it generates a momentary pulse of energy at the correct time for the coil to spark. This is when you will feel the magnetic pull on the flywheel. This is why I've mentioned the magnet's position being important, there is a very narrow segment of rotation where this pulse is generated strongly and it must coincide with the points starting to open.
  Pity you're not local (well to me) as I feel sure there's nothing too drastic wrong wrong, but small magneto two strokes can be very fussy and some experience with them goes a long way.

Colin
1926 Magnat Debon, 1953 Bantam, 1955 Ariel Huntmaster, 1961 GPO Bantam, 1979 GS 850, 2001 Burgman 400, 2004 Burgman 650

Offline mini-me

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #136 on: March 27, 2018, 11:24:34 AM »
Why don't you just rig up a battery and coil  through the points and eliminate 50% of your suspects?

Offline Terrotmt1

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #137 on: March 27, 2018, 05:01:38 PM »
I can't see a way (if I had them) to rig a coil etc as I have nothing 6V and there are no holes to get wires though and electrically sound, though admitted, this is hardly an expensive bike..

Just come in from the garage this afternoon.

Tried the original carb again, nothing happening.
Went back to the big Chinese carb, much the same though I thought it might start a few times, and I spelt some carbon monoxide once.

Decided to try different flywheel positions, 8mm btdc, 5mm btdc, tdc, 2mm Atdc.
Of all these 8mm seemed to sound like something might suddenly happen, but no.

I have no idea what to do next, utterly sick of the thing.

I stood staring at it and pondered if there is something really fundamentally wrong here but know so little about magnetos etc (as you can tell). Because the whole thing is so simple there must be a glaring fault.
Maybe there is not enough compression.?

Anyone know of a classic bike restorer in the West Midlands?
I only know of Villiers Services. I think I'll ask if they can look at it. They offer an engine restoration service but I think this is for Villiers only.

Offline mini-me

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #138 on: March 27, 2018, 05:28:59 PM »
The clue is in the name Villiers, I doubt they'll want to know.

A classic restorer? no one worthy of the name will touch it, short of letting them have access to your bank account. I speak as one who used to be. After all, bluntly speaking, you want it sorted not restored, and its not a classic,not by any means.

"my mate has serviced it and it won't go can you fix it" I still have nightmares about such phrases.

I only ever worked on old British bikes, yet the number of times I'd get some fool with a  broken FS1E or similar shit come in and then get the hump when I refused; one idiot even brought his Dad round, the big sign on the door said "Vintage British motorcycles only catered for." yet still they came..... >:(

you need a 6v battery and coil, wire it through the existing points.

After following your saga I am doubting if either of the items you chop and change really are the problem. No amount of fidgeting with ignition timing will sort it.

Now you know why old gits like me get so ratty when old french bikes :'( come on here.

You could always fit a generic chinese engine or even a Villiers?

Have you set the tappets?



Offline Terrotmt1

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #139 on: March 27, 2018, 06:06:41 PM »
I'm sure there MUST be some tappets in there somewhere!
Gave me a smile that one.
I'll ask V Services, but suspect you are right.

Offline Rex

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #140 on: March 27, 2018, 09:26:39 PM »
As a last resort you could post a for sale ad with a nice picture of it, and put that immortal phrase in...."fully restored and now just needs timing doing to finish".
Jury-rigging coil and battery has to be a good way to go, and it doesn't have to be 6V.

Offline Terrotmt1

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #141 on: March 27, 2018, 10:38:06 PM »
What about poor primary compression?
The seals are very weak on this engine by design.
I'm thinking of stripping it all down again and fitting sealed crank bearings maybe removing the inner bearing seal?

Offline The Artful Bodger

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #142 on: March 28, 2018, 12:05:26 AM »
A drop of petrol down the plug hole eliminates the oil seals from the equation, at least as far as staring is concerned. The seals are only relevant to getting the petrol from the carb to the combustion chamber, put petrol in the combustion chamber and it should go bang. Only two other components are needed for the bang, compression and a spark at the correct time.
 Compression on your engine is down to two things, piston and rings being good or the head gasket. Usually you will hear a head gasket, or since you've had it running see some external sign on a leak. Older small two strokes often appear to have very little sign of compression compared to a 4 stroke. One thing which will alter the compression felt is having the carb totally closed, this restricts the air entering the engine therefore how much gets gathered on top of the piston to get compressed.
 Going the battery coil route is always a good test route, only one wire needs to be led into the magneto to the points. Battery pos. goes to the coil, battery neg goes to earth on the engine and the other low tension wire from the coil goes to the points and condenser. Since this doesn't involve the bikes electrics in any way either a 6 or 12 volt coil can be used, just use the relevant battery for the coil.
 Timing can be checked simply by turning the engine over from the flywheel with the coil in circuit and the plug will spark when the points start to open. If not you have a points / condenser issue. Perfect way to test how you've timed the engine as you'll get a spark you can see as you check the piston height BTDC.
  You must be able to get either a cheap coil (older car or bike) from a breakers or cheap off eBay. To test an old battery coil simply put a plug lead into it and a plug, earth the plug to the neg. of a battery and take a pos. and neg. wire from the battery to the low tension side of the coil. Fix one wire and touch the other to the terminal on and off, every time you take it off the spark plug will spark.
  This is all you're doing with it on the bike except the condenser will stop the points from getting burnt by reducing the current across the points face.
  If you intend to have another project bike in the future having a test coil sitting on the shelf ain't such a bad idea?

Colin
1926 Magnat Debon, 1953 Bantam, 1955 Ariel Huntmaster, 1961 GPO Bantam, 1979 GS 850, 2001 Burgman 400, 2004 Burgman 650

Offline Rex

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #143 on: March 28, 2018, 09:13:20 AM »
What about poor primary compression?
The seals are very weak on this engine by design.
I'm thinking of stripping it all down again and fitting sealed crank bearings maybe removing the inner bearing seal?

But this has been the design of it since it was built, and clearly it has/does run.
I would suggest that you have a failing and degraded flywheel mag probably through age, and while it's possible for the plug to give a spark outside the cylinder it's a lot more difficult under compression.
The carb swapping doesn't help, and the continual tickling and choking probably means you get one chance to kick her into life before excess mixture makes the plug even less able to work properly. When it does run the spark will be stronger as the engine is rotating much faster and a rich mixture won't be so problematic, but then the mag is warming up leading to more problems with weak coils, failing capacitors and poor magnetism with the heat.
I still recommend an external coil and battery.

Offline Terrotmt1

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #144 on: March 28, 2018, 09:26:02 AM »
Thank you both so very much, just the info I need.
I have 12v battery and good coils, just not 6 volt, so I can do as you suggest, hopefully today.

I don't want to strip this engine again, making paper gaskets etc is a chore.

The magneto was re magnetised by V Services on their rig, I had no spark at all before that.
Right, that will be the next step to bringing this bike to heel!

Offline The Artful Bodger

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #145 on: March 28, 2018, 10:00:12 AM »
One thing I forgot to mention in the last post was have you filled the crankcase with petrol again? Remember that every time you kick it over petrol is drawn in, if it doesn't fire then it's still kicking around in the engine and exhaust. A wet plug is the symptom of this so a new plug after much kicking over with the plug out will help.
  The advantage of a battery coil is a much fatter spark which will help. The one good thing with a 100cc two stroke is it's a lot easier on the leg than say a 600 single in a non start situation!

Colin
1926 Magnat Debon, 1953 Bantam, 1955 Ariel Huntmaster, 1961 GPO Bantam, 1979 GS 850, 2001 Burgman 400, 2004 Burgman 650

Offline Terrotmt1

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #146 on: March 28, 2018, 01:49:08 PM »
Primary petrol fill;
Yes, I think I have.
During all this kicking I end up trying combinations of choke on, throttle closed, to choke off, throttle wide open.
Some tome ago I tried petrol down the plug hole, not a peep which make you think about the magneto coil.
Last time I put petrol in the plug hole I kicked it to death so somewhere in that lot the mixture must have been 'right' for some kind of combustion.

I did have a leaking head gasket. When the engine ran at a million rpm the oil leaked out under the head to the top fin.
I found an (incorrect) ring in France and fitted that but ended up having two copper rings and the head is tight.
Not ideal. The design is for head-to-cylinder contact with a gasket trapped in a groove. The original gasket was in the engine and is 'C' shaped in section with a fibre in-fill into the C cavity that obviously crushes down when new. The replacement was just a solid copper ring of too small a dia to fill the groove. Cost 30 euros too....

The new contact breaker points arrived today. These are replacement pads to be riveted onto the points. Ordered them ages ago, but will replace the pads, sort the Battery/coil and test.
They are 2 x the thickness of the point pads in the bike.
This will restore the range of adjustment available to get the 0.4mm gap required.

Feeling better today, want that rosette so cruelly deigned me!  ;D

Offline Terrotmt1

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #147 on: March 28, 2018, 05:55:09 PM »
I decided to replace the point contacts before I started which was a bit of a fiddle but all together in the end and I was able to get the 0.4mm gap with the point's heel on the cam.

I rigged-up the 12v battery, coil etc as explained above.
When I made the last connection, earthed the battery to ground on the bike, there was a current flowing. I did not expect that, however:

With the wires all connected (I bought the points/condenser lead out of the lights hole, quite convenient) and the plug sitting on a head bolt I turned the flywheel slowly by hand.

The spark flew exactly on my 5mm btdc ( :) ). I triple checked it, and it was repeatable. I used a heavy gauge wire for the HT lead, doubt that makes much difference for this test.

Put the plug back in, original HT lead back on, and with the throttle wide open got kicking.
After 6 kicks I closed the choke and 3 kicks later it fired and ran. (this is with the large Chinese carb).
Bit smokey; I think I do have too much oil in the fuel so will dilute it tomorrow, but responded to throttle well.
After 10 secs I removed the choke, same smoke level.

The down pipe is still a bit leaky and the residue getting out whilst running is oily where the pipe is clamped to the cylinder head. got to be far too much 2 stroke oil?

After a minute of blipping the throttle I closed it and the engine died after 3 secs, a good stop.

It will not re-start, BUT it tried a few time to re-start.

Time for Tea, so packed it all away, but progress!

Should I try to start the bike with the battery and coil rigged up?
No harm should occur?

I feel that Rosette getting closer.  ;D
« Last Edit: March 28, 2018, 06:30:17 PM by Terrotmt1 »

Offline The Artful Bodger

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #148 on: March 28, 2018, 06:42:52 PM »
Be interesting to see how tomorrow goes, from your post I'm assuming you fired it on the magneto? If so it seems a little playing with the mag gets it going for a spell. Be interesting to try it on the battery coil, if you haven't done so?
 All old two strokes will smoke like mad when started on choke and will take up to a 1/4 of a mile thrash up the road to clear themselves out. We were going to a show once and I made the mistake of following three Bantams from my house, being a sociable fella I made everyone a cuppa before we set off so the engines were cold needing choke to start. I couldn't even see the road for two stroke smoke following them, didn't do my lungs much good either!
  My research on my 1926 M/Debon is to run it on a 10 / 1 mix, I had an old Sea Gull outboard years ago and that also ran on a 10 / 1 mix. The reason for this amount of oil is a lack of oil seals, the thicker "brew" helps the plain bearings to seal. Might be a reason yours is supposed to be running oily?
Colin
1926 Magnat Debon, 1953 Bantam, 1955 Ariel Huntmaster, 1961 GPO Bantam, 1979 GS 850, 2001 Burgman 400, 2004 Burgman 650

Offline Terrotmt1

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Re: Terrot MT 1, 100cc 2 stroke: non-starter!
« Reply #149 on: March 28, 2018, 07:46:55 PM »
I suspect I have too much in the tank. The fuel is a pale green!

I'll dilute it tomorrow and see. Within a reasonable amount, can you have too much oil such that the fuel is hard to start?
When it started last week and screamed it's head off for ages the smoke did disappear after a minute of those revs, so this could all add up.
Will try the start tomorrow off the battery/coil.

The spark I had when looking at the timing seemed as intense as the magneto with plug out.
The running this afternoon was on the bike's magneto.

Fingers crossed for tomorrow pm. :)