Terrot MT 1, 100cc 2 stroke: non-starter!

[Terrotmt1]

Hello, I am at the near end of my restoration of my 1950 Terrot MT1, very much the French equivalent of a BSA Bantam.
single 2 stoke, all stripped, new rings, super clean carb and re-magnetised magneto. Fat blue sparks when you turn it over by hand on the kick start.

Should start?
Not a chance. Fresh fuel etc but absolutely nothing.
The plug has never got wet while I have tried and tried to get it going. I've tried Easy Start too, nothing. All the passages in the barrel are clear as is the lower crank case, head gasket it tight.
I've tried different timing positions, the French say 5mm piston Down from TDC, I've tried this and 2mm, nothing. Points gap is 0.4mm.

The fuel level is exactly to the top of the vertical main jet that the tapered needle goes into, the carb is an AMAL/AMAK and every hole (there are not many) is clear.

I am at a loss what to do try next, but the skip next door is tempting....
What am I missing here?

Hope somebody can help. The people on the Terrot.org site are not very forth-coming.
Thanks, Graham.

[33d6]

Two things.
First. the initial start of a two stroke after an engine rebuild can be a right stinker. No problems after that first start but that first start can drive you nuts. Don't ask me why. I've been known to use a large socket mounted in a big drill to spin an engine over at warp speed in this situation. It worked.

Second, the dry plug is telling you something. It doesn't matter what you say you've done if the plug is dry then no mixture is getting through the engine up to it. What does it have in the way of crankcase seals? Some rely on the presence of a lot of oil to work efficiently.

Many two strokes need a good flooding for the initial cold start but not once they're warm. Yours sounds as if it may fall in this category.
Cheers,

[Terrotmt1]

Thank you very much for your reply. Another has said the first start is 'irritating'...
The engine has 2 seals, felt, in steel carriers. There are no spared for these engines, so I put them back, but just how effective they are....
The dry plug is a real signal as you say, and it seems to refuse to send a charge to the chamber.

I will see just how leaking the case is today. I'll hold the crank at 1/2 stroke which I think will have the inlet port exposed, the exhaust masked by the piston and with an foot pump pressurise the chamber and listen.

I had already thought of using a power drill to wind it up, but not sure if I could get the 16mm socket off the crank/flywheel nut fast enough if it fired.


If I have to I'll pull the whole engine apart and fit modern sealed brgs as a last attempt.
One seal is shown (# 33457) but the magneto side seal is missing off this diagram (it is the factory drg)

http://terrot.club.pyreneen.free.fr/basse_resol/pieces-detachees/100/mt1/pd6-22.jpg

[murdo]

Looks nice job.
I have used the 'big drill' and socket many times on a Villiers engine. The socket will usually just fall off when the engine starts, if not stop engine and try again.

[Terrotmt1]

Thanks, it is a nice bike and I chose it to have a bit of a challenge after the easy-but-expensive Lambretta and the similarly ££££ Honda CB 175.
I was hope for this start-up to be easy!

Getting info on this bike is hard work, even the French Terrot site is lacking in response as these bikes I think were not popular in their day. Parts are even harder, no gasket sets etc let alone more intricate parts, like crank shaft seals!

[33d6]

It sounds like your seals are worn out. Personally I would prefer to make new felt seals than use sealed bearings but that's just my preference.
If you talk to an industrial felt supplier you will find they have very constructive suggestions on how to go about it, what clearances would be appropriate and what grade of industrial felt to use. I would expect it to be the hardest grade. Some suppliers can make up the seals for you but if not they can be water jet cut very accurately. They need to be an air tight fit on the crankshaft with the oil soaked in to provide the air tight seal. I would soak them in oil for at least a week before fitting.

Let us know how you get on.
Cheers,

[Terrotmt1]

Yes, I am sure you are correct.
It is not too tricky to get to the seals which are both felt in a steel ring.
I have just looked at Nitrile rubber seals, the type you have in modern machinery as opposed to the oil impregnated felt, but will try to get close to the original design first.

Modern 2 stroke engines seem to hold 6 or so psi case pressure for minutes under test, surely felt seals can do that?

Hope to get the seals out today, will report back.

[Terrotmt1]

Did some probing this morning. Set the piston at TDC and put some air pressure into the case via the inlet manifold having removed the magneto and the clutch side cover.
This exposes the 2 crank seals so with some soapy water drowned the magneto side. Air simply gushes out of the seal!
On the clutch side there is no air passage at all, possibly because the other side leaks so much.

next stage is to try to seal the mag side seal to force the pressure against the clutch side seal.
The crank case gasket seal is leak free.

Hard to take a picture while pumping air into the engine by hand!

[Terrotmt1]

Well, another few hours in the garage, but little progress.
Suggested by a French Man, I sealed a  latex glove onto the inlet port and turned the engine over rapidly using a socket set with the plug out.
The glove inflated! Thus there must be a pressure coming out of the case to the inlet manifold.

This cannot be correct.

The 'seal' on the magneto side is in fact a brass bush neatly machined with a revers 'scroll' to return any oil back to the case and away from the magneto.
Thus, absolutely nothing I can do to enhance the seal.

Bad bit is I had to tear the whole engine down to find this out!

Half way back together, but the assembly of the (un sealed) kick-start shaft refuses to line up so enough for the day. Another play tomorrow.

There are no seals on the shaft and it sits right in the bottom of the oil sump that serves the gearbox by splash lubrication, so I am expecting the oil to simply come out of the bottom where the shaft comes out of the case!
Stupid design!?

[Rex]

I think you'll find it's common for two-strokes to puff out the inlet tract.
Way back when scooters were cool a workmate had a Lambretta with a polished alloy external air intake. At tickover it was possible to see oily mixture coming back out of the inlet.
As for "stupid design" it's lasted this long so can't be that bad!
{Though that said, it is French!}

[chaterlea25]

Hi
There is a business near me that makes all kinds of custom seals
Their CNC "lathe" turns out many different designs at very reasonable costs
They have made seals for my projects as small as a 3 x 3mm section
http://www.abbeyseals.ie/
On a recent project engine I shortened the bush in the clutch chainwheel and fitted the custom seal
In a bid to keep the heavy gear oil away from the clutch

From my limited experience of 2 smokes with plain crank bushes (seagull outboards ) 
they need a high oil / petrol ratio, 10 or 12 to 1
usually SAE40,
I don't think modern 2 stroke oil works with them ?

John

[Terrotmt1]

Thanks John.
Terrot designed this engine this way as a cheap but reliable bike and there are YouTube clips that show them firing up in one kick!
The crank runs in 50mm dia ball bearings, the magneto side has this 15mm long bush, about 12mm ID and the scroll cut into the inside bearing face. Other (clutch) side is a simple felt seal.
So the mag side has a large ball bearing and then immediately the brass sleeve running very close on the crank shaft.

I'm going to leave this arrangement as original and try to sort out why there is a positive pressure from the inlet manifold when the engine is turned over quickly.

I think the piston is worn.

[chaterlea25]

Hi
There will always be some blowback pressure with two stroke engines turned over at low speeds
due to the transfer ports being open after the exhaust port closes as the piston rises
when the engine is running gas inertia reduces this to negligible amounts
Apply some heavy oil or grease to the bush and felt seal to see if it will seal enough to draw fuel into the engine

Theres no harm in using modern materials to get and keep an old bike running
If the material was available back then they would have used it

John

[33d6]

The close fitting bronze bush type of crankcase seal works very well. My vintage Villiers two strokes use nothing else. In fact their crankshaft main bearings are nothing but a long bronze bush on each side. It was common practice in early two strokes.  Making sure these plain bearings are properly lubricated does emphasise the need to use the manufacturers recommended petrol/oil ratio and not reduce it because "modern oils are better". (I never could see the thinking behind that one.)

And as CL25 says, there always is some blowback from the inlet manifold. It performs a useful function in keeping those old fashioned wire mesh air filters effective by constantly spraying a little fresh oil on them. The mesh stops gravel getting in the motor, the oil catches the fine particles.

It sounds like you have the seal problem under control. I look forward to you reporting the engine start.
Cheers,

[Terrotmt1]

Thank you both.
I imagine the faster the engine turns the less leakage as the change cannot move fast enough to leak out, but I'll measure the piston skirt clearance while it is apart again.
I've rebuilt far more complex engines than this one so frustrated this simple device is so troublesome.

I have another far larger project that needs starting asap and wanted to get this bike done to make way.
Time slips by quickly!