Mountfield SV150 - No Spark

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Chris G
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Mountfield SV150 - No Spark

Hello all,

I am new here, so if I have posted this in the wrong place, my apologies up front..

Looking for some advice on getting my old SV150 started, it was getting a bit hard to start but now will not start at all.

I am getting fuel (and a wet plug) but no spark, so I ordered a replacement coil module, but still no spark. Plug is gapped correctly and I have tried another.

So I am thinking it might be the brake switch? I have cleaned it and it seems to depress and release ok but as its a sealed unit I have no idea if its actually working ok..I can't see what else would stop it from getting a spark.

I have seen the whole break / switch assembly on ebay for sale for about £20, but after buying the coil module and it still not working I am a bit weary..

Would you think it is likely that the break switch is at fault?

Is there a way to over ride the break switch to test if that is the issue?

Can the switch be purchased without having to but the whole break assembly?

 Many thanks for any advice, 

Chris

hillsider
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Hello and welcome to the OLC

Hello and welcome to the OLC Forum,

Your first move is to follow the cable attached to the brake switch back to where it attaches to the ignition coil. Disconnect the cable from the coil then check for a spark if a spark is now present and the engine is able to run you have isolated the problem to the brake switch or the cable attached to it. Check that the cable has not been trapped or damaged anywhere along its length - I have seen a couple of these where the cable has melted and stuck to the engine causing a short to earth.

You should also check the brake switch itself preferably with the aid of a multimeter, sometimes the switch plunger becomes stiff from accumulated dust around the switch plunger and a squirt WD 40 or similar will normally cure that problem. I have also seen engines where the operating lever has become bent over time and requires a small adjustment to reset it.

When the brake switch is working correctly you can usually hear the switch contacts click as they make or break. 

 

 

Chris G
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Hello Hillsider, thank you

Hello Hillsider, thank you for the welcome!

I follow exactly what you are saying, great advice.

May have to annoy the wife and give it a go after tea :-)

Fingers corssed.

Best

Chris

 

 

 

 

 

Chris G
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Fired up first tug!

Fired up first tug!

Many thanks for the advice.

I will check out the cables / routing / bad wires better tomorrow, but admit it all looked ok.

If it does end up being the switch itself, any idea if these can be had seperatly?

Cheers Chris

 

Bozzy87
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I believe the switch comes

I believe the switch comes with the brake assembly.

type this number in to google,118550021/0. Pretty much anywhere sells them as it is a common problem with the engine. 

sourced from: https://www.worldofmowers.co.uk/mountfield-spare-parts/ggp-engine/lawn-m...

hope it helps.

 

 

Chris G
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Thanks Bozzy,

Thanks Bozzy,

I can't seem to find the switch sold separately either, have googled the name and serial number on the switch to no avail, so will bite the bullet and buy the whole mech, which is a bit annoying as it looks like a 50p switch!

Oh well, safer than pulling the spark plug cap to stop it :-)

Cheers

Chris

 

wristpin
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That switch is very similar

That switch is very similar to the ones that were in old style dial telephones and also to the ones in the motorised valves in my central heating system. RS Components (Radio Spares) are almost certain to have one. The switch itself has probably got its manufacturer's name molded into it.

Search on Micro Switch - there are lots

eg

http://www.ebay.co.uk/itm/Micro-Switch-Lever-Vintage-Radio-Spares-317-88...

Here's another. UK seller free postage!!

http://www.ebay.co.uk/itm/Push-Button-V3-Microswitch-SPDT-16A-Micro-Swit...

I'm told by a man who knows that they respond to a squirt of contact cleaner.

Bozzy87
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Unfortunately, manufacturers

Unfortunately, manufacturers who know they will make £0.02 from selling a micro-switch, will tend to attach it to something more substantial and raise the price, therefore making some profit and worth making the items, especially when it is a known fix to a common problem.

I cannot for the life of me remember how they are attached to the plate (screw/locator pin/glued) but it may be worth going to a local recycling centre and stocking up on a few for next to nothing if you are mechanically minded. There tends to be a few of these at most tips with a con-rod through the case etc.

otherwise as suggested... find someone like RS who will sell it im sure, as a seperate item..

Chris G
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Thanks both very much,

Thanks both very much, especially as this is not particularly a vintage mower - although I must admit I am getting somewhat tempted to dip my toe :-) I work on air cooled Kawasaki motor bikes as a hobby (some of them turbo charged) so I'm not too bad on the spanners but definitely a metric man in this imperial world! 

Those links show very similar switches, the switch is positioned on the plate by screws and the mounting point has to be the same for the cam part of the mech to actuate the switch, similarly the switch arm needs to be the same length / position. But it can't be a unique switch so will be making a nuisance of myself with RS! 

From memory RENEW is the manufacturer stamped on the switch, I am going to get all the numbers and spec off it and ping RS an enquiry. Electrically I think the one on the mower is a Norwegian Blue, I can get no continuity or resistance readings from the contacts, before or after contact cleaner / air line treatment. I will of course be cutting it in half to see once I get a replacement - sad I know..

I basic service my dads Honda every year, may have to ask him if he would be interested in an older machine as a project...may need a roll cage tho, most of the repairs I have done on it are where he has managed to propel himself through the neighbours fence - quite an achievement for a 90 year old !

wristpin
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https://www.ebay.co.uk/sch/i

https://www.ebay.co.uk/sch/i.html?_odkw=micro+switch&_osacat=0&_from=R40...

This one appears to have the screw holes and lever in the right places and from a UK seller at couple of quid with free postage has to be worth a punt.

Who dares wins........!

Chris G
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Cheers Wrist Pin, looks good!

Cheers Wrist Pin, looks good!

Punt taken and will report back.

Best Chris

 

Chris G
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I received the switch and

I received the switch and after some small modifications in shortening the lever, removing the additional output tab and making some wiring & connectors (as these are push fit connectors rather the original screw on type) tested all connections and installed. Nothing, not a peep.

At this point I am quite perplexed.. It has to be the switch, because bypassing proves this, and it can’t be 2 duff switches and a switch is just a switch right? – Well, it does not appear so. When I looked carefully at the microscopic writing on the original micro switch, I see it is rated for AC & DC - the replacement one for AC only, Googled it a bit and there is an electrical reason why an AC only rated micro switch will not work in a DC application – I lost consciousness reading about it as many would reading this J

Not to be beaten,  another look on the auction site comes up with the exact AC/DC rating albeit slight lever arm and tab mod needed as before.  £2.50 for 2.

http://www.ebay.co.uk/itm/1-x-PAIR-Momentary-Lever-Roller-Micro-Switch-AC-DC/272553976077?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2648

Installed, started first tug, happy bunny J

In the unlikely event…Hope this helps anyone with the same issue, and thanks guys for the help in solving it!

hillsider
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It sounds as though you are

It sounds as though you are on a steep learning curve about micro switches.

First a question - have you proved the operation of your switches using a continuity tester? This would show you if the switch is actually operating.

I suspect that your replacement switch could be wired to be normally open or normally closed - you mentioned removing a spare terminal. If you had used the second terminal your result might have been different,

 

wristpin
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As soon as I read about

As soon as I read about removing the " spare " terminal , I had the feeling that  I knew what was going to follow!!!

AC or DC no issue in that application but knowing whether you need naturally open or closed definitely is! The rejected switch offered the option.

 

Chris G
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Hillsider, Wristpin, Pictured

Hillsider, Wristpin, Pictured from left to right..

1st is the original switch

2nd is the AC rated only switch which did not work

3rd is the AC/DC rated spare unit, the other which is modified to fit & and working.

The terminal connection diagram on all 3 is identical

The originally installed switch also has the 2nd same tab removed as I did.

Plain continuity did not flow on the OE switch but did on both 2nd & 3rd including modified connectors.

Possibly the 2nd switch could have been faulty and it has nothing to do with AC/DC rating. But if you are saying the removed tab would have made the circuit good then I think that is wrong given the wiring diagram on all 3 switches and the fact that the OE switch had the same connector removed.

hortimech
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If you look at the terminals

If you look at the terminals on the original switch, there should only be continuity between them when the lever is pressed down, this is because it is an normally open (NO) switch.
Normally open means that current doesn't flow through the switch until it is operated by the lever. If the second switch doesn't work in this way, then it may be a normally closed (NC) switch, (the circuit is opened when the switch is operated) but from what is shown on the switch, it should work like the original switch. The third switch is a bit different, mainly because it has three terminals and as such, can be an NO or NC switch, depending on how it is wired. Using the same terminals as the original switch, it would be an NO.

If the second switch does not have continuity without the lever being operated, it is NO, if it does have continuity without the lever being operated, it is NC, if doesn't have continuity whether the lever is operated or not, then it is faulty

wristpin
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Don't think that anyone has

Don't think that anyone has suggested that removing one terminal  would " make the switch work" ; what it did was to remove one of your options in setting it up as normally closed or normally open.

If you consider what you are trying to achieve it's not difficult to work out which terminals to use. In your application you need the coil to be grounded when the OPC bar is released and the brake applied ; so with the machine at rest with the brake on it just necessary to select which of the two terminals are showing continuity . Then just a matter of connecting one to ground and the other to the coil.

Considering that an instant cure in the form of a complete Mountfield switch / brake assembly costs a bit north of twenty pounds, a couple of quid for a switch and a bit of thought has to be worth while.