Ransomes Mercury Villiers 7-1 Engine

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Series3boy
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Ransomes Mercury Villiers 7-1 Engine

I have a Ransomes Mercury, the engine is in good condition I have rebuild the carburettor, change the condenser, spark plug and points. I have a good spark showing and fuel to the engine.

The engine starts and runs but cuts out after about 10 minutes without misfiring and is reluctant to start back up. 

I thought it was fuel starvation but have fixed this problem, the mower still cuts out. I wondered if it might need a new coil? As I have heard that that a weak coil will play up when the engine is under load?

Has anyone had any experience with this engine or coil problems. 

It is quite expensive to have the coil reconditioned so did not want to go down this route if it is not the problem. The coil looks in good condition from the outside has anyone else experienced them failing on this engine?

The engine just stops with no misfire so it starts when it has cooled down so wonder if this points to the cause.

Any help or advice would be great.

Thank you

Rob

wristpin
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As soon as the engine stops

As soon as the engine stops check for a spark. Plug out (HOT) , plug cap off the HT lead, hold the lead with the bare end a few mm from unpainted metal and pull the starter briskly .  If you have a spark it’s probably not the ignition system but remember the condenser can fail as well as the coil.  Worth checking the valve clearances.

Series3boy
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Thank you again for your

Thank you again for your advice, I did what you said and there is a strong spark when it stalls. I swapped the carb onto a mk 7 villiers engine and that ran fine.

So I checked the valve clearances the inlet valve clearance is fine but there is no clearance on the exhaust valve ? Does this sound like the problem as the engine lacks power when hot hot.

I just wanted to check with you before i file the valve stem down?

 

Thank you Rob

wristpin
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Nil clearance when cold means

Nil clearance when cold means a non sealing valve when hot and is almost certainly the cause of your problem.

Make sure that you check the clearances with both valves shut and the piston about 1/4" down the bore past top dead centre. If hand filing the valve stem do your best to file it level and flat. You will need to take a little bit off the stem to create enough clearance for you to lap the valve to the seat with fine paste. That will close the clearance and you will then have to file again  to get your finished clearance. While you are about it, lap the other valve and set the clearance on that as well. 

As you have found, no amount of fiddling with ignition and carburettion will compensate for bad valves - worth spending time getting them right. My book for the Mk7 and 7/1 says 10 - 12 thou for both the inlet and exhaust.

Series3boy
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Thank you again for the

Thank you again for the advice, I have a lathe do you think I would be better off facing the the valve stem off as it would give a flat surface?

Thanks

Rob

wristpin
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With the lathe and requisite

With the lathe and requisite skills you have all that's needed to archive an accurate cut and and remove precise amounts of material . As you have no clearance at all on that valve you can safely remove the minimum clearance, lap the valve, recheck the clearance, do the maths and then remove the precise amount needed to archive the final gap. 

In days of old when cars needed a ten thousand mile decoke and valve job, every village garage had a valve re-facer and stem grinder to do those jobs. I bought my  Black and Decker Valvemaster , very second hand 45 years ago and it has been invaluable.

  

Vernier stem grinding attachment