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Collection, Preservation and Display of Old Lawn Mowers

Timing on MK25

Hi I brought an Allen Scythe it worked for a week or two and then conked out. It's languishing in the shed and I want to get it going before spring.

There is a spark and petrol flowing and it won't start so I wanted to check the timing. I have taken the centre part of the flywheel off to access the points.

I now need to put it all back together with the timing correct.

I have read the manual here…

But I must admit I still can't work out what to do. Could someone write me an idiots guide to doing the timing?



hortimech Mon, 12/01/2015

Well it has been quite sometime since I last timed a Villiers MK25 engine, but from memory it is quite easy:

Remove flywheel by belting the wrench to shock it undone

Remove and clean the points

Refit the points, making sure to put all the fiber washers back in the right order and place

refit flywheel but do not fully tighten the nut, this is so that the flywheel will spin freely on the crank without excessive wobbling

set points to 12 thou

Spin flywheel to test spark, if no spark, find out why, it could just be dirt introduced with the feeler guage.

If there is a spark, you now have to get the piston to top dead Centre (TDC) and then turn the crankshaft in reverse rotation so that the piston goes down the bore by 3/16 of an inch (this is easier to see if you remove the cylinder head)

Holding the crankshaft so it will not turn, slowly turn the flywheel (in the direction the engine runs) until the points just begin to open. At this point, tighten the flywheel nut firmly. check that the points still are just opening at 3/16 of inch before TDC and if everything is ok, Belt the wrench again to ensure that that the flywheel nut is as tight as possible.

Check spark again.





sam_uk Mon, 12/01/2015

Thanks for your reply hortimech. It's basically what I have been trying to do. However I have been trying to do it with the head on, which basically results in guesswork. I also find it hard to see when the points are opening.

I guess I need to just keep trying :) I'll unbolt the head to see if that makes it easier.

Could you explain this bit of your comment?

"set points to 12 thou"

How do you do that? What does 12 thou mean? 

I don't suppose there is anyone within 15-20 miles of Bristol who could help me sort it out if I bring the mower & some beer tokens?




hortimech Tue, 13/01/2015

I guess I must be a lot older than you and have never really been metricated


12 thou is shorthand for 12 thousands of an inch, which I believe is 0.3mm

You need a set of feeler gauges, these usually have the thickness printed on each blade



wristpin Tue, 13/01/2015

I'm no Allen Scythe expert but the Mk 25 was a big lump of a four stroke and as far as I know never fitted to one. The Mk25c however, was a small two stroke used on many variants of the Allen Scythe.

Could be the reason that you are having problems relating your engine to the manual that you have downloaded?

If yours is a 25C two stroke note that the points gap and timing figures given by Hortimec don't apply. Same for the pre decimal parts prices contained in  the attached manual!

This may be of assistance.

hortimech Tue, 13/01/2015

You can update your knowledge Wristpin, the MK25 was fitted to the allen scythe. there were several engines fitted over the years, not just the two stroke Villiers. When I first started work, I was involved in changing various kaput Allen scythe engines for nice shiny new Kohler K91T ones.


wristpin Tue, 13/01/2015

Noted and updated!

Only four stroke that I've seen on an Allen Scythe was an F15 . The Mk25 must have been a fair old lump hung on the back..

sam_uk Wed, 04/03/2015

I'm at my wit's end with this machine. It's a big expensive lump of annoyance!

Is there anyone within 30 miles of Bristol who could help me sort it out? I'd bring the mower to you and pay you for your time..






wristpin Thu, 05/03/2015

So where have you got to?

Points clean and set at between 12 and 15 thou ?

Timing set at 3/16" before top dead centre?

​Still no spark?


sam_uk Sun, 08/03/2015

Hi Wristpin

I don't have any feeler guages, so I have left the points as they are (I have had a spark all along, so I don't think it's the points that are the problem.

I have had the head off and set the top of the piston 4.7mm below the top of the cylinder housing.

All very frustrating.

I'd love to pay someone to show me how to do it at this stage. Anyone near Bristol?