Correcting fixed ignition timing

[davidbliss]

Its a bit modern but earlier this year a friend had stood two mowers out to go to the tip, the little rotary no idea of make had apparently been outside for many years all the control cables had rusted off and as being one of the modern types as soon as the hand controls are released it cuts the ignition and applies a brake on the flywheel so couldn’t tell if engine felt good by turning it over. I got if you can do anything with it take it, it was very easy to work on, got the pull start off, flywheel brake tied back and refitted the pull start, it was now nice and free and if you had seen the coil with the rust expanded leaves the coil is on you would have said you’ll be lucky well there was a good spark at slow speed. Cleaned the carb, renewed the rubber pipes, petrol and was away running like a sowing machine until it started to knock and clatter very loudly. It was very lucky as the plastic infill bits on the flywheels outer edge with rust had lifted them and the extra centrifugal stain caused them to catch the coil leg bits so was very lucky it didn’t damage anything. Done away with the powered drive so now easy to push forward and backwards. So now my daughter has a very light easy to use mower and gets on very well with it, that is until the pull start kicked back and bit her a few times one day, I did have it kick back but as long as you pulled it gently over compression and then gave it a good pull was ok, the last time it did kick back it bent the pig-tail some bit thats up the handles. So have had it apart(flywheel was on very tight is a understatement) and the key was intact, only one thing to try I machined a .030 thou stepped key, so fare been gentle as a kitten, just remember its not just a joggle but the joggle is at an angle so has to be set and machined. Anyone know the make as its usual in that engine crankcase splits diagonally.

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[sidevalve5]

That is very interesting. Have a Hayter Condor mower fitted with a Kohler K181 engine that’s always been a pig to start. The automatic compression release does not operate on every pull of the cord. Or it kicks back. It used to burn oil for fun, so I took the engine apart and then got a pattern re-build kit from the USA. After a rebore I put it together and the engine itself ran beautifully. Starting though was still a pain. I adjusted the ACP tab, made sure I still had a 6mm spark in air and the carb was still supplying fuel, but still no better. It’s not helped with the pull cord handle being under the machine’s handlebars. I then got a Ransomes Bobcat zero turn mower, so put the Hayter at the back of the shed.

Just checked the Kohler engine manual and the ignition should be timed to 20 degrees BTDC. Your post have given me some thought and will again have a look at the timing. If anyone has any tips on what to look out for on the Kohler engine, I would be very grateful. From what I understand they are often difficult starters. As the ignition is fixed, the spark excellent and compression was good, I mostly blamed the carb. But think that’s fine, but the timing could be out.

[davidbliss]

I got the key width wrong it was .035 thou wider and that amount of joggle would retard it quite some bit and has worked as with every thing fixed being modern so there no way of adjusting and I wouldn’t have thought such a small engine could be that vicious but it was. I have worked on the really old 40s Briggs with the peg that ran onto the crank then later they ran it off the camshaft that with wear was rather touchy, think the Kohler done same idea. nothing like the good old Villiers.

[sidevalve5]

I had the opposite problem with a Barrowmix mixer that had a small Briggs and Stratton engine on it. I bought the mixer for the drum, as mine had started to rot away (tip, if you are going to store a mixer, do not leave any water in it). Thought I would get the engine going as it seemed like it had not had much work. Could get it to pop and bang, then run for a bit, but no power or even revs. Thought I would check the flywheel key, it is a soft alloy and designed to shear if the engine’s machine came to a sudden stop. It had a step in it which was similar to the 0.035” you moved the timing by. But in this case it prevented the engine from running correctly. Think someone had overloaded the mixer and the key partially sheared. Which was my good fortune as I didn’t pay much for it and now the engine runs as sweet as a nut.

Someone gave me a Villiers armature plate and flywheel with the crank sheared right off. It came from a water pump, the user did not fit a strainer to the suction hose. It pulled up a stone, stopped the impeller and with a steel key the flywheel’s momentum sheared about a 7/8” shaft as clean as a whistle. Have a Villiers Mk25c on a Clifford roteo, when I replaced the coil I only gave the flywheel nut a few light taps to tighten it up and glad I did. I hit a big stone, the engine stopped dead, but the flywheel moved on the taper, so no harm was done.

Yes, there is a little plunger rod on the Kohler that operates the exterior points and when it kicks back it is really vicious. Looking at the manual it appears that fine tuning the timing can be done by adjusting the points gap. But have not done this before, have always set the gap to the manual’s recommendations. Would be good if anyone has had a similar experience to me with Kohler engines and subsequently have got the ignition set up spot on to get them to start better. Am going to dig the Condor from the back of the shed this weekend and have a look. Don’t need a mower at the moment though. In the Vale of Evesham we have not had any significant rain since the end of Feb. The grass is not growing and feel for those who make a living from the land.

[andyfrost]

Grahame , if you don’t mind me asking , which model Villiers was the one with your sheared key problem , I’m guessing F series ???.

Andy.

[sidevalve5]

Hi Andy,

I do not know the model the armature plate and flywheel came from. I purchased a Clifford roteo with a Mk25c engine about 15 years ago. The vendor was honest and said he thought the coil had packed up and suggested an external coil from a Honda C50 could be rigged up as a fix. Did try, but through lack of knowledge I think I omitted to remove the secondary windings from the duff coil. Also it was highly likely that the original coil still did not have enough primary windings to induce the secondary. The ratio needs to be around 100 : 1. A friend gave me the parts with the sheared shaft to see if the coil would fit. It didn’t, so I got a replacement that George Shead was selling at the time that required a little bit of work to fit. I have never tried to remove the sheared shaft from the flywheel to see if the woodruff key has bent over or sheared too. In fact I do not even know if there is one, it could be just a plain taper like the Mk25c. If so, its an example of someone over-tightening the flywheel nut.

David’s post has reignited (pun intended) my thoughts about the timing on my Kohler K181. The Condor was always a bad starter and it was not helped with the usual drag problem with belt clutches preventing the engine from turning over as rapidly as it should with a hand start. When I got the Ransomes Bobcat, I retired the Hayter. After I wrote my reply yesterday I did a bit of research and found a lot about timing the K series engine. Apparently unless the ignition is spot on, the problems I was having manifest themselves. One chap said he initially set the points to 0.020” and even reducing it to 0.018” with static timing from the flywheel marks made a vast improvement. Others say more accuracy can be obtained with a strobe. But the consensus was that just setting the points to 0.020” was not good enough, they then need adjusting to the timing marks. If using a static method, the old fag paper trick is not good enough, you need a multimeter. Many years ago I had a tuned Yamaha RD400 with a twin set of points and ignition timing had to be checked every 700 miles. I got a plug adaptor so a dial gauge could measure the piston position to 0.1mm and used the multimeter to see when the points opened. Am going to have a good look at the Condor this weekend and give the ignition timing a thorough checking over. Looking forward to it.

Grahame

[andyfrost]

Ah , I read in your previous post that you said it had sheared the steel key , if it were a MK12 , which was the most common Villiers fitted to Alcon and like type pumps , it would have taper lock timing , if it were an F15 or F17 , then yes it would have keyed ignition timing.

Andy.

[sidevalve5]

This old dog leant a new trick. The problem with the Kohler ignition timing was twofold. Firstly, the manual’s instruction was incorrect. It stated that the points should start to open when the flywheel timing mark S was next to the armature plate mark and AFTER that, adjust the points gap to 0.020”. Yet this action altered the ignition timing. The correct method, which I found by reading posts on forums, was to set the gap and THEN adjust it so the points open at S. I originally followed the manual’s method and it resulted in the timing being too advanced by 8 degrees. The engine was difficult to start and in the end, impossible. The second problem was that I did my usual method of honing out pits on the point’s contact surfaces. This resulted in changing the timing and something I was not aware of. When I tried to adjust the points so they open on S, they did not open at all. The fix was to file some material off the heel that goes against the rod that opens the points. However I am going to get a new set of points as they are readily available.

The engine still did not start after the third pull, which is what I like them to do. It did get going in the end though and ran well. Am still not sure if it’s getting enough of the correct fuel/air mixture in the combustion chamber to start easily. Also it’s big heavy lump to pull over, the recent rebore meant it’s still a little tight, the starting handle position just below the handlebars is awkward and the belt clutch on the mower deck creates a lot of friction. All combine into me putting in a lot of effort and still having just one 4 stroke cycle which I hope will fire strongly enough to go to the next cycle. But at least I have a good runner now, the timing was the key and it was David’s original post that set me on course to fix it. It has also made me think that if an engine is mechanically good, the carb appears to function correctly and the spark is 6mm, but it is still a poor starter. Then the timing could be out and from now on am going to check this on ignition systems with points. From what I have read in the forums, wear on certain parts in old engines can effect the ignition timing. If I get this problem on what should be fixed timing and going to use the adjusting of the points gap as a method to getting it to the position the manufacturer’s recommend. Got to be careful the points still have a gap that is close to the recommendation too as otherwise the dwell angle may not be right.

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