My 1943 M20 has been in the garage for 12 months and just wanted to get it started but it's being a bit reluctant, no spark at plug as yet, but ive been given an electric shock from the lead so there's life in the old girl yet (she's been named Doris).
I'm just checking the valve clearances and noticed that if I turn the cam follower by 180 degrees on the inlet cam follower, then the clearance is allot less than when it's in its original position, this is obviously down to wear but has anyone got any advice if the followers have to be replaced and at what point is this a major issue?
Kind regards,
Julian
email (option): 79Aust@sky.com
Hi Julian,
The cam-followers are designed to rotate when the engine is running to obtain even wear. This is done by placing the follower not excactly above center of the cams but at a little offset.
If the valve clearances change when the followers are being turned than I would think this rotating design feature has not worked for a while. Maybe a bend stem or not a smooth surface anymore ??
If you decide to replace them: One of our fellow enthousiast from downunder had a very handy tip for taking out the guides (thanks again!!) : make a suitable socket and to hold it in place with a ring and nut on the follower stems. (and maybe heat the crankcase a little when it is real stuck). I can post pictures of the tool I made, works a treat!.
Good luck!, Michiel NL.
Also bear in mind that the tappet adjustment on an M20 is not the usual procedure due to the overlapping cam and has to be done according to the workshop manual. I run mine at 2 thou under the manufacturers recommended and I gather that Ian Wright and Mick Holmes run even tighter clearances.
Also if you haven't already. I would drain the sump as it's probably wet sumped by now and try a different spark plug. Ron
email (option): ronpier@talk21.com
If you have varying tappet clearance as the tappet is rotated it is most likely that the stem of the tappet is bent...
Should you decide to remove them from the engine for remedial work you will need a puller to remove the cam spindles from the tappet chest as well as one to undo the tappet guides from the crankcase...
The tappet stems can be straightened using CAREFUL application of force applied with a light copper or alloy mallet...The stems will need to be 'clocked' in a lathe or using a V block and dial gauge to check progress...
It is also possible to do this job with the tappets in place in the crankcase if the barrel is removed...It is important that in either case only the minimum of force is applied to achieve the required result or a broken tappet stem will be the result...
Note that the two tappets are not identical..The exhaust tappet has a hard chrome plated 'foot' whereas the inlet one doesn't so they must be replaced in the correct position if removed...
The foot of the tappets should be smooth and unworn..For the reasons noted in a previous post the tappet feet do not tend to wear much...However, it can happen if the engine has been run with insufficient or dirty oil for long periods...If worn they must be replaced...
If that is the case also check the condition of the cam lobes...Minor wear here can be removed using an oilstone...
If at any time the engine has been fitted with the later pattern cam spindles these must also be replaced in the correct position. Later spindles are marked 'in' and 'ex' on the inner end...
The tappet heads are also likely to be worn if they haven't been replaced for a number of years or if the engine has been run with insufficient/dirty oil...
These have a fairly shallow case hardening so simply regrinding and replacing them is not a good option...In that case they will wear again rapidly...
The heads must either be replaced with new components or as an alternative option they can be reground and then rehardened using 'Kasenit' hardening compound or similar....
email (option): ian@wright52.plus.com
Thanks guys for your excellent advise and thanks Ron for your recommendation to drain the sump.
As the bikes been sitting for a year without use, does the magneto need re-polarising and could this be a cause for a weak spark?
email (option): 79aust@sky.com
Now I'm scratching my head and need help please, drained sump and bought new plug NGK BP6HS and set the gap to 0.35mm and can only see a small/weak spark, with a voltmeter it shows up to 16v -18v when kicked over between multimeter lead on the spark plug cable end and the other lead end earthed to a head bolt.
Is the magneto a problem or is any spark a good spark at the plug?
email (option): 79aust@sky.com
never heard of using a voltmeter to check HT voltage. The voltage would be at least 10,000 volts. Get an old spark plug open the side electrode to about a 1/4 inch gap attach to plug lead and earth plug to engine and kick bike over, spark should jump the gap with a nice blue spark. If you have a weak spark outside of the engine it will be blown out under compression.
Thanks for all your advice, I've spent this morning tinkering and now rewarded with a running M20 that sounds and runs a treat. It appears that the magneto had oxidised a little and after cleaning the spindle and polishing the copper spindle ring and graphite pickup the spark suddenly got allot stronger and kick starts first time.
Great to have her back again.
email (option): 79aust@sky.com