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K2F mag auto advance/retard unit

Submitted by russ_payne1 on Tue, 18/04/2023
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Heavy Twins

Does anyone have a spare auto advance/retard unit for a Lucas K2F for a Domi 88/1957? 

Seems very difficult to find - this is the last major headache on my scratch-build 88 which has actually gone very well, thanks to the plentiful parts supply (and, shout-out, RGM !). 

I have bought a really good magneto (big spark @ low revs), but cannot find the auto advance unit and correct sprocket anywhere.

russpayne999@gmail.com  07968 277059

 

cheers all, 

 

 

 

 

Submitted by robert_tuck on Thu, 20/04/2023

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Hi Russ,   These units are usually well worn and the self releasing thread stripped making them not a good bet. You could be better off  fitting up the mag for a manual control . This will give you full control of a slow idle and an easier time setting up the ignition ,plus one more interesting thing to fiddle with.   Especialy nice if you are a control freik like me.Wont be cheaper but more predictable .

Submitted by howard_robinson on Thu, 20/04/2023

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Hi Russ - As Robert says most 'used' automatic advance/retard units are fairly worn out.  The springs are available and the special fitting/removal bolts.  I've also bought the C washer and the top cover that engages with the two pins on the top. Most engineering workshops can re-bush them as well.  If you do go the way of fitting a manual magneto remember that it must be counter-clockwise.  When you time the ignition it is normal to do it with the cam ring in the fully advanced position at 32 degrees before TDC.  Also remember that as you manually retard the ignition you are moving away from the maximum flux density position so the spark diminishes. This is usually fine on an 88 because they are easy to start but not so on the 99, 650 and 750 varieties.  With the automatic advance/retard unit the points always trigger at the point of maximum flux density so the spark is constant.  That is why the Norton factory only specified the manual mags on the 500cc twins. Good luck, Howard

Submitted by david_cooper on Thu, 20/04/2023

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There are two kinds, opposite handed.  Which makes finding one a bit more difficult because I believe the Norton ones are less common.  If you do find one, check the workshop manual picture to ensure it's correct. I have a spare but the wrong one.

Submitted by russ_payne1 on Fri, 21/04/2023

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Thanks everyone - this is all immensely useful info for my first build of a 'bitsa' 88 magneto engine. I successfully built a distributor 99 engine that was a doddle to set up and ran well first time straight out off the shed.  This I think is testament to the Company - the idea of a vaguely 1960 engine being built from bits collected from all over the place, running really well from the start. This is also the idea behind my 88 engine (to go in the Slimline 99 at some point).

I have plenty of experience with the mighty 16H's M01 magdyno set-up, and likewise, that's never caused any issues, but I hear the K2F 88 is a tricky set-up, and I guess I will only work it all out by getting the build done, as you all have clearly accomplished. Jacking the weight-springs with a stud to set it up is in the Hayne's Manual, I just noticed!

Anyway, thanks to a super NOC member, I have the correct unit arriving any day now, so thanks to all - I have copied all the correspondence above and saved in my own help file. 

 

Russ Payne 

 

 

Submitted by david_cooper on Sat, 22/04/2023

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The K2 isn't any more tricky than a single.  It does allow you to cut the engine with the earthing button, which you need since you have no decompressor.

The only tricky thing is if the cam ring is not symmetrical.  So it is worth checking the timing is the same on both cylinders. 

Fitting the bottom bolt is a pain.  You need a spanner with edges ground away.  A special long nut is sold, but won't fit mine because it hits the flanges of the crankcase.  I imagine you could file them back a bit .

 



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