Interesting 2T problem

[Frank]

Chaps, this one has got me scratching my head.

I recently bought the points conversion after a discussion in another thread. I fitted it last night, but could not get the bike to run properly. It went on the right hand pot but the left would not fire. After much fiddling and adjusting, I got it to run on both, but the left was spitting and coughing. Finally I decided to reinstall the old points, get it going and then start again very carefully with the new installation in case I had missed something.

I set up the old points on the right pot, but when I came to set up the left one using my tdc indicator, I found that tdc on the left was coming up at about 3/16 higher than tdc on the right pot; in other words, the left piston is not the same as the right one, which accounts for my inability to get the points conversion to run properly - the timing on the left side was thrown out. My suspicion is that I've got two unmatched pistons in there. When set up on the old points, the bike runs perfectly, as the difference in tdc and therefore timing can be accounted for in the adjustment to the left side points plate.

Until I can find the time to do a proper strip and get the head and barrels off, am I likely to do any harm?

[Colin Sparrow]

I think you may have hit on the problem with the 2T points conversion.

Although on the face of it it seems like a good idea to put both sets of points on the one backplate so that in theory timing one cylinder automatically times the other, in practice the Villiers twins are not always aligned precisely, so the pistons are not quite 180 degrees apart. This seems to vary from engine to engine which is why the conversion works fine on some.

I could not get my 3T to run right after doing the conversion; I've now put it back to the originals and it runs fine.

Such is life...

[Frank]

Thanks Colin

that has put my mind at ease. I'm taking the bike on a fairly long local Club run on Sunday and had visions of cooking something along the way. I figured at first that somebody had bodged a piston in there at some time, then I started to worry that the crank had slipped (I'm still finding my way round the Villiers engines and not sure if the crank is one-piece or built-up). If some aren't quite at 180 from the factory, I can live with that. It doesn't run badly on the original points, but I was getting a super spark with the conversion and it is a pity that it won't have it. I've now got a spare conversion, and perhaps just might happen upon another Greeves that does have a 180 degree crank..............

Your very prompt reply and my feeling of relief are a testament to the utility of this Association.

Thanks once again for taking the time,

Frank

[John Wakefield]

Frank
1) The Villiers crank is a pressed up assy. so it is conceivable that the cranks may not be set exactly at 180 degrees as Colins says. If this is the case then you really do need to dismantle the engine & get the cranks realigned. I must admit this is the first time I have come accross this problem. I dont think they would have been out of alignment when they left Villiers but may not have been reassembled correctly on subsequent rebuilds. Villiers would have had jigs to get it right.
2) Your other diagnosis, one piston being shorter than the other (unlikley but possible) Its worth taking both heads off to see that both pistons come to top of bore. If they do then its the crankshaft thats out of alignment.
3) It is possible that the back plate on the Pete Savage conversion may be faulty & the points are not set at 180 degrees. Maybe you should speak to Pete & return them to him for checking & possible replacement, errors can happen. I have a set of Pete's points in my 4T & they are fine, however I did have to file the adjustment slots longer to get the timing set correctly.
4) With regards the individual timing adjustment on the original Villiers points, I have often wondered why they should be individually adjustable, alignment accuracy of the crank may be the reason.

[Brian Thompson]

Thanks Frank.

Your very prompt reply and my feeling of relief are a testament to the utility of this Association.

Thanks once again for taking the time,

Frank

That's such a lovely thing to say Frank, and I for one really appreciate it, as I'm sure will Colin when he sees it.

Goodness knows we try to get it right, we really do...! Thank you so much for the kind words, it truly means a lot.

Brian.

[Frank]

Next move

After reading John's thorough analysis, I think my next move is to have the heads off and see what is going on in there. One curious thing is that my tdc indicator behaves differently when it contacts each piston; if I'm not careful, it jams up on the right hand one, yet will ride up and over with the left hand with no snagging. I can smell a crank rebuild coming up this winter. But then again, it'll keep me out of the house . As 'er indoors says, all I need is a bunk out there now. I'm working on it.

I can't find any torque values, by the way, so if anyone can give me a clue on the loading on the head bolts and also sequence of doing them up I'd be grateful. And Brian, over my many years of motorcycling (I hate the term "Biking"! I think that Bikers and Motorcyclists are different species. Perhaps I'm just getting old.) I've had all sorts of machinery and been a member on and off of several one-make clubs. No doubt about it in my mind, this one is the best by a mile, for its accessibility, its friendliness and the quality of the advice.

All the best to all,

Frank

PS I've just had a phone call from Pete Savage. He had been alerted by John to a possible problem and was keen to offer me my money back if I was not happy with the conversion. I was able to reassure him that the problem lies within my bike and not with his points set-up. A very genuine and honest bloke!

[merlin]

Have to say my 4T conversion works really well.
Regards
Stuart

[John Wakefield]

Cylinder head torque for head bolts is 220 in/lb sequence is working diagonally from inners. there is a diagram in the Villiers 4T workshop manual (publication VEC 641). You should be able to find one on eBay. Worth having.

[Frank]

Thanks John

I'll keep an eye open for one. I'll also update this thread as and when I take the lid off and see what is lurking inside.

[Frank]

Heads lifted and.....

.........here's what I found. The pistons matched, but somebody seems to have either put a new one in one side or cleaned up the top, as the other one was quite crusty. It was the crust that was sticking on the tdc indicator, while the other one was able to allow the indicator to ride over it. With both cleaned and a dial gauge applied it turned out that the crank is indeed slightly out of true - enough not to allow the bike to run smoothly using the points conversion. A job for the winter to correct this.

In the meantime I refitted the old points and adjusted each side using the gauge. No problems now with the spark. However, I did notice that when I observed the points with the garage lights off, there was a good deal of arcing across them. I had a couple of spare (and I think sound) condensers so I fitted these as a test and the arcing continued unchanged. I re-checked all the gaps with the feelers and all were OK. With the lights on, the arcing across the points appeared negligible, so the question is, how much arcing is acceptable? Have I got two sets of dud condensers, or what?

Any observations gratefully accepted.

Frank

[John Wakefield]

If the condensers were faulty the engine would miss fire & not run properly, unlikley two sets (4 condsensers) would be at fault. If it runs ok I would not worry about it, ride & enjoy.

[Colin Sparrow]

[QUOTE=Frank;3797With both cleaned and a dial gauge applied it turned out that the crank is indeed slightly out of true - enough not to allow the bike to run smoothly using the points conversion. [/QUOTE]

I wonder if slight misalignment is not unusual with 1960's twins. If not, why did Lucas develop the 6CA contact breaker assembly in 1967/68? That unit had individually adjustable points and apparently made it possible to time Triumph twins more accurately.

With more than two cylinders (car engines for example) any discrepancy would iron itself out and not be so apparent.

Just thinking out loud, really, anyone else have any thoughts on this one?

[John Wakefield]

Crankshafts

Which cylinder has the 'new' piston fitted Frank? If its the flywheel side this may point to a previous seizure on this cylinder thus causing twisting of crankshaft.
With more than two cylinders (car engines for example) any discrepancy would iron itself out and not be so apparent.
This problem would not occur in forged cranks (as in cars) as these are machined and ground to fine tolerances.

[Frank]

"New" piston

Interesting discussion, chaps. The crusty one was on the nearside (left) while the cleaner, newer one was on the right, or points side.

[John Wakefield]

Piston

As I suggested, looks like its had a siezure on the right hand cylinder & a new piston fitted, whats the bore like? is it scored? Also check that that cylinder has not been rebored oversize. Oversize should be stamped on piston. Not good practice to rebore only one cylinder, but some may do it to keep the cost down.