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[555]

Have started the strip down, the plug was a bit black and sooty, would that not suggest a rich mixture? Or is it oil getting past the rings? The bore looks ok, but will do a closer inspection in the daylight. The bore was matched to the piston by a reputable company so as far as I can see it the only possible problems are

1 Oil starvation, - on stripping looks like there is pleanty getting around
2 Weak mixture, - I had it set on the middle notch, so move it down to the bottom notch, lifting the needle up. Amal carb by the way
3 Timing - I had it serviced not that long ago, distance wise. Would have gone off since then?

So other than inspect for scoring on barrel and piston and fix. Richen the mixture, and check timing that's it?

Any simple ways to check the timing?

Thanks
A

[another Allan]

Not really a suggestion for a solution to the problems you're having, but has the same 'reputable' company you mention carried out all the work on your bike? Is there a chance that they are getting it wrong consistently?

[Mark M]

Keep going with the engine strip and find the source of the problem first before you go back to asking questions about the carb or anything else. In any case, just playing with the needle position won't make much difference (if all the other carb settings are correct) certainly not enough to make it seize from weak mixture. Your problem may not be piston to bore seizure in any case so speculation at this stage isn't helpful. Stick at it, you'll get there!

REgards, Mark

[Dennis C]

The problem now with these old design engines is that current reputable companies don't understand that they are designed to run a greater piston clearance to modern engines and they are prone to re boreing them too tight.

[PeteF]

I second Dennis on this. I would be carefully measuring the bore and piston to see what's what.

[WDCO42]

Hello 555, Here are Hepolite instructions for clearance (revised february 1968 !!) :

"Pistons : Cylinder bores must be finished on the nominal size (as shown on the label of the carton), plus the required oversize to a tolerance of - .0000"/+0.0010" or -.0000/+.25mm

"Piston rings : all engines, except air cooled racing engines, .005" per inch of bore (.127 per 25.4mm)"

I allways have, for my CO (70mm bore), at least 0.10mm oversize, for instance.
Hope it will help you
Claude

[simon]

.0035" at the bottom of the skirt is I believe the advice from Mr H. Seemed to work ok for me although I have also run bikes with .005" clearance with no worries and no noticeable knock.

[papasmurf]

Frome the manual for my Electra X piston to bore clearance New minimum, 0.08mm, New maximum, 0.10mm Service Limit 0.30mm.

Personally I would have thought 0.08mm a tad tight for an air cooled engine.

[Nettshubby]

WDCO42, if the tollerance is zero to 0.001" then that should be zero to 0.025mm, not 0.25mm. That is 0.010". Prbably a quick miss press on the keyboard?

[Dennis C]

We are as expected getting various different clearances advised, this is not really surprising as different makes of piston will need different clearances.

Most reputable makers supply full instructions either on the box or on a slip inside if this is not supplied it is best to go for a higher clearance or if bought from our host then they will give the best advice.