Piston Ring Query

Morning All,
after all my adulation about the 4hp Bamford going so well, it's become a very
grumpy starter. So going through the divine
checklist, fuel - tick, spark - tick, compression-hmm, blowing out through the
moving contact on the igniter. I fiddled with
that and stopped the blowing.
Still no start, this engine has gone from being a prime mover to an exercise
machine (Lots of cranking, while adjusting fuel
settings).
It's alway been relatively easy to turn over compression, but it started, so I
assumed the rings to be satisfactory. So out with
the piston and happily, there are no obvious horrors, such as a broken or stuck
ring or a holed piston crown. I can get a 12 thou
feeler gauge in with the ring in the first groove. The other three rings (all
plain with 45 degree gap) are slightly tighter in
their grooves but not much. The piston is 4.75" maximum outer diameter (though
it's a bit less at the crown end) and the rings
are 0.25" wide and 0.155" deep. The piston is stamped -007 on it's crown (James
Bond strikes again in Uttoxeter). The bore feels
quite good, something of a lipat the head end , bit I've felt much worse. At
the crank end, a lip is just discernible for about
90 degrees of the 360 ( from five o' clock to about 11 o' clock).
I can get replacement rings relatively cheaply and quickly, the question is,
with that sort of slop in the groove, should I buy
3/16" wide rings and machine the grooves (or should I say get them machined as
I'm too chicken) true, or is it not that critical.
Could I get away with just plonking in 4 3/4" x 1/4" rings and eliminate the
wear on the circumference of the ring.
What clearance should be allowed if machining the grooves?
Any other ringlore or advice on this matter would be gratefully received.
Regards,
Arthur G
Reply to
Arthur Griffin
Loading thread data ...
12 thou does sound a tad baggy, I have no info to hand but I would suspect that the correct figure would be closer to 5. However the main effect of worn rings/grooves is to draw oil into the combustion chamber rather than lose compression (particularly with a not much:1 compression ratio) hence high oil consumption and smoky exhaust in old cars which still perform perfectly well, hardly a concern on the average SE though.
Also, from your description this is a recent development so, as you are unlikely to have added much to the state of wear of the engine, as long as the compression still feels nice and 'bouncy' I would look elsewhere for the cause of your poor starting.
Ps. Standard separator engine is a pretty little thing isn't it.
Reply to
Nick Highfield
Sorry Hit send before I was finished!
Dont know what sort of mag the Bamford has but try battery and coil (be careful to ensure mag is completely disconnected first, passing a current through it can demagnetise the magnets as I found out to my cost with a webster!). A twelve volt battery and ballast coil pinched out of an old flourescent ligt fitting should produce sparks which look as if they would light water! Probably not too good for the ignitor points in the long run but useful for finding out if that's where the problem lies.
Reply to
Nick Highfield
Thanks for your thoughts, Nick. I had already substituted another (known good) Webster for the Bamford's own, with no change. My feeling is that the compression is just barely enough, and there's certainly fuel available, if the normal slobbering noise from the carb and the amount of unburnt fuel in the cylinder (after a several minute cranking exercise session) is anything to go by.
Nigel McBurney's advice was to try Clupet rings, and that was my initial thought, until I heard about the price, and worse, the 10-12 week waiting time. The Clupet man suggested cutting the cost by using two Clupet rings for the top two rings and plain for the other two. I think I will try four new plain ones which I can get quickly and cheaply and see what the results are. If it's still not good enough.then I'll get two Clupets for the top two rings.
What is the best method for dealing with the ridge at the top of the cylinder? Regards, Arthur G
Reply to
Arthur Griffin
OH. Are Clupets expensive then? I'd never asked ...........
Regards,
Kim Siddorn
Reply to
J K Siddorn
Ah. Expensive but not desperate I'd call that!
Regards,
Kim Siddorn
Reply to
J K Siddorn

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.