Possible nip up seizure

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Geoffrey Lord
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Possible nip up seizure

Post by Geoffrey Lord »

Since I got my 1930 Model A on the road in the spring I have covered over 200 miles of wonderful, trouble free riding. However last week I had my first 'incident'. I was on the return leg of a 30 mile trip going up a long shallow hill when I lost power along with some significant clattering noises from the engine before it conked out. I had the clutch in pretty quickly as I was on the blind side of a bend and wanted to coast as far as possible for safety. I checked around as best as I could given the precarious stopping place and all the relavent bits seemed to be in place still. The engine turned over ok so I decided to attempt a start so at least I could move to a safer spot. It started first kick and seemed fine so I motored to the top of the hill in 1st. Everything sounded normal so I continued on gradually opening up and going through the gears. I got home with no further incident.

There were a couple of things different about this particular ride which are making me wonder about what happened. First it was a cooler day by about 10 degrees than any of my previous rides. Secondly the ride itself was without any stops, there was very little traffic (for once).

So, I wonder if the cooler barrel simply didn't expand as much as in the hot weather? I also wonder if I should be changing to a lighter oil from the straight 40 grade?

The day after the ride I drained the sump on the lookout for tell-tale bits and was a bit surprised by how little oil drained out - probably a couple of tablespoonfuls. I had an oil pressure of about 7psi when riding (up a couple of psi from the summer) and flow back to the tank.

Should I have the barrel off for inspection or leave alone?

I would appreciate any thoughts and comments.

Cheers

Geoff
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Roger Gwynn
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Re: Possible nip up seizure

Post by Roger Gwynn »

Seizures are not unusual on side valves. It has happened to me several times and as long as the bike runs OK, without undue noise I would leave it alone. If it had remained seized for some minutes I would strip it down and check the piston, with a partial seizure I usually coast until almost stopped and then gently let the clutch out, whereupon the engine will re-start. Should it happen again it would be worth having perhaps 1/2 a thou honed out of the cylinder, which is what I eventually did as the beast would seize anytime she was pushed. I don't think that the ambient temperature will make much difference but a higher one could tip it over the edge, consider 200-250 degrees in the cylinder, another 5 in the ambient .... chicken feed. The lower temp will make it less likely to seize as the aluminium alloy of the piston will expand much more than the cylinder, hence the huge gap between the 2 of 5-7 thou, modern machines run .001.
The amount of oil in the sump is correct.
Roger Gwynn, Membership Secretary, curator of the Machine Register and the works drawings. Director of Draganfly Motorcycles, Craven Equipment and Supreme Motorcycles mostly retired.
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Re: Possible nip up seizure

Post by Knud.Degnbol »

I second that. Leave it. It will loosen up later.
Geoffrey Lord
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Re: Possible nip up seizure

Post by Geoffrey Lord »

Thanks Guys, great advice.
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Re: Possible nip up seizure

Post by nevhunter »

Don't go to light (viscosity) oil. They used a 50 grade. A bit of two stroke in the petrol won't hurt a new motor. About an egg cup to a tank. If it keeps doing it hone a bit out of the bore. Nev.
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Re: Possible nip up seizure

Post by JohnnyBeckett »

hi or use a bit of RED X in the petrol
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Re: Possible nip up seizure

Post by nevhunter »

Also when you hone it the ring gaps will increase. Nev
Geoffrey Lord
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Re: Possible nip up seizure

Post by Geoffrey Lord »

Thanks again for the advice. I took it out again today for a short 10 mile run with no issues at all so very happy.
It might be of interest to some that my particular engine (my fathers originally) was rebored to +60 some time quite probably before the war as my father was not a motorcyclist and used it as a generator at home around 1938 before storing it and heading off to the army. When I inherited it it was clear that it had done little work since the rebore (honing marks clearly visible) but had had a seizure. Surprisingly there was no corrosion in the barrel and I simply gave it a hone. The seizure had pinched up the ring grooves which needed a little attention. Running it as a stationary engine was probably not the best thing to do!
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Re: Possible nip up seizure

Post by nevhunter »

If the piston is machined properly the ring land area will not contact the cylinder wall at any time. If it does you risk the nipping trapping the ring in the groove and not having much compression.. Forming a small chamfer with a fine file when the piston is in a lathe helps to prevent the ring being trapped also. Nev
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