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Help with JAP Model 0

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Help with JAP Model 0

Post by Rooneysowner on Sun Sep 22 2013, 14:19

I am restoring a 1940 (I think) JAP Model 0 34cc and have hit a couple of problems. I am a new one at this hobby and any advice would be welcome.
1. how do I get the flywheel off to look at the points. They look dirty and appear to be sticking so I need to get at them. I have tried tapping the end of the crankshaft with a hammer but this has not worked. The back of the flywheel is recessed into the magneto backplate so there is nowhere to apply any leverage at the back. I think I may have to buy a puller but the flywheel retaining screws are small and the pullers on line look as if they will be too big to fit the threads.
2. I took the head off to check for piston wear and any scoring. There wasn't any but by the condition of the rings this engine has hardly been run or the rings are new. When I got it I was told it hadn't run for 10 years.
Anyway the problem is that the rings are tight and I cannot get the piston back into the bore. Any ideas how I can do this?
Incidentally when I took the head off I noticed there was not a gasket, nor was there one where the cylinder bolts on to the crankcase. Is this normal?
Sorry to be so long winded but I am a learner so need all the help I can get.

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Re: Help with JAP Model 0

Post by kevjhnsn on Mon Sep 23 2013, 03:07

the jap 34cc i did this summer with the wico flywheel ignition system was a tapered and keyed flywheel to crankshaft
and there was a nut in the end of crankshaft i removed to get the flywheel off, this is inside the pull start pulley if yours has one fitted
so you have to remove the starting pulley to find and remove the retaining nut, only use a soft hammer i.e leather or rubber or the flywheel maybe damaged
as for the piston rings being tight "thats how they should be, but one end or the other on the bore they usually machine a gradeant slop into the cylinder for easing the rings back in the bore ,but you also will need a small piston ring compresser for the size of the piston ,but if your steady you could do it with somone adding a small amount of pressure to the top of piston as you work the rings in one at a time down the bore using clean old flat screwdrivers
and get it going in from one side and then use the screwdrivers to add the rest into the bore,take your time as the are very fragile and crack with ease

as for the head gasket theres usually a solid alloy or thin tin gasket in betwen the block and head
kev

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Re: Help with JAP Model 0

Post by Rooneysowner on Mon Sep 23 2013, 17:15

Thanks Kev, I'll try what you said
Alan

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Re: Help with JAP Model 0

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