Re: {Neracar} Digest for neracar@googlegroups.com - 4 updates in 1 topic

[Joe Joseph]

 I have a US Model B two stroke, with a standard cast iron piston and crankshaft. While not silky smooth (!) it doesn't vibrate to the extent that the whole machine shakes - it just numbs the hand after a while!!

Do you mean the 255cc engine, rather than the 285cc? The piston pin boss on my cast iron piston measured 15.96mm and I used a Yamaha pin that measured 15.99 (16.00mm). Of course, I cannot find the receipt for the pin I ordered and so can't tell you from which Yamaha it came from. I believe Scott.Parts.Co.UK have piston pins that will fit.

I have a standard cast iron piston and crankshaft, but don't know the balance factor. I assume your main bearing is in good condition?

On Wed, Apr 7, 2021 at 5:33 PM <ner...@googlegroups.com> wrote:

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• Simplex engien - 4 Updates

Simplex engien

andy pugh <bodg...@gmail.com>: Apr 06 10:44PM +0100 > I have owned a 1925 Neracar MK B since 2014. I also have aquestion about the simplex engien: do the 2 storke engiens vibrate very strongly ? > when you accelerate it shakes the whole machine, the front fende has already cracked.   Mine vibrates a bit, but not to the extent that you describe.   Do you know if it has the original piston? Someone here a few years ago calculated that the engine is over-balanced, in that the crank weights are a bit bigger than necessary for the piston. So if, for example, your bike has an aluminium replacement piston that is lighter than it should be you would get vibration.   It is also possible that the crank-pin / big end is worn or that there is a problem with the engine bearings.   I have had a problem with mine where the rivets holding the flywheel to the keyed hub became loose. That created a noise, but not really the vibration that you describe.   -- atp "A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics." — George Fitch, Atlanta Constitution Newspaper, 1912

Franz Rongen <fron...@gmail.com>: Apr 06 03:38PM -0700 Thank you for your prompt replay. We have re-stored the crankshaft. Yesterday I removed the cylinder to check the piston ,wich is made of cast iron and very heavy . However , the piston pin has som play. Likely that will be the culprit. You don`t happen to know the weight distributon from the piston to the crankshaft of the 285cc engien ?

andy pugh <bodg...@gmail.com>: Apr 07 12:02AM +0100 > Thank you for your prompt replay. > We have re-stored the crankshaft. Yesterday I removed the cylinder to check the piston ,wich is made of cast iron and very heavy . > However , the piston pin has som play. Likely that will be the culprit. You don`t happen to know the weight distributon from the piston to the crankshaft of the 285cc engien ?   I don't.   I have several Model A engines that I could weigh, but that wouldn't help.   -- atp "A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics." — George Fitch, Atlanta Constitution Newspaper, 1912

Ben <b.geu...@hccnet.nl>: Apr 06 10:29PM -0700 Hello Franz, I encountered the same problem and secured all bolts and nuts with Loctite medium strong. Later found that the engine was overbalanced. I made a new piston which is hevier than the old one. By increasing the weight of the piston with piston rings from 423.3 to 533.9 g, the balance factor was reduced from 70% to 58% . This reduced the vibration, which we could measure with sensors. But, the vibration was certainly not over. See atachment for details. More details upon request. Good luck. Ben.

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[Franz Rongen]

Hello Joe Joseph,

a Simplex motor is installed in my Neracar.

We have all replaced the bearing on the crankshaft, unfortunaly we didn`t look closely at the piston pin, which is now 15,85mm. 

We will open the engine again to measure the weights so that we can balance the engine.

Have you alredy drive your Neracar , how fast can you drive with them ?

Thank you for your tips too.

Nice weekend

 Franz