Help me....Motobecane engine saga continues...

I installed my spare engine with new rings and gaskets on my '77 Motobecane tonight. When I first tried starting her up, I had nothing. No engine starting noises whatseover. I then checked for spark, but couldn't see any, so I cleaned up the points. I also installed a cleaned up spark plug (not new). I checked for fuel flow and it was OK. This time I got a spark and tried to start her up again. The engine did make some turning over type noises, pops, etc., but nothing that was sustainable. The throttle had no effect on turning the engine over. After a few attempts, it wouldn't make any kind of starting up noises until I pulled and cleaned the plug. The plug would be covered with gas.

Where should I look now? This engine had not been run in several years. The points had a lot of white powdery residue on them before I cleaned them up. I have not yet attempted to adjust the timing. I do not have a compression gauge, so I couldn't check for low compression. I just had the cylinder honed and new rings installed.

Please help me avoid using the sledge hammer on this bike.

Thanks,

Larry

Re: Help me....Motobecane engine saga continues...

david f martin /

Pull the spark plug, spray some WD-40 in the spark plug hole, try it again tomorrow.

david

More info....

David,

Because the wire from the coil to the condensor (flywheel) had been cut, I had to use an electrical connector thingy to make the wire long enough to reach the condensor. I used one of those quick connector type fittings. Could this connection weaken the electrical flow enough to cause the bike not to turn over? I'm not sure what is meant by a "fat spark". I get a blue spark, but not what I would consider "fat". Also, if I removed the cylinder to replace the rings, etc., would the timing automatically be off?

TIA,

Larry

Re: More info....

Don't worry about timing for now .. removing the head and cylinder will have no effect on timing.

GET A NEW SPARK PLUG .. get a couple .. run the W&D sandpaper thru the points and clean them again.

Thats probably all it needs.

.. one of those electrical splice connectors should work fine for now .. (though I always try to solder any ignition connection like that .. as a more permanent reliable fix)

Re: More info....

Hi Fred,

Thanks for the advice.

I don't have a compression gauge, but I placed my thumb over the spark plug hole as your guide advises, and had my son pedal. My finger was not "blown" off the hole as I thought it would be. Do I have low compression?

The only thing I did which could possibly be related to the problem is that I used an "E" marked piston with an "L" marked cylinder. The "E" cylinder that I have developed a small "hanging spot" when I had it honed, so I opted to use my spare "L" marked cylinder. Could this be the cause of the problem?

I was really trying to get this bike road ready by the end of the week, but my hopes are fading quickly.

Thanks,

Larry

Re: More info....

Oh well .. I know next to nothing about Motobecanes .. So you've got me there .. you will heve to get some info from somebody who knows thern.

But .. with a freshly honed cylinder and new rings and some oil on assembly... it should certainly blow your finger off the spark plug hole during cranking .. if your finger was a 'tight seal' so to speak.

One thing you should do is check the piston to cylinder clearance .. (you can use feeler guages for a good rough measurement)

Check it at the base of the cylinder and the bottom of the piston .. stick feeler guages in there and see how much of a gap there is ... I would think it should be less than .003 or .004"

Re: More info....

david f martin /

Sorry, Larry. I just re-read your first post and realized you've replaced the rings and had the cylinder honed, so WD-40 shouldn't make much difference. I was giving you advice for a piston and rings that have been sitting for a long time.

How much did you have the cylinder honed? Did you get oversized rings (I'm not sure if they exist)? You may have to go with an oversized piston to match the bore.

With a Honda engine, you can just take the piston and cylinder to the dealer and have them check 'em out, but I'm not sure about Motobecane... Seems like any motorcycle shop SHOULD be able to check it out for you, but I don't know fer shure...

david

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account