Hello there. M900 Refurb

[Darren69]

It looks to be coming together nicely now. You have been extremely unlucky with the stud snapping flush as they when they usually break and they usually do, it is nnearer the centre. At least in my case on my old 900SS it did, so didin't even need to take out the motor.

So this is a weird one. The bike is nearly complete (pictures to follow soon) but when I went to spin it over the starter was very slow. So popped it on a booster. Better but still way too slow. Ive double checked and the motor turns freely by hand. Timing is correct. I have shorted straight to the starter motor with a booster and it's still slow. Today I took out the starter motor. It spins fine when connected to battery but I stripped it down anyway and the brushes all look ok.
Anyone got any ideas? I don't want to fork out for a starter on a whim.

[slob]

poor or dirty connections on the cables or solenoid contactor plate?
check the battery earth cable and the little braided one on the back of the footrest hanger too.

[350TSS]

Agree with all Slobs advice. With the starter out it may be worth cleaning the commutator with some 800 grit wet and dry (cleaning any abrasive off afterwards with brake cleaner and /or airline) and checking the continuity across the poles on the commutator. I do not know how to check /test the field windings in the motor case, doubtless someone will be along to let you know how or just google it.

Thanks guys. I already bypassed the earths by clipping - direct to the engine and + to starter. Checked the continuity across the poles and cleaned all the brushes and commutator and still the same. Might have to take a punt on an aftermarket motor.

[the lodger]

Kev, you might try removing the starter motor to solenoid cable and replacing it with a similar length from your local car spares supplier ( Halfords will have something ) . A cheap fix which stands a good chance of working ( assuming your battery is ok )

[350TSS]

I used 16mm welding cable for all my battery leads which is finely multi-stranded so flexible and comes with black insulation so is not an eyesore and is easily capable of handling starter current draw.

https://www.ebay.co.uk/itm/Copper-We.../233285626643?

https://www.ebay.co.uk/itm/Copper-Tu...ter-Ring-Crimp

[Mr Gazza]

From what I'm reading the starter itself and the leads to and from are okay.
You have not indicated what the battery voltage is, or what the battery condition is.
A voltage drop test will tell you something about the cranking amps available.
The battery should show about 13 volts before the test, then crank away and note what the voltage drops to during the cranking. Also observe what the voltage recovers to after cranking, both if the engine starts and also if it it doesn't.
It shouldn't drop much more than 2 or 3 volts during cranking and should recover to close to it's original voltage afterwards with the engine stopped. You'll probably see charging voltage of about 14 volts if it starts.

An excessive voltage drop and poor recovery might indicate a loss of the cranking amps from the battery. In which case the only answer is to renew the battery.

However you have just rebuilt the engine, so it would not be unreasonable to see some stiffness in that initially. That would account for slow rotation on the starter and also a large voltage drop, due to the extra load.

I would pop the spark plugs out and whirl it over for a while to loosen it off a little and also check that the oil light goes out, whilst listening for any untoward noises.
You say in post #32 that the motor turns by hand, but don't specify if that was the engine or starter motor?

I don't want to judge your engine building skills, but it's all too easy to bolt something up without an all important spacer washer or some such , and cause some unwanted binding! For instance I believe that there is a troublesome spacer behind the flywheel that is extremely easy to displace when assembling?

Hmm this is turning into a mystery. I have entirely bypassed the starter relay and cable by connecting a powerpack straight to the starter motor so that eliminates relay and cable issues. I have managed to borrow a brand new starter, so that eliminates that. The engine turns over easily by hand and I have double checked the cam timing and still it struggles when turning over. At a loss I pulled the flywheel off to see if anything was amiss but all looked fine.
So I'm stumped. Next option is to drop the engine back out and strip and start again....

[Mr Gazza]

If you oiled the pistons and rings up well when you assembled the engine, they will have a really good seal in the bores and give maximum compression.. Something that always makes a fresh engine a bit on the stiff side to start up. It might even have oiled the plugs up before getting a chance to fire?

It should start after a revolution or two, but if it has a vacuum fuel pump that might take quite a few revolutions for the fuel to get through and fill the bowls, so it will be dragging the battery down trying to prime it.. Did you check the battery condition?

Have you tried taking the plugs out and giving it a good spin over? That could tell you if the engine is stiff or just producing lots of compression. It will also help drag the fuel through, so you can try again with freshly charged battery and clean plugs.
Once it's started and run it will probably be fine.

So it,s been a while due to injury, Christmas etc, but a quick update.
I took the belts off to see how things looked as I was convincved something was rubbing, causing the slow engine turn over. When I took the bottom pulley off I discovered that the (new) circlip had failed and the pulley had pushed the woodruff key out and smeared the oil seal behind it. I'm perplexed as to why this might happen but I have replaced all the parts and put it back together. Hopefully this will sort it out. I'll let you know how it goes...