Starter and Big bore

[JohnGoodenough]

I'm not rebuilding the bottom end, and the top end is stripped mainly for cosmetic purposes.

Polishing of parts etc.

Top end looks fine.

New cam chain guide is all that's going in new.

 

[riksoto]

I use welding cable for all battery cables, they are very flexible and are designed to carry lots of amps.
For the ground I like to weld a stainless bolt to the frame and attach the crimped ground lug. I also remove all paint from engine mounting points on the frame to ensure a good ground.
The next weak point that I have run into is the starter solenoid, sometimes the contacts get dirty/burned over the years and need to be replaced. You can test the voltage on both sides of the solenoid while cranking if there is a drop in voltage across the two large terminals you just located an issue and the solenoid needs to be replaced.

Test for voltage drop from battery positive post (not the cable crimp terminal) to starter terminal.
And test voltage drop from starter case to battery negative post (not the cable crimp terminal) while cranking to determine if you have an electrical or mechanical problem.
There should be less than 0.5 VDC any more and threr is a problem in the circuit being tested,

This should get you going in the right direction.

V/R
Riksoto

 

[JohnGoodenough]

Thank you Riksoto
Still building, but I'll definitely try that!

 

[willy]

Try the all American anti gravity battery, it more power than any of the usual batterys and is half the size.......

 

[JohnGoodenough]

Thanks Willy!!

 

[mbeilstein]

Amazing Machine you have there.
I'm building a TX650 right now. I want a real Dual Sport Machine when complete.

 

[FLEA]

the 750 /rephrased project motor is finally in the bike and running ,auto elect tested starter motor before hand all good except bendex trouble with the starter but a new spring fixed that ,std size battery 3months old doesn't like kicking the motor over ,put on charger so fully charged ,my thoughts ...bad battery (does happen) or what are the symptoms if the safety relay is playing up ..definitely need the e start due to dodgy legs

 

[XSLeo]

One way to check for safety relay issues is to bypass it. Unplug it and jumper the two red/white wires. These are the ones that supply power to the starter relay.
As mentioned another thing is to run heavier cables, the stock 10 or 8 gauge are ok but 6 or 4 carries the current better. Also run an extra cable from one of the starter mount bolts to battery negative. This will improve the current flow to the starter.
Leo

 

[FLEA]

thanks leo ,have a pamco ign as well if jump the 2 wires any chance of cooking the pamco ,planning on upgrading cables shortly anyway (extra 1 from starter to battery sounds like a good idea as well) but would like to cure the problem first rather than symtoms ,everyone I asked in oz who have done upgrade says seems to be no difference with std battery (works well) the battery lead (from po) could be a mikes xs one as the wiring harness ( fk nightmare,but bikes been on the rd and running ok with original motor ) is one of theirs ,was having simmiler problems with original 650 motor but not quite as bad

 

[Brokenspoke]

thanks leo ,have a pamco ign as well if jump the 2 wires any chance of cooking the pamco ,planning on upgrading cables shortly anyway (extra 1 from starter to battery sounds like a good idea as well) but would like to cure the problem first rather than symtoms ,everyone I asked in oz who have done upgrade says seems to be no difference with std battery (works well) the battery lead (from po) could be a mikes xs one as the wiring harness ( fk nightmare,but bikes been on the rd and running ok with original motor ) is one of theirs ,was having simmiler problems with original 650 motor but not quite as bad

 

[Brokenspoke]

For those who have had starter problems and seems like a week battery make sure you have a good ground for the starter. I fought this and had thought the starter was not able to turn it over because of the 750 big bore installed on the bike. Turns out the problem was the powder coated frame and engine did not allow a good ground circuit. I ended up installing a ground wire from a bare steel engine mount boss to the one of the starter bolts. No further problems.

 

[Ed Zornes]

I built an XS2 based 750 back in the day, ran 10.5:1 pistons, and the starter would not spin the crank fast enough to fire, or, it caused the voltage to drop to where the coils wouldn't fire. I ended up kick start only. Fast forward to today. I'm putting together another high compression 750, and my right knee has issues that make me NOT want to use the kickstarter. I'm going to install 2 of the V twin solenoid controlled compression releases in the back of the cylinders to bleed off part of the compression, just like the Maicos and Yamaha big bore Enduros of the 70's. I'll have to weld a couple stubs onto the cylinders to thread the compression releases into near the top of the cylinder. I plan to control how much compression bleeds off with the diameter of the hole/passageway that runs into the bore area. I have done this with a big bore kit on my dirt bike, and it works great. Without the compression release, the dirt bike runs 250 PSI of compression.( liquid cooled motors can handle a lot more compression) By slowly enlarging the hole, trial and error, I have 130 lbs of compression, just a bit less than most air cooled engines normally have...and enough to start easily without much effort. It may be several months for this to come to fruition, as I'm just starting the build. Should not be a big deal to drive both the solenoids and the starter motor simply by engaging the electric start button: release the button when the engine fires, and the compression releases close as well. Any thoughts..?

 

[retiredgentleman]

I think the stock starter motor will work for you. However, you want to have a good strong battery and a good charging system.
Read the comments by XSLeo. His idea to use heavier cables is a good thing to do. The extra cable from the starter motor frame back to the battery negative is also well worthwhile. The high current of 80 to 100 amps loves a low resistance path.

 

[Brokenspoke]

Ed, I understand not wanting to kick. I tried mine and it would be a bear! and I am 200 lbs. It sounds like you might be adding a lot of complexity that might not be needed. I had my starter off three times which is not all that much fun when the engine is in the frame. Two easy bolts and two not so much. Every time I had the starter off I would jump it to the battery and it worked fine. The first two times I put it back in and it seem to work and then stopped working and I just thought I had a bad battery. the second time I made sure there was no powder coat on the engine bosses where the starter mounted. I had to clean the power off them. The starter worked when I installed it and for a couple of times there after then it stopped working again. You could hear the starter relay clicking and I had voltage to the starter. The third time it happened I left the start installed and just pulled the cover and gear. I hit the button and the motor would turn but was very week. I could stop it with my fingers. I installed a jumper wire from one of the mounting bolts to a good ground on the frame and the start then worked properly. I knew then it was the ground. Frame and Engine are powder coated and so there still must have been enough resistance to not allow the starter to work. I fabricated about a six inch six gage wire with eyelets and installed one end to one starter motor mount bolt and the other end to the aft lower engine mount bolt behind the countershaft sprocket. (see photo in previous post) I cleaned all powder coat from the frame tab so I had bare steel before installing the ground wire. I have and no further problems and the starter has no problem turning the 750 engine over.