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Old 11-19-2010, 11:02 AM   #46
fadingfastsd OP
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Hey guys thanks for the input.

Yes I know the 12AH battery is undersized for what the manual calls for (24 AH I think). The 12 is the largest my local shop has in stock and should be enough to crank the bike over when fully charged (I'll replace it soon with a larger batt).

Regardles, that is why I showed the video using the car battery and jumping the starter directly. It acts the exact same way with a fully charged 100% good car battery.

The starter works perfectly on the bench with no load.
I checked the bushings/bearings when it was apart, they all looked perfect!
Greased everything, cleaned up all the contacts in the starter body and solenoid. But it just won't turn the engine over when installed.

It did when I brought the bike home, although very slowly.

I'm going to go pull the plugs and crank it over again. Make sure its not compression that its struggling with.

Also, this just popped into my head, if I set with the valves too tight (which I'm absolutely positive I didn't), I could be fighting the valvesprings to turn the engine over. (I did this on my old 55 Pontiac and couldnt figure why it was barely cranking!)...but I've doublechecked the valves, and they are set correctly.

Hmmm
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Old 11-19-2010, 11:23 AM   #47
Renner
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you might consider posting this question over on the Airheads list.

no need to be an ABC member to do so and you'll reach a more centric audience.

to subscribe:
[FONT='Calibri','sans-serif']http://micapeak.com/mailman/listinfo/airheads[/FONT]
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Old 11-19-2010, 12:35 PM   #48
fadingfastsd OP
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OK with the spark plugs out, it cranks the engine what seems like full speed.
Maybe the starter is ok? Thats still some load on it right?
Or with the plugs removed and no compression to fight, is the load of turning the flywheel and crank/cam negligible on the starter?

What the hell is going on here!?
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Old 11-19-2010, 12:54 PM   #49
wirewrkr
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Quote:
Originally Posted by fadingfastsd
OK with the spark plugs out, it cranks the engine what seems like full speed.
Maybe the starter is ok? Thats still some load on it right?
Or with the plugs removed and no compression to fight, is the load of turning the flywheel and crank/cam negligible on the starter?

What the hell is going on here!?

Check both of your battery cables very carefully.
They have a tendency to build up internal corrosion causing too much resistance.
PM me if you need some I manufacture reproduction cables and have them in stock and ready to go.
I use a little heavier gauge cable than BMW and retain extreme flexibility, which is very important for the POS cable inside the starter cover.
Robert
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Old 11-19-2010, 01:34 PM   #50
Renner
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Quote:
Originally Posted by wirewrkr
Check both of your battery cables very carefully.
+1

I once had a POS cable corroded at the terminal end, battery connector.
So much corrosion hidden under the insulation that the resistance prevented adequate amps from getting to the starter.

right-on suggestion Robert
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Old 11-19-2010, 01:50 PM   #51
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Yes, that needs to be looked at, I re-soldered mine after sprucing it up. But if you watch the video he was using jumper cables to the starter and bypassing the bike's connections. Obviously the cables need to be making a solid connection with enough contact to handle the amps too.
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Old 11-19-2010, 02:46 PM   #52
fadingfastsd OP
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Good suggestion Wirewrkr & Renner, I thought of that first, but like Jasper said, I've eliminated poor battery connections (I have brand new battery cables though) by jumping the starter directly off a car battery, using good jumper cables.

Just triple checked the valves to make sure they werent too tight.
All the valves are set dead on to clearances in the shop manual.

I put my compression tester on each side, and with the opposite side's spark plug out, it still barely cranks over. It barely hits 90 lbs compression on each side. This might be a little low because of the low cranking speed.
Shop manual says 110lbs or less is low/poor compression.

I think at this point I've exhausted everything else.
It HAS to be the starter taking a dump when it has the load of compression on it.

That being said, does anybody local to San Diego have a known good starter I could swap in quickly and try to make sure? (or would somebody mail me one to try, i'll pay shipping, and will send right back after testing).

Problem is, I'm just broke as hell at the moment, and need to be 100% sure it's actually the starter that needs replacing before I dump money into one.
Can't afford to replace it if its not for sure the problem.

Thanks guys!!
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Old 11-19-2010, 05:26 PM   #53
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Quote:
Originally Posted by fadingfastsd
I put my compression tester on each side, and with the opposite side's spark plug out, it still barely cranks over. It barely hits 90 lbs compression on each side. This might be a little low because of the low cranking speed.
Shop manual says 110lbs or less is low/poor compression.

It HAS to be the starter taking a dump when it has the load of compression on it.
I have no faith in the compression check at this point. You need a good battery and starter to begin with. Also, if you didn't remove the carbs then the compression test is no good. Plus, the engine is cold. I think that's a red herring at this point.

If you had a strong battery with good jumper cables running straight to engine ground and the starter and it's not turning the engine something seems to be wrong with the starter.

I'm not sure how precise you were with the visual inspection but it seems to me that field coils could be weak and the bearings worn to where it doesn't work with a load.

I sent my Bosch that was acting that way (v. weak when installed but spun on the bench) to Rick and he replaced bearings and the field coils, etc. and it came back working like a champ. They do wear out.
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Old 11-19-2010, 05:29 PM   #54
fadingfastsd OP
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Quote:
Originally Posted by fishkens
I have no faith in the compression check at this point. You need a good battery and starter to begin with. Also, if you didn't remove the carbs then the compression test is no good. Plus, the engine is cold. I think that's a red herring at this point.
Fishkens, I totally agree about the compression test. It's pretty much inconclusive at this point. I think all signs point to the starter.
I'm just trying to find a known good starter to check with so I can be 100% sure. If that proves the starter is bad I'll replace it right away.
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Old 11-19-2010, 05:41 PM   #55
fishkens
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Quote:
Originally Posted by fadingfastsd
OK I'm about to go crazy with this bike!

It will not run! When I brought it home it ran fine. Started very easily, and idled and ran fine.

However, now after carb clean/rebuild, new points, condenser, and plugs, set the the valves and checked timing, it won't run. It cranks, pops and backfires. Will run for a few seconds every now and then, but is uneven between cylinders, and very rough, and then dies.
I just re-read the thread and saw your post about it not starting.

I'm guessing that you may have cranked it quite a bit trying to get it to start (only assuming that because that's what I did when my bike wasn't starting). I agree, it's frustrating as hell.

I believe that I cooked my starter trying to do that and landed in the bottom of a descending cycle of misery: bike's out of tune (or something's wrong), use the starter to crank it, starter fails, bike can't be started. I believe I cooked my starter trying to do that and that led to it's rapid demise.

Rebuilding the starter and engine work got it back into tip-top shape.

I know what you mean about wanting to confirm that it's the starter before spending $150 on a rebuild though.

Given what you said about how the engine worked before hand it doesn't seem like something went wrong with the engine that's keeping it from spinning.

FWIW.
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Old 11-20-2010, 05:18 AM   #56
DoktorT
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Quote:
Originally Posted by fadingfastsd
What other tanks are interchangeable with this frame?
I'd like a larger tank for sure.
/6 big tank will do you proud. /7/S/RS/RT through 80 at least, the tank and seat will fit. I've heard there are issues with /7 tanks and /6 seats.

Nice project. Know that the 74 tranny is an albatross. Most demonstrate short life for the kickstart, and unique internals that make rebuilding expensive. 75 was improved, then again in 76. Very good function for long life is to be found with anything 76-mid 80's. 80 was last round air filter type.
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Old 11-20-2010, 10:53 AM   #57
Twistyblackmetal
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I have a BMW R75/5 LWB...

and I love that solo seat on it when you first got it- If it's still available at a good price, Consider me interested. I also have the stock seat from my 74 LWB for trade if you are interested, very good condition. Cool Project!
-tbm
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Old 11-20-2010, 01:46 PM   #58
bmweuro
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Quote:
Originally Posted by Sniper X
BUT, did you get both the key for the bag and the key for the lock to lock them to the bike? What numbers are on the keys if you DID get them? I can reference that number for vintage of the luggage.

thanks,

Kevin
Around the outside of the lock where the key fits in there is a key number beginning in S, like S150, S324, S326 and S328. I have the S150 keys.
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Old 11-22-2010, 08:57 AM   #59
wirewrkr
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Quote:
Originally Posted by DoktorT
/6 big tank will do you proud. /7/S/RS/RT through 80 at least, the tank and seat will fit. I've heard there are issues with /7 tanks and /6 seats.

Nice project. Know that the 74 tranny is an albatross. Most demonstrate short life for the kickstart, and unique internals that make rebuilding expensive. 75 was improved, then again in 76. Very good function for long life is to be found with anything 76-mid 80's. 80 was last round air filter type.
All your trans advice is spot on, the issue with a /7 tank and a /6 seat is that the tank is almost 2 inches longer, hence seat not fitting.
1979 was the last round filter. 1980 had the first flat filter with a unique air cleaner top that was aluminum instead of plastic.
The starter cover was a one year only also with a metal scoop instead of the previous rubber.
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Old 11-22-2010, 11:16 AM   #60
fadingfastsd OP
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Well another update for you guys.

I borrowed a known good working starter from Renner on here, (great guy, lives right by me! - Thanks!!!) and swapped it out in the bike yesterday afternoon.
And....exact same problem. Bike will barely, barely turn over with a good starter.

So it looks like my starter is NOT the issue. What the hell is causing this extremely slow cranking.

Recap:
The bike ran well when I brought it home a month ago or so.
I noticed what I thought was slower than normal cranking when starting, but it would start within 2 revolutions or so, and ran well. Tranny shifted fine, everything worked as it should.

What I've done:
*Adjusted the valves. They were slightly tight (not much at all). Adjusted to spec in manual. Have doublechecked valves twice now. Pushrods spin a TDC on each side (so theyre not too tight and im fighting valvesprings).
*Replaced points, condenser and set timing to static 'S' mark on flywheel.
*Changed shaft & final drive oil.
*Replaced clutch, and both throttle cables. Clutch cable is adjusted and engaging/disengaging correctly.
*New spark plugs (stock Bosch)
*Cleaned and rebuilt carbs with rebuild kits.
*New tires and air filter

But at this point, I'm just trying to get it to turn over normal speed. I'm using a known good car battery (starts my 56 Pontiac w/ a 316 v8 right up), and jumping the starter solenoid directly, bypassing all bike wiring and relays.
It still cant turn over.

What am I missing here!???
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