1988 DR750 Big rebuild
#1
Hello Smile

I have just acquired a DR750 Big. The bike was on the Channel Islands although I am not sure this is were it originated.

I have rebuilt a few bikes now including my first bike a GSF600 bandit and a BWM F650ST

Anyway back to the BIG. The bike is a non runner and has covered 17000 miles in its 30 years, This appears to be genuine as overall it is in good condition for its age and the type of bike.

It would appear that it has suffered from being turned off and catching the compression stroke. This has spat all the starter gears out destroying the cover and crankcase.

I have sourced a pair of crank cases, a NOS stator cover, and some replacement gears and pins. 

The engine is out and stripped and using the technical data from a Suzuki manual it all appears to be good and well within tolerance with further indicates the 17000miles as true.

I plan to get the engine rebuilt and running and then consider what to do cosmetically with the rest of the bike.

obviously from checking through the forum original paint/colour is out of the question. I need to decide what to do with the engine colour before I rebuild it as the flaky blue paint wont do.

So thats a little bit of introduction for now anyway.

https://photos.app.goo.gl/Y3TzqXDw4kVHspHh8
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#2
Ouch! That made a real mess of the cases etc. You are not the first either.
Definitely replace the crank bearings. The first model used a decideldy inferior bearing on one side that was uprated for the following year.
The bearing rarely fails but makes one hell of a racket and sounds like the big end is about to go.
You will probably end up replacing the starter clutch as well as it was probably the cause of the failure.
No doubt you will be asking all the questions we have been asked many times. Not to worry as we know all the answers.
Definitely get the genuine manual. RTFM.
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#3
(13-06-2020, 07:45 PM)BigBob Wrote: Ouch! That made a real mess of the cases etc. You are not the first either.
Definitely replace the crank bearings. The first model used a decideldy inferior bearing on one side that was uprated for the following year.
The bearing rarely fails but makes one hell of a racket and sounds like the big end is about to go.
You will probably end up replacing the starter clutch as well as it was probably the cause of the failure.
No doubt you will be asking all the questions we have been asked many times. Not to worry as we know all the answers.
Definitely get the genuine manual. RTFM.

I had to google RTFM - and ended up ROFL, I've always been more TIAASIICFOHTPIBTA* Smile

I'm definitely no expert, but other than the obvious horrors she looks great, nothing some tlc won't sort out


*take it apart and see if I can figure out how to put it back together again
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#4
Great to see another one being rescued! Keep us updated with a steady diet of picsSmile
There was a Dr750 owning member here who lived in Guernsey was it? Rick Le Ray? Maybe he can shed some light on the bikes history for you?
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#5
And here’s the most important part......

Once you get it running again - Shut the engine off with the decomp lever ONLY.

Do NOT turn the ignition off either with the handlebar switch or the key.

Ignoring this will have you replacing starter gears again.
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#6
(13-06-2020, 12:14 PM)dougiehowser Wrote: Hello Smile

I have just acquired a DR750 Big. The bike was on the Channel Islands although I am not sure this is were it originated.

I have rebuilt a few bikes now including my first bike a GSF600 bandit and a BWM F650ST

Anyway back to the BIG. The bike is a non runner and has covered 17000 miles in its 30 years, This appears to be genuine as overall it is in good condition for its age and the type of bike.

It would appear that it has suffered from being turned off and catching the compression stroke. This has spat all the starter gears out destroying the cover and crankcase.

I have sourced a pair of crank cases, a NOS stator cover, and some replacement gears and pins. 

The engine is out and stripped and using the technical data from a Suzuki manual it all appears to be good and well within tolerance with further indicates the 17000miles as true.

I plan to get the engine rebuilt and running and then consider what to do cosmetically with the rest of the bike.

obviously from checking through the forum original paint/colour is out of the question. I need to decide what to do with the engine colour before I rebuild it as the flaky blue paint wont do.

So thats a little bit of introduction for now anyway.

https://photos.app.goo.gl/Y3TzqXDw4kVHspHh8
I probably have all the parts you need , looks like you are already sorted
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#7
Any progress on the DR Doctor Howser? Smile
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#8
(21-06-2020, 08:27 AM)H_Lime Wrote: Any progress on the DR Doctor Howser? Smile
Hi all,


Sorry for the delay in progress. What with lockdown, home schooling and health issues I had not even looked at the bike since I striped it.

Anyway I have now rebuilt the engine and got it back in the bike. Starting it was the next issue.

I had a quick look at the carbs , im assuming at this point that it was running when the starter gears exited the casing. They were a mixed bag. One of the floats had been replaced and the level tang on the other had been well abused. gave them a quick rinse out, checked the float levels and fitted them.

I had discovered when stripping the bike that the 3 yellow wire off the stator had melted the connector plug and had to cut them to get it off.  Also the wires to the ignition pickup were badly frayed and had been repaired before. So obtained a new stator and got a reg/rec while i was at it. So I fitted the stator when the engine was rebuilt. I did not reconnect the yellow wires yet as just wanted to make sure the bike ran.

next was no voltage at the instrument cluster, badly corroded connector on the ignition plug had caused the red 12v feed to snap off so this was fixed. Then attempted to turn it over. nothing when pressing the start button. checked voltage at the solenoid, nothing.  Checked side stand switch and seems ok and connected. Neutral switch ok and neutral light on. tried it with clutch pulled in and out but nothing.

So I decided at this point I needed to know if it will run before I start pulling the electrical system apart. So ran 12v straight to solenoid. It turns, I have spark :O)

Turned it over few times to circulate the oil. Added fuel. checked forums for starting process :O) decomp lever first.

it tried to fire. and basically will run if kept at a very fast idle....2000rpm or so. as soon as i back of the rpm it dies.

next removed the carb and cleaned it in my ultrasonic bath. blew it out with an airline, made sure all o rings ok, float level ok again, checked the needles were on the correct setting , mixture screws 2 1/2 turns out. replaced the float with the messed up level tang with a spare I had (same carbs on the F650 bmw) I also checked the carb inlet rubbers and they again seem fine. I did replace the o rings in them when i rebuilt the engine. 2 new spark plugs, put the carbs back on the bike and the same..

SO......
 it will start with throttle part open and kept at higher than 2000rpm, after cleaning the carbs it did seem to run better and would rev but was clearly a lot of unburned fuel coming out the pipe (black/grey smoke)

I am running the bike from a remote fuel tank and direct into the carb , bypassing the fuel pump. I have plugged the vacuum inlet on the carb that drives the fuel pump also.

Is it because basically I don't have a functioning charging system? as the stator is not connected yet. I did read somewhere that these bikes are very fussy to voltage.

cant see what could be wrong with the carbs...i have checked all rubber parts, diaphragms, needles don't look worn.... cleaned them and to be honest they don't look that bad, was no corrosion inside and the bike had obviously not been left sitting with fuel in the carbs.

Could be an poor connection elsewhere in the system? I have not resolved the starter switch issue yet as bypassed it for now.

Im sure is probably something very simple I am overlooking

https://photos.app.goo.gl/Y3TzqXDw4kVHspHh8

Also when i sourced the starter gears I bought them from a DR800 thinking they are the same. The DR800 gear is slightly taller than the 750 therefore jamming when the stator cover is put on. I had obtained a NOS cover that looks to be from an 800 (it has a big cylinder bit sticking out at the starter gears end) but that has same problem. lots of parts diagram and forum digging later reveals the parts evolution. So the 750 starter gear i need is like a hens tooth. The one I have functions but the teeth are damaged and I don't like its long term prospects.
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#9
Going through some testing , I have a Gunson colourtune. If you don’t know it’s basicly a spark plug with a viewing window so you can see combustion. 
Anyway...result was interesting. Once running it did appear ok, you can see wether it’s rich or lean and it appeared fine. However again when dropping the rpm to idle it just stops . And looks like the spark just stops as the fuel is still there and can’t see any spark through the colourtune plug.

I have ordered some clear tube to test the level in the carbs. Also will get the stator wiring sorted properly before trying again . 

Should have some more progress/or not by the weekend ?
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#10
I now have a functional charging system, and also figured out why the starter button was not working...side stand, neutral, clutch in...and decomp lever...I had not pulled the decomp lever when previously trying to start.

So still the same issue. will start on throttle, but will not even consider running at anything close to idle speed.

Carbs off again and stripped into as many parts as i can get them and in the ultrasonic bath for a couple of hours, turning periodically as well as blowing through every orifice with the airline.

we will see...
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