CB750 scrambler project
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I think I know the issue. The pulse generator had a load of oil in there. Doesn't put out 0.7v
When I crank the engine I can feel pressure of air blow past the crank seal
the crank seal itself might not be broken but the pressure bypasses it.
I can't see this seal on fowler's diagramsAll cylinders seem to have good compression so can think why the crankcase has so much pressure. Unless it's a blocked pcv.... Not sure if they have valves ....
Lots of ball aches...
I couldn't really test any of this before fitting the engine all together. -
Damn, wtf.... Surely you shouldn't have an access window to the side of the crank (bottom of engine)
https://i.imgur.com/7LrE6wS.gifv
See the video -
Damn, wtf.... Surely you shouldn't have an access window to the side of the crank (bottom of engine)
https://i.imgur.com/7LrE6wS.gifv
See the video -
You mean the hole at 9 o’clock on the pic? Yeah, it could be oil bathed. Specially if the cover had a oil proof gasket. 4 strokes are ‘different’
I’d look into the voltage issue.@SpookDog yes I think my main concerns now is why is there so much pressure in the crankcase? Manual said 3.5L oil with a new filter..... I wonder if it's wrong and over filled
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Right, I thought "oh shit the crank seal is gone"
Looking at all diagrams..there isn't a seal!
Anyone else who wants to help confirm I'm not going made... Please do
The oil literally returns to the sump through that window where you can see the crankshaft web.... Strange right... But makes sense why there's a "return" to the sump
The side cover is a sealed type so that's why oil doesn't drip out.The oil is about 0.5l -.6L over filled from having the wrong information in a manual I have..
Manual states oil capacity (when replaced) 2.8L without filter and 3L with filter. (Dipstick still doesn't show anything... Perhaps from another bike)
I believe this caused there to be oil on the pulse generator = no pick up pulse.....
Drain the oil time tomorrow. Refill to correct level.
Clean up pulse generator... If still not producing 0.7v I need a new one.
This is the issue. -
4 strokes always have air movement in the case/block, the pistons pumping up and down displace air. You can get over pressure from worn rings/ piston blow-by...
You ain’t going mad, sanity is just a learning curve 🤪@SpookDog I think actually how this works now
Apparently the pulse generator is supposed to have oil in there (oil cooled)... Which is great because there is no oil seal on the crankshaft that can go wrong......If you remove the cover when it's on the side stand (the only Stand I have)lots of oil will pour out...
Only a small amount of oil come out on the centre stand....
The pulse generator seems to not put out enough voltage so I've ordered a new one.As I've done lots of tests it is is the pulse generator that I believe is the issue.
There's also supposed to be a proper gasket for the cover which I've ordered
The CBX 750 which is almost an identical engine have the oil filler cap on the left-hand side.
As the cbx750 shares a lot of parts
On my bike this has a cap saying "do not open"
On the left casing (where the oil filler is on the CBX)if you open this when it's on the side stand oil will pour out as well..
. I'm guessing at the CBX 750 at the side stand on the right hand side.
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@SpookDog it's not even mentioned in the manual about not removing the left-hand pulse generator cover on the sidestand
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I have no idea when I use the shrug emoji it changes it to a girl and the gender symbol
After further investigation... My cdi which was sold by a bike breaker written in white paint "cb750 1997" ... I cleaned off the paint carefully and the part number just about readable is
MASG G
571UWhich is a cbr900!!!
Whether or not that's a problem, I've got another one from another spares breaker with the correct part number for the cb750 sevenfifty
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Same here. Should be beasty.
I knew the electrics would be the hardest part.
All lights and horn was easy.
Starter circuit was ok.
Just the ignition circuit
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It WILL fire up with a new CDI, unfortunately online buying is a fukin shark feeding frenzy of a$$hol£s all caring about one thing. The amount of times I’ve been shafted on fleabay is unreal. Brought a headlight that came without the bulb holder or rubber, the bloke had the neck to tell me that I was confusing his with another listing, conveniently after his pics were down. The only reason I nodded was cause it was complete...
Another bloke changed the listing twice while I was between messaging. Once to up the price £40 then to change from 3 wire to 5wire servo! Same listing number an all... -
It WILL fire up with a new CDI, unfortunately online buying is a fukin shark feeding frenzy of a$$hol£s all caring about one thing. The amount of times I’ve been shafted on fleabay is unreal. Brought a headlight that came without the bulb holder or rubber, the bloke had the neck to tell me that I was confusing his with another listing, conveniently after his pics were down. The only reason I nodded was cause it was complete...
Another bloke changed the listing twice while I was between messaging. Once to up the price £40 then to change from 3 wire to 5wire servo! Same listing number an all...@SpookDog I know the feeling. Many sellers have lots of similar items for sale but send the wrong ones.
The problem is I built this bike with parts from about 30 bikes... And no real way to test it will work together until I try -
I've got sparks on the plugs.... Just need 1 more part before I start up....
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She runs and runs beautiful!
I'll do a video when fully warmed up.
And not pouring rain.It was screeching when I started it., Originally thought it was the starter, but when running it was awfully loud. I thought "here we go" something major.
I had a suspicion it was the generator....
Look what I found...
A tiny recess where a slightly bent fan blade was rubbing the cover.Really easy fix and now sounds great!
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Have a little listen
ears are bleeding
