'76 R75/7 restoration

Discussion in 'Airheads' started by Steril, Mar 26, 2021.

  1. BJMoose

    BJMoose that trick never works Supporter

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    " In the old days we would say a puddle of oil was a sign of a healthy engine because it had oil."
    You must have owned a Norton.
    #41
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  2. korinthias

    korinthias slightly behind the curve…

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    Or any other British bike over a certain age. The engine plates and lower frame tubes of my Ariel are in perfect condition, thanks to that happy conjunction of gravity and oil…

    I think all of Disston’s points above are very much to the point. Just to add, if fuel was running down past the float needles and flooding into the intake, it would also be dripping out of the carb overflow, in traditional ‘wet boot’ style.
    #42
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  3. Steril

    Steril Another Millenial

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    Sure enough, there's plenty of gas in the right cylinder. I've dipped a piece of paper in the spark plug hole. It shows a level of around 1cm. My electrics is still apart (waiting for the damn connectors delivery), meaning I can't crank it and blow the gas out. I hope that letting it ooze/drip for another day or two won't make things worse, since I have no way of getting the gas out of there now.
    No signs of gas or a leak anywhere else than under the right side pushrod seals and down the oil sump.
    #43
  4. Beemeup

    Beemeup 1978 R100/7

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    A couple of days ago I went to take off on a ride and when starting gas shot out of the left float bowl like I never saw before. It was on the center stand too. Came out like a garden hose.

    I shut her down and waited tried again and gas shot out of the exhaust nut! Fortunately I was at home and took the plug out and blew it dry with an air hose. Then all was well but I just now put the pipes back on after going through the annual nut maintenance only more so. I cut silicone gaskets because I discovered the nuts bottom out with the spacers in place.

    I took it as a sign that it wasn't as air tight as I thought. Float bowl exams are next.
    #44
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  5. seaswood

    seaswood seaswood

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    A friend rebuilt a r75/7 with 906 pistons that I own omg that bike is a blast.
    Even tho it is rebuilt some time ago there is always something to fix.
    I have several straight petcocks if you are interested in parts spares.
    #45
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  6. Steril

    Steril Another Millenial

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    My electric connectors finally arrived, so I changed all the starter relay connections + the relay itself. It was probably the original issue, everything lights up and the starter turns reliably, hooray! Tomorrow I'll drain and change the oils.
    My Motobins order is stuck somewhere btw, was shipped on 26/04 and I'm still, rather impatiently, waiting for it.
    #46
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  7. Steril

    Steril Another Millenial

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    I had to get a heat gun to get the oil pan off, working on the airhead is expanding my toolset by the day!

    One pleasant surprise was to find no metal shavings or any solid pieces whatsoever in the pan.

    Not-so-great things that I stumbled upon was that one of the threads for screws that hold the oil pan was stripped and repaired with some epoxy. The screw went back in but I torqued it a bit less than Haynes told me to.
    The oil drain screw was clearly overtightened too, it was a pain in the butt to loosen it and the pan is slightly cracked around it. The crack doesn't go all the way through so I'll hope it will hold and pack some extra JB weld to my travel toolkit.
    IMG_20210512_142920.jpg
    The Motobins package has arrived today and the new front brake switch looks and works great.
    IMG_20210512_164834.jpg

    Getting the new fuel tap spring in took me at least an hour, I must have been doing something wrong because it barely fits there compressed all the way, and turning the tap goes really hard now. I'll settle with that for this riding season, as long as it won't leak - will see that tomorrow when I'm hoping to put everything together and go for a short ride.
    #47
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  8. Beemeup

    Beemeup 1978 R100/7

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    I wouldn't be too comfortable with the drain hole cracks, I'd take it to someone that could do a little aluminum welding. Looks like a ham fisted guy had the bike, I'd look over everything.
    #48
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  9. sprouty115

    sprouty115 Long timer Supporter

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    Not being judgmental, just curious as to why not go the welding route and be done with it?
    #49
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  10. Steril

    Steril Another Millenial

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    The workshops I asked about welding it are backed up for at least two months, so I want to finally get it running, clock up some miles, and solve these things at the end of the season.
    #50
  11. Steril

    Steril Another Millenial

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    My short ride plan was foiled by the weather. It's been raining for days and the forecast doesn't promise it getting better.

    That means I had time to open up my carbs. Getting them actually open was another story though. The screws holding the diaphragm cover are absolutely seized. No amount of WD40 and heat gun treatment made them move at least one bit.
    That made me limit the carb overhaul to opening the low ends, letting the oily substance in the bottom out, cleaning the holes such as overflow, changing the O rings that can be reached from there, and setting the float according to a video I found online.
    IMG_20210514_182630.jpg
    I'll leave it like this for now and do a complete overhaul including the needles/float needles in the autumn. Getting the top part off will require some more research of suitable methods.
    The carbs are on the motorbike now, syncing them is clearly necessary, I'll do it once the timing lamp arrives so the timing can be checked/set properly first.
    #51
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  12. korinthias

    korinthias slightly behind the curve…

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    I have had problems in the past with those screws and had to resort in one case to drilling one and using a small diameter stud extractor. Because they are countersunk and also exposed and subject to corrosion, plus fuel vapour galling, they can get seriously stuck. If you go the drill-out route, you can find that the drilling process itself puts enough torque on the screw to jolt it into action.

    The moral of the story is to put some anti-seize on when you replace them and just tighten them quite lightly – not much force at all. In actual fact, the diaphragm has effectively an integral O ring, that is the thing that actually seals the carb-tops; if that wasn’t there, no way would the two screws in-of-themselves prevent air leaks, no matter how tightly fitted…
    #52
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  13. seaswood

    seaswood seaswood

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    Bing has good information on web site the one I know of is Bing USA
    http://t.bingcarburetor.com/tuningaids.html
    they may have some advice to remove the screws, when I got last bike with Bing’s there were ss Allen screws I believe.
    #53
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  14. sprouty115

    sprouty115 Long timer Supporter

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    Before you start drilling get a small bit wrench and a clamp. I think someone here posted an image, but I can't seem to find it so...

    But the idea is basically to use the clamp to press/hold the bit in the screw as you rotate the driver...
    #54
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  15. ccmickelson

    ccmickelson MonoMania Supporter

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    I like the method sprouty suggests. I've also had luck using a manual impact driver with a pozidriv-type bit (I think it's a #2) which I find fits the OEM Bing screws very well...supporting the carb from below is key so as not to break the carb top flange.
    #55
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  16. Disston

    Disston ShadeTreeExpert Supporter

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    The Allen screw top cover mod is a nice enough item. Problem is that they can be over tightened way more than a screw given the length of Allen wrenches. Be careful. Always use Anti Seize But Loctite will work too because it fils the area the corrosion grows in.
    #56
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  17. sprouty115

    sprouty115 Long timer Supporter

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    That's interesting, because my luck with posi-drive bits is pretty consistently bad (they stripped/damaged most of what I used them on before I realized that there was a difference).
    But this is Bing so who knows!
    #57
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  18. ccmickelson

    ccmickelson MonoMania Supporter

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    They only work on the appropriate screw heads. I believe the OEM carb top screws are pozidriv. I’ve found the mounting screws in ski bindings are as well.
    #58
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  19. korinthias

    korinthias slightly behind the curve…

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    I have tried the impact driver approach, buttressing the carb body against the anvil on the vice, but without result, in my case. I guess in the back of my mind was the thought — one false move here, and I’ll be looking for a whole carb, not just a replacement screw! Probably stopped me from hitting the driver hard enough to actually dislodge the damned thing.

    PS – plus point with a Pozidriv screw — its already ‘centred’ ready to drill…
    #59
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  20. Steril

    Steril Another Millenial

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    My carb screws are flat-head, the worst option, in my opinion. I'll probably drill them out and replace them with allens.
    I'm looking at fiche on realoem to see the screw type/dimensions, and it only says "Csk.fillister head srew", Haynes only says "screw".
    This thread
    says they are "1.0 X 5 oval head" and bmwmotorcycletech says "The screws for the carburetor top cover are M5 x 12 oval head". I'll go with M5x12 and see if it fits.
    #60