Hi all,
I just bought my first airhead and I am very much looking forward to fixing it up and riding it.
It is a R100/7T from 1980.
I found a chunk has broken off of the engine housing and I could use your advice on this.
IMG_8480.jpeg (472.25 KiB) Viewed 827 times
It doesn’t seem to be leaking oil or something and it looks to be some access point to the drive shaft.
Is there a way to properly fix this without taking the whole engine apart? And if it does not need fixing for mechanical reasons, is there a nice way to mend it visually?
Well... first of all, that's the gearbox rear cover, not part of the engine housing. The damaged part is the take off point for the speedo drive gear. The hex headed socket screw securing the main ground lead is not stock. There should be a (special vented) bolt where the damage is. This has three functions 1) to hold the speedo cable in place, 2) to secure the main ground lead and 3) to vent the gearbox (and drive shaft void), so...
a) If you are able to function without a speedo or there is an aftermarket solution in place and b) there is no collateral damage to the gearbox outbut shaft, there is no mechanical reason why this arrangement shouldn't work, however you should ensure that there is some form of venting to the gearbox otherwise, with changes in temperature and air pressure, the whole gearbox and drive shaft void will become pressurised and this could lead to further complications.
The other solution would be to replace the gearbox rear cover... however, that would require the gearbox to be rebuilt which is something that many home mechanics don't like to attempt because it needs specialised tooling and expertise.
Of course, the other option (possibly the easiest and most satisfying) is to source a replacement gearbox.
You have no speedo cable, so probably no speedo or a GPS one. but that's not your problem, right?
I've seen a lot of people use a cell phone GPS app as a speedo.
Works perfectly, but won't pass a DMV certification.
Function:
As far as gearbox venting goes, drill a small hole (1mm) right through the screw on top of that plug so pressure, if any, can escape. Ideally you don't want water getting into the gearbox, but unless the bike sits in the rain for long periods or is driven through deep water, it shouldn't be to much of an issue. If your gear oil looks like a chocolate milkshake, there's water in it. The stock vent hole is through a screw that's positioned horizontally to minimize water infiltration but the part that holds it has been broken off your transmission. TIP FOR DRILLING IT: If you want to drill a perfecty straight hole through a small screw like that and don't have a drill press, put a layer of tape around the screw threads, put it in a hand drill, put the drill bit in a vice and go for it. If the screw is spinning instead of the drill bit you'll end up with a perfectly centered and straight hole every time.
Appearance:
Fill in the missing metal with some JBQUICK, sand or file it sort of smooth and dab a bit of aluminum paint on it. I bet nobody will ever notice it. The relocated ground wire is a dead 'bodge' give away to anyone who knows these bikes. I'd remove the allen bolt in the back of the transmission (the one visible in your pic), substitute it for one that's 1/4 inch longer, and connect the ground wire there. I extended and relocated my main ground wire to one of my starter mounting bolts, which is the best electrical path possible (and neatens up appearance). I now use a GPS speedhut speedometer but I left the cable (cut off under gas tank) because I didn't like the look of an aftermarket plug in its place.
Attachments
Untitled.jpeg (94.06 KiB) Viewed 813 times
Mechanic from Hell "I remember every raging second of it...
My bike was on fire, the road was on fire, and I was on fire.
It was the best ride ever!"
Thank you both so much for the elaborate explanation. This is all really helpful. I wasn’t aware that this was the speedometer cable interface.
You are totally right, at the moment there is no speedometer and if I would want one I would probably go for a gps type anyway.
I live in the Netherlands and for motorcycles and especially old ones there are not a lot of dmv type of regulations. (The police might not like it though since legally you should be able to know how fast you are going)
I will go for the aesthetic fix and the vented bolt. Thank you for pointing that out. I think I wouldn’t have known the venting function if you hadn’t said it.
This would be something I will be doing this summer hopefully. First priority is being able to drive it. Some other stuff is going on, but I’ll get to that in another topic if I can’t find the solution in an older thread.
