I
Irish John
Guest
Fixing front end of motor to downtube
Firstly I love your bike - are those colours the final colours or just the undercoat. In semi-gloss finish those colours would look great.
Uncle Punk says not to drill a hole in the downtube and I agree with him but only because it is a vintage bike. Structurally a neat hole to take an 8mm dia bolt (not chinese - US hard steel only) would not weaken the downtube to any significant ammount - especially at the lower end of the downtube where there is less stress than at the very top. Even on a good alloy frame it is OK if done properly and if you maintain the engine mounts so they are always held firm and stay away from really bad pot holes. I've mounted many engines this way on several bikes and I sometimes use a 6mm dia bolt. Because aesthetics are important on such a beautiful bike however you fix the front end needs to look tidy and not like an afterthought. If you can fabricate a spunky looking bracket as per Uncle Punk's suggestion it could look really good but I worry about welding onto the tube. I wonder is it alloy or steel tubing. I attach a photo of the set up I'm going to use on my Schwinn cruiser to take my 70cc 2-stroke until I get the 4-stroke I'm wanting. I've used another engine spacer and made 2 special length bolts to fasten the clamp through the spacer to the engine block. The clamp has an 8mm bolt through the middle of itself and straight through the tube. The whole thing is held tight with a large diameter thick washer and split washer and nylock nut on the far side of the tube.
I've never had a front fixing bolt fracture but I've had a few rear fastening studs breaking over time because there is more vibration off the 70cc motor and the rear studs have to be 6mm dia which is just too small. I've learnt to spot the breaking bolts as soon as I feel a change in vibration through the saddle. I have never had a downtube fail - I've done 1200kms on the same bike with 4 engine changes. That's on a good Merida alloy frame. Anyway I thought I'd chip in my opinion but Uncle Punk's idea is the go if you design the bracket to look good. From your colour sense and general good taste I reckon you could draw up somthing that all us cruiser owners would want to copy. Good luck and keep the pictures posted.
Firstly I love your bike - are those colours the final colours or just the undercoat. In semi-gloss finish those colours would look great.
Uncle Punk says not to drill a hole in the downtube and I agree with him but only because it is a vintage bike. Structurally a neat hole to take an 8mm dia bolt (not chinese - US hard steel only) would not weaken the downtube to any significant ammount - especially at the lower end of the downtube where there is less stress than at the very top. Even on a good alloy frame it is OK if done properly and if you maintain the engine mounts so they are always held firm and stay away from really bad pot holes. I've mounted many engines this way on several bikes and I sometimes use a 6mm dia bolt. Because aesthetics are important on such a beautiful bike however you fix the front end needs to look tidy and not like an afterthought. If you can fabricate a spunky looking bracket as per Uncle Punk's suggestion it could look really good but I worry about welding onto the tube. I wonder is it alloy or steel tubing. I attach a photo of the set up I'm going to use on my Schwinn cruiser to take my 70cc 2-stroke until I get the 4-stroke I'm wanting. I've used another engine spacer and made 2 special length bolts to fasten the clamp through the spacer to the engine block. The clamp has an 8mm bolt through the middle of itself and straight through the tube. The whole thing is held tight with a large diameter thick washer and split washer and nylock nut on the far side of the tube.
I've never had a front fixing bolt fracture but I've had a few rear fastening studs breaking over time because there is more vibration off the 70cc motor and the rear studs have to be 6mm dia which is just too small. I've learnt to spot the breaking bolts as soon as I feel a change in vibration through the saddle. I have never had a downtube fail - I've done 1200kms on the same bike with 4 engine changes. That's on a good Merida alloy frame. Anyway I thought I'd chip in my opinion but Uncle Punk's idea is the go if you design the bracket to look good. From your colour sense and general good taste I reckon you could draw up somthing that all us cruiser owners would want to copy. Good luck and keep the pictures posted.