It's done it again, engine slips

[retromike3]

Just when I thought I had this problem taken care of I found my chain off and floating on the bolts that hold my rear cog on. Turns out that the bolt that holds the engine on to the seat tube has striped. Last time about two hundred miles ago I had the same bolts brake off. This problem happened on my last build and also seems like the hardware is not up to the task of holding the motor in a fixed position. when it slips down the seat tube it causes the chain to get loose.There has to be a better way to hold the motor in place.

I was thinking of welding a bracket to the frame between the bottom bracket seat tube and the down tube. I would make it out of a triangle of steal and a plate. with the gap filled there would be no place for the motor to go.

I really like that little motor and would like to keep it going(I have a spare I bought "just in case" ,But I would like to keep this guy going.

Mike Frye

 

[AussieSteve]

Sounds like you might be over-tightening.
Did you replace the stock studs with decent steel ones when you put it together? The stock ones are s..t.

 

[retromike3]

Not quite

I tried to find mounting bolts long enough so I could double bolt them but I could not find any. So I bought some threaded steel rod and drilled and tapped two new holes in the back of the engine.(the stock ones broke off flush) and then used spacers to get the right torc (I thought).

I have had two engines now with the same problem, engine slips down the seat tube and then the chain goes slack. Somebody has to make a better mount than the stock one. If all else fails I will make my own.

MIke Frye

 

[AussieSteve]

I did the same - bought 6mm x 1mm threaded rod, washers, spring washers and nuts, (good quality steel), and haven't had a problem.
Not much torque is needed on 6mm studs.
Honestly, if decent steel studs are stripping/breaking, you're torquing them too high.
I'd be more concerned about the alloy thread in the casing stripping - then you're in deep s h i t.
Do you use a torque wrench?

 

[Dilly Bar Rob]

I have had two engines now with the same problem, engine slips down the seat tube and then the chain goes slack. Somebody has to make a better mount than the stock one. If all else fails I will make my own.

MIke Frye

Weld the mount that keeps slipping on you to the frame (or even better, weld both of them)- just a little tack on top & bottom of it should do the trick. After that you don't have to tighten the heck out of them anymore to keep the engine put. If you ever need to de-motorize the bike it's easy enough to grind the welds off.

 

[retromike3]

I don't think I over did it but

I don't think I overly tightened the bolts(they held for about five hundred miles.) I think what happened was that when I had a problem starting the engine, It jammed and locked up the rear wheel. then after about an hour riding my mounts slipped . I think this is when things went wrong. I will try to make a bracket so that it won't slip down in the future. I might even have to weld a plate onto the frame of the bike to make it a more permeant fixture.

how often do I ride that bike without the motor? Never.

So here I go again.

I will keep you folks updated.

Mike Frye

 

[retromike3]

next step stronger bolts

Well to day I found that one of the mounting bolts had indeed broke. this time it broke about 5mm in the hole. I had a devil of a time getting the hole centered for the easy out so I had to get a small Dremel tool in the hole first and then drill a hole and then I finally got the 6mm section out.

Since it has failed before, I phoned a good hardware store downtown and found some grade 8 bolts to replace the ones I had in there before. Unfortunately the fellow at the hardware store I went to today sold me a set of bolts that were stainless and he said they were harder, But I found out they were just as weak as the ones I took out today. Well at least I am not out that much cash:-/.

Update you later.

mike frye