Motor mounts frequently coming loose on ct70

[JRuw91]

As the title says I’ve been having issues with my 2 motor mounts coming loose on my 125cc swapped Ct70. I’m using stock mounts now but they will come loose and I’ll tighten them a number of times. Then eventually the motor mount breaks. Any ideas?

 

[scooter]

Thoughts similar to response that I wrote on the vibration at high rpm

If you’re bottoming out on the threads before enough tension is developed on the bolt you’re not really tight.

Add an extra washer to ensure you’re not bottoming out on the threads. Even add a lock washer

 

[cjpayne]

lock washers

 

[JRuw91]

That’s what I was thinking. I can’t even get a washer or lock washer on there because the bolts aren’t really long enough.

 

[scooter]

If they’re not bottoming I’d go with some medium loctite

 

[JRuw91]

I’ve tried medium loctite and high strength loctite

 

[JRuw91]

There’s a picture of both bolts. I’ve got no room for washers.

 

[JRuw91]

Bottom mount

 

[69ST]

Those are not OEM bolts. They're way too short and there are no washers.

Time for a different approach...longer bolts, with washers where they're supposed to be and, perhaps jam nuts. Maybe apply blue Loctite to the threads used for the jam nut. It really shouldn't be necessary to take things quite that far, let alone any further (i.e. safety wiring). Like scooter said, the motor needs to be tight between the frame mounts, for structural strength. Test both mounts to verify fitment. Install one bolt, torque it fully, using a long punch for the other mount; then pull the temporary mount and attempt to rotate the engine on the one remaining in place...it should be TIGHT. If not, there's your problem. If there's enough clearance, add a shim washer between the frame & engine; if not, the washer(s) will have to go outboard of the frame.

 

[JRuw91]

I’ll definitely look into shimming it and see what I can do. Thanks for the input.

 

[JRuw91]

Do you know what the size of the standard oem motor mounts were? I would probably need get 5mm longer or so to get a washer or anything else to fit on the end of the bolt.

 

[JRuw91]

The bottom mount is an oem bolt. The top one is from chp.

 

[JRuw91]

Is the size M8 x 110mm? I was looking into titanium motor mounts that were M8 by 120mm. That should give me enough room to run a washer on each side of the mount and a lock nut. Figured I’d start there.

 

[kirrbby]

Does your motor vibrate badly?? Maybe you have a problem with the clutch or flywheel? Have you been into the engine at all, or is it new?

 

[JRuw91]

The engine is brand new. It doesn’t vibrate horribly by any means.

 

[JRuw91]

When your going 45-50 it vibrates but I don’t think it’s more than ordinary.

 

[kirrbby]

On the inside of the frame, where the motor bolts go thru, there should be spacers welded in at 3 of the 4 holes. I've seen those broken and or missing, many times.

 

[kirrbby]

If you were missing the spacer from the top right hole, it would have your engine cocked a smidge sideways. I'd imagine that could wreak a bit of havoc.
Looking at your pic, I think yours could be missing.

 

[69ST]

Dunno what to advise you regarding titanium motor mount bolts. Ti is light and strong, it's also brittle. I've used grade 12.9 steel bolts but it's been almost 15 years now, since I last spec'd them, so I can't remember the lengths. OTOH, that's ~18K miles worth of riding and no problems.

 

[red69]

Here are the stock engine fasteners. The shorter one is 115mm long and the bottom one is approximately 142mm.