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Hopefully someone here can help, but I know this is a job that's normally done by an LBS.
I have a 2022 SC Bullitt, which has a dead EP8 motor. I have a new EP8 motor. Remove the old one, fit the new one, simple, right?
So, removed the old one. Plugged in the new one, then I go to bolt it into the frame, using the six M8 bolts. But this is odd, I notice that the gap in the frame is about 1mm wider than it needs to be.
On further inspection, I notice that the new EP8 motor (and indeed the old one) has threaded "top hat" inserts on one side of the motor, but not on the other side.
In addition to that, SC's exploded diagram of motor fitment states that the driveside bolts must be torqued up before the non-driveside bolts. The top hat insert things are on the non-drive side.
So I think I understand. For whatever reason there's a tolerance issue for the fitment. Whether Shimano couldn't get frame manufacturers to agree to a tight enough tolerance, or because they think the motor will swell with heat at times, or something else, I'm not sure. But I think the idea is that you bolt the driveside up dead tight, and then when tightening the non-driveside M8 bolts, these inserts will fractionally pull out of the motor body, before butting up against the frame and allowing the bolts to be torqued.
Indeed, on my old motor I can see all of the inserts have a gap of between 0.5 and 1mm between their shoulders and the motor's body.
Thing is, on the new one, they don't move. I've tried tightening the bolt until my carbon frame started to deflect... didn't like that. I've tried putting a bolt in the insert, then driving it out from the other side, but they don't seem to move.
Does anyone know what the mechanism is to get them to move? Is it just a "reet tight fit", and I need to **** it harder? Should I be hitting them with some penetrating oil etc?
Shimano's dealer manual doesn't mention these things at all - they do say to tighten driveside first, but that's as much detail as is given on the subject.
Ta all!
You’re right in that it’s to allow for variations on manufacturing tolerances of the motor mount on frames.
I’d find a spacer that has an ID slightly bigger that the OD of the NDS top hats, and use that along with the mounting bolts (or longer bolts of the same thread size/pitch) and washers if required between the head of the bolt and the spacer to coax the top hats into moving with the motor off the bike to prevent damage to the motor mount/frame. Allows you to give the bolts some welly without frame anxiety.
You want maximum thread overlap to prevent stripping the top hats but without the risk of the bolts bottoming out in the casting.