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Old 11-13-2012, 10:03 AM   #1 (permalink)
IronButt
 
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Motor Mounting Problem

I am doing a chopper build and ran into a little issue. The frame is an aftermarket unit. When I put the motor in I noticed that the motor would rock a bit side-to-side. Traced the problem to the rear motor mount seat, that is the flat plate welded to the seat tube. First I noticed that the weld itself spilled over to where the motor was sitting on it. I ground a bit of the weld off to provide a flat spot for the motor to sit. That helped significantly but there was still some rocking going on. Turns out the rear motor mount is welded on to the seat tube a bit crooked. Using a torpedo level and some shims I was able to determine that (relative to the front mount seat) the rear motor mount seat is higher on one side by approximately .017 to .020". Using a hand grinder and a flat file I managed to take the high side down. Right now the difference is down to about .010". It has been slow going, but with frequent checking using a machinists straightedge I have been holding the surface pretty flat while I take down the high side. I intend to work it till I get the gap all the way out, but I am curious- Is there a "tolerance" on motor mount seats? I have never ran into this but then again it could be I never noticed. Anyone ever run into this- any insight?
BTW, I have the build thread posted here in the Chopper forum but wanted to split this off and solicit some opinions.
Thanks
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Old 11-13-2012, 03:19 PM   #2 (permalink)
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What do you mean by "tolerance" on rear motor mount? Do you mean how thick or thin the mount needs to be after you've taken off .010"? If so, I would think you'll be okay. I think there is more torque on the front motor mount when the engine is running. I would say keep working at it until you get it level. You still may need to shim the motor anyway.
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Old 11-13-2012, 05:14 PM   #3 (permalink)
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No, not how thick or thin the motor mount seat can be, but how far from level it can be. Doesn't really matter, I am going to keep taking it down till I get as flat as possible. Was just wondering if
And yeah, from what I have seen so far it looks like I may need to shim the motor as well, but I want to shim it on two relatively parallel planes.
Thanks for the response. BTW, don't know if you caught my remarks to you in a different thread- NICE job on the Frisco shovel!
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Old 11-14-2012, 09:15 AM   #4 (permalink)
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Quote:
Originally Posted by ramcr913 View Post
No, not how thick or thin the motor mount seat can be, but how far from level it can be. Doesn't really matter, I am going to keep taking it down till I get as flat as possible. Was just wondering if
And yeah, from what I have seen so far it looks like I may need to shim the motor as well, but I want to shim it on two relatively parallel planes.
Thanks for the response. BTW, don't know if you caught my remarks to you in a different thread- NICE job on the Frisco shovel!
ah yes, thanks for the compliments... Getting those mounts level as can be will be the key. Kind of a bummer they didn't weld them level to begin with.
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Old 11-17-2012, 08:23 PM   #5 (permalink)
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Well I got back out there today and finished flattening the motor mount boss. Stayed on it with a hand grinder- light passes checking it with a straightedge. Pictures are kinda deceiving but the seat is now pretty flat.


I set the motor back in and the "rock" was gone. Got the tranny in, then the motor plate. Tightened down the rear mounting bolts and checked the front mount for clearance. I managed to get a .003" feeler gauge in there but it was a tight fit. It was a tedious job, but I guess it was necessary.
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Old 12-09-2012, 11:06 AM   #6 (permalink)
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Quote:
Originally Posted by ramcr913 View Post
Well I got back out there today and finished flattening the motor mount boss. Stayed on it with a hand grinder- light passes checking it with a straightedge. Pictures are kinda deceiving but the seat is now pretty flat.


I set the motor back in and the "rock" was gone. Got the tranny in, then the motor plate. Tightened down the rear mounting bolts and checked the front mount for clearance. I managed to get a .003" feeler gauge in there but it was a tight fit. It was a tedious job, but I guess it was necessary.
Looking at your photo, it looks to me like you have a bad weld at the rear motor mount to center post. I don't know what it looks like on the bottom, but the top looks week, and this is an important connection. The motor torque will be pushing down on this mount, so if it were me I'd get a better bead put on that connection before anything else. The misalignement of the mount could have been a result of this bad weld.
I think for the money the Ultima products are well worth using, I built one, but look the welds over and be sure they look trustworthy before you cover them up!
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Old 12-09-2012, 08:59 PM   #7 (permalink)
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tc96evo-
I will take a closer look at the weld. I am not much of a welder myself, but I have a friend who is a welder by trade. He looked the frame over last summer and said it was good, but after finding a crooked mount, I will get a couple more eyes on it.
Thanks for the insight.
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