Sloppy frame mounts

Ron L

Ron L

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Has anyone else noticed that the lower front engine mount stud is 5/16 inch (because the engine case bore is 5/16 as is the lower front engine plate bore), but the tube in the frame through which this stud passes is 3/8 inch!? While there are several frame attachment points, the front mount has only two. My fix is to use a two inch section of stainless tube that is 3/8" OD and .020" wall as a shim/spacer in the frame mount tube. This isn't a perfect fit, but takes up most of the .0625". I am amazed that this space wasn't shimmed at the factory.
 
Yep my lower front mount is also loosey goosey.
I am wondering why as well. Could it have been from the Matchless single cylinder to Norton twin transition? :?:
Cheers,
Thomas
CNN
 
Could it have been from the Matchless single cylinder to Norton twin transition?
Click to expand...

I suspect you are correct. However, I am surprised that ZDS motors or the Norton factory did not put a bushing in that hole!
 
Ron L said:
........ My fix is to use a two inch section of stainless tube that is 3/8" OD and .020" wall as a shim/spacer in the frame mount tube. This isn't a perfect fit, but takes up most of the .0625". I am amazed that this space wasn't shimmed at the factory.
Click to expand...

I have never hesitated to stray from originality when I thought there was room for improvement.

Slick
 
The P11 frame lug holes aren't 3/8" (I know that's what's called out), they're 10mm. I suspect that's because these frames were made at the time that British industry was transitioning from English standard measurement to Metric & it was considered 'close enough'. This accounts for the continuing issue with engine mounts loosening on these bikes. Once they loosen a bit the spacers fret the aluminum frame plates & the issue just gets worse.
My fix, on my 3d P11, was to ream the engine mount holes to 10mm & make M10 studs. In 8 years of VMX competition they've never loosened & vibration was significantly reduced. It did require cleaning some fabrication trash from the frame lug holes, but NOT enlarging the holes & all the studs were a nice tight moderate push fit.

Mark in SC
 
Perhaps they were 10mm or perhaps they were 3/8 (9.5 mm) and were beat out from the vibration of the 5/16 studs.

Your solution of confirms my suspicion, that this was at least one of the causes for the problems of loose fasteners and vibration cracks.
 
Ron L said:
Perhaps they were 10mm or perhaps they were 3/8 (9.5 mm) and were beat out from the vibration of the 5/16 studs.

Your solution of confirms my suspicion, that this was at least one of the causes for the problems of loose fasteners and vibration cracks.
Click to expand...
What about making new spacers with a boss that is the same diameter and thickness of the frame fixing lug and the hole for a 5/16" stud? :idea:
Another option would be to just make a short spacer to fit the odd size hole in the frame and drill to the bolt size.
Cheers,
Thomas
 
If you try the hole spacer or spacer/boss route you'll wind up with a wall thickness of 0.009".
Good luck with that!

Mark in SC
 
OldForge said:
If you try the hole spacer or spacer/boss route you'll wind up with a wall thickness of 0.009".
Good luck with that!

Mark in SC
Click to expand...

10mm = 0.394" (3/8" = 0.375")
5/16"=0.3125"

0.394-0.3125=0.0815"
0.0815/2=0.0408" wall thickness
 
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