73 750 commando frame dimensions

I have just installed new isolastics and was in fact unable to fit the second bolt through the frame/isolastic interface when reinstalling the engine. I pulled the engine out and checked the frame dimension between the isolastic mounting lugs. Specifications say 464.31mm, (18.28"). My frame reads just shy of 18.5", way too much to force fit. There is no obvious deformity and both sides read the same, 18.5". I cannot see how the dimension could have increased as it seems to me any bang up should have reduced that dimension. The reason I replaced the isolastics was that there was extreme movement in the swing arm and anyway I thought the vernier type would be simpler to adjust. I have had the bike for nearly 20 years and have been slowly reconditioning it, finding various examples of butchery and poor mechanics as I go along. Any comments would be appreciated.

Misalignment when installing isos can be played with by jacking up various areas of the engine or frame to get the bolts to pass. A tapered drift or two is very useful for this too.
Russ

Thank you Russ,
I did try a tapered drift but the problem is that the mounting lugs on the frame are just too far apart according to the specified frame dimension, and visual sighting when attempting the engine installation. I hesitate to force this as I feel the isolastics will unevenly loaded. What is your experience with the accuracy of the frame specs vrs real life measurements?

Unfortunately the file is not handy, but several years ago I had a friend that is very proficient in AUTOCAD place the info presented in the frame checking data into several file formats. The idea to preserve the info and have it available to modify to aid in racer projects. The tube angle depicted as 67 2/3 degrees would not bring the points together once the other data had been entered. Based on the industry standard engineering software from the 2005 time period, this info has some subtle errors. If the design draftsmen from the 1970s possibly made errors, maybe the craftsmen @ Reynold made errors also. If that is the case, the isolastics would be preloaded to get the hardware to fit. Maybe not optimum, but if it worked good before it would likely work good again. Add the frames that were made in Italy and the variables are multiplied.

Thank you again. Your points are well taken. As a matter of fact, I did a quick autocad dwg of the engine mounts, using the data from the shop manual,(same as your attachment), to check the height of the forward engine mount tabs from the base of the frame. My existing front mounts are about 1.5" lower than the autocad dwg, so obviously something is badly amiss. The rear mounts are about right. Your summation becomes more likely. Thanks again.

On mine I don't use the vernier type adjusters but can usually get the end pieces in by hand. Maybe a little tight. The front downtubes are like wet spaghetti by themselves being movable by 2 x 4. I never measured the separation.