strenghtening rear frame loop

My rear loop has dropped about an inch at the back but this was not noticed when frame was powder coated an as I did not have all the rear mudguard fitting it did not show till the bike was almost finished. I have since rode the bike a it handles very well far better in fact than I thought I would so I have decided to fix the rear loop as it is nagging at me that its not right.
I sawed it off about 1/4 of an inch past rear shock mounts then hammered in some tubing that was close fit. It goes in frame for about 3 inches till the bend stops it and in the rear loop about 7 inches till the bend stops it. Then after measuring an test fitting seat an rear guard I welded loop back together .
Then to both inner and outer plates of rear shock mounts I welded 2mm thick plate about 8 inches long tapering off from about halfway along from 1 1/4 inches deep to miss the shock down to 3/8 deep. As I have seen similar repairs done and even new built racing frames with a similar long plate in that area .
So now am wondering if I should extend the shock mounts downward on the other tube till they reach the ISO bracket level or am I just getting carried away now????

Yep... stop where you are..... the rear loop in most cases just supports a few light and a mudgaurd... . Im suprised you didnt just "bend" the loop up with a bit of force.. (the same way it drooped)... .........

The factory improved the support on the MK3 frame by extending the inner gusset plate so it was approx 3" long on the tube and tapered.

I think you have already done enough

I did not have anything suitable to heat the loop with an did not want to risk damaging the frame somewhere else by putting to much force on by trying to just bend it back cold. Also i thought that by cutting the frame I could put sleeve in them to help line it up which it did and check the tube inside for rust which it only had a few small areas of very slight surface rust. The inside of tubes looked as it must have done when they were made 40 years ago but the air trapped in the frame for all that time smelt horrible an made you feel sick so much so I had to take a break

not suppose to put your nose inside the old tube :shock:

toppy said:

I did not have anything suitable to heat the loop with an did not want to risk damaging the frame somewhere else by putting to much force on by trying to just bend it back cold. Also i thought that by cutting the frame I could put sleeve in them to help line it up which it did and check the tube inside for rust which it only had a few small areas of very slight surface rust. The inside of tubes looked as it must have done when they were made 40 years ago but the air trapped in the frame for all that time smelt horrible an made you feel sick so much so I had to take a break

Click to expand...

I think that rear frameloop bent downwards a bit from years of loads n'weights is easy enough to set straight cold. Simplest way assembled would be to remove seat ,roll bike under a counter-pressure beam or bar at the sag point eg.where it happened (shock upper area) then grab the back of loop and heave upwards until happiness. Seems the problem with taking on a heavy passenger is the seat compresses down to rest that weight on the fender which transfers it to the fender fixing point at the end of the loop where it has the most damaging leverage forces pushing down. A pal here Reuben Tang showed me a tip to overcome this issue ,he made a seatbase with a sheetsteel tongue extension under rear of seat going backwards that takes the weight only forward to the upper shock-crossbrace area,not allowing that sag to fender. One day I will make a steel seatpan with this extension.

Ugh, unless the tubing is about to break from flexure you should not be able to bend it up by normal human strength w/o long lever and tying of trapping bike on the ground. The easiest way is how hobot did it, took new power coated frame and slammed down on floor with a throw rug between a few times till eyeballed right. The hard down side to my way is obvious. Could drain fluids and flip bike over a pivot and stomp down to lift the old gals
sag. internal rod or tube will stop it bending at the original point but still risky to carry over 50-60 lbs over rough stuff w/o putting struts from Zplates. I backed up next Peel with carpentry square plate extending about half way to carry more w/o the struts.

2x4 from the bottom of the back end of the loop, resting the front end of the board on the aft portion of the top tube, a little upward force and voila, simple easy way to bend it back.

I have seen your picture of your rear mounts Hobot an that's what made me start thinking of extending mounts downwards. I have made up a rear rack an it has bracing bars going down to passenger foot rest. I like to carry a strong chain so I can park it an hopefully it will still be there when it come back. An I don't use it off road or take passenger as its for me time away from kids riding so i think I may have done enough

Past Peel used alloy bar, almost square and current Peel used oval steel tube that was a loop on some tractor implement I could slice in half to end up with 2 mirror image struts with the ends angled for better alignment to the alloy rack. Main thing is clearing the shock springs so may have to space strut out 1/2" off Zplate or provide so bow to em. I try to use cycle for cargo trips, cases of beer, feed bags and of course now and then over loaded axle stressing luggage for distant rally with tools and spares and stuff for sale.

here's a decent view, spacer at the Z plate and clamp on mounts on the loop. The luggage rack forward bar ran outside the strut.


Hard bags cleared and struts used as part the mounting.

I like that 2 x 4 idea. Leverage is so powerfull. I use that idea occasionally as a beadbreaker.