New bike build.

[Mack]

Hey fellas,
Ever since ive had my bike ive had troubles with my chain rubbing on the top side of the swingarm up near the front sprocket. It started by just making a mess of the crappy weak rubber swingarm protector. I then made the problem worse by gettin a smaller rear sprocket which has created more of an angle between the two sprockets, and now my chain has just starting to eat the **** out of my swingarm. What should i do??? if i put some chopping board **** on there it will just increase the angle even more and create much more friction, but i have no idea how strong this **** is sooo.....
Is it possible to get smaller rear shock, im saying this because if i get a smaller/shorter shock it will decrease the angle of the swingarm.
any help would be appreciated!
cheers, Michael

Yes this problem exists on many bikes. The frame geometry is poorly thought out. Some of the newer frames are lowering the swingarm mounting point finally. A good frame has the swingarm pivot about level with the second engine mount. The really bad ones will have the swingarm pivot anywhere upto an inch higher. It is worsened when smaller sprockets are fitted and/or a longer shock.

You can fit a shorter shock and it doesn't have to be very much shorter to make a difference.
You can adjust the shock mounts by welding them up and redrilling the holes where you want.
You can weld up and redrill your engine mounts to raise the motor if you have room.
You can cut and remake the swingarm pivot spot to lower the swingarm.

The last option is my choice. I'm doing one for myself as we speak. I have cut the entire lower section from an alloy BBR pro copy and am lowering the swingarm pivot and also making it into a very strong cradle mount. This has the advantage of raising the rear to match a longer set of forks, being able to run a longer shock and gain extra travel to match the front and limited friction and damage from chain rubbing. Overall it means the bike can be set up exactly how you want it.

 

[Mack]

The point of no return.....



This is the original mount spot. Its a bit hard to see but it is well above the engine mount. Always had a bad chain rub this frame.



This is where its going to be. Lower and further back for a little more wheelbase length and will take a longer shock with more travel.



It will all swing off this. I can't show it in position properly 'cause the footpegs are still on that motor, but it is 10mm T5 Plate. I will jig it all up so the steering tube is actually 90 degrees in relation to the swingarm and everything is spot on square, then weld 'er all up (few other pieces box that lower cradle section up) and Bob's your uncle!

 

[Mack]

Heres a little update on my frame mods.


Here you can see the new swingarm pivot tube welded up underneath the old one. I have lowered it an inch and also moved it rearward an inch.


It is still hot from welding in these shots, but will get tidied up and polished to match the rest of the frame next.


Those two cradles are 10mm high tensile plate. I haven't drilled the new engine mounts yet. The hole you can see is the old swingarm hole. I am going to just put a 10mm bolt through it just because its there and every little bit helps.....


In going through this process with a frame it really allows you to build the bike exactly the way you want it. I'll tell you a few reasons why.

No. 1 and the biggest reason! Most of the frames I have seen are not very well jigged if they are at all! This frame for e.g was out a mile. ( for the eagle eyed ones you can just make out the up and down discrepancy in the top pic. You can't see though the other directions it was out!) You can see it is out With the front forks installed and set to exact same lengths on either side, I install the axle and then sit the frame on a truing jig so that the swingarm pivot can be checked against the front axle with the frame dead square from the forks. The original swinger pivot was not even close to being level.... or straight.... or the left to right axis correct! So with the frame jigged like this I welded the new pivot tube onto the bottom of the old one so that it is dead on to the front axle. This is one of the no. 1 causes of the bike feeling like it is tram tracking and handling like ****. Also your rear suspension will not work properly and most likely keep failing.

2. Many of the frames I see have a multitude of steering head angles and I doubt much thought has gone into this at all, so you can set your preferred angle and set the cradle to suit.

3. Still on the engine, you now have the chance to level the engine with the front axle and swingarm pivot and in doing so can get perfect alignment of your front sprocket. Not to mention the fact it no longer rubs on the swingarm, it also reduces the risk of premature wear of chain and sprocket. It also reduces the chance of coming off when its not 'sposed to.

4. I was able to reset the brake master cylinder position which was in a **** of a spot and collected the swingarm on big hits. Plenty of clearance now.

The swingarm itself is having the crap inner bushes bored out and new bearings installed inside and out. The bush setup on many of the China bikes is one of their worst shortcuts IMO.

Finally when the new shock arrives the shock mounts will be bored and fitted with decent bushes and trued vertically so that the rear shock can be setup just how you like it with zero side thrust or unwanted grabbing at the pivot points. Then both wheels will be correctly spaced and aligned and bingo...she's nearly ready to take the 160 ya got sitting on the bench....

 

[unit_mx]

nice bit of work there

 

[Hillz]

nice MACK! that's a nice frame, if ya do up a STOCK crf 50 frame like that with gussets, under $650 i will happy-ly purchase 1.

 

[cass38a]

Looks very well made. Are you going to get the frame heat treated to remove stresses before you finish? Have you got any pictures of your Jig?

 

[Mack]

No it won't be getting heat treated, it should be very strong as is. I have never been able to find anywhere that will heat treat for you, as in the past I have investigated this. No luck.

For a bike jig I just use a length of ' I ' beam I had ground flat years ago. You check the forks for square and equal length then clamp your front axle to it and take all other measurements from the beam and axle. You could use anything like this. Even a length of 100x100 square tube or something similar. Even by eye, as soon as you start to setup you will see clearly which way your going to have to go to correct the bike.

 

[cass38a]

If you are looking for a place to heat treat it I may be able to help let me know and I will see what i can do.

The guy that made my daughters custom wheelchair had it heat treated so I can get you his details.

 

[50s BRotherhood #1]

nice frame man... good weldin job.... looks the goods

 

[Mack]

If you are looking for a place to heat treat it I may be able to help let me know and I will see what i can do.

The guy that made my daughters custom wheelchair had it heat treated so I can get you his details.

Yeah cass' I'd be real interested in that. I'd be stoked if I could find a source for getting that done to alloy frames.

 

[daniel40]

hey looks good

 

[Mack]

(Daniel asked if I made it all from scratch)
No, it's a Taiwanese alloy frame. If the mods would bring the first shots of the project across from the other thread you'll see what has been done. I've PM'd foolspeed so we'll see.

 

[cass38a]

Ill PM you the guys details, Let me know if you have any luck.

 

[Mack]

...after a polish...




phone cam sneak preview....

 

[THUMPY125]

frame looks excellent, did you do anything to the motor before putting it back in. like upgrade to a new motor, bored it out.

 

[daniel40]

looks really really good looks real strong

 

[Mack]

Well that is a temporary engine for fitting purposes. The engine going into it is being built concurrently with the rest of the bike.