Hardtail frame question

[solidstateirons]

I am being offered another hardtail frame that a friend was working on but he has no time to finish. I went to look at it and I noticed something that caught my eye and got me curious. The welded hardtail instead of being straight where the rear tire fits forming like an H shape, it kind of goes in a little (like \ / this, exaggerating of course, its just a little bit). Will that affect the bike performance in any way? or i would have to re weld the whole frame again with a new hard tail kit.

Please inputs?

Thanks in advance

 

[fredintoon]

Hi solidstateirons and welcome,
of course hardtailing affects performance, without rear suspension you will feel every bump in the road.
But that's just my prejudice against hardtailing.
If you mean that the hardtailed frame in question is trapezoidal in plan rather than square, all that matters (besides the welds being good) is that the rear wheel lines up square with the frame, with it's drive sprocket aligned with the engine sprocket and that it's tire will clear those narrowed frame rails.
Drop a rear wheel in the frame and check all those things, eh?

 

[solidstateirons]

Thanks for your reply!!

I have been told that I will feel every bump on the road but that doesnt concern me, maybe eventually when I get to feel it haha. But anyways, yes I was told everything mounts good on that frame but I will need to see it myself to make sure everything is in working conditions. I was just a little concern that the frame goes IN a little bit, it isnt too much but it does go in. I will post a picture tomorrow to give a better idea!

Thanks again!!

 

[59Tebo]

Solid,
Welcome to the party! Sounds like you're getting yourself into somebody else's headache. It could be the PO did the hardtailing "by eye". A frame jig would help a lot in keeping everything square. Alignment and uniformity are crucial. I don't know about a new hardtail kit, but you should probably scrutinize all the welds. There should be enough info in 'Xs650 Tech' (top of the page), frame chapter, to give you an idea how others have used jigs, plumb lines, etc. to verify their frame geometry. Good luck, and post us some pics on your project/progress!

 

[59Tebo]

...ooops! Not 'Frame & body'. Sorry. But click on the "Xs650 Tech" and put "hardtail" in the search window. THEN you'll get some useful info...

 

[gggGary]

It's a hard tail, grab a chunk of all thread, some nuts and washers, install through the axle slots. squeeze or spread as needed, check alignment. If it's trapezoid get out the maul and "adjust" til the sprockets line up. High tech; heat the tubes to dull red with a torch near the frame welds to relieve stress.

 

[solidstateirons]

Okay i will revise all of this info! I will head over now to take some pictures and show you guys what im dealing with. Also, in worst case scenario, would I be able to re-weld the frame with a jig this time?

Thanks everyone for your input

 

[solidstateirons]

So i finally got some pictures to show you guys. I noticed that I cannot fit the rear tire with the stock spacers, maybe to align the chain I would need to make my own spacers? Will the frame give me problems with riding if I just go for making my own spacers?

Here are the pictures.

^^ Here im pointing out what I think could be the problem. This tube is shorter than the other ones giving the frame that trapezoid look.

^^ Here shows that the space between the axle plates is 8" exact and not 8.5" like i saw in other threads.

^^ Here different views of the rear of the frame and the last picture is just the tire in place with just one spacer on the left side.

Let me know what you think!

Thanks in advance!

 

[figure8]

Based on that last pic something definitely seems off to me, but then again I'm hardly an expert. Would it be possible to throw the engine in and check alignment of the sprockets?
Speaking of the engine, can I just not see it or is the lower rear engine mount gone?

 

[hard_y_rd]

Pull that cheapo scissor jack from the trunk of your car and put it between the axle plates. Crank it out past 8.5 cause it will want to bend back in. I don't know how much. Probably 9 or 9.25 inches. The support tube was likely welded without a 8.5 inch tube in between the plates. The heat from welding shrunk it. As for alignment, you'll have to get the wheel in there with the spacers and axle adjusters. You may have to add washers in there.

 

[solidstateirons]

Yeah all the mounts for the engine are there. Thats gona be my next step after i figure out how to center this tire. Im thinking about buying a bunch of washers and add one by one until i see the tire centered and then measure the washers all together and make spacers out of thick pipe. You think that would work? Also I have noticed that all the support tubes measure 8.5. Only the distance from an axle plate to the other is 8", so just that part is off. Should i spread them out or should I find a way to make some spacers for it.

Im going nuts

 

[Ranger]

If the cross braces were welded in without the axle plates being braced the proper distance apart, then the welding would pull them together. I've been there with another frame I was working on. I just put a bottle jack in between the axle plates and cranked on it until it was right.

 

[solidstateirons]

so that would pretty much fix the problem? wont have any problems riding the bike?

 

[Ranger]

so that would pretty much fix the problem? wont have any problems riding the bike?

Unless something else was done wrong, my guess is this would fix your problem. At the end of the day, as long as your neck lines up perpendicular to the center of your rear axle, the rest of your frame could look like spaghetti, and you'll track a straight line.

I think you still have the right idea of playing with your rear wheel spacing using 20mm washers to make sure everything lines up properly before you make spacers.

 

[solidstateirons]

I shall give it a try with the washers then and if it works out i wont mess around with the frame. But if i need to mess around with the frame i will do what you guys said. UNLESS!! it is obligatory that the space between each axle plate has to be 8.5"

 

[fredintoon]

Hi solidstateirons,
Tee-joint welds ALWAYS warp the top of the tee so it ain't straight no more, because there's a (hopefully) full penetration weld cooling and shrinking on one side but not on the other.
Betcha your hardtail started out at the correct 8-1/2" spacing and was only 8" after the welds cooled.
Back in the day I worked with a guy who knew how to fix warped weldments.
He'd go around the warped weldment making chalk marks on it:-
"Lay an X long x 1/8" weld bead here and a Y long x 3/16" weld bead there and it'll pull straight again".
And it did.
But you ain't got the decades of training and experience it takes to be able to do that.
Like hard y rd said, jack it back out to 8-1/2" again and use the stock spacers.

 

[mrtwowheel]

Don't alter the stock spacers until you spread the axel plates out to 8.5 inches. Don't alter the stock spacers until you line up the sprockets. This is what I would do.....install the engine, spread the axel plates, bolt a 8.5 inch pipe between the plates. clean the front sprocket, use a string tied in front of the front sprocket face then slide the string over until it touches the rear of the front sprocket face to get a mark on the pipe in line with the front sprocket. That mark on the pipe should be 3/4" from the inside of the left axle plate. In a perfect world, using the stock adjusters, you will have 1/8" washers against the outside of the axle plates and 1/16" washers against the inside of the axle plates. So, in this order from the outside, adjuster-1/8" washer-axle plate-1/16" washer-adjuster, both sides being the same, stock spacers in place.

Scott

 

[solidstateirons]

Hi solidstateirons,
Tee-joint welds ALWAYS warp the top of the tee so it ain't straight no more, because there's a (hopefully) full penetration weld cooling and shrinking on one side but not on the other.
Betcha your hardtail started out at the correct 8-1/2" spacing and was only 8" after the welds cooled.
Back in the day I worked with a guy who knew how to fix warped weldments.
He'd go around the warped weldment making chalk marks on it:-
"Lay an X long x 1/8" weld bead here and a Y long x 3/16" weld bead there and it'll pull straight again".
And it did.
But you ain't got the decades of training and experience it takes to be able to do that.
Like hard y rd said, jack it back out to 8-1/2" again and use the stock spacers.

yeah that is definitively something a scientist would do haha! I will just stick to the jack. I just wish I had tons of knowledge about welding lol

 

[gggGary]

Spread the axle plates with all thread and nuts then heat the tube dull red at the cross braces, let it cool. Do check the perpendicular.

 

[solidstateirons]

Don't alter the stock spacers until you spread the axel plates out to 8.5 inches. Don't alter the stock spacers until you line up the sprockets. This is what I would do.....install the engine, spread the axel plates, bolt a 8.5 inch pipe between the plates. clean the front sprocket, use a string tied in front of the front sprocket face then slide the string over until it touches the rear of the front sprocket face to get a mark on the pipe in line with the front sprocket. That mark on the pipe should be 3/4" from the inside of the left axle plate. In a perfect world, using the stock adjusters, you will have 1/8" washers against the outside of the axle plates and 1/16" washers against the inside of the axle plates. So, in this order from the outside, adjuster-1/8" washer-axle plate-1/16" washer-adjuster, both sides being the same, stock spacers in place.

Scott

This took me a few mins to understand haha but I kind of get it. Only part that confuses me a little is the part of the string. Would there be a way to do like a diagram so I can have an idea?