Kawi2strokes.com Forum

Opinions okay or not okay ,straightening slightly bent fork tubes?

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1975 S3 project bike
1974 H1 project bike
1972 Yamaha R5
1974 Yamaha RD350

Only one vote - peace of mind and accuracy for 100 dollars!

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"One day, your life will flash before your eyes. Make sure it's worth watching." : anon.

I agree with Rod. Go to http://www.jessbikes.com and see what Jess has. If you find them in his ebay store ( jessbikes ) , contact him thru the website and save 10% off the ebay store price ( no fees so he passes on the saving )


Jeff

Lots of "IF's" here, but, IF you have decades of experience straightening bent fork tubes, IF you have the right equipment to do so, and IF the bends are very minor, go for it. IF any answer is NO, buy a new, or good used, STRAIGHT set of tubes.

Well I've been reading the S3 fork tubes wanted post and I know S3 tubes are hard to find cause my S3 had slightly bent tubes but luckily III aka Steve sold me a super straight S3 front end and that solved my fork issues , but after reading the wanted post got to think about the bent tubes I think they can be straighten, back in the 80's we straightened quite a few bent dirt bike tubes with nothing more than two V blocks and a hydraulic press it was easy too and pretty darn accurate, we never did a street bike but I think it would work just fine.

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1975 S3 project bike
1974 H1 project bike
1972 Yamaha R5
1974 Yamaha RD350

I had a problem with my H2 and found a very slight bend between the triple clamps up untill then I would have straightened them but for the hassel I had , no more unless you carnt get repos but thats H2s not S series some one must be making fork tube some where in this site or Know some one

Many years ago I had a set of H1 tubes straightened by a machine shop. I didn't see them do it, but it was explained to me the tube was mounted in a machinist's lathe. One end was gripped in a three jaw chuck and the other end was supported on a live center in the tailstock. A pressure block/roller of some sort was installed on the cross slide to apply pressure to the tube as it turned.

The tubes had a gentle bend in them amounting to about 3/4 in. deflection from straight. After the lathe treatment they were quite straight.

J

+1

Some of you know that I am looking for fork tubes for my S3 right now. They are not as available as H1 and H2 parts and they cost more. It will be about $300 per pair including shipping. Fast from the Past has them listed for $128 and 5 week delivery. I don't care about the delivery time. But my measly budget is strained already.

Jack - If mine were free of pits and slightly bent I would straighten them. I have done it once for a dirt bike and it was no big deal. It is worth a try in my opinion.

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Rotortech
Indianapolis
1974 S3

There are a few problems inherent in straightening tubes.

The pillows to set the tube in must be round, not V shaped, and there needs to be 3 of them, one on either end of the bent, and one at the center.

A lathe with some sort of pressure point won't be as good as using the pillow blocks in a press, and can also bend the lathe ways trying to push the tube straight from the under side of the tube.

Iy is very easy to permanently make the forks tubes un-usable by pressing with the wrong design pillow blocks. A V block puts pressure on two points of contact on the round section of the tube, NOT supporting the rest of the tube material, so, when tension is applied, those two pressure points can flatten out, causing the round cross section of tube to literally either dent, or mis-form into flats on the radius of the tube, binding them in the slider/bushings when reassembly occurs.

If pillow blocks are not used at all, the possiblilty of making the tube cross section flat on three points is very real.

There are a LOT of drawbacks to straightening tubes, but, if you have the RIGHT tools, fixtures and experience, it usually isn't a hard task to accomplish correctly. I am a great one for making as many of my own tools and fixtures as I possibly can, and have made a number of different size pillow blocks to use in straightening things like fork tubes. I am now working on a GMC 305E V6 for my flat bed truck, and it tossed an intake push rod a couple of months ago. I wanted to run the engine while waiting for a new rod, so, I straightened the pretzel of a push rod, and stuck it back in, ran the engine. Some, you get away with, some, you don't.

I also straighten a LOT of rear axles for ATV's, 3 and 4 wheelers, they seem to bend them here with great regularity, some really good bends as well.