Vintage Dirt Bike Q & A

I have both types of plastic tubing to use for Preload Spacers in my forks. Which material is stronger?

J

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

IMO: Go with ABS. PVC has problems.

Thanks! That's probably why RaceTech puts ABS in their spring kits. I have both types of tubing and just wondered if PVC would work.

J

_________________
#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

I was thinking that PVC would be stronger based just on where I've seen the two materials used in construction? PVC I've seen used for plumbing where there is pressure whereas ABS seems to be used for sewage return lines where there is no pressure. (But then it's been many years since I've been around a construction site.)

Enlighten me please?

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Those who can make you believe absurdities can make you commit atrocities.

Loren Davis
51y

PVC works fine in a buried pipe but wouldn't be good in an exposed use. In general ABS is more stable and structually sound then PVC. ABS should have better heat stability too if an exhaust pipe happens to be near it.

PVC could be made to work by adding UV protecters, fiber fillers, and anti oxidants during manufacture but I wouldn't count on anything that I didn't know for a fact had the extra ingredients added.

I put pvc in a bike I had before my elsinore and I had no problems with it and it was stable and reliable.

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1974/75 Honda MT 250

Rules are put there to be broken.

ricortes,

The PVC would be inside the fork tube, so exposure to UV would not be a problem. I was worried about the strength factor since it would be 100mm in length and preloading the spring.

J

_________________
#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

abs is def. stronger than pvc. take a piece of each and smash with a hammer. pvc shatters into lots of little pieces, abs absorbs the blow.

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1980 CR250R Elsinore

Then the only thing you would have to worry about is compatibility with fork oil. IIRC PVC uses DEHP for a plasticizer and it may leech out or the plastic may be attacked by fork oil additives. That is an easy one to check though: Just leave whatever plastic you choose to go with in warm oil overnight. You shouldn't have to go too hot, just body temp or maybe ~120 degree hot tub. Look for dimensional changes or surface softening.