Building NEW oil lines for a GT750

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The1970's
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Building NEW oil lines for a GT750

Post by The1970's »

Hi all,

I've had my GT750 for several years now and one problem that I have been constantly plagued with is old, brittle, and cracking oil lines. I'm on my 3rd set now and am sick of buying $80+ replacements from Ebay and hoping they were better than the last set. Surely there is a better way. In my spare time over the past few months I've done lots of research and testing to come up with a solution and I have solved many of the problems, but I've gotten a bit stuck and think some of you may be able to help.

Suzuki originally built these lines out of Polyamide (Nylon 6) in a few main "components" they are:

The manifold: The small injection molded ring which is sandwiched between the top engine case and the oil pump.
The Lines: Obviously these carry the oil from the oil manifold to the check valves. They are 4mm O.D.
The check valve fittings: Small fittings at the end of the lines which adapt the 4mm O.D. Nylon line to the larger ~6mm check valve barb.

The lines were then hand assembled by routing them through the two rubber grommets and slid into the manifold, where they were bonded in place along with the check valve fittings on the opposite end.



Injection molding new manifolds is very cost prohibitive, $2,000-$3,000 to have an injection mold made doesn't make any sense only to produce probably a handful of parts. However, I've made a computer model of the manifold and can have it machined out of a Nylon sheet by a few different mail order manufacturers at a cost of roughly $30/part. So that should take care of that part
manifold.png
The lines themselves aren't anything special, I have bought a 100' roll of off the shelf 4mm O.D. Nylon tubing and experimented with several different ways of forming it to the correct shape. The best option I have come up with is using a fixture to keep the tight bends from kinking and then running steam through the line to keep it's "memory" of the desired shape. At this point I THINK I have an acceptable method of reproducing the lines.

I haven't done any work with the little push on fittings at the end of the lines but I think these could fairly easily be machined out of Nylon bar stock and then bonded onto the lines. The originals were likely also injection molded and pumped out by the hundred, but the same issue applies here as the manifold.

Now here's where I get stuck: Bonding the parts together

Nylon is a notoriously hard material to glue. Originally I suspect the parts were bonded together with a Phenol procedure which essentially melted the nylon together (almost like plastic welding). Nowadays Phenol is highly regulated and can only be purchased by researchers or companies with a valid need to use it for production. I have tried a few different types of glues including cyanoacrylate, epoxy, a few loctite products, etc. None of them really produce a comparable result to the originals. A few of them would likely do the job, but I could still get them to fail after a some heat cycling and exposure to oil/fuel. I know a few members here have had success in splicing lines together, which adhesives have you used that have worked?

Some of the other issues I have run into is finding someone to produce the rubber grommets at a reasonable cost, and obviously the check valves have been an ongoing issue on all GT's. At this point, this has been a much bigger undertaking than I originally thought. I would be happy with making new lines and having to re-use original check valves/grommets/retaining rings. But I still list it here in case anyone has more experience with these things than I do.

It's a lot of work to make these things but someone has to do it if we're going to keep these bikes on the road...I went looking yesterday and was only able to find 1 serviceable set of lines on Ebay at a listing price of $180!
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Alan H
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Re: Building NEW oil lines for a GT750

Post by Alan H »

How about cutting a thread on the pipes and manifold and screwing them together? Kawasaki valves are easily obtainable for the engine end too. Perhaps someone with a 3D printer might have a play with your detailed info?
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jabcb
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Re: Building NEW oil lines for a GT750

Post by jabcb »

Interesting. Looking forward to see how well this works out.
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The1970's
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Suzuki 2-Strokes: GT750, GS750, TC185

Re: Building NEW oil lines for a GT750

Post by The1970's »

Alan H wrote: Thu Jun 10, 2021 12:02 am How about cutting a thread on the pipes and manifold and screwing them together? Kawasaki valves are easily obtainable for the engine end too. Perhaps someone with a 3D printer might have a play with your detailed info?
Threading them together is something I haven't thought of, and probably would work to seal the pipes, but physically couldn't be done given the fact that the lines have to be routed through the rubber grommets before being attached to the manifold.

I do have a 3D printer but it is more of a hobbyist model. Admittedly I don't have much experience in printing Nylon parts but I think it would present a bit of a challenge to produce parts that are strong/temperature resistant enough to be used on an engine.
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Re: Building NEW oil lines for a GT750

Post by Zunspec4 »

There was an article in the Oct 2020 issue of Classic Motorcycle Mechanics covering the refurbishment of Kawasaki oil lines. The adhesive recommended for joining the oil pipes was JB Weld Plastic Bonder. Might be worth checking out.

Cheers Geoff
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Alan H
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Re: Building NEW oil lines for a GT750

Post by Alan H »

I used nylon/something else? flexi tubing on the SRIS lines on 3 GT550s yes I know it's not 'proper' but it works, goes where I want it and does the job. I'll find a link 'soon'


Ish.
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Re: Building NEW oil lines for a GT750

Post by joolstacho »

For gluing... Try this stuff. It's specially formulated to glue those 'difficult' plastics.

https://www.amazon.co.uk/gp/product/B00 ... UTF8&psc=1
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