GT750 oil pump

Everything you want to know about oil but were "afraid to ask"!

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tz375
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GT750 oil pump

Post by tz375 »

I recently bought an oil pump of ebay for one of the project GT's. It was used and cheap and described as being in excellent condition.

When it arrived, it looked clean, but when I rotated the shaft, there seemed to be no resistance to rotation. Sure that felt good, but I had a nagging feeling that I should be able to feel something even at IDLE position. So I cranked the lever up to full open and rotate it and no difference. At that point I knew for sure that something was wrong. Turns out that both pistons were jammed and not moving. Had I fitted that pump disaster would have followed as surely as night follows day.

The Pump page has been updated at Here.
two-stroke-brit
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Re: GT750 oil pump

Post by two-stroke-brit »

thanks tezer i have just bought a NOS pump from ebay and i will check it out as per your link,
very handy referance site.
cheers mark
She will never be pretty but hoping she will be a fun ride.

1973 SUZUKI GT750K.=SOLD
yamaha speedtwinn 100 barn find =SOLD
1x 1973 kawasaki H1 (restored)
1x 1973 kawasaki H1 (basket case) =SOLD
1982 HONDA CB900F =SOLD
1982 YAMAHA RD350LC.
1985 RZ350N
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tz375
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Re: GT750 oil pump

Post by tz375 »

Thanks Mark,

More of a collection of random thoughts than a reference site really.
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oldjapanesebikes
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Re: GT750 oil pump

Post by oldjapanesebikes »

tz375 wrote:Thanks Mark,

More of a collection of random thoughts than a reference site really.
But a very useful collection of thoughts I think !

I wrote about a test rig I used here. It was a bit of work to set up, but it was a quick way for me to sort through the bin of collected pumps I had sitting there. I've put the two 'dead' ones to one side for possible future rebuilding using Richard's information as a guide.
Ian

If at first you don't succeed, just get a bigger hammer !
two-stroke-brit
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Re: GT750 oil pump

Post by two-stroke-brit »

oldjapanesebikes wrote:
tz375 wrote:Thanks Mark,

More of a collection of random thoughts than a reference site really.
But a very useful collection of thoughts I think !

I wrote about a test rig I used here. It was a bit of work to set up, but it was a quick way for me to sort through the bin of collected pumps I had sitting there. I've put the two 'dead' ones to one side for possible future rebuilding using Richard's information as a guide.
i like the test rig and the link to the water pump trick.
cheers mark
She will never be pretty but hoping she will be a fun ride.

1973 SUZUKI GT750K.=SOLD
yamaha speedtwinn 100 barn find =SOLD
1x 1973 kawasaki H1 (restored)
1x 1973 kawasaki H1 (basket case) =SOLD
1982 HONDA CB900F =SOLD
1982 YAMAHA RD350LC.
1985 RZ350N
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tz375
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Re: GT750 oil pump

Post by tz375 »

Anyone that knows me, knows that I preach from the gospel of St Gordon (Jennings) about more oil making more power.

That's fine and I still believe that, but on the street I'm not using full throttle and I'm making so much smoke that it's getting to be annoying. Of course I have no idea which bottle of oil I tipped in there, but I think it was Yamalube S which is fine on my RZ once it warms up.

Dyno testing showed that it does in fact run clean when the pipe finally gets up to temperature, but idle and low revs in this weather make for a very smokey exhaust and I don't need to draw any more attention form concerned citizens or or town's "finest".

So I decided to adjust the oil pump slightly and low and behold I could not find a reference in the manual to setting the pump on a late model GT750.

Does anyone have a reference to the correct adjustment for a 74 on pump? I may end up having to modify the pump lift cam to get less oil at low to mid revs and the stock amount at full open, but I should start with it adjusted by the book. Anyone got that book?
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Re: GT750 oil pump

Post by oldjapanesebikes »

tz375 wrote:Does anyone have a reference to the correct adjustment for a 74 on pump? I may end up having to modify the pump lift cam to get less oil at low to mid revs and the stock amount at full open, but I should start with it adjusted by the book. Anyone got that book?
There is info on the Resources site - check the owners manual for the GT750 - page 46. 8)
Ian

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tz375
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Re: GT750 oil pump

Post by tz375 »

Thanks Ian,

I hadn't seen that page before. It's basically the same as the Haynes manual but clearer than my pdf copy which is pretty dark.

The real issue here is that with 3 pipes the smoke is more diffused and with the single pipe, all that smoke is coming out of one hole, so it looks much worse. I was surprised by the film of oil after 5 minutes of running. I expect it to be oily, but not that much. Of course the pipe wasn't hot enough to burn off the oil and on the dyno, the first few runs were very smokey, but later runs were fine after the pipe was up to temperature.
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Re: GT750 oil pump

Post by oldjapanesebikes »

tz375 wrote:The real issue here is that with 3 pipes the smoke is more diffused and with the single pipe, all that smoke is coming out of one hole, so it looks much worse.
Yep - although I'm not sure it makes a lot of difference actually as I see the same with stock and spannies when the engine is cold and has been sitting for a few months. And the black and whites don't like too much. Last spring on the first run my engine was still cold when I pulled out onto a main road, and opened up just a little bit to get up to speed - all I could see behind me was the dim glow of the flashing lights looming through the haze :? He let me off, but was not amused...................... 8)
Ian

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tz375
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Re: GT750 oil pump

Post by tz375 »

I had reason to suspect that my bike was hemorrhaging oil internally, so I checked the oil tank and that didn't look good. I removed the oil pump and oil line covers and could see that they all contained oil and no air bubbles. I removed the oil pump and drained the oil tank and noticed that one of the lines were no longer the same color as the rest.

Either I had a chameleon oil system capable of changing color to blend in with the surroundings, or else I had a problem with leaky check valves.

Image

The quick and dirty plan was to pump alcohol down that line to flush out the dirt and if I did that I'd have to drain the crankcases. Off came the carbs, pipes and radiator bottom hose, followed by the SRIS block off bolt in the right cylinder and out poured 250ML of injector oil. Then I flushed the line with alcohol followed by injector oil and the pipe just drained before my eyes.

It refused to come good and close, so off came the radiator bottom connector to get to the center SRIS screw and then the bypass hose and starter cover came off to get to the banjo bolts. Another 200 ml came out of the center pot and few cc out of the left side.

I flushed all 6 lines with oil, degreaser, carb cleaner and fresh oil and two lines just bled out each time I left the octopus for a few minutes it drained.

I had three sets of oil systems. One on the bike bled out on three lines when held up, a spare set bled on 2 and the third set had a leg missing. Not an auspicious sign. I ended up stripping the check valves out of one set.

Image

The second and 4th are missing their balls - well actually they are inside the springs. See this one for a clearer view of that.
Image

I believe that is caused by the use of compressed air to clear out the pipes. The springs are ruined and will have to be replaced. And those legs are now not usable, so the parts will be kept to repair the main set - I hope. I need to wok out how to repair the hoses and to work out why one cylinder has a springless check valve in mid stream
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Re: GT750 oil pump

Post by RING_DING »

TZ....this is great stuff, so many thanks. The repair procedure is eagerly anticipated!
1973 Suzuki GT750K with Sidecar - Bonneville 2020
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tz375
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Re: GT750 oil pump

Post by tz375 »

I keep waiting for that episode too. Ian (OJB) pointed me to a couple of threads on repairs and to a splicing suggestion from Chris (Coyote). I'd like to use a flexible line like they use on Yamaha RDs and Kawasakis so I tried a couple of things so far and they are not good. The problem is that the main Octopus is some form of molded nylon which is rigid and old and brittle.

And the other issue is that the banjo ends are fairly large compared to say an RD or a snowmobile, so that complicates matters.
It might be possible to change the crankcase ends to push in types with smaller barbs like the SRIS nipples and use in-line valves.

My short term fix is to order yet another one off ebay and to do a lot of praying that it works. I chose a dirty one because it looks like no one ever cleaned it (with compressed air) but it may just be another leaker to add to junk pile.

I still have no idea why that one in-line fitting is different to the rest and has no spring.
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Re: GT750 oil pump

Post by oldjapanesebikes »

tz375 wrote:It might be possible to change the crankcase ends to push in types with smaller barbs like the SRIS nipples and use in-line valves.
That's an interesting idea :up:
tz375 wrote:My short term fix is to order yet another one off ebay and to do a lot of praying that it works. I chose a dirty one because it looks like no one ever cleaned it (with compressed air) but it may just be another leaker to add to junk pile.
My own experience doing this has been poor - just one really good set out of the last three or four that I've bought. On the positive side, it has given me a selection of good ends for splicing, and I now have a couple of sets that appear functional. 8)
Ian

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tz375
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Re: GT750 oil pump

Post by tz375 »

It's too early to tell but the oily dirty octopus arrived and after a good clean up, I flushed the lines with carb cleaner followed by WD40 followed by clean oil. Then I strung them up to see if they bleed out like the others. So far so good. Held oil for 2 hours so far.

On that short center check valve, I took another look at it and there is a spring inside it. That surprised me, but it does solve one mystery. And the reason it's in-line does appear to be a lack of space between the starter motor and the crankcase. So it's al making sense now.

I still need one more octopus, so I'll experiment with different techniques and see if I can come up with something useful.
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tz375
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Re: GT750 oil pump

Post by tz375 »

I had another really good look at that in-line valve and of course it has a spring in there.

This is what I saw at first
Image

Then I tried from a slightly different angle and saw this
Image

Then I fished the spring out and it appears to be the same as the rest of them.
Image

So far the replacement octopus has held oil for around 8 hours which should be good enough. I'll check it again in the morning and unless one of the lines has bled all the way down, I'll use it. Now all I have to do is to make one good set out of two plus spares.
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