gt750 oil pump ???

[Eddie]

HI, I HAVNT BEEN ON HERE IN A WHILE BUT I HAVE A QUESTION, HOPE YOU GUYS CAN HELP, I HAVE A 74 GT750, THE RIGHT CYLINDER(IF YOUR SITTING ON THE BIKE/ LEFT CYL. IF YOUR LOOKING AT THE BIKE) SEEMED TO NOT BE GETTING OIL, I TOOK LINES OFF AND PUMP AND I THOUGHT THE ONE LINE WAS CLOGGED SO I TRIED TO UNCLOGG IT BUT COULDNT, SO I ALSO WENT THROUGH THE EBAY THING ORDERING LINES I THINK I FINNALLY GOT A GOOD SET BUT NOW I THINK THE PUMP MIGHT BE MESSED UP NOW. THE QUESTION IS,,, WHEN I ROTATE THE PUMP SHAFT WITHOUT THE LEVER BEING OPENED IT PUMPS TO ALL BUT THE ONE LINE(TO THAT CYL.) BUT IF YOU OPEN THE LEVER(FULL THROTTLE) THEN IT PUMPS TO THAT LINE, SO COULD IT BE THE PUMP WORKS ON ALL LINES BUT THAT ONE? BECAUSE WHEN LEVER IS OPENED THAT LINE GETS OIL AT THE BANJO, SO IM THINKING THE LINE IS NOT CLOGGED BUT MAYBE PUMP IS BAD, IF I ROTATE THE PUMP I FEEL SOME RESISTANCE BUT THE SHAFT DOES NOT GO IN AND OUT LIKE IT DOES WHEN THE LEVER IS OPEN ( I THOUGHT THAT WAS NORMAL), BUT THEN I TRIED ROTATING ANOTHER PUMP THE SAME WAY(BY HAND) AND THE SHAFT GOES IN AND OUT ALOT, JUST LIKE MY ORIGINAL PUMP DOES AT FULL THROTTLE, SO IF YOU TURN THE SHAFT ON A PUMP WITHOUT THE LEVER OPEN, HOW SHOULD IT FEEL? SHOULD THE SHAFT GO IN AND OUT THE SAME WAY IT DOES AT WIDE OPEN OR IS IT LESS?/??? I HAVE 3 PUMPS AND 2 OF THEM GO IN AND OUT ALOT BUT ONLY WHEN THE LEVER IS OPENED ALL THE WAY, BUT 1 PUMP GOES IN AND OUT WHEN LEVER IS NOT OPENED BUT WHEN YOU OPEN THE LEVER THE SHAFT STOPS GOING IN AND OUT? WHICH PUMP IS WRONG? I EVEN MOUNTED THE PUMPS TO TEST THEM AND THEY OIL THE LINES WHEN WIDE OPNE BUT AT IDLE (LEVER) THEY BARELY OIL, EXCEPT THE 1 PUMP I HAVE ONLY OILS AT IDLE AND NOT WIDE OPEN? SORRY FOR THE LONG POST......

[tz375]

If it doesn't pump at low opening angles but pumps OK at larger angles, that suggests a partial blockage in one line that needs to be cleaned out.

All GT750 oil pumps work the same way but there are minor design differences. As the driven shaft rotates, the face cam on the upper end of that shaft pushes against a pin in the top pump cover. As the lever rotates to Wide Open, the shaft will reciprocate further than with the lever "closed".

[Eddie]

Ok so then the one line might be clogged, and not the pump? I was thinking that it was the pump because the line gets oil but only at wide open, I compared three pumps by turning them by hand and like I had sad two felt the same and one was different it seemed to have more resistance when lever was not open. Ok so I will try the lines again thanks for the help....

[Eddie]

I HAVE A FEW QUESTIONS//ok, I have 3 pumps, one only pumps when the lever is down (idle), i took it apart and nothing is stuck (plungers), but it looks like it is missing the shaft that hits the lever inside( i will try to upload a pic later), the other 2 pumps work really good wide open,(the lever) and they seem to work ok at idle, but my question is how much oil should be coming out when the lever is in idle position? it seems like not alot comes out at all. I can turn the pump and feel resistance when the lever is at idle position, im wondering if i should take the other pump apart and if i do, and i replace the cover gasket does it have to be the same thickness? also i have tried cleaning my sets of lines with carb cleaner, wd-40 and sea foam, also ultra sonic dipp as well, and it seems that all my lines have the same problem, they all get oil when pump is turned and lever is at idle position,, except the second line to the left which is the line that goes to the far right cyl, if you are sitting on the bike.. what is the chances that 5 sets of lines would have the sAME exact line clogged? thats why i keep thinking its a pump issue, and my final question is i primmed the lines and hung them upside down , one set had no leaks, and one set had a very small amount come out of 2 lines ,, but this is the best set of lines i have, so is it ok that a small amount of oil comes out after 2 days of being upside down? or is any amount of oil bad?????? the set of lines that has no oil coming out when hung upside down, does not get oil to the line that goes to the far right cyl.,,when pump is turned and lever is at idle but the other set of lines seems to get a little more oil on that line when i test it with the same pump??? sorry for the novel i just wrote/.....

[tz375]

Some pumps had a [pin and some did not. See http://pinkpossum.com/GT750/Oilpump.htm" onclick="window.open(this.href);return false; for more details.

On the octopus (oil feed manifold) I usually use a small oil can and pump oil through each line. If it's easy to pump through it's probably not blocked. You could use a mitivac to test the pressure at which the check valves crack open.

The crank side pumps 7cc per HOUR at 2166 engine rpm at almost all revs (fixed output). The cylinder side pumps zero at closed throttle, rising to 48cc at 2166 rpm and teh crank turns 63.72 turns per pump revolution if you want to set up a jig to test output.

[Eddie]

THanks FOR THE INFO, I DO HAVE A TEST JIG, BUT I DO NOT HAVE A MITIVAC, SO THAT MEANS IF I HAVE PUMP SET UP AND IM TURNING THE PUMP WITH A DRILL, AND THE LEVER IS CLOSED THERE SHOULD NOT REALLY BE ANY OIL COMING OUT THE LINES? OR AT LEAST VERY FEW DROPS,,, IF THAT IS THE CASE THEN MINE IS WORKING OK. I NEED TO TAKE THE PUMP OUT AND LINES THAT I CURRENTLY HAVE ON IT, I HAD REPLACED THE ORIGINAL WITH THIS SET AND NOW IT SMOKES LIKE CRAZY FROM ALL CYL. BUT THE FAR RIGHT ONE STILL!!!! SO NOW I THINK THESE LINES AND PUMP THAT I HAVE BEEN TESTING ARE OK I CAN INSTALL THESE, THE LINES I HAVE ON IT RIGHT NOW LEAK, AND WHEN I TRIED TO START THE BIKE IT HYDRO LOCKED!! I HOPE I DIDNT BLOW A CRANK SEAL! BECAUSE IT SMOKES BAD NOW, HOPEFULLY ITS JUST GETTING TO MUCH OIL AND ITS NOT THE CRANK SEALS,,, ALSO JUST WONDERING IF THE CRANK SEALS ARE BAD THEY USUALLY RUN LIKE crap AT IDLE RIGHT???? OR THEY WONT EVEN IDLE? OR DO THEY JUST SMOKE REAL BAD????

[tz375]

If you know the drill speed, work out what engine RPM that would equate to and do the match to work out how much oil should come out of each line. Set up a graduated container under each oil feed lone banjo and crank it up for say 10 minutes wide open and see how much oil is in each test container.

That will tell you if the pump is OK.

Remove the exhausts and carbs, and take out the SRIS valves from the crankcase and drain out the oil from each crank chamber before any damage is done. Refit them and do a leakdown and compressions tests to see if the seals are OK.

And please turn CAPS LOCK OFF.

Caps are considered to the the internet equivalent of shouting at people.

[Eddie]

sorry about the caps, i didnt even notice they were on,,, i was half asleep when writing this, and when i did noticed i didnt go back i just left it alone, the problem is that the motor hydro locked but i didnt realize it, the starter wouldnt turn it over and i thought the starter took a crap, so i went to kick it over and thats when it was apparent, i couldnt kick it over , but i got it to budge a little, i took plugs out, and let it sit, i also took disconnected the oil tank so no more oil could get it, i came back the next day and it felt kinda hard but kicked over and started, so im not sure if dammage was done, as far as compression check goes what is normal range? the bike has 14,000 miles on it , and it might sound stupid but how do you recommend doing the leak down test? i have heard different methods just wondering how you guys do it?

[Coyote]

You need to remove the SRIS valves and allow the crankcase to drain. Compression is arbitrary. 95/120. What is more important is that all 3 be within 10 of each other.

[Eddie]

the compression is 110/105/105 the 1st time i checked to the compression before i changed the lines was 110/108/75 the 75 was on the cyln. that i was worried about , but after changing it, it went up to 105 and the cyl. that had no oil getting to it was 110? weird/ but the lines that i put on apparently leak, and they leak bad, i took one off and over night it drained oil out bad, so i hope the only reason why it smokes so much is because of this. I have drained the sris system 2 times now, this next time will be the 3rd time. I was going to rebuild the motor myself just so I know everything is the way it should be, but i have no time right now so i might have someone else do it for me , but every time I have work done by someone else it ends up worse! so im not sure, what is a good price for having it rebuilt, I have new pistons and gasket set, but my water pump is leaking and i might need crank seals but not sure yet, im just looking at my options i might still do it might self if i can get the time, I have never rebuilt a gt750 but I have rebuilt a few other bikes, (cb72/cb77/r5 350/) and i have worked on other bikes (bsa/matchless/cb450/kx250/) but never a buffalo , I saw a guy on line that got his rebuilt, (bored ist over, crank seals, everything done water pump, etc...) for around 1,200.00 i thought that was expensive but like i said i have never rebuilt one so i dont know how difficult they are or how pricey the parts are.. Thank you guys for your help!!!1

[tz375]

I haven't checked my files, and I'm not sure that I want to, but I'm sure my last rebuild cost more than that for parts and services and I did the work in house.

Cranks and seals plus 3 x bore & hone + 3 sets of pistons plus machining plus water pump etc adds up pretty fast. Rebuilding a GT750 motor is not difficult but it helps to have a couple of special tools and a meticulous approach. Just think about the number of threaded holes that all have to be cleaned out and faces chamfered.

It's a simple engine to work on, but there are a whole lot of parts that all need to be cleaned and inspected and measured and maybe replaced. It just takes time.

[Eddie]

Thanks for the info, and help. I am not sure yet what to do, I think i will first change the pump and lines to see if this helps, the bike did not smoke bad untill i put those lines and pump on, at the time I did not know how to check the valves in the lines untill I found this site, I never primmed the lines and hung them upside down to see if they leaked. I remember trying to suck threw the ends to see if they were not clogged because another guy told me to do that, and when i did that, I was able to suck through them very easily, so I think somebody had cleaned them with compressed air and got the valves stuck. (I admitt i had done this to the original lines because one was clogged but i did not know any better) so once i change the pump and lines and drain sris system i will run it, and if it still smokes like crazy i will try the leak down test , then i should have a good idea if it is the crank seals, and if it is the crank seals i will probly sit in the corner of my garage and cry with my cat for about an hour then have a beer so i can feel somewhat like a man again.....

[Eddie]

Well, I just took apart and cleaned a later model oil pump (it has no rod that rides on the shaft), I cleaned everything very good, the plungers work great, evrything seemed to be in working order. I mounted it to my test lines and it does no pump when lever is at idle just when lever is opened! this is a problem that I have been having with most of the ones i test, I tried a different pump on the same lines and it pumped with it at idle, oil got to the ends of banjos, just not alot, and one of my lines must still be clogged because it didnt drip oil like the other ones, anyway I cant figure out why the 1st pump isnt working? the springs feel really good, and i dont see anything that is wrong inside? anybody have any ideas? they do say that they are not supposed to be rebuilt, but i dont know why? maybe this is why,,,

[tz375]

Fitting a late model top cap to an early model pump or vice-versa would be a major disaster. Please check that the rotor body is the correct one for that top. It should be possible to rotate the drive shaft and see the rotor move up and down slightly even at idle. If it is not reciprocating then there is an issue.

[Eddie]

Well , I know that the rotor and the top are the right ones, I checked that as well, If i run the pump on the lines and lever is at idle position it doesnt really get oil, but as soon as I open it up to full throttle it gets oil really good, so I thought it was the pump, and i cleaned it all, then I read the pink possum oil pump section and he says to either take the bike for a short ride or hold lever to full throttle position and if all lines are purged with oil then its ok?,,,, well if i hold mine wide open it does get oil, but thats the only time it gets oil? it should be getting oil at idle also I would assume, because if not thats crazy.... so Im back to square one, I have a total of 4 pumps, I have checked 3 of them , the other is on the bike and I have to drain coolant,take carbs off, and starter so i can take the old lines off so its going to be a while before i get to testing that pump, Im thinking maybe its my lines? but why would the other pump oil it better than the one i was trying ? if it was the lines it shouldnt get oiled no matter which pump I use. I know im probly driving someone crazy with me asking the same thing over and over so, once i figure out what the hell is wrong I will post what it was, instead of going on and on about it, sorry and if I dont post for a while its because I havnt figured it out, which is probly what is going to happen, so talk to you guys later , not sure when .....