Two Stroke Pumps

Post your problems / information on the smaller GT Models here
Post Reply
User avatar
Harrymail
Posts: 639
Joined: Thu Jul 07, 2016 8:35 pm
Location: East Yorkshire

Two Stroke Pumps

Post by Harrymail »

The pump on my 550B is leaking from the leaver shaft. Must be the oil seal on the shaft, which Suzuki never made a replacement for. I have a good pump from a GT750, which other than the lever arm having 310 stamped on it looks identical from the exterior. My 550 pump has 341 stamped on the lever. I have read elsewhere that the pumps for GT750/GT550 have different outputs. I have removed the top from both pumps and the tops and shafts appear identical, so my plan is to swap the pump tops over so that I have the good one on the 550 body.

Can anybody confirm that the pumps do have different outputs ? Does anyone see a problem with my solution to swap the tops ? I have a new gasket arriving tomorrow. I have also read the info on the pumps on OJB pages and Pink Possum. I will make sure I don't get the arm 180 deg out. Any help much appreciated.

Paul
Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
User avatar
Alan H
Posts: 12104
Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: Two Stroke Pumps

Post by Alan H »

AFAIK, the pumps are different. I do have some spare 550 pumps though if you need bits or a pump.
Proof that four strokes are over complicated
User avatar
Harrymail
Posts: 639
Joined: Thu Jul 07, 2016 8:35 pm
Location: East Yorkshire

Re: Two Stroke Pumps

Post by Harrymail »

Alan H wrote: Wed Oct 27, 2021 8:12 pm AFAIK, the pumps are different. I do have some spare 550 pumps though if you need bits or a pump.
Thanks Alan. I am going to measure the cam on the lever shaft of both pumps. If they are the same I can swap the shafts over. I could try and swap the oil seals over if the cams are different. If all fails I will give you call as I will need either a lever shaft with a good seal, or a complete pump.

Cheers, Paul.
Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: Two Stroke Pumps

Post by teazer »

Alan,

Does the GT550 workshop manual have specs for oil pump output the same way as the GT750 does? That could be enlightening. And if the bodies are the same, it might come down to minor differences in the face cam i.e. the stroke.

Edit: I checked the '72 FSM for both and the 550 and 750 pump the same amount at full throttle to the cylinders and half as much to the big ends, but it gets there at slightly higher throttle opening.
User avatar
Harrymail
Posts: 639
Joined: Thu Jul 07, 2016 8:35 pm
Location: East Yorkshire

Re: Two Stroke Pumps

Post by Harrymail »

I have now had time to look at both pumps side by side. It looks like the difference is the lever arm. Although similar, they are a different shape. When the alignment marks are lined up, the arm is in a different position. My feeling is that the pumps are the same, its just the relative position of the arm at different throttle openings as Teazer mentions above. Also makes sense that the part number is on the arm rather than the body. I will take a close look at the cam, but hopefully I can just swap the arms over between the two pumps.

Edit: I have now looked at the two cams and they are both identical. Also both rotors (pumps) are identical. Having studied the info on the 750 pumps, I think the arm with 310 on it that I have, does not belong the pump. It should have had a 312 arm on it. So a previous owner has swapped this pump out at some point and changed the arm. I'm not using the lever arm so it doesn't matter to me, but does show that 2nd hand parts can have been messed with.

Gasket has arrived from Astrax so can rebuild the pump now. Going to use the top from the 750 pump complete with cam and put it on my 550 body, which I know pumps ok.

Paul
Attachments
20211028_093238.jpg
Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: Two Stroke Pumps

Post by teazer »

310 arm belongs on any J or K with VM style carbs. 312 is for rod linkage on J-B models. Looks like the 550 arm may be shorter or is that just a perspective thing?
User avatar
Harrymail
Posts: 639
Joined: Thu Jul 07, 2016 8:35 pm
Location: East Yorkshire

Re: Two Stroke Pumps

Post by Harrymail »

teazer wrote: Fri Oct 29, 2021 5:58 pm 310 arm belongs on any J or K with VM style carbs. 312 is for rod linkage on J-B models. Looks like the 550 arm may be shorter or is that just a perspective thing?
It is just a perspective thing. The two arms do have the bend in different places, but end up the same.

I ended up with both pumps stripped to their component pieces. Other than the arm there is no difference at all between the two pumps. So I ended up going with the full 750 pump as it was in better overall condition. Fitted to the bike, and primed, I then spun the pump by hand to check that oil was pumped from all 6 oil ways. I also primed the lines, as much of the oil had drained back, only from 3 of the lines though ?? I must add, I could not detect when the one way valves cracked open but all took plenty of oil. After initial start-up I could see bubbles in the lines, and these moved along uniformly with the pump held open, so I am happy that oil was being pumped down each line. A quick ride around the block and all bubbles have disappeared.

The only concern I have, and this was the case before I changed the pump, is that the LH pot does not smoke much at all at tick over compared to the other two. Even with the pump held open there is little smoke to be seen. Also in comparison the end of the pipe is not as oily as the other two. Not sure why this would be. Perhaps it is the way the SRIS system works ? Perhaps the one way valve on the line to this cylinder does not crack at the same pressure ? I am told that there is uniform smoke from all pots when riding. I think all I can do is remove the spider and test on the bench with an oil can. Maybe I am be overly cautious, as the bike runs fine otherwise, and has not seized up !

Any thoughts anyone ?

Paul
Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
wardy
Posts: 1244
Joined: Tue Jul 13, 2010 5:36 pm
Location: north lincolnshire

Re: Two Stroke Pumps

Post by wardy »

Paul; I've just replied to your ebay enquiry about my pump that I have on ebay...I woulnd't know how to test the seal to see if it's good or not I'm afraid.#

I've also been told that because it has 331 on the arm, it is for a late model 380. i wouln't want you to buy it without me telling you. if there's a way to test the seal, I'll gladly do it for you. 9i'm only in Scunny anyway. cheesr Andy
Andy;
1976 gt750A; 86 FZ750
1977gt380A
1982 z400j
1981 z650f.....1988 Sufolk punch 14"
"look;it's my bike; when you own it ,you can paint it any colour you like!"
(I once painted my Z650 PINK and had the pink panther logo on the tailpiece)
User avatar
Harrymail
Posts: 639
Joined: Thu Jul 07, 2016 8:35 pm
Location: East Yorkshire

Re: Two Stroke Pumps

Post by Harrymail »

Hi Andy

I thought it was perhaps yourself selling the pump on eBay. I think the only way to test the seal would be to fit it to a bike. I'm only wanting a spare in case I need it in the future. I've tried to get a new seal for my original pump at a couple of places in Hull but not been able to get one.

Has anyone successfully replaced the seal on the spindle ? Or know where to get one.

Cheers, Paul.
Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
Post Reply