Transmission oil leak, '76 GT550

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nickst4
Posts: 37
Joined: Wed Feb 19, 2020 7:31 pm

Transmission oil leak, '76 GT550

Post by nickst4 »

When I first got the bike on the road, I soon realised the gear oil level was low and assumed I'd stupidly miss-read the numbers on the side casing and only put 500ml in instead of 1500ml. Now I have oil dripping from underneath, and its coming not from the drain bolt or gear index plug, but from the edge of the starter motor cover, where there is a drain cutout. At the same time, the starter motor has failed. Looking at the parts manual, I think there is an O-ring and a shaft seal to the starter that are supposed to stop oil draining from the clutch cover via the starter compartment. Hopefully I shall soon find out, and I won't need to get into the motor beyond the plate underneath.

Has anyone else been around this scenario? I don't suppose the seals in that area have been renewed in 45 years!

Nick
asco58
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Joined: Sat Nov 21, 2020 2:24 am
Location: London

Re: Transmission oil leak, '76 GT550

Post by asco58 »

On the parts diagram it appears that the Nippon Denso starter motors have a shaft seal (31153-31010) inside the starter motors and an O-ring on the outside where it fits into the crankcase (09280-22004).

I'd think an oil leak from inside the starter motor compartment would probably be caused by one or both of these seals leaking. If oil is leaking into the starter motor that could potentially stop it from working in some circumstances but then again, it could have failed for an entirely different reason.

Suzuki seem to have discontinued these parts but I did see an old thread from the Suzuki Two strokes forum where someone appears to have fitted a 26mm x 30mm x 2mm O-ring and had success with it
http://www.suzuki2strokes.com/forum/vie ... a5a12f888d

As for the oil seal in the starter motor (31153-31010) I saw this thread viewtopic.php?f=11&t=11289 where someone has said they'd been told that it's a 14mm x 24mm x 5mm oil seal. I have no idea if this is correct so if you choose to take your starter motor apart then you could measure the oil seal and verify if this is correct unless someone else on here knows. Hope this helps. Ash
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Alan H
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Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: Transmission oil leak, '76 GT550

Post by Alan H »

The O rings just get tired eventually. I had issues with the one on the Yeti - HERE and also put one on the 'nose' of the starter motor where the casting changes size as extra insurance.
Proof that four strokes are over complicated
nickst4
Posts: 37
Joined: Wed Feb 19, 2020 7:31 pm

Re: Transmission oil leak, '76 GT550

Post by nickst4 »

Ash and Alan H,

Thanks for your comments. It does sound like an O-ring problem, and I'll know when the GT550 gets to the top of the list to sort out!

Cheers,

Nick
nickst4
Posts: 37
Joined: Wed Feb 19, 2020 7:31 pm

Re: Transmission oil leak, '76 GT550

Post by nickst4 »

Wow, I see I reported this problem in July last year! :oops: The thing is, having a garage-full of bikes, there's usually several others available for riding, so dead ones don't get fixed quickly...

Anyway, I started on the 550 today and was amazed to find the starter motor completely loose and resting on the closing plate! :roll: Both retaining bolts at the tail of the motor had come out, the seal to the primary case was obviously compromised and the starter had no effective earth connection to the engine. I know I swapped those bolts for stainless hex-head screws of the same length, but it turns out they were 6mm or so shorter than they could have been. I've now drilled the heads of two longer screws and lock-wired them, since I didn't fancy stripping the threads by getting excessively-physical in tightening them.

Bottom line is the starter motor now works again very briskly, and the O-ring on the nose of the starter motor has some Three-bond silicone on it to help keep oil in the primary case. The exhausts will go back on tomorrow, but the bike may have to wait for mud and/or salt to be washed off the roads around me before I can check that all is well again and the running-in can resume.

That's the sort of nice easy fix I like! :D

Nick
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Alan H
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Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: Transmission oil leak, '76 GT550

Post by Alan H »

Only took 7 months! Remember to do an oil change and top up properly while the exhausts are off.
Take out the VERTICAL drain plug under the gearbox, NOT the one on an angle and use mineral oil, not synthetic.
Proof that four strokes are over complicated
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