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RD400 Left Side Oil Leak

Started by Organicjedi, September 28, 2020, 08:47:37 AM

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Organicjedi

I've been struggling with this left side leak for some time now, really ever since the restore.

Gearbox oil is dripping off of the bottom of the neutral switch. It only appears after I ride. I first swapped the neutral switch o ring and eventually glued it on with high temp silicone. The issue did not go away.

I also hit the sprocket nut with an impact to make sure it was tight and then coated the blanking plugs with ultra black. The leak is still there.

In my mind, this leaves two options. The sprocket seal or the clutch push rod seal. All of the seals are new and the push rod is straight with no grooves.

I'm wondering if there are any tips to test where the leak is coming from or how to stop it.

I'm going to run it with the sprocket on and the side cover off to see if I can spot a leak coming out of the sprocket seal.

I'm for sure going to swap the sprocket seal with a new one and will probably put some ultra black around the sealing surfaces.

It's hard to find an oil trail under here due to all of the flinging oil with the spinning chain. Plus the left bottom side of the neutral switch is the lowest point so the leak could be coming from several places.

I'm bound and determined to find this and seal it up.

Any advice would be appreciated.


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Arrow

Get some white spirit and a paint brush and have a good clean up. Much easier then to see where the source of the leak is.

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Arrow

Lol, when I posted I could not see the photos.

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quocle603

some people like to spread baby powder to the area to see where it is actually leaking from.
Do not underestimate the power of a two-stroke.

1975 Yamaha RD350 (modified), 1973 Yamaha RD350 (stock), 1971 Suzuki T500, 1981 Yamaha XS650 HS2, 1982 Honda MB5, 1980 Puch Maxi, 1979 Puch Magnum, 1993 Tomos Bullet, 2003 Malaguti Firefox F15 LC

Czakky

Not familiar with the 400s but on my R5 I had a leak in the tach seal that drive me nuts for a long time and it would show up on the left quite a bit...

Organicjedi

Quote from: Czakky on September 28, 2020, 10:51:26 AM
Not familiar with the 400s but on my R5 I had a leak in the tach seal that drive me nuts for a long time and it would show up on the left quite a bit...

I did rebuild the tach drive because it did start leaking. That part is dry now.

paul1478

#6
Quote from: Czakky on September 28, 2020, 10:51:26 AM
Not familiar with the 400s but on my R5 I had a leak in the tach seal that drive me nuts for a long time and it would show up on the left quite a bit...
my 400 had the exact same leak. it wound run down through the hole in the top of the cases. never would have guessed that it was a tack cable from where the oil was showing up.
76 Team Scream RD400
1993 FJ1200
2006 Goldwing
2022 Ducati V2 Panigale

Yamaha 179

If/when you replace the sprocket seal clean the area with laquer thinner or acetone very well and assemble the new seal dry; do not put Yama-bond on the OD of the seal.  Put all the case seals (and bearing surfaces) up clean and dry.
Lyn Garland

Organicjedi

Thanks for the tips so far!

Arrow, yes I have it all cleaned up as you see now in the pictures.  :thumbs:

Diablo007

@Yamaha179

Why install the seals dry vs. using Yamabond?  When I built my last engine I was advises to use Yamabond.
2 stroke junkie:
Too many motorcycles to list.  The highlights:
1973 Yamaha RD350 Cafe Racer project; 1983 Suzuki RG250 YammaGamma project; 1988 Yamaha YSR50/80 project; 1984 Yamaha RZ350; 1984 Yamaha RZ500

Barrie

I recon that a bit of liquid gasket helps lubricate the seal during install
I can't fix stupid , but I can give it a bill !

quocle603

I've always installed my seals dry. Some yamabond will get on it from the two halves meeting.
Do not underestimate the power of a two-stroke.

1975 Yamaha RD350 (modified), 1973 Yamaha RD350 (stock), 1971 Suzuki T500, 1981 Yamaha XS650 HS2, 1982 Honda MB5, 1980 Puch Maxi, 1979 Puch Magnum, 1993 Tomos Bullet, 2003 Malaguti Firefox F15 LC

Yamaha 179

Yamaha designed the seals to be installed dry and taught in their schools that they should be installed dry that is why I mentioned that.
You see no mention in any service or technical manuals of the use of bonding agents on the OD of seals while you are instructed to seal the case mating surfaces.
Lyn Garland

rd400canuck

I have the EXACT same issue. I totally rebuilt the bike last winter and all this season i got a few drops of oil after every ride on the left hand side. Driving me nuts lol...   going to use everyone's suggestions here and have a look for it.