Oil leak on top of cases.

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tonup69
Posts: 60
Joined: 22 Sep 2010 19:17

Oil leak on top of cases.

Post by tonup69 »

Went for a good burn up this past weekend out in the forest. When I stopped at lunch, I noticed some oil burning on my right hand exhaust pipe, just under the clutch housing. Following the trail, I found that it was coming from the crankcase joint just where the ground wire is attached. I also noticed that a previous owner has put some orange RTV silicone there - most likely in an attempt to seal the leak. Any suggestions or concerns about this? The bike runs great, so I am not eager to change the crankcase gasket.

LTR in Memphis, TN
George 350
Posts: 450
Joined: 16 Jun 2007 09:43
Location: Northampton

Re: Oil leak on top of cases.

Post by George 350 »

Hi,
My bike has suffered from this in the past, and I put it off, not wanting to tear it down for a small film of oil. Several months went by and I had to remove the rear cylinder (slightly melted a piston trapping a ring) and after rebuild the top of the crankcase remained completely dry. The leak was actually at the cylinder base gasket.
If this is the source of your leak it is much less painful to fix than a full teardown!
You could get a can of "Crack Detection Developer" (Rocol do it, as do many others) and spray this on the area where the leak is occurring and you will be able to pinpoint exactly where the source is.
Firstly clean the area thoroughly with brake cleaner and allow to dry. Spray the "developer" on - it is like chalk dust or talcum powder in a fine liquid spray that leaves everything it touches matt (flat)white. Again, allow to dry while you get ready to ride the bike.
Go for a ride and keep stopping until you see evidence of where the leak is coming from, and then you will know what is reqiured.

The developer will rinse off afterwards with water.
Hope this is of use,

George.
George
350 sport 1978, 350 Strada 1978
650 Norton 1967, 650 Kawasaki 1977 and 650 Enfield 2019
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: Oil leak on top of cases.

Post by 3potjohn »

I too have a slight leak around the rear cylinder base area. I cannot decide if it is from here or somewhere along the crankcase top before the clutch cable.I've tried cleaning along the joints and rubbing some three -bond into them.Clearly a bodge.One that didn't work.So i guess I need to investigate. Having had 2 Tridents I am more than used to waterproof trouser legs!
Alfonso70
Posts: 31
Joined: 04 Feb 2012 08:47
Location: Asturias, Spain
Location: Asturias, Spain

Re: Oil leak on top of cases.

Post by Alfonso70 »

Hi, not sure if this may help, but many years ago i rebuilt my 350 and suffered the same problem, a small oil leak that appeared to be coming from where the crankcases join just behind the rear cylinder. I took the barrels off and tried new gaskets, no better, then gaskets and goo but still the leak persisted. It was when discussing the problem with NLM they said "you did put copper washer on the two hidden crankcase bolts rather than steel ones didn't you?", "what copper washers" i said!!!! To quote someone famous "Dooh". So a couple of new copper washers and a partial rebuild latter....no oil leak!!

I don't know if this is the problem you have, hopefully it will just be a base gasket, but just thought i would mention my experience in case it helps
Tony
MickeyMoto
Posts: 2415
Joined: 22 Nov 2008 17:41
Location: Even further oop North

Re: Oil leak on top of cases.

Post by MickeyMoto »

Are you sure the engine breather is not leaking? My Kanguro is rust proofed beyond doubt here so that is the first thing to check for me...... I don't like pressure washers so need to find a way of cleaning it all up....
tonup69
Posts: 60
Joined: 22 Sep 2010 19:17

Re: Oil leak on top of cases.

Post by tonup69 »

Alfonso70 wrote:Hi, not sure if this may help, but many years ago i rebuilt my 350 and suffered the same problem, a small oil leak that appeared to be coming from where the crankcases join just behind the rear cylinder. I took the barrels off and tried new gaskets, no better, then gaskets and goo but still the leak persisted. It was when discussing the problem with NLM they said "you did put copper washer on the two hidden crankcase bolts rather than steel ones didn't you?", "what copper washers" i said!!!! To quote someone famous "Dooh". So a couple of new copper washers and a partial rebuild latter....no oil leak!!

I don't know if this is the problem you have, hopefully it will just be a base gasket, but just thought i would mention my experience in case it helps
Tony
Very interesting! So can you get to these "hidden" crankcase bolts easily or does it require the partial rebuild? If I have to tear it down too far - I will live with the leak - the bike runs great. Thanks!
tonup69
Posts: 60
Joined: 22 Sep 2010 19:17

Re: Oil leak on top of cases.

Post by tonup69 »

MickeyMoto wrote:Are you sure the engine breather is not leaking? My Kanguro is rust proofed beyond doubt here so that is the first thing to check for me...... I don't like pressure washers so need to find a way of cleaning it all up....
I really WANT this to be the problem - but it doesn't look like it. Easy fix if it was....
Alfonso70
Posts: 31
Joined: 04 Feb 2012 08:47
Location: Asturias, Spain
Location: Asturias, Spain

Re: Oil leak on top of cases.

Post by Alfonso70 »

Hi there, sadly you have to take the whole clutch and also the side casing off to access them (and all other bits and pieces removing the casing involves) not a two minute job but not too bad. Do you have a parts book? if so the washers are on Table No. 1 item 29 (Part no. 21.01.53). You'll notice you only need the copper washer on the clutch side of the bolts.

Does the leak appear to be around where the clutch cable locates into the crankcases?

Hope this helps?

Tony
julianharty
Posts: 478
Joined: 15 May 2016 16:34
Location: High Wycombe
Location: High Wycombe Area (Bucks)

Re: Oil leak on top of cases.

Post by julianharty »

Here's an update on an old thread. I had a similar problem with a 350 I'd bought about 18 months ago. I finally convinced myself to remove the clutch cover with all that entails. I discovered there was what seemed to be a reused copper washer on the central top crankcase allen bolt. I fitted a new one, then remembered that I have PTFE tape for plumbing connections https://en.wikipedia.org/wiki/Thread_seal_tape and decided to apply that around the shank (the length before the threaded part of the bolt partly as there was a small gap around the inner hole of the washer. Anyway, I put several layers of the tape around the shank and refitted it and everything else. So far, so good, albeit I've only ridden the bike for about 30 minutes so far (other problems need fixing too e.g. an alternator fault I've found and fixed). Previously I'd see oil emerging as soon as the engine got warm, even running it at idle in the garage for 5 minutes so the oil leak is certainly better than it was.

Some comments on using the tape:
- The tape is apparently rated to 260C and from measuring the temperature of my engine cases they don't get close to that temperature so that should be fine.
- I've discovered from the Wikipedia article that there are special types of the tape, including one specially designed to help Stainless Steel fastenings from locking together. I'll see if I can find this tape and try it in future.
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: Oil leak on top of cases.

Post by 3potjohn »

DId not realise how long it was since my last post on this thread. had to have the motor apart 3 years ago to give it the once over,new pistons,rings and big end shells.i really concentrated on getting the crankcases back smoothly with a thin smear of 3bond on the faces and now there is no weep from that area. john
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