Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Erwin83 on October 01, 2020, 07:42:27 AM
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Hi everyone.
I'm having difficulties beating an oil leak on my CB350f.
I've already replaced the O-ring (#13) with a OEM Honda one (6 euro for an O-ring ;D).
Cleaned the hell out the area where the plug (#3) goes, took the plug out and cleaned again. Added a tiny smear of gasket to the plug on the outside of the O-ring... Still leaking. And not a weep, but quite big drops. Too much to ride around with.
The area above the plug is dry as bone, so I have no reason to assume it would be the crank oil seal.
There are also no visible oil traces from the oil pump area (on the side stand, it would drip to the lowest point on the casing, which is where I am leaking oil)
Am I missing something? Do you have any suggestions?
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It needs to be tapped in to place. Obviously not too hard, but firmly.
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You did fit it with the pin facing outwards? and the generator cover needs to be fitted to hold it in.
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It needs to be tapped in to place. Obviously not too hard, but firmly.
Hmm, ok. I just pressed it in with my thumb. It is snug though. The O-ring definately seems to be compressed.
I'll try to give it a tap, see if it goes any deeper.
You did fit it with the pin facing outwards? and the generator cover needs to be fitted to hold it in.
Yes, pin facing outwards. Cover mounted. I've not yet gone to the lenghts of making a plate to keep the plug in and be able to run the engine without the cover.
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OK, I was actually able to gently tap the plug in about a millimetre further.
I'll give her another warm up later today and see if there's still a leak. Fingers crossed ::)
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If the cover is on it will push back out till it touches the cover, thats what the pin is for.
If it leaks either the bore is damaged or the O ring got damaged
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Yeah, it didn’t make any difference. Bummer.
I’m a bit out of ideas now.
How about making a little spacer so the plug is kept in deeper?
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Should need it unless the plug, O ring or bore is damaged
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First off you must find if it is the bung leaking. I have never had one leak before after a engine rebuild, new 0'ring, a smear of red rubber grease and push in.
I would clean the whole area down with clutch and brake cleaner including under the engine, cover the area in talc power and you should see any wetness straight away.
6 euro is crazy for that 0'ring, i get them in trade packs for about 60p each ;)
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Just a quick query from a numbnuts, never having taken this part of the motor apart before, but I was under the impression that the alternators actually ran 'wet', and occasionally the seal where the wiring exits would sometimes leak. Am I out of touch?
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"Wet" alternator only on 750, smaller ones are dry and have a seal behind the rotor
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I’ll go for the talk powder test. Although it looks bone dry in the area above the plug (direction crankshaft seal), I guess you never know.
I can safely run the engine without the alternator, as long as I unplug the fieldcoil, right?
Oh, and I’ll make some plate to prevent the plug from plopping out...
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Nope, if you run the engine with the alternator cover off that plug will disapear to the darkest, dingiest corner of your garage never to be seen again and a large puddle of oil appear under the engine
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"Wet" alternator only on 750, smaller ones are dry and have a seal behind the rotor
Y'know, I always regard it as a good day when you can honestly say that you've learned something new. My age is above the national speed limit, and only ever having performed mechanical 1st Aid as opposed to full surgery, I never knew about the wet/dry facts re. the alternators. Your knowledge also meant that I learnt a 2nd new fact in one day regarding the differing current directions from a single coil. It is due to the good people such as yourself that make this forum so readable. Thank you everybody. Michael.
PS. If you want to go into a fit of the screaming ab-dabs, I will admit to all and sundry that I still time my ignition using a fag paper (not mine!) trapped between the points!
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Always used paper and a pencil down the plug hole for Triumphs with a mag. Im 68 and still learning
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Erwin if it’s definitely that leaking I was thinking of suggesting looking at the CMSNL site as sometimes they state the dimensions of the O rings, but it is not shown for this one. If you measure the thickness and inside diameter with a digital caliper micrometer it could be worth trying a fractionally fatter one. eg if the thickness is say an odd 2.8mm get the common size of 3mm with the same inside diameter (cheap on eBay)
It might just provide a tighter seal? Subject to views of those better qualified than me!
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If your sure you have the correct seal and that's undamaged the only other cause is damage in the bore or to the plug. Get a strong light and magnifying glass and check for scores or even a small crack in the bore. On the plug, remove the seal and make sure nothing is underneath it causing a pressure point against the back of the seal. With hot oil at pressure it really doesn't need much damage to cause a leak.
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I have a parts list that describes it as O ring-9131930000-13x2.5mm
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Ditto. I thought my brake caliper was fine but the groove the seal went in was minutely corroded or discoloured and leaked.
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Always used paper and a pencil down the plug hole for Triumphs with a mag. Im 68 and still learning
;D ;D
That’s how I got started in motorcycle mechanics. I tried to find TDC on a CB125S – my first bike – using a pencil with the inevitable result.
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Nope, if you run the engine with the alternator cover off that plug will disapear to the darkest, dingiest corner of your garage never to be seen again and a large puddle of oil appear under the engine
So I made a little plate to keep the plug in.
Uuuuunfortunately...
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Not so much a puddle.. just a good 5 yards of spray, oil on the ceiling, bike's left side covered...
At least no questions about the performance of the oil pump...
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With regards to the solution of the actual leak.. I found that the plug was snug in the bore when the outside of the plug is around 1 mm deeper than the surface of the cover. That would mean that the oil pressure always pushes the plug out that 1mm, creating a gap between the bore and the aluminium of the plug. As such completely relying on the O-ring for sealing.
I have now placed a small bit of gasket material between the plug and the actual gasket, therefore keeping the oil plug in a bit deeper mechanically.
I also did some better cleaning of the bore and plug.
Let’s see if that does the trick.
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Not so much a puddle.. just a good 5 yards of spray, oil on the ceiling, bike's left side covered...
At least no questions about the performance of the oil pump...
;D ;D
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This suggests to me that the "pip" on the plug has been shortened somehow
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This suggests to me that the "pip" on the plug has been shortened somehow
Should it indeed be flush?
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The "pip" should be flush with the gasket surface, if you look inside the generator cover there is a part of the casting that holds it in, if this pip has been damaged or shortened for some reason the plug will not be far enough in.
I have never seen this happen in 40 yrs but offer it as a possible explanation
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Are you sure that you have a 333 bung as, the 323 bung is shorter ;) The 323 bung has a depth of 16.50 mm but the 333 is longer .
Also if the bung has been pulled out with pliers, this damages the pip.
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Never looked closely at the 400 one only the 500/550 so Trigger is probably correct
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Are you sure that you have a 333 bung as, the 323 bung is shorter ;) The 323 bung has a depth of 16.50 mm but the 333 is longer .
Also if the bung has been pulled out with pliers, this damages the pip.
I don’t really know. The pip doesn’t look damaged at all. Could I have a 350cc and 400cc bung mixed up? Is that the difference between the 323 and 333?
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NO 333 is 350/400 323 500/550
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As I mentioned in a previous post somewhere, I have never performed major engine surgery, only 1st aid, never having gone any lower than the cylinder base gasket! Therefore I think that this permits me to ask stupid questions, such as, if the plug has to be held in by the generator cover, and you don't want any oil leaking out, why is there a plug there, and what purpose does it serve? I feel today could be a good learning day! Michael.
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The plug is there to blank the hole left when the main oil gallery is machined in the castings. The other end has a screwed in cap but there isnt room for that at generator end.
Also so you can clean the gallery
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Thank You for that Bryan. In those immortal words - "Now why didn't I think of that?". A good learning day indeed, enough to give me inspiration to open up the garage, let the wintery, watery sun shine in, and attack the beast in readiness for replacement of front mudguard, and complete front brake system. (When the last few parts arrive!)
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Tenuous link, but reading about the replicas made of the 250 six cylinder Honda racer, the blue prints have been "misplaced" at Honda and no contemporary people could remember all the internal oil ways etc. They had to x-ray original castings to rebuild the blue print library and so facilitate the new builds.
These production engines really are miniature masterpieces of original engineering, some absolutely superb thinking and application went into them. And of course they came from the thinking and expertise gained from those fabulous racers.
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For those that haven’t seen it, there are some wonderful YouTube videos like “Honda RC166 disassembly work” ! (and note the choice of tyres!) 😉
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Well, after having removed the plug, checked and cleaned the bore and the plug, and the O-ring multiple times... Not to forget clean my entire garage, floor, ceiling, door and part of the driveway of oil spatter...
I have accepted defeat and used a small smear of "liquid gasket" if that's the right word, on the outer ring of the plug. Let it sit for a night to cure and seems like it's staying dry now. Fingers crossed.
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Went for another ride the other day and AGAIN oil leaking. Sigh.
So tonight I borrowed another set of eyes and together with the owner of those eyes, we finally diagnosed the oil leak: it was in fact the crank seal and not the plug. :o
Replaced the seal and tomorrow, if the weather is OK, I’ll go for another test ride. Fingers crossed.
B.t.w. The original seal has a lip, which makes removal a bit of a difficult task (without splitting the cases). The replacement seal (out of a complete kit with all the engine seals) comes without a lip. So it slides right in.
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Went for another ride the other day and AGAIN oil leaking. Sigh.
So tonight I borrowed another set of eyes and together with the owner of those eyes, we finally diagnosed the oil leak: it was in fact the crank seal and not the plug. :o
Replaced the seal and tomorrow, if the weather is OK, I’ll go for another test ride. Fingers crossed.
B.t.w. The original seal has a lip, which makes removal a bit of a difficult task (without splitting the cases). The replacement seal (out of a complete kit with all the engine seals) comes without a lip. So it slides right in.
Strange, never seen a crank seal without a lip 🤔🤔🤔🤔
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Went for another ride the other day and AGAIN oil leaking. Sigh.
So tonight I borrowed another set of eyes and together with the owner of those eyes, we finally diagnosed the oil leak: it was in fact the crank seal and not the plug. :o
Replaced the seal and tomorrow, if the weather is OK, I’ll go for another test ride. Fingers crossed.
B.t.w. The original seal has a lip, which makes removal a bit of a difficult task (without splitting the cases). The replacement seal (out of a complete kit with all the engine seals) comes without a lip. So it slides right in.
Strange, never seen a crank seal without a lip 🤔🤔🤔🤔
https://4into1.com/crankshaft-oil-seal-91201-323-005-30x45x8-cb350f-400f-500k-550-650/
This is the one.
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Went for another ride the other day and AGAIN oil leaking. Sigh.
So tonight I borrowed another set of eyes and together with the owner of those eyes, we finally diagnosed the oil leak: it was in fact the crank seal and not the plug. :o
Replaced the seal and tomorrow, if the weather is OK, I’ll go for another test ride. Fingers crossed.
B.t.w. The original seal has a lip, which makes removal a bit of a difficult task (without splitting the cases). The replacement seal (out of a complete kit with all the engine seals) comes without a lip. So it slides right in.
Strange, never seen a crank seal without a lip 🤔🤔🤔🤔
https://4into1.com/crankshaft-oil-seal-91201-323-005-30x45x8-cb350f-400f-500k-550-650/
This is the one.
That is not the correct replacement seal. The correct one has a lip on it, for a reason.
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I guess I'll find out.
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All the sets ive had had lipped seals
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I guess I'll find out.
Yes, you will find out when you are doing 120kph and the seal pops out and the engine blows up. That design was put there for a reason :o
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Strange, I have two kits on ‘stock’. One for the 350f, one for the 400f.
One from Cruzin image. One from my dutch parts dealer. Both have the same seal without a lip, and checking parts sources online, like the link I posted, but also cross checking the OEM part number, you do come across the lipless replacement part quite frequently.
We’ll see what it does, if I still have a leak, you can count on an honest review here.
If it works.. great news because obviously not having to split the cases is quite a big deal.
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https://www.davidsilverspares.co.uk/CB400F-SUPER-SPORT-FOUR/part_41831/
Another lipless version.
Also in this kit:
https://www.davidsilverspares.co.uk/CB400F-SUPER-SPORT-FOUR/part_28468/