Oil leak oil plug left side engine

[Bryanj]

NO 333 is 350/400 323 500/550

[TrickyMicky]

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.

[Bryanj]

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

[TrickyMicky]

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!)

[K2-K6]

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.

[JezzaPeach]

For those that haven’t seen it, there are some wonderful YouTube videos like “Honda RC166 disassembly work”  ! (and note the choice of tyres!) 😉

[Erwin83]

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.

[Erwin83]

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. 

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.

[Nurse Julie]

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. 

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 🤔🤔🤔🤔

[Erwin83]

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. 

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.

[Nurse Julie]

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. 

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.

[Erwin83]

I guess I'll find out.

[Bryanj]

All the sets ive had had lipped seals

[Trigger]

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 

[Erwin83]

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.