Author Topic: CB400F help: What is this rubber plug next to my sprocket? (Read 7984 times)

stickfigure · « **on:** January 14, 2012, 07:41:38 pm »

Hi - I have a '75 CB400F that seems to be leaking oil from a rubber plug next to my sprocket (see attached). Does anyone know what this plug is? I've been flipping through my Clymer manual and I think it may be an oil seal for the main shaft of the transmission. I could be totally wrong though.

When I removed the crankcase cover, there was heavy oil/gunk build-up around this area and under my sprocket. After a good cleaning, I started my bike and I could see oil starting to creep around this plug/seal after a couple mins.

MoMo · « **Reply #1 on:** January 14, 2012, 08:39:04 pm »

That seal requires splitting the cases. Try running an ounce of Seafoam per quart of oil to see if that helps to eliminate or minimize the seepage...Larry

dave500 · « **Reply #2 on:** January 14, 2012, 08:50:38 pm »

you dont need to split the cases to replace that seal,it might have had a thicker o ring chain used at some point and rubbed it through like on 500/550s?

grcamna2 · « **Reply #3 on:** January 14, 2012, 08:53:46 pm »

Quote from: photolar on January 14, 2012, 08:39:04 pm

That seal requires splitting the cases. Try running an ounce of Seafoam per quart of oil to see if that helps to eliminate or minimize the seepage...Larry

+1 on that.

dave500 · « **Reply #4 on:** January 14, 2012, 09:14:24 pm »

you might try cleaning the area up really well and trying to force some case sealant around and into it,how does it look behind the sprocket?

stickfigure · « **Reply #5 on:** January 14, 2012, 10:00:24 pm »

Thanks for the replies, guys. Can anyone confirm what that rubber piece is?

Larry: I looked up Seafoam and I see that it can be used for breaking down crud and some top-end ailments. I didn't see anything about it fixing leaks though; is that also one of purposes?

Dave: I really hope I don't have to split the case b/c I think that's beyond my skill set. Things looked pretty tidy behind the sprocket, so I didn't take it off. I'll probably pull it tomorrow just to be sure. Case sealant seems like it would be worth a try if this thing is too difficult for me to tackle.

In addition to this leak, I have a leaky cylinder head and cam cover!

MoMo · « **Reply #6 on:** January 14, 2012, 10:26:34 pm »

Seafoam is worth a shot, my Silverwing used to leak a half quart every oil change and once I started to put Seafoam in it is down to very minor seeping. The case has to be split, refer to part 25 on this microfiche and note the little tab that locates the seal. The tab sits in a recess in the upper case.
http://www.mrcycles.com/fiche_section_detail.asp?section=121663&category=MOTORCYCLES&make=HONDA&year=1975&fveh=2911

The cylinder head and cam cover can be done in the frame...Larry

dave500 · « **Reply #7 on:** January 14, 2012, 10:53:35 pm »

snip that tab off or use a brass freeze plug in its place,i dont think your up to prying the old one out etc,,use carb cleaner or turps etc and really clean that area with an old toothbrush,use compressed air to really blow it all out clean,then use a case sealant smeared in to it.

crazypj · « **Reply #8 on:** January 15, 2012, 12:03:33 am »

There's oil pressure behind it to lubricate transmission

dave500 · « **Reply #9 on:** January 15, 2012, 12:23:19 am »

theres no real oil pressure behind those plugs,,there is oil splash though,i think the advice given so far is pretty good crazypj,your sign off says it all.

crazypj · « **Reply #10 on:** January 15, 2012, 12:37:18 am »

Hi Dave, not sure if your being serious or sarcastic? (either way, don't matter

)
Anyway, there is pressure behind that seal, it may be low but Honda felt it was necessary to put a rather large lip on the seal.
There is an oil feed into center of shaft.
It may be possible to 'glue' over it, if it works, great but it will leak again in the future

dave500 · « **Reply #11 on:** January 15, 2012, 12:43:58 am »

im going with the stickfigures feelings that hes not confident in removing the seal in situ or splitting the cases himself,,it wont cost him anything to try and do a good clean up and external seal without tearing the engine out,and he can still ride it,now if youll retract the shady bodgers comment please?

crazypj · « **Reply #12 on:** January 15, 2012, 01:16:15 am »

OK

Site was real slow after I posted OK

dave500 · « **Reply #13 on:** January 15, 2012, 01:19:13 am »

cool.

strynboen · « **Reply #14 on:** January 15, 2012, 02:00:46 am »

hey dave..500 and 400 f are not same engine. 400 are next generasion..that plug have small"dots"..to hold it in place .so the oil pressure not blow it aut..
that gear have oil lines build in..like the 550
DONT pull that plug it break...and you can nog get a proper plug in witaut open the blok

edit yes it are not high pressure..prob it are the finale gear who are oil presure lubed..

klik on photo to get it bigger..its no 21..

klean it proper,,and try to seal it from autside. still leaking..then break it aut,,and try to find a alternative.. just try...

dave500 · « **Reply #15 on:** January 15, 2012, 02:09:26 am »

the oil pressure is fed to the counter shaft with its own little pump on the 550s,the pressure behind that plug is minimal and not like the full pressure at the main or bigend bearings.

stickfigure · « **Reply #16 on:** January 15, 2012, 05:58:32 am »

Thanks for all of the info! For now, I'm going to try an external seal and I'll see if I can get my hands on some Seafoam too. Hopefully, that will keep this leak in check for now. Thanks again, guys.

Ernest T · « **Reply #17 on:** January 16, 2012, 08:32:24 am »

That seal won't come out without splitting the cases. I happen to have mine apart awaiting parts so I can show you what you have facing you.

As you can see, there isn't a lip, but a a tab which inserts into the case. Its a hard rubber seal and you won't squeeze it in there.

I doubt you'll make a permanent repair from the outside, but if you don't mind messing with it occasionally you should be able to stop the leak.

dave500 · « **Reply #18 on:** January 16, 2012, 11:44:19 am »

anyone with a little nouse will be able to hook that old seal out and use a 34mm brass freeze plug in its place,,too easy.

Rgconner · « **Reply #19 on:** January 16, 2012, 12:20:50 pm »

Quote from: dave500 on January 16, 2012, 11:44:19 am

anyone with a little nouse will be able to hook that old seal out and use a 34mm brass freeze plug in its place,,too easy.

*Files that one away for future reference*

bollingball · « **Reply #20 on:** January 16, 2012, 12:49:41 pm »

I don't see why Dave's idea would not work. But Dave would you put any thing on the plug or in the hole as a sealer or put it in clean and dry?

Ken

TwoTired · « **Reply #21 on:** January 16, 2012, 01:28:10 pm »

Just thinking out loud here.

Has the rubber plug sustained physical damage or has it just shrunk with age and heat?

Assuming the latter...

Why not rejuvenate the rubber in situ with the wintergreen oil and xylene treatment?

Clean and dry the area. Build a little dam or half cup around the seal with modeling clay then and fill the half cup with the wintergreen/xylene mix. Put a piece of plastic baggie over the top of the "cup" and let is sit for a while. Check the seal for over-swelling periodically.

The xylene should soften and expand the seal, and the wintergreen oil should keep the rubber resilient.

No, I haven't tried it. But, I would sooner try that than any other method I've read in this thread. Worst case, you just delayed doing something far more invasive.

FWIW
Cheers,

dave500 · « **Reply #22 on:** January 16, 2012, 07:48:49 pm »

i would remove the old plug ken,then insert a small piece of rag against the bearing and then brighten up the housing with steel wool where the seal lives,use a little magnet and make sure any steel wool is removed,then pull out that rag and clean the seating area with turpentine or what ever and make sure its clean and dry,then i would steel wool the outer seating edge of the brass plug and aslo clean it with turpentine or similar,id smear a small amount of hard setting gasket compound in the opening and also sparingly on the plugs edge,,then insert it squarely,it wont leak,the brass cup is slightly flared and will have a sort of barb effect as to being pushed back out,,if your pulling the cases apart use the correct seal,,this will fix it without splitting cases in about 45 minutes,stickfigure is going to have a go at sealing it externally because this method he says might be too much for his skills so far.

dave500 · « **Reply #23 on:** January 16, 2012, 08:33:40 pm »

to try and stop the leak without changing the plug i would first with a needle or small jewellers screw driver and the bike leaning over to the other side to stop oil re-seeping, gently scrape in a circular motion around the gap at the join to remove any loose crud,use carb cleaner or similar and blow it out clean with compressed air aswell,then steel wool that outer edge of the case and clean it up well with what ever,than useing the same hard setting compound try to pack it into the gap around the seal like packing a bearing with grease,then stick paper masking tape over it to keep the sealant in and just leave the tape on,,id sooner do the brass plug though.

bryanj · « **Reply #24 on:** January 16, 2012, 10:09:30 pm »

OK heres by 2 penorth,

Have rebuilt too many hondas to think about, unless there is physical damage to the outer of the rubber or inner of the bore (this could ONLY happen with the engine in bits!!) the clamping fit should be too tight to allow leakage

SO

EITHER
(1) It's been apart and bodged

OR
(2) It's leaking from somewhere else and is just pooling around there.

Dave,

If yoou can get one of those plugs out of a 400 without damaging the case you deserve a medal mate due to the tight fit and depth, never mind the peg

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Author Topic: CB400F help: What is this rubber plug next to my sprocket? (Read 7984 times)

bollingball