Author Topic: oil leak through tach cable port  (Read 4889 times)

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Offline Serge

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oil leak through tach cable port
« on: December 16, 2006, 08:17:36 pm »
Hi, I am struggling with oil leak through tach cable port.  I put a new plastic spacer inside which I bought from Honda, tried make-a-gasket in addition to standard o-ring, and teflon tape, but nothing seems to seal it well... What is your experience with this? What size of o-ring fit best in there?  thanks !
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Offline mick750F

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Re: oil leak through tach cable port
« Reply #1 on: December 16, 2006, 08:28:20 pm »
   Which bike? If it's a 750 then all you need there is the proper seal from Honda with some Hondabond applied to it. Also, the seals from the later DOHC bikes work better. If it's for another bike someone else will have to jump in.

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Offline seaweb11

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Re: oil leak through tach cable port
« Reply #2 on: December 16, 2006, 09:26:47 pm »
I bet is you put the new one in on top of the old one.

Was the screw a bit tight when you tightened it in?
The old ones get real squeezed in there and are almost impossible to see.

Offline jdpas29

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Re: oil leak through tach cable port
« Reply #3 on: December 16, 2006, 11:09:58 pm »
the old seal on my K8 was cooked on and i had to literally scrape it off and try to smoothe the metal ring off to seat the new seal... as you could imagine, this was a difficult process given the tiny hole you have to work with.  it slowed the leak but it's still there even after the new seal was installed.

but i'd rather lose a drop of two of oil out of the tach cable housing thingy than it be pushed out somewhere more important.  so i left it a little leaky. 
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Offline scondon

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Re: oil leak through tach cable port
« Reply #4 on: December 17, 2006, 12:45:23 am »
    The standard method of removing the old seal is to screw a wood screw into it in order to pull it out. If the wood screw contacts the aluminum housing during this process then it will cause gouges that oil will seep past. I found that the only way to fix this was to use JB Weld to make the housing walls smooth again and to place the new seal(with Hondabond as Mick suggests) before the weld dries.

     You can fit an o-ring to the tach cable but the screw that holds the cable will push right into it and break the seal. If you want to use silicon sealant or Teflon tape to help stem the leak then make sure to build it up on both sides, but not in, the o-ring groove(tach cable) before inserting it in the valve cover. This is a messy option since there is a lot of clean-up if you need to replace the cable in the future.

Edit: I used the the term "o-ring groove" so you'd know what I was talking about. People often put an o-ring there to "help?" stop leaks but it is only a groove for the mounting screw to seat in. If you try building up sealant in the groove then the mounting screw will just push it in, away from the wall, and break the seal.
« Last Edit: December 17, 2006, 01:08:31 am by scondon »
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Offline Jonesy

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Re: oil leak through tach cable port
« Reply #5 on: December 17, 2006, 04:19:33 am »
Once you get the old seal out, you have to make sure the new one is fully seated in the bore. I went through that on mine...
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Offline eurban

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Re: oil leak through tach cable port
« Reply #6 on: December 17, 2006, 07:02:37 am »
People do try to seal the tach cable fitting by using sealant, teflon tape or by puting an oring on grooved portion of the (750 style) tach cable fitting.  This really misses the point however as the tach cable itself is not sealed to the housing so oil will just end up being pushed up the cable.  This may or may not cause oil to drip out of the upper fitting depending on a bikes particular tach seal failure and crankcase pressure.  To properly fix this problem you should replace the seal which is located at the bottom of the tach cable hole in the valve cover. 

Offline scondon

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Re: oil leak through tach cable port
« Reply #7 on: December 17, 2006, 10:01:22 am »
People do try to seal the tach cable fitting by using sealant, teflon tape or by puting an oring on grooved portion of the (750 style) tach cable fitting. This really misses the point however as the tach cable itself is not sealed to the housing so oil will just end up being pushed up the cable. This may or may not cause oil to drip out of the upper fitting depending on a bikes particular tach seal failure and crankcase pressure. To properly fix this problem you should replace the seal which is located at the bottom of the tach cable hole in the valve cover.

     Took me a bit to comprehend why there was engine oil leaking from the tach on one of my bikes. PO had used sealant at the valve cover to such good effect that the leak no longer spilled onto the cover but travelled up the cable and into the tach. When I cleaned out the silicon "fix" and re-inserted the tach cable I found that the leak was quite severe( not just weeping but running down the valve cover ).

      No one I talked to had ever heard of this happening. Thanks for confirming it was not some freak occurance, eurban. If there is a plus side, it is that the cable and tach were always well lubed. :D
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Offline Gordon

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Re: oil leak through tach cable port
« Reply #8 on: December 17, 2006, 10:13:05 am »
No one I talked to had ever heard of this happening. Thanks for confirming it was not some freak occurance, eurban. If there is a plus side, it is that the cable and tach were always well lubed. :D

Same thing was happening on my 750 until I replaced the seal.

Offline mick750F

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Re: oil leak through tach cable port
« Reply #9 on: December 17, 2006, 10:24:50 am »
   After I had replaced my seal which was definitely leaking I noticed that I still had a small amount of oil running down the valve cover. WTF!? I knew the seal was good because it took a bit of running for the leak to show itself. A close inspection of the cable revealed a small nick in the sheath about 4" up the cable on the frame side where it wasn't apparent. Replaced the cable...no more leak.

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Offline Serge

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Re: oil leak through tach cable port
« Reply #10 on: December 17, 2006, 03:02:33 pm »
Thanks a lot for the replies! I think I need to replace both cable and seal. Indeed there is some leak from cable housing, what indicates that the seal does not really work. I did take the old one out with a small screwdrive and I did not use any hondabond or JBweld on the surface... Sean, did you do that trick with JBweld while engine was out ? 
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Offline scondon

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Re: oil leak through tach cable port
« Reply #11 on: December 17, 2006, 03:39:35 pm »
 I used the JB weld with the engine still in the bike. It was a bit tricky to work in there and I forget what I used to smooth the surface of the weld. I installed the seal while the weld was still wet 'cause I didn't see any way to sand or shape the weld once it dried. Seal is good now but I wouldn't use JB weld unless the aluminum is actually damaged and needs to be filled.
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Offline gmen0101

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Re: oil leak through tach cable port
« Reply #12 on: March 14, 2011, 08:40:28 am »
Great thread, thanks to the OP for starting this.  I traced a leak back to the tach cable port on my 78 CB750 and found that the PO had installed a new o-ring/gasket on top of the old one.  I was able to pry both of them out, the 'new'/outer one came out with no issues and looked to be in great shape.  The inner/older one took some persuasion, but came out without doing any damage to the port walls, just messed up the gasket a bit.  I put some bond on the newer gasket, re-installed it making sure it was fully seated in the port.  Let the bike sit overnight then drove it to work this morning with no signs of the oil weep that had been plaguing me.  What an easy fix, thanks to everyone who contributed, as all of the posts helped me get this problem resolved.

Offline climbingaz

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Re: oil leak through tach cable port
« Reply #13 on: March 14, 2011, 08:57:11 am »
Mine leaks too, great info!