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Author Topic: Leaky tachometer ouput  (Read 872 times)

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Offline 70CB750

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Leaky tachometer ouput
« on: October 07, 2018, 05:34:09 pm »
On the valve cover.

I used just a generic o ring there, but it did not work so well so i found a seal that belongs there - by the part number.

It still leaks, any tricks to it?

Not sure it matters but the engine is 78SS CB750.
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Offline jgger

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Re: Leaky tachometer ouput
« Reply #1 on: October 07, 2018, 05:38:15 pm »
Is your oil breather tube clear? Just a thought.
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Offline 70CB750

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Re: Leaky tachometer ouput
« Reply #2 on: October 07, 2018, 05:45:07 pm »
Good point, I will check.
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Offline spotty

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Re: Leaky tachometer ouput
« Reply #3 on: October 07, 2018, 05:48:54 pm »
get rid of the tacho, epoxy a coin over the hole...sorted, well it sorted it on my old 750 anyway but that didn't have a speedo either
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i blame Terry

Offline ekpent

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Re: Leaky tachometer ouput
« Reply #4 on: October 07, 2018, 06:12:02 pm »
Did you seat the seal in well with a socket a little smaller then the fitting hole ? Couple light taps with a small hammer.
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Offline JerryWayneCattle

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Re: Leaky tachometer ouput
« Reply #5 on: October 07, 2018, 08:35:10 pm »
Make sure there isn't an old o-ring still deep in there. PO of my '74 CB750 had the correct seal AND an o-ring in it. He might have not even known. It held the cable out and didn't let it seat correctly.  I bought a new one that fits a DOHC 750. Read on this site that they fit better.

Sent from my SM-N920T using Tapatalk

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Offline PeWe

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Re: Leaky tachometer ouput
« Reply #6 on: October 07, 2018, 09:56:48 pm »
Correct oil seal will not leak. If hammer too hard the bottom of the cover can crack, alu chunks fall into the cam holder.  Especially when removing the old seal with tools from the outside. Somehow, I know ;)
Frame kit is good in that kind of situation.
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CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Marks78

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Re: Leaky tachometer ouput
« Reply #7 on: October 08, 2018, 08:26:18 am »
I'm not positive (as I can't find the reference) but it seems like HondaMan recommends using the tach seal from a double overhead cam Honda as a viable alternative. The DOHC seal is just a tad bigger, so it seals better. Best of luck!
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Current Stable:
1978 CB750K
1982 XT200J
1982 XJ1100 Maxim
1985 V30 Magna
1998 VT1100 Spirit
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Offline evanphi

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Re: Leaky tachometer ouput
« Reply #8 on: October 09, 2018, 07:28:34 am »
Mine leaks also, and also with a properly seated new rubber seal. I did just a few wraps of PTFE tape on the end of the tach cable and that snugged it up perfectly. No more leaking.
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--Evan

1975 CB750K "Rhonda"
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K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
Calculating the correct input circumference for digital speedometers connected to the original speedometer drive

Offline 70CB750

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Re: Leaky tachometer ouput
« Reply #9 on: October 29, 2018, 05:06:00 am »
Well, turns out if was a false flag.  The tachometer cable sheathing was cracked quite a bit and the oil was leaking from there. 

Luckily I spotted it before digging out the seal  ;D
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