Topic: Tach oil seal

[Gordon]

Tach oil seal replacement is a ten minute job.

Less, if you have the part in hand and don't stop too often to sip your beer. 

mystic_1

In addition to the beer sipping , I was allowing extra time for cleaning up the gas you spill when you disconnect the fuel line while removing the tank after forgetting to shut off the petcock, then more extra time for cussing at the tach cable screw that won't budge so you have to get out the impact driver, and then just a little more time for contemplating the new oil seal trying to figure out which way it goes in because you didn't pay attention to how the old one was in there before taking it out.

[tydeus]

I have the same oil leak on my 77 CB750K. What part do I need to order? I'm scouring the online part schematics and  I can't find tach oil seal.

[Inigo Montoya]

I dont know about the earlier bikes but I just tilted my tank to the side and was able to use an angled philips to loosen the screw so I could take it out by hand. 77K.

[bryanj]

750 sohc 91211-286-003 4.8x14.5x4
750 dohc 91256-425-005 4.8x14.5x5

so the later one, being thicker, will be pushed down a bit by the cable

[mystic_1]

750 sohc 91211-286-003 4.8x14.5x4
750 dohc 91256-425-005 4.8x14.5x5

so the later one, being thicker, will be pushed down a bit by the cable

Is this a known trick, using the DOHC seal?  Never heard of it myself.  1mm height difference doesn't seem like much but may make it hard to align the groove in the cable end with the screw hole in the valve cover?

mystic_1

[Gordon]

750 sohc 91211-286-003 4.8x14.5x4
750 dohc 91256-425-005 4.8x14.5x5

so the later one, being thicker, will be pushed down a bit by the cable

Is this a known trick, using the DOHC seal?  Never heard of it myself.  1mm height difference doesn't seem like much but may make it hard to align the groove in the cable end with the screw hole in the valve cover?

mystic_1

I've never done it before, but it's something that others here have reported doing with success.  I just changed the seal on my K1 recently (stock size) and there definitely seems to be enough play in the cable to be able to fit a slightly larger seal.   

[mystic_1]

750 sohc 91211-286-003 4.8x14.5x4
750 dohc 91256-425-005 4.8x14.5x5

so the later one, being thicker, will be pushed down a bit by the cable

Is this a known trick, using the DOHC seal?  Never heard of it myself.  1mm height difference doesn't seem like much but may make it hard to align the groove in the cable end with the screw hole in the valve cover?

mystic_1

I've never done it before, but it's something that others here have reported doing with success.  I just changed the seal on my K1 recently (stock size) and there definitely seems to be enough play in the cable to be able to fit a slightly larger seal.   

Cool, I'll have to give that a go next time I need to replace a tach seal.  That was the very first thing I replaced on my bike when I acquired it years ago. 

mystic_1

[Inigo Montoya]

I just wonder if squashing a larger seal might cause even more inaccurate tach readings. Probably not but tach seals are cheap and do not wear out that fast.

[mystic_1]

Yeah that seal I replaced has now been in there for a good 14 years or so, no leaks

mystic_1

[Johnny5]

I just wonder if squashing a larger seal might cause even more inaccurate tach readings. Probably not but tach seals are cheap and do not wear out that fast.

Nah, it doesnt hinder the spinning gear inside the valve cover. Mine has been flawless since installing it.

[MCRider]

I just wonder if squashing a larger seal might cause even more inaccurate tach readings. Probably not but tach seals are cheap and do not wear out that fast.

Nah, it doesnt hinder the spinning gear inside the valve cover. Mine has been flawless since installing it.

YEah at that end we're talking about the camshaft driving that spindle. Nothings going to stop that or effect it. Might rob a teeny tiny bit of HP.   

Its inside the tach head where all the slop is. Condensation, which washed out the lube, along with gravity, affects the tach accuracy. Maybe a fagged out cable, too.

[jerimiah797]

I just bought this one:

Part # = 91256-096-651
Part Description = OIL SEAL - (replaces 91211-286-003)

for about 6 bucks, including shipping.

Can't wait to go back there and show him the old seal. :-)

-Jerimiah

[SKTP]

http://www.bikebandit.com/houseofmotorcycles/honda-motorcycle-cb750k-1978-cylinder-head-cover/o/m9458sch400490

I know I'm late on this...but for my 78K its part #12

$3.80. Mine just started leakign and smoking...good times!

[SKTP]

I am waiting for my gasket...I left the mess from the past few days to confirm with you guys that this is ho your leak looked...its a little smokey but does not actually drip on the ground. It seem to drip down and across the from then down the kickstand side of the engine...if I leave it for 2 day it will smoke from the left hand farthest out pipe...sound familiar? I hope so I am praying its not a head gasket leak!

[Gordon]

I am waiting for my gasket...I left the mess from the past few days to confirm with you guys that this is ho your leak looked...its a little smokey but does not actually drip on the ground. It seem to drip down and across the from then down the kickstand side of the engine...if I leave it for 2 day it will smoke from the left hand farthest out pipe...sound familiar? I hope so I am praying its not a head gasket leak!

I don't see any evidence of oil coming out from the tach cable housing.  You sure it's not leaking from the valve cover?

[SKTP]

If it is leaking from the valve cover, do I need to pull the engine? (please say no!!!!!)

[Gordon]

If it is leaking from the valve cover, do I need to pull the engine? (please say no!!!!!)

The 750 valve cover cannot be removed with the engine in the frame.  It can be lifted slightly, and it's apparently possible to slide the new gasket over the valve cover and replace it without pulling the engine, but I've never tried it.  Doing it that way, however, would not allow you to completely remove all traces of the old gasket if/when parts of it stick to the mating surfaces. 

[SKTP]

well if that wasn't the problem, it sure was ONE of the problems...new versus old Tach oil seal...spend the 3 dollars people

[SKTP]

So I am fairly certain I have a minor head-gasket seal leak. I only own the bike and it is my daily driver to and from work so I really want to avoid pulling the engine for as long as possible. The leak is minor enough to never pool under the bike. It just collects on the engine (that shelf part, pictured in the photo a few posts up) and if I wipe it with a shop towel ever other morning of so its a non-issue.

Is there a type of liquid gasket I can use to delay the inevitable?

[MCRider]

So I am fairly certain I have a minor head-gasket seal leak. I only own the bike and it is my daily driver to and from work so I really want to avoid pulling the engine for as long as possible. The leak is minor enough to never pool under the bike. It just collects on the engine (that shelf part, pictured in the photo a few posts up) and if I wipe it with a shop towel ever other morning of so its a non-issue.

Is there a type of liquid gasket I can use to delay the inevitable?

Above "The shelf part" would mean it is a cam cover gasket and not the head gasket. The cam cover gasket can be replaced without pulling the engine, there are threads here how to do it. Its tricky but it can be done. The head gasket is an engine pull for sure.

The head gasket is below the larger fins making up the shelf but above the part of the engine where the fins are much smaller (the cylinders).

To your question, clean it real good with acetone or the like, and try some silicone. Since its on the outside it can't hurt and may slow it down. Doubtful.

[SKTP]

Sweet, I'm crossing my fingers for the Cam cover...I will have a better look ASAP

thanks...its time I got to know my engine anyways

[SKTP]

So these are the ones that I want to replace...the O-rings (marked in Blue look pretty easy to do). Anything special about swapping those out?

Any info or experience swapping the other two is greatly appreciated

[MCRider]

So these are the ones that I want to replace...the O-rings (marked in Blue look pretty easy to do). Anything special about swapping those out?

Any info or experience swapping the other two is greatly appreciated

The blue #13s would be easy, but they seldom leak. You would see a trail of oil down from the bottom of the cap to the "ledge"if they were leaking.

The red #5 is the culprit usually. Without detail, you can raise the cover #1 about an inch or so, scrape the old one out and wiggle the new one in, I've been told by some here who have done it, I never have. But i can tell its possible, without pulling the engine.

#3 seldom leaks.

[Gordon]

With the leak as slow as you say it is, I would just keep wiping off the oil every couple of days until I had the time to pull the engine and replace all of the top end gaskets and oil seals at the same time. 

While it is possible to replace the valve cover gasket with the engine in the bike, I can imagine it would be a huge pain in the ass to remove all traces of the 30+ year old gasket by just slightly lifting up the valve cover.  There are a lot of things that will get in your way when trying to do this, and it would be very easy to accidentally knock small pieces of the old gasket into the engine where you don't want them.     

[754]

If you did that to the seal removing it, I hope you didnt score the shaft..

 If you did, you have a new problem.. it involves lots of seal replacement, or pulling the motor..