Replaced valve stem seal, but still leaking

I've been trying to chase down this oil leak since I bought the bike, and about five gasket changes later I think I've narrowed it down to the valve stem seal. It's an 80 kz750e.

I replaced all the seals last summer while doing some other maintenance, so I discounted that as the problem when the bike continued leaking. So I went and changed the base gasket & several head gaskets, but the leak continued.

I did the foot powder trick and it looks like it's coming from above the head gasket and near the inside of the third header, making me think it's the valve stem seal.

If it does turn out to be the stem seal, does that mean I need a new valve, since the new seal I installed last year didn't stop the leak? Are there any other possible causes/sources of the leak?

I have heard that the aftermarket valve stem seals are no good. Mine sofar have been fine, but I guess some people find they leak shortly after install.

If in dead you are leaking threw the stem, and the seal is new, than the stem is shot or it is not tight in the head. I use nothing BUT Viton aftermarket seals and have had much better results than with OE seals. You must remember that a stem can seam as being tight in the head while replacing the seal but once heated up, the stem being steel, will loosen up in the head when the aluminum head heats up and expands. This is the reason why many people go to brass valve stems, because the thermal expansion of aluminum and brass is very close. Unlike aluminum and steel or iron. This is also the reason why you must use special head gaskets on engines that have aluminum heads and Iron blocks.

Are you sure it's not coming from the tach cable connection? On the KZ650 that seal is very close to the 3rd header.

chrispysaki wrote:

I've been trying to chase down this oil leak since I bought the bike, and about five gasket changes later I think I've narrowed it down to the valve stem seal. It's an 80 kz750e.

I replaced all the seals last summer while doing some other maintenance, so I discounted that as the problem when the bike continued leaking. So I went and changed the base gasket & several head gaskets, but the leak continued.

I did the foot powder trick and it looks like it's coming from above the head gasket and near the inside of the third header, making me think it's the valve stem seal.

If it does turn out to be the stem seal, does that mean I need a new valve, since the new seal I installed last year didn't stop the leak? Are there any other possible causes/sources of the leak?

No matter how much oil is passing through the exhaust port, none of it should leak past the gasket between port and header pipe.

A loose header pipe clamp nut may allow seepage past the gasket.

A brand new gasket should be fitted, as re-using an old gasket often results in leakage.

Would concur with 650ed about possible leak at tach drive (past 0-ring and/or shaft seal).

Another possibility could be that the split collars are too short and failing to sufficiently compress the gasket.
Some aftermarket exhaust systems need longer split collars (which are usually provided with a new system).
This is due to slightly thinner flanges on the aftermarket pipes compared to the thicker flanges on oem pipes.

Z1E also has optional thicker gaskets (i.e., Suzuki gaskets) which might resolve the issue, and without needing longer split collars. At least for the large fours --- but don't know if applicable to 750.

Good Fortune!

i am sure he's right...how sure ??? 100% sure...

a seal on a valve will not let oil outside the motor...all other things in correct order..ie valve cover gasket...
a valve cover gasket WILL seep oil...but i am sure you have a loose tach to engine cable connection or the small o ring at the tach cable to engine, where it threads onto the motor there is a small o ring fits in between the two before threading on and tight,it is broken or missing...many p.o will let it fall out and not know or care to find it and reinstall before threading the cable on....


650ed wrote:

Are you sure it's not coming from the tach cable connection? On the KZ650 that seal is very close to the 3rd header.

if its leaking that much oil the plug or plugs should be fouled, did you run a compression check on the motor at any time?
is there a lot of smocke comming from the tail pipe?

I am leaning like others that its a valve cover, tach seal leak as opposed to a valve stem seal

you may have damaged the rings or they may need to be replaced if it is having that much blow by.

If longer split collars are needed, but not readily available, could try adding an old flattened gasket along with the new gasket, plus Permatex high-temp copper silicone sealant, which gaskets together should effectively serve as an extra thick gasket.

Another thought would be to use the sealer on both sides of a new gasket during reassembly, and hope the sealant alone will sufficiently seal the interface to prevent leakage around the gasket.

Good Fortune!

Like Patton says, no amount of oil leaking past a valve seal will cause a leak outside the engine. Check the valve cover/head mating surface for a groove or notch that oil can seep past and check the tach drive cable.

I suspected the tach drive seal, too, but I removed the tach cable, used some Permatex Ultra Black around the inside of the tach drive holder and filled in the hole with silicone. I guess it could be that, but it didn't look like the oil was coming from there during the powder test.

My initial thought was that it was the valve cover gasket, so I just reinstalled it with some permatex on both sides of the gasket. I haven't tried it out yet, but upon inspecting the surfaces of the head and valve cover, they both seemed blemish-free, so I lost hope for that being the cause.

The collars for the head pipe seem to fit nice and tight, and they're the same ones for the rest of the ports, so then it can't be the valve stem seal if there's no oil escaping from the exhaust port?

The plug isn't fouled at all and there doesn't seem to be any smoke coming from the exhaust. I don't know, maybe it is the valve cover gasket after all. If that doesn't seem to work, I'll take another look at the tach drive seal.

One area I found to be a problem were inconsistant length cylinder studs. I tried to retorque mine and never felt confident that the nuts were sitting properly on the washers. I looked at some other cases and found differing stud heights (1/16"-1/8") and after trying some APE nuts which have a taller internal thread, the problem went away. You could opt to try and remove some thread if you have the head off or try adding another washer below the stock nuts. My bike used to leak from the same area and drove me crazy until I tried this fix. Good luck! David;)

Well, I took her out tonight after adding some sealer to the valve cover gasket, and it looks like that may have been the problem. I took it pretty easy (below 6k or so) and only went a few miles, but in the past that would have been enough to get some oil dripping. I'll give it the full test on the way to work tomorrow.

Thanks for all of the feedback everyone!