Baffling find in the breather....

So, just to give context, i freshened the top end this winter, replacing a bad head gasket and bottom gasket. After the initial ride last weekend, the right cylinder was smoking quite a bit, and oil consumption was high. Like 1 litre per 100km high.

Pulled the plugs, oil soaked. Kind of baffling. Checked compression, was fine at 125+. Checked the valves, and looked into the intake runners - intake was greasy, which was weird, since the guides were perfect, and new valve guide seals were installed.

Started checking things out, and after finding that my crankcase breather vents into the stock airboxes weren't passing a lot of air, thought maybe the breather was clogged, which would cause excessive crankcase pressure, and certainly push oil down the valves. (and out various engine seals, and and and... Everywhere, really.

I found two rubber plugs in the vent. They had holes through them. They looked like designed reducers - they took the hole from the 8mm or so that they are to 1mm.

Sooooo... I've never found something like this before, and from an engineering point of view, it seems... Non-optimal, to be generous. You *want* the crankcase to be able to easily vent, or possibly under a slight vacuum.

These were restricting so badly, that when you shut the engine off, you could actually hear the engine de-pressurizing with a "phewwwwww" kind of sound.

Anyone else ever seen something like this?

Do you mean this? Sorry, for the fuzzyness. There's one on the other side also, but it's pushed up in.

No, sounds like the po tried to stop the oil leaking out of the vent. probably why the gaskets were leaking

If the vent holes are too big (which Yamaha found on the earlier models and made the reducers) and you are not using one way breather then a lot of air will go in and out the breather holes ....it will bring more oil out......(80 and later models had one .220 thousands hole which was right)...sounds to me the rings aren't seating.....they may or may not at this point.....I know how to fix that with baking soda but I always get beat up for mentioning it.........

xsjohn

dlabkeeg said:

Do you mean this? Sorry, for the fuzzyness. There's one on the other side also, but it's pushed up in.

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Yep, that's it! What the hell? These aren't in the parts manuals...

xsjohn said:

If the vent holes are too big (which Yamaha found on the earlier models and made the reducers) and you are not using one way breather then a lot of air will go in and out the breather holes ....it will bring more oil out......(80 and later models had one .220 thousands hole which was right)

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Hmmmm... But... But you're effectively pressurizing the crankcase... That's never a good thing, is it?

...sounds to me the rings aren't seating.....they may or may not at this point.....I know how to fix that with baking soda but I always get beat up for mentioning it.........

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This is possible. I deglazed the cylinders, but didn't do much else.

I'm always interested in new and interesting techniques - even if i may not end up agreeing with them.

Oh - the end point of the story: before removing reducers: smoke and oily plugs. After removing reducers, no smoke, and plugs look normal.

Well, if I get smoke I know the first thing I'm going to do. How did you get them out?

You may have fixed it but here is th baking soda thing........

All right then.......I did the same thing a few years back and it wouldn't break in.....didn't smoke like you described but the plugs were dark and compression was down.........seems you said 130 in your post.....

Here goes.......
1 Level """teaspoon""" of baking sodas down 1 of the spark plug holes......(don't do both at the same time).....turn the engine over a few times...then put the plug back in and start it......it may clatter just a bit for a few seconds but it will clear....that is the valve that may be held slightly open by the baking soda....won't hurt anything......run it till it idols decent and then do the other side.......and take the bike out an run it........(may have to repeat one or both sides)

Did that to mine 3 years ago when I had it down for R/S crank bearing and only broke the gleaze like you did.......anyway these pistons have 76 thou on the an drukn great with good clearance and compression...so it didn't hurt it.......

Should never take the pistons out of a bore that has good compression and the pistons don't rock forward and back but just a tiny bit...........new break in a assoiciated wear greatly reduce engine longivity........I have found over the years.....


Best to raise the cylinders and pull the pins and leave the pistons in the bore....if everything checked out before the dismantle.....

xsjohn

dlabkeeg said:

Well, if I get smoke I know the first thing I'm going to do. How did you get them out?

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They were fairly well lubed, and sticking out a bit. Just grabbed them with my fingers and pulled them out.

john: i had definite concern that i might have had a bad ring. Mostly it was a bad head gasket, but the bottom gasket was leaking as well.

I might try your baking soda trick if this doesn't clear the problem up.

I'm not there but have been there if you know what I mean......I would bet that taking them out of the breather wasn't the problem but....some have put them back in to solve oil excaping from the breather.....I hope it is your problem though.......if not well you have another plan...like I said next time it's running good and have to go below the barrels for some reason just lift the barrels on some wood blocks and lock the crank and pull the pins.......leaving the pistons and rings in the bore........good compression should be somwhere around 150

good to remove the sharp edge on used rings with some 320 sand paper....hell I do it on new rings.......will last a long time then.................

Sundie.......you could just run it for a 1000 miles and see of it comes in if the breather wasn't the problem....sometimes they do......?

xsjohn

that's my plan at the moment. But if i'm losing less oil through the breather than i was, i'm fine with that. The baking soda is a last ditch option before i just yank the engine again.

I doubt i'd ever put them back in again. Running the crank case under pressure just seems the most insane thing ever, and solving the wrong problem. I mean, if oil is leaking out your breather, fix your catch system.

Sundie;
I recommend you leave those breather vents (rubber plugs with small holes) as stock. Yamaha engineers knew what they were doing, and sized those correctly. I have found that these breather vents work very well with the stock air box directing the venting into the intake of the engine. (not sure if you are using the stock air box?)

1 litre of oil in 100 kms................that's really excessive! When I got my 78SE, it was using 1 litre in 333 kms. I considered all the usual suspects...............rings, valves, valve seals etc. , but the real problem was a leaking head gasket. Why do head gaskets leak? I believe my problem was due to the PO opening up the engine and then doing a poor job ( incorrect torqing of the head studs) when putting everything back together. I lived with that oil consumption for a couple of summers, and then re-built the top end last winter. My motor now uses almost no oil, and runs extremely well. As xsjohn mentioned, the compression should be 140 to 150 psi.

I followed tips from 650garage forum such as the "leakless assembly", which I believe was written by 5twins and grizld1. I trust their experience and it has worked well for me.

As for the head gasket, this is how I installed mine. Use some laquer thinner to clean the the top of the cylinders and the bottom of the head. Run a small line of 3bond 1104 gasket sealer around the centre camchain tunnel and the 4 outer large studs that are exposed to oil pressure (both sides of gasket). Leave the top motor mount off to allow re-torqing the head studs. Once the engine was together, I let it sit overnight, and then re-torqued. I drove it for 150 kms and then re-torqued. I drove it for another 125 kms and re-torqued. I drove it for another 165 kms and then re-torqued. I would see some rotation during the first re-torques but by the third re-torque the nuts did not move.

I just recently re-checked my torque on the head studs, and they are still at the correct torque numbers.

Use 30 ft-lbs for the 8, large 10mm studs
Use 14 ft-lbs for the 6, 8mm studs
Use 7 ft-lbs for the 1, 6mm bolt at the engine back centre

I threw in some pictures of what oil leaking past the head gasket looks like...............not a pretty site So is head torquing important................oh yeah, very important.

yeah, my head gasket was visibly distorted when i did it this winter. To the point that it was touching the piston. I have worse pics than that.

The rings specced out within tolerances, so i reused them, due to budget considerations at the time.

If removing the restrictions gives acceptable oil loss and running for this summer, i'm fine with that. It's getting a planned 750 kit next winter regardless.

I'm afraid that you'll never convince me that running pressure inside the crankcase is a good idea. The restrictions look to me like solving one problem but creating another.

Sundie;
If I understand this thread correctly, you did a top-end "refresh" this winter, and now you're using 1 litre oil in 100 kms. I'd say you still have internal engine problems, and opening up the engine venting system or adding baking soda is not going to solve this.

As you say, maybe you can run the bike this summer and go for a 750 kit next year. However, I'm still curious what the real problem is. I have to ask..............did you use a new head gasket, and are you doing a proper retorque procedure until the nuts don't rotate?

RG.........using that much oil is not what I encountered when I did that...oil consumption was not even why I did that to start with.........you are probably right and something is amiss somewhere......

xsjohn

retiredgentleman said:

Sundie;
If I understand this thread correctly, you did a top-end "refresh" this winter, and now you're using 1 litre oil in 100 kms. I'd say you still have internal engine problems, and opening up the engine venting system or adding baking soda is not going to solve this.

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Using more than that, i would say. And you're right, it may or may not solve the problem. I'm trying to avoid pulling the engine again.

As you say, maybe you can run the bike this summer and go for a 750 kit next year. However, I'm still curious what the real problem is. I have to ask..............did you use a new head gasket, and are you doing a proper retorque procedure until the nuts don't rotate?

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new parts:
- headgasket
- bottom gasket
- brass rings on the headbolts
- valve seals

The head was fully disassembled, cleaned, checked for wear, and turned out to be perfectly fine. Valves were given a hand lapping and everything re-assembled.

Jugs were removed, cleaned, light honing to break the glaze, and ring end gap was checked in the bores. No obvious ovaling was noted with the micrometer, and the rings measured up to spec.

Bottom gasket was installed as per MikeXS instructions with no sealant. Jugs were slipped over the pistons (which never had their circlips disturbed). Headgasket was installed (with no sealant - although someone mentioned yamabond around the oil galleys - will be a good idea for next time), head installed, , then a skim of sealant applied to seal the valve cover. Valve cover installed, every bolt was torqued in pattern to 10lbs, except for the back which was a hand guessed 7lbs, then the head bolts were torqued in patterned staged to 20 then 30.

Hm. I think that covers it? the rest of the re-assembly was basic.

I *haven't* checked the torque since i installed it. Perhaps i'll go try that now. But my experience with the brass bushings on top is that they don't release torque like the rubber ones do.

Welp, checked the head bolts torque, and they were fine. re did them anyway, just for kicks, since i had the head stays off anyway to check them.

- wonder if youve disturbed your oil rings when reinstalling, also, the expanderers lose their shape, but can be retensioned over an old piston

just in case.....
When retorqueing its important to loosen each nut slightly before retorque, or you wont get a true retorque value.
Years ago I was blowing 750 kit head gaskets regularly cos I wasnt backing each one off a bit prior to torquing it.
just thought Id mention it.

EDIT,,,Just noticed thread is almost 8 yrs old.....