Help needed- TY250 A Dipstick question

[feetupfun]

7 hours ago, Tillerman6 said:

Feetup fun- I will check the level again this morning, but if it is still high I will be pulling off the clutch cover and have a look-  Just going off of faint memories- I think I used to be able to take on a liter with no issues before the engine overhaul.  I checked the top case vent to see if it was clogged - not clogged.  What do you suppose it is? 

My first thought is something that is acting like a weir between the gearbox and the primary drive compartment.

There's another test you can do before taking the clutch cover off if you want. If you drain the gearbox via the drain plug and yet still have a high level when you dip the primary drive compartment, then that will prove that there is something stopping the oil level from equalising between both compartments.

If there is something acting as a weir, it's possible that whoever built the engine made their own gasket and didn't put the bottom hole in the gasket for one of the passages where the oil flows back and forth between the gearbox and primary drive.

There are also other possibilities but no matter what it is you or someone will need to take the clutch cover off to find out what is going on

[Tillerman6]

2 hours ago, feetupfun said:

My first thought is something that is acting like a weir between the gearbox and the primary drive compartment.

There's another test you can do before taking the clutch cover off if you want. If you drain the gearbox via the drain plug and yet still have a high level when you dip the primary drive compartment, then that will prove that there is something stopping the oil level from equalising between both compartments.

If there is something acting as a weir, it's possible that whoever built the engine made their own gasket and didn't put the bottom hole in the gasket for one of the passages where the oil flows back and forth between the gearbox and primary drive.

There are also other possibilities but no matter what it is you or someone will need to take the clutch cover off to find out what is going on

Feetupfun,

  Before I read the above- I took the clutch cover off-   Cases were empty at the time- I didn't see anything unusual - mostly because the clutch basket is blocking most of the view behind it.  Anyway I found an opening in the casting above and behind the clutch basket-  Started adding ATF with the syringe-   When I had 950 cc's added- the ATF started coming out of the 8MM hole which is to the left of the clutch assembly and slightly below the axis of the clutch.   This hole is also above the upper line on the dipstick by about an inch.

So this is telling me that there is not much circulation happening between the clutch side of the wall and the gearbox unless the oil is at or above that 8MM hole.

I have looked at pics of the raw case halfs on Ebay and tried to figure out if and where there might be another hole in the wall in another location that is not occupied by a gearshaft or some other parts that are mounted in the gearbox.  

You would think that there should be another hole somewhere lower down than the 8mm hole on the left side of the clutch- which would allow oil to circulate thru the wall more freely, but unless there is one behind the clutch basket, I am at a loss to find it.

That is brought home by the idea that nothing is coming out of the wall until the oil gets up to the 8MM hole on the left - unless you count a very slow drip that seems to be coming out from behind the clutch.  

 

[Tillerman6]

With about 950CC's added directly to the gearbox via the syringe, the oil level on the stick is normal- no waiting. I added the other 50CC's into the dip stick hole after the clutch cover was re-installed and now the oil level on the dipstick is normal.

This still does not give me any confidence that things are really normal because there won't be full circulation thru the wall.  With only the one hole high up functioning- it would seem possible that most of the clutch oil would be slung thru the 8mm hole because of the large spinning clutch and more or less stay there as long as the engine is running. 

 

[Tillerman6]

Feetup fun- I don't think there are any gaskets that go INSIDE the gearbox, so not much chance of a bad gasket being installed there- more like a loose rag or something like that?  I might be able to find my borescope and have a peek inside the gearbox.  Right now, any oil that is above the rim of the clutch but below that 8mm hole would be trapped there- the drain plug is on the other side of the wall!

 

[feetupfun]

On the motor I took the photo of, the drain plug drains from both the clutch casing and from the gearbox. The drain plug hole is open to both sides. I suspect that this could be where your problem lies. For some reason your drain plug may not be draining both compartments.

Before I went and found the engine casing to take a photo of, I was expecting that there would be a dedicated hole near the bottom to let the oil levels equalise, but Yamaha have designed it for the levels to equalise via the the shift drum hole and the shifter shaft hole, both of which have rotating components that are a loose-enough fit for oil to pass through.

[Tillerman6]

1 hour ago, feetupfun said:

On the motor I took the photo of, the drain plug drains from both the clutch casing and from the gearbox. The drain plug hole is open to both sides. I suspect that this could be where your problem lies. For some reason your drain plug may not be draining both compartments.

Before I went and found the engine casing to take a photo of, I was expecting that there would be a dedicated hole near the bottom to let the oil levels equalise, but Yamaha have designed it for the levels to equalise via the the shift drum hole and the shifter shaft hole, both of which have rotating components that are a loose-enough fit for oil to pass through.

feetup fun!  Take another look at that casting pic you sent- there is a hole  thru the wall - looks like just in front of the left most threaded hole boss at the bottom left corner-   I looked at my pics again and I had too much ATF still in puddles to see if mine had that hole open or not- but it looks big enough to equalize the two sides if it was there and if it was also open.!  And I don't think that's the same hole as the drain plug hole is it?  But even if it was the same hole- when the drain plug is installed- it would block off any oil that wanted to flow thru the wall.  My problem is not when the oil drains anyway- that's fine- it's only when you fill it up that the imbalance starts.

 

 

Edited March 14, 2021 by Tillerman6
correction of my mistakes

[feetupfun]

2 hours ago, Tillerman6 said:

feetup fun!  Take another look at that casting pic you sent- there is a hole  thru the wall - looks like just in front of the left most threaded hole boss at the bottom left corner-   I looked at my pics again and I had too much ATF still in puddles to see if mine had that hole open or not- but it looks big enough to equalize the two sides if it was there and if it was also open.!  And I don't think that's the same hole as the drain plug hole is it?  But even if it was the same hole- when the drain plug is installed- it would block off any oil that wanted to flow thru the wall.  My problem is not when the oil drains anyway- that's fine- it's only when you fill it up that the imbalance starts.

 

 

Yes that's the drain hole

[Tillerman6]

10 hours ago, feetupfun said:

Yes that's the drain hole

That's right!!  I was expecting another thru the wall hole somewhere, but that appears to be the only one there is that is down low.

Now the question is - why does yours cross- feed so well and mine is stuck?  

I have an idea that is sort of a bandaid fix- make another drain plug that is much shorter- That should solve the problem providing it does not leak.- it will only have 4 exposed threads above the gasket.

 

[Tillerman6]

1 minute ago, Tillerman6 said:

That's right!!  I was expecting another thru the wall hole somewhere, but that appears to be the only one there is that is down low.

Now the question is - why does yours cross- feed so well and mine is stuck?  

I have an idea that is sort of a bandaid fix- make another drain plug that is much shorter- That should solve the problem providing it does not leak.- it will only have 4 exposed threads above the gasket.

 

Got the bike running today- Hurray!  It has the short drain plug I made today in it- There is enough room above the drain plug to allow some oil to pass over it into the gearbox.  But warming it up just basically slung oil everywhere inside the clutch housing, so you have to wipe off the stick to get a reading of course- the level still looks high- about 1/2" above the top mark on the stick.

[Tillerman6]

23 hours ago, Tillerman6 said:

Got the bike running today- Hurray!  It has the short drain plug I made today in it- There is enough room above the drain plug to allow some oil to pass over it into the gearbox.  But warming it up just basically slung oil everywhere inside the clutch housing, so you have to wipe off the stick to get a reading of course- the level still looks high- about 1/2" above the top mark on the stick.

Feetupfun- well after all this oil draining, measuring and pulling off the clutch cover- and with the aid of your advice, I have discovered two things about the oil level on the dip stick. #1 - The oil drain plug is built so that it sits between the gearbox compartment and the clutch compartment, and because it is made with about 15 threads, when installed, it blocks off any oil moving between the clutch and the gearbox- that is oil that is at the bottom of the gear and clutch housings.  There is another thru hole further up the wall that separates the two compartments, but for it to pass oil, the engine would have to be running. The splash of the clutch would throw oil up and into the gearbox compartment until it could not scavenge any more oil from the supply that was there when the oil was first filled.  Whatever was left in the clutch housing area would not circulate with the rest of the oil until the oil was drained again.  

#2- Because of your input- you gave us pictures of the dipstick on your bike and it showed the oil to be more or less at the upper limit mark on the stick.  So for whatever reason- you have better circulation between the clutch housing and the gearbox compartment.  

This is hard to explain assuming that the engine cases are identical, and I cannot see any evidence from any source - Ebay pics, your pics, or my own inspections that show another hole low down on the wall.  

So this only leaves one possibility- either the drain plug you have installed is different than mine, or the casting itself is different to allow the oil at the bottom to flow freely back and forth.  

And since I am not in the mood to tear down the engine again to chase this down I decided to make a shorter drain plug.

This creates a path for the oil at the bottom of the cases that does not depend on the splash of the clutch assembly to flood the gearbox with oil.   The new plug has only 4 threads above the gasket instead of 15 on the original plug.  The plug size and thread pitch is 14 x 1.5mm and I was able to buy a bolt at the hardware store to fabricate my own replacement drain plug.   I also made a nylon washer which is sealed from behind with non- hardening gasket maker cement to make sure there are no leaks.

If you or anyone has any more input on this, I would be glad to answer any questions.  

P.S. - I have been on Facebook at the TY owner's and appreciation group and I have gotten word that this "overfull" condition is not unheard of- at least two others on there have said they have the same problem.

I think my solution is fairly easy to do, and it will probably make everyone's bike start a lot easier- seeing as how the clutch will not be 50% covered up with oil.

 

[dpyam]

This issue is known about on the Yamaha RD 2 strokes of the 1970's so seems to be a Yamaha 'feature'.  By the filler on the RD's it says "1500cc" but if you perform an oil change and try and put 1500cc of oil in, it will show on the dipstick as massively overfilled.  Going for a short run and re-checking means the oil level shows as not as badly overfilled but still over full.

From experience you learn to put about 1200cc in and that's usually about right. Oil seems to sit somewhere that never drains out.

I've never filled a new/rebuilt engine so can't comment on that.

  

[Tillerman6]

 I really don't remember if the first fill was able to absorb a full 1000CC's or not.  But now that it has had about 4 drain and refill cycles and none of those was able to use 1000cc's  more like 750 would put it on the upper mark.  But right now it has about 800 in it and the oil level is about 10mm above the high full level mark on the dip stick.  But thanks for the information on the other 70's Yamahas.  It's starting to look like a fairly common issue.

[Tillerman6]

So now I took some more of the excess oil out of the gearbox- the level is getting closer to the upper mark on the dip stick with the dip stick loose.  Result- starts easier and has slightly more power.  Started on 3rd kick instead of the 10th one.  This is because the clutch is partially submerged in the gearbox oil.  Probably the lowest inch or so of the perimeter of all the clutch plates, so the engine has to spin all this oil out of the way or just churn it constantly.    The measurement was taken with the bike on the stand and on the 74 the stand is opposite of the dip stick, so it's still got more oil in it than it needs.