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brucey

Tiger Cub Push Rod Tube Oil Leak

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O.k.  I fitted the earlier 'R' Cam to my late engine, no problem.  Replaced the primary drive chain and it now runs smooth and quiet.  Made some parts to allow me to run the bike without the right hand outer cover on.  This would allow me to spot any oil leaks from the gear lever shaft and outer cam bush.  I also replaced the push rod tube top and bottom gaskets with new items.

 

All is well apart from oil spewing out of the top of the push rod tube around the gasket.  (see photo).  I tried the thicker one when I assembled engine (without the push rods fitted) but it seemed to be holding the head off the barrel.

I put a smear of sealant around the push rod tube flange on assembly and straightened a small dent in the flange which I was convinced was the cause of slight oil leak I had originally. 

Oil now drips out of the top of the push rod tube as a constant rate as soon as the engine is warm.  I am running out of ideas.  This engine was built from spare parts so the barrel and head haven't actually been together for any length of time but the barrel and push rod tube were together on my other (Armac Cub) engine.  I upgraded the Armac Cub engine to 230cc and had barrel, piston and push rod tube left over.

I'm beginning to wonder if the head and/or crank case has been modified in the past for the oil to return down the barrel stud holes but the 2 original oil return holes in the head are both clear.  I therefore can't see why it should make any difference.

I also ran the engine with the top push rod inspection hatch (in the head) removed.  The push rod tube doesn't appear to be flooding, there is just a steady stream of oil from the head running back down the push rod tube.

I'm fast running out of ideas.  I guess I can try and lift the head enough to put the thick top gasket on as I have nothing to loose.  Otherwise its engine out again after just 10 minutes running ? 

Any help appreciated.

 

pushrod tbe oil leak.JPG

Edited by brucey
correct typos

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Cub engine modified to allow me to run with outer cover removed to spot oil leaks.  Unfortunately not required as the oil is easy to spot running out of the top of the push rod tube!

old cub engine rhs.JPG

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What type off gaskets do you use I use an o rings top and bottom A black square section type on the bottom and a red round section at the top If the tube is seated properly and no damage it should seal mine do alright

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10 hours ago, naichuff said:

What type off gaskets do you use I use an o rings top and bottom A black square section type on the bottom and a red round section at the top If the tube is seated properly and no damage it should seal mine do alright

I'm using the black one at the bottom and what's meant to be a superior gasket at the top that comes in 2 thicknesses.  Saying that, I may try fitting the original red 'O' Ring ?

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I’ve ordered a nice new alloy push rod tube. Apparently it has a better location and thermal expansion rate. Fingers crossed ??

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Tounge in cheek the oil may be coming from the big hole just above it:).

Seriously what is this hole for? Is it made so that the pushrods can be located easily?

I have also had problems with sealing but used a thicker softer material (cannot remember what) but more like a square edged O ring (which I got from Martyn Adams I think).

Lets us know if the alloy tube does the trick.

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1 hour ago, mattylad said:

Tounge in cheek the oil may be coming from the big hole just above it:).

Seriously what is this hole for? Is it made so that the pushrods can be located easily?

I have also had problems with sealing but used a thicker softer material (cannot remember what) but more like a square edged O ring (which I got from Martyn Adams I think).

Lets us know if the alloy tube does the trick.

Yup, It's a mod I did to both my Cub engines (shown to me by a guy called Henry Boudery) to help locate the top of the push rod.  I normally dab a bit of grease on the bottom of the push rods and hold the rockers in their 'up' position with an elastic band. 

The top of the exhaust push rod is also painted red. 

Probably all a bit over the top but nice to know everything is correct before tightening the head down ?

I have high hopes for the alloy push rod tube and I will also be using a bit of sealant as recommended by Bob at UPB ? 

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On the twins there are more than half a dozen different tubes, and at least 5 different seals i can think of.

The non o ring square seals have 3 different thicknesses alone.

On mix 'n'match heads and barrels and engines of unknown origins (ie how many times has the head been skimmed etc), the tech (mechanic) needs to measure what is known as "pushrod tube seal squish".

This is assembly of the motor WITHOUT any p/rod tube seals and measuring the gap.

Once this is established, then the correct width seals can be chosen and fitted.

I would presume it is similar on a Cub.

If a tube is stopping a head being bolted down, then  there is already a problem.

Alloy tubes are, indeed, a good idea and i run them on my twins. The chromed steel tube in the pic looks rather manky.

Regards.

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Just a quick update. I fitted the alloy push rod tube without push rods and gaskets and measured the clearances as Thai-ty has mentioned above. I then select the appropriate top gasket to give me about 1mm clearance at the bottom of the tube.  I also used a bit of tribond  (?)  sealant for good measure either side of the top gasket.  Hey presto, no leaks......yet??  

thanks for your advice ??

 

Edited by brucey
Auto correct typos?
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