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brucey

Smoking Cub help

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Further to my post regarding the Cub oil return mod, I have now started stripping the engine to find a cause for the smoking.

The engine was built from bits and pieces and put in my spare frame for my Son to ride.  It starts and runs ok.  He entered its first trial and almost completed the first lap with no issues.  It then started smoking badly on tickover so we retired the bike.

I carried out a number of the usual mods when I built it including adding a blind camshaft bush and putting a large breather in the unused distributor hole, Alpha big end, etc etc.  I also fitted a new (later type) oil pump.

I measured the clutch and gearbox oil when I removed it and am pretty sure it's engine oil thats being burnt.  My findings so far are as follows:

1. Piston and rings look fine (I suspected a broken ring as a possible cause)

2. Oilways from head to crank case appeaer all clear.

3. I drained 300ml oil from crank case (virtually no oil was left in tank so I lost at least 300ml of engine oil)

4. There seemed a lot of oil in the cavity where the oil pump sits. May be a re herring.

5. There are no ball bearings and springs inder the oil pump as I was told the later oil pumps didn't use them.

6. I recently replaced the oil feed pipe gasket as the ild one split and was leaking.  On removing the oil feed pipe and turning over the engine, a hollow dowel popped out of the front hole nearest the front! there doesn't appear to be a hollow dowel in the rear most hole.  May be another red herring but could be missing.

7. Oil was evident in the breather pipe when the engine was running/smoking which would indicate too much oil in the sump.(especially considering how much I drained out of it!)

I will be removing the valves to check the guides but they are phos bronze and look ok.

I would dearly like to find something wrong before I reassemble the engine!

 

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If you drained 300ml from the crankcase that's your problem, I am not familiar with the cub engine but somehow you have 'wet sumped'  so that's either the pump not returning the oil at a high enough rate ( if at all ) or the oil system is simply draining itself into your sump due to lack of non return valves ??

I would suggest you get yourself a schematic of the oiling system and find out how it is meant to work.

Edited by collyolly
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Cheers collyolly.  Makes sense, I just need to find out how and why.  I need to check the hollow dowels (which I can do by checking my other cub.  I'm still not convinced the latest type pumpdidn't have ball bearings and springs under the mounting.

 

 

 

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Brucey why not speak to Morgo http://www.morgo.co.uk for information about the Cub oil pumps, they make them so should be able to help.

I tend to think all piston pumps would need one way shut off valves whereas a gear pump would not as the flow would be continual rather than intermittent as on a piston type.

Edited by trialsrfun

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Thanks guys,

Looking at the pump I think I've been given some duff information.  The latest type pump still has counter sunk holes in the back which indicates it should have non return balls and springs.  I questioned this when I bought it and was told they didn't !

 

Can anyone confirm if the oil feed pipe should have hollow dowels in the crank case inlet and outlet holes?

 

Unfortunately I seem to be unable to upload any photos even though I have reduced the file sizes.

 

Edited by brucey

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I have just googled your style of oil pump and it is similar ( the same ) as used on an Ariel, the larger of the two pistons is the return pump. It is larger to ensure it is able to pump more out than is being put in, under the square headed screw is a spring and ball one way valve, I suggest a bit of muck has stopped this valve from seating properly and the return pump is then not doing its job.

How old is the pump ? It could of course just be worn out as it is a simple close fitting plain piston in a smooth ( ! ) bore, I suggest you remove the pump and inspect. The ball and spring behind the pump is really a back-up you have got to get the pump right first.

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collyolly,

The pump is brand new.  I looked at the Morgo Website and it appears the latest type (square slider) pumps don't have springs and balls under them!  Interestingly, my pump doesn't have Morgo written on it.  I think it as a 3 digit number.

 

naichuff,

Thanks for the info.  I believe that is what I have but the dowel was fully inside the crank case and only popped out when I had the feed pipe off and turned the engine over!

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Managed to upload a couple of photos by deleting some old ones :-)

Should the oil pump chamber have oil in it?

Countersunk holes on back face of pump may indicate it should have balls and springs to stop wet sumping in my opinion.

Morgo Oil Pump base - small.jpg

oil pump side case.jpg

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17 hours ago, trialsrfun said:

Brucey why not speak to Morgo http://www.morgo.co.uk for information about the Cub oil pumps, they make them so should be able to help.

I tend to think all piston pumps would need one way shut off valves whereas a gear pump would not as the flow would be continual rather than intermittent as on a piston type.

Any reciprocating pump must surely be fitted with one way flow control valves otherwise the only pumping will be 'to me to you'

Edited by trialsrfun
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O.k.  Just had a chat with an expert on Cub engines.  He confirms the bike is wet sumping and it is probably a bit of muck in the oil pump internal return valve.  I can (and will) fit additional balls and springs as a 'belt and braces' measure although they are not really required on the late (slider) pumps.

I have also been advised to run the bike without an external oil filter and to replace the semi synthetic oil I'm currently using with a standard SAE30 oil.

While I'm at it, I will also replace all the plastic oil feed and return pipes as they have become a bit stiff over the last 10 years! 

That should keep me busy for a while :-)

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It's wet sumping.

Every plunger oil pump ever made for any Triumph has non return valves inside on both the feed and return side. They are called balls & springs.

Somebody is feeding you misinformation. I've been a Triumph mechanic for over 35 years. Buy yourself a genuine parts book & workshop manual. They are not expensive.

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Plunger pumps are generally very reliable, one thing they don't like is dirt.

Be scrupulously clean on assembly. Cleanliness is next to Godliness.

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