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Crankcase Pressure


Darren Groves
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I'm pretty sure my engine is (and has done very a long while) suffering from excessive crankcase pressure, the result of which is a series of small but unstoppable and irritating oil leaks. The engine and gearbox will be coming out in the winter, so I can look to fix properly then, but in the meantime I was wondering if there's any measures to help in the meantime.

 

Currently the crankcase breathing is open via a hose tucked down the back of the engine, is there any point in using a catch tank and/or a PCV Valve?

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With the engine warmed up and running, take off the oil filler cap.

There should be the gentlest zephyr of a breeze coming out.

If there is a mighty wind then your diagnosis is correct, but there are so many other causes of oil leaks, designed in by Triumph in the interest of corrosion protection.

Where are they?

 

John

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catch tank collects any drips but does not aid breathing

 

you need a sealed system to use a PCV or it will just suck air from the open breather and seriously mess with the mixture so you could add one to the manifold vacuum  but must cork up the any existing breathers.

 

Pete

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Bit more than a gentle breeze unfortunately, it leaks mainly from the oil filler cap, rocker gasket and front plate to block (just below the alternator). For a short period I put a cheap crankcase filter on which just made them all leak more as it was increasing the pressure.

 

I appreciate just adding a catch tank won't help with the pressure, but if routed with a PCV valve and back into the inlet manifold is that going help? If not then I will just have to live with it.

 

Apart from piston blow-by are there any other causes for excessive pressure? Or is the only likely cause an issue with one or more compression rings? 2 cylinders do have lower compression. I will do a leak test when I get a moment.

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No, that's what causes it, as confirmed by two pistons with reduced compression.

A leak test is redundant.

 

John

 

I guess  so, other than to see if some of the drop is also valve related, but a bit academic I suppose.

 

This is on an engine that was re-bored and had new pistons & rings 3 years/10-12k miles ago, any thoughts on why failing so soon?

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A compromise may be to use a sealed catch tank, and have a return pipe into the air filter? used on a fair number of oe applications over the years. The catch tank will hopefully remove most oil, and still have some vacuum to help the engine breathe. 

A chap who has a semi-race engine uses just a breather to a bottle, but had to weld on a 3/4" breather to the rocker box as the 1/2" was too small.

 

Another thought you are using megajolt, and electric fuel pump? if so you have opportunities for extra block beathers.

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Good suggestions Clive, thank you.

 

This morning I was at the engineers who done the work on my engine 3 years ago, old school guy that done his apprenticeship on Triumph engines so knows them inside out. Last time I was there with my cylinder head was to get the compression ratio to 9.6:1 to better match my camshaft. We were discussing this problem and why it should have happened, his reply was that's what you get if you raise the CR, something is likely to give and in your case the rings or poor quality pistons/rings.

 

Is 9.6:1 excessive for these engines? As for the Pistons I'm pretty sure they were County which I thought they were decent, but he said he never touches County pistons as they are poor quality.....

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My current 2L six runs 10.5:1

Previously I've gone as far as 10.78 calculated), but that's the limit without higher octane fuel than current pump fuel.

Your  engineer friend is far too conservative.

 

But I thought you said you built the engine?

John

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My current 2L six runs 10.5:1

Previously I've gone as far as 10.78 calculated), but that's the limit without higher octane fuel than current pump fuel.

Your  engineer friend is far too conservative.

 

But I thought you said you built the engine?

John

 

He done the machining, I built it.

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Ah! Same as I do.

I'm afraid your least option is head off inspect the bores.

But I've seen borescopes now that yojh plug into you're mobile! For less than £20!

Try that?

They're only for Android phones so far, but a burner phone may not the the cost beyond reach.

John

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Thanks John, I know somewhere I can borrow a boroscope so will have a look.

 

I have a spare block that I will reassemble ready for a swap in the winter. It needs some machining, but will decide to what once I have found a set of Hepolite or equivalent pistons. All the regular traders sell County and I'm not going that route again.

 

Cheers

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That's the bunny!

Glad to hear that they aren't rubbish.  I might invest.

I have a iPhone, so can't use that,  but also a Kindle Fire that runs Android.  Will that have "OTG Function" and connect via it's mini-USB port?

 

John

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