Blow by

[Spitfiredriver71]

I have an oil leak from my spitfires dipstick.

The car does not do many miles each year and has done less than 10,000 miles on the current pistons and rings but I seem to have excessive blow by. 

On a standard compression tester I get good  readings on all 4 so was advised to try a leak down test instead. 

I am getting 30-40% leakdown. I assume  this will be a ring problem as the air is coming out of the dipstick but wondered what numbers are realistic for an old triumph. 

Modern engines achieve 10-15% but I assume they run tighter tolerances. 

There are no marks in the cylinder walls  and there is no measurable step at the top.

The car runs and drives well apart from its incontinece.

Any ideas? 

Alan. 

[johny]

how is the crankcase ventilation system on your engine? My Vitesse has a diaphragm operated valve that opens to discharge any pressure to the inlet manifold and this, of course, must work correctly to stop crankase over pressurisation....

[Spitfiredriver71]

Mine is just venting to atmosphere thought a small filter attached the the rocker cover. There just seems to be to much for the filter to vent. 

[johny]

That doesnt sound like the standard set up and the filter could be blocked. Dont forget that if the vent is connected to the inlet manifold any gases are sucked out of the crankcase but of course even then if the flow is too much it will affect the fue/air mixture going to the engine....

[Pete Lewis]

For any advice on just what breather you should have we need to now just what spitfire you actually have???

I agree on a blocked breather  if the dipsiçk breathes more than the main breather you have a breathing problem

 

Also worth calibrating the dipstick an incorrect stick can seriously overfill the sump  

What rocker cover do you have ,  does it have a hidden gauze flame trap at the breather outlet......????

[Spitfiredriver71]

It is a mark Iv but is a long way from standard. The rocker cover is the aftermarket  aluminum  Style and I just have a filter on the breather.

The car is running fuel injection and fueling is good. It used to have hs4 carbs that sucked the excess crank case gasses but has always  leaked oil. 

I built the bottom end 7 years ago and I wonder if I got the ring gaps wrong as it has excellent  compression, starts first time and does not burn oil.  It just seems to push it out. 

If it take the filler cap off the oil leaks stop and it will sit on the drive running for 30 minutes without  losing a drop. 

 

 

 

 

 

 

[Colin Lindsay]

14 minutes ago, Spitfiredriver71 said:

If it take the filler cap off the oil leaks stop and it will sit on the drive running for 30 minutes without  losing a drop. 

You just beat me to it... I was wondering how it would perform with the filler taken off. Clean your filter, or the filter mechanism if there's a flame trap in behind, and see how that improves things; I'd also try a different filter as the one you have may require too much pressure to work.

[Steve P]

I fitted a catch tank with a filter to my 1500 Herald,seems fine now.

https://www.ebay.co.uk/itm/0-3L-Oil-Catch-Breather-Can-Universal-Baffled-Aluminum-Reservoir-Tank-Black/192635177615?hash=item2cd9f38a8f:g:A8UAAOSwQmhbfl6p:rk:13:pf:0

Steve

[Pete Lewis]

I used a add on external gauze filter on the alloy cover outlet on my Vit6  it didnt last a season soon got dumped and a catch tank open breather hose fitted .

Pete

[Spitfiredriver71]

I will try removing  the filter this afternoon. Has anyone done a leakdown test? 

I did have a catch tank on a previous  setup but it still had a filter on the output.

This is an ongoing  issue over many years. I might be trying to achieve the impossible with a triumph  that does not mark it's territory.

Since the fuel injection I drive it a lot more and the oil everywhere I park is getting really annoying.

[Clive]

Have you got th efelt seal on the dipstick? Mine was missing on a poorly engine with similar issues (100 miles a pint) but adding the felt seal halved oil consumption!

I am struggling with my engine (ford running ITB's in my spit) as it seems to throw oil out at high rpm (7000+) which can be an issue. Looks great until you get the clud of smoke...

If you have a plenium and single TB you can use a pcv valve into it. On ITB's it is tricky. I am wondering about joining the runners with a length of 1/2" tube or suchlike as a balance pipe, and connecting that to a pcv valve. But some engine need a vacuum to keep things under control. 

At one trackday with a load of TR's, there as a 6, it had a 32mm breather pipe from the rocker box!

[SpitFire6]

4 hours ago, Spitfiredriver71 said:

*****************

On a standard compression tester I get good  readings on all 4 so was advised to try a leak down test instead. 

I am getting 30-40% leakdown. I assume  this will be a ring problem as the air is coming out of the dipstick but wondered what numbers are realistic for an old triumph. 

************************

5

Hi Alan,

at what pressure were you getting 30-40% leak-down?

Cheers,

Iain.

[Spitfiredriver71]

 Clive

I was trying  to avoid connecting it to the manifold  as I think it will upset the vacuum. It used to cause problems  with the carbs which is why  I fitted the lambda sensor in the first place.  With it connected  on overrun the car would stall (really  lean)   With it vented it worked fine. 

Ian

It was at 40psi. The instructions said to set the compressor to between  40 and 60psi.

I will try warming it up this afternoon  and trying again at a higher  pressure.

It's certainly not a high quality  tester but I was hoping to find a definite problem.  It was just about in the green on the gauge  but I thought  it should  be higher considering the mileage since the rebuild. 

[Pete Lewis]

still convinced this is simple lack of breathing , taking the filler cap off proved the point 

if you get oil up the dipstick but not out the breather then ...its not breathing 

Pete

[hugh]

Put a 205 1.6 on a leakdown test, hot before a rolling road session the leakdown figures from a pro machine were 2%, 3%, 3%, 2% the rolling road man said if it was over 8% he would have sent us away, your figures are poor, I think you have a ring, bore problem, I have seen many 1500 engines particularly tuned ones knackered at 10000 miles, 1300 is better but not much when tuned, you are not going to like this ,its take it apart time

[SpitFire6]

2 hours ago, Spitfiredriver71 said:

**************

It was at 40psi. The instructions said to set the compressor to between  40 and 60psi.

I will try warming it up this afternoon and trying again at a higher pressure.

****************************

 

Hi,

 If you increase the pressure your readings will be worse. Maybe the leak-past is normal?

Cheers,

Iain.

[Clive]

2 hours ago, Spitfiredriver71 said:

 Clive

I was trying  to avoid connecting it to the manifold  as I think it will upset the vacuum. It used to cause problems  with the carbs which is why  I fitted the lambda sensor in the first place.  With it connected  on overrun the car would stall (really  lean)   With it vented it worked fine. 

Ian

 

Interesting. Did you have a PCV inline? that should stop excessive vacuum.

The other plan is maybe attach the breather to the airbox, ideally with a catch tank inline? That will give a small vacuum... especially at higher RPM. And use a large breather hose...

One other thing. When you mentioned the bores earlier, you said no marks. Where there no honing marks? You did hone the bores?

[Spitfiredriver71]

Hello Clive

I did some testing  again today and with the breather filter removed, the oil stopped coming  out.  As soon as I put it back on, oil came out the dipstick.

I can blow straight  through  the filter and it offers next to no restriction but without it connected it does not leak. 

I was thinking the same thing earlier about connecting it to the throttle body. There should be a slight vacuum as the main air filter will cause some restriction. As it would be on the outside of the butterfly  it should  not affect the vacuum reading  to the ecu.

I will try the leakdown test on another  engine when I get the chance. It may be that my tester is rubbish.

The bores were honed when I rebuilt it.  It was a replacement engine so I stripped it as a precaution and as everything was in spec I just replaced bearings and piston rings. 

 

[Nick Jones]

The cheapo ebay leakdown testers seem to be utter shite and you should probably disbelieve that 30 - 40% result.  An engine with that level of leakage would not produce decent compression test readings.

As Clive says, you cannot connect directly to the  inlet manifold (not on the engine side of the throttle anyway) without some sort of control valve (PCV).  Any chance of a pic so we can see what you have?

Nick

[Anglefire]

9 hours ago, clive said:

Have you got th efelt seal on the dipstick? Mine was missing on a poorly engine with similar issues (100 miles a pint) but adding the felt seal halved oil consumption!

Actually that  is interesting - I need to check to see if I have a filter as my consumption is higher than I'd like, and can't say I've noticed if one is there or not!

[Spitfiredriver71]

I tried connecting the rocker cover to the air filter side of the throttle body today and after 15 minutes  not a drop of oil. The port on the throttle body looks like it acts like a venturi so seems to work for my needs. 

The piping was just what I had lying around to do the test so will need sorting but I have attached a photo. 

I tried to make the manifold look similar to a TR6 plenum.

[Nick Jones]

Looks good. Which ECU are you using?

Nick

[Spitfiredriver71]

It's an MS3. 

I am also playing around with a Bosch knock sensor.  I have made a circuit to filter the low frequencies out and just need to fine tune the gain. Then I can advance the timing a bit without having to worry.