The oil burning question

AliK

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Finally! I managed to get home before 20:00 and able to spend 40 mins playing with z before dinner time. I warmed the car up to temp and did a compression test using a Draper gauge. NB all plugs removed but the throttle was closed during the test.

The results have me scratching my head a little.

3azy4u5y.jpg



No.1 has the driest spark plug but shows the lowest compression of the lot - could it be valves not sealing well enough? I did the test twice to be sure the gauge was tight enough the first time; with near identical results.

The oily plugs are 3-6, yet the compression is higher than 1.

So, with your expert opinions, how do these figures fare and do they warrant a rebuild any time soon/show anything interesting? (Me being a geek excluded!)

Thanks in advance,
Ali
 

Rob Gaskin

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Well off the top off my bald head they don't look bad. No 1 is down on the others but not terrible.

Why was the throttle closed during the test, it needs to get air in to compress?

So is the oil smoke coming from worn valve guides on the overrun?
 

AliK

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Thanks Rob, always appreciate your thoughts.

To be (embarrassingly) frank, I was on the clock and simply slipped my mind until I had put the plugs back in and dinner was laid up!

I get whispy smoke on start up and when blipping the throttle after idling for a while. I'm driving to Goodwood on Saturday so I will keep an eye out for smoke on overrun.

My father in law tell me that one test for valve guides is to drive down a longish hill, off throttle and engine braking, then blipping throttle repeatedly in neutral at the bottom to look for smoke. What do you make of this?

Thanks,
Ali
 

Rob Gaskin

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I think the theory is that when you are on the over-run i.e. throttle shut but engine still spinning, the vacuum in the cylinder on the induction stroke sucks oil down the inlet guide.
 

AliK

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Andrew, everything I'm reading says it should be between 170-185 PSI and a decent reading is over 160.

This is also surely dependant on air pressure at the time of testing? Or does the gauge compensate by virtue of it's function?

Bear in mind I have no real experience of compression testing!
 

Rob Gaskin

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Andrew, everything I'm reading says it should be between 170-185 PSI and a decent reading is over 160.

This is also surely dependant on air pressure at the time of testing? Or does the gauge compensate by virtue of it's function?

Bear in mind I have no real experience of compression testing!

I think those figures are a reasonable range. I used to get very close to 200 on my old car but of course it's dependant on CR and cam.
 

AliK

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Update:

I'm confused and hoping for some experienced opinions...

Having convinced myself that the head was to blame due to smoke mainly on overrun and good compression test PSIs I had it reconditioned by Fourways. They found all exhaust valves were pitted (replaced), some guides were relined and a couple of valve seats were found to be loose and reseated + the usual re grinds etc.

Here's the confusing bit...

The car is now noticeably more smokey. I'm getting it when I stop at the lights (kinda embarrassing when you stop and a blue cloud overtakes you!), on power over 4k RPM, touching throttle on over run and on start up. Even the chaps at Fourways commented on the smoke.

Has anyone else experienced this after a head rebuild? I imagined it should be less smokey especially on the over run! No?

Thanks,
Ali
 

Mr.F

Inactive
I would suggest that having buttoned up all the potential leakage from above that the cylinder pressure on the rings is now greater than ever, giving increased oil burning.
 

AliK

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Mike, I was having similar thoughts, so good to hear it from someone that knows what they're talking about!

Rob, great questions. When I asked they said they checked the bores and there was some wear but nothing unusual or too great. Nothing was said about piston rocking though.

I'll do a compression test tomorrow to see where we're at now.

I've also read about a PCV valve which I like to check ... see pic below, any thoughts on where such a thing may be hiding itself!?



9yty8uqu.jpg
 

Rob Gaskin

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What do your crankcase (block) breather and cam-cover breather connect to?

Normally they are connected to the air filter case - if so is that area clean or covered in oil?

It would be interesting to rig-up some system to see if you could suck through them (bike pump perhaps?).

Also make sure the breather hoses are clear and not kinked.
 

AliK

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Thanks Rob. I had a good play today.

I couldn't see a crank case breather hose, Mike said it would be on manifold side but no can see!! Am I being dumb and missing something obvious? Is it front/back/centre of block?

The rocker cover breather hose to the intake is completely clear and the intake housing is clean of oil. Interestingly, I found that there were no gaskets between the breather housing and carbs. So the engine kept going nearly at normal idle speed even though I plugged the intake trumpets with my palms. Not much of a vacuum in there normally then!!

I made two up using a cork gasket sheet and now I can make the engine stall instantly by covering the trumpets.

So I'll give it a few miles and check how clean it is again.
 

MaximG

Well-Known Forum User
The crank case breather is at the front of the engine just behind and below the dizzy about an inch in diameter. It would have had a braded hose that connected to the centre of the tube bit of the inlet manifold.
 
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Rob Gaskin

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Yes handy Mike.

Some people remove the breather tube (metal) from the block if they have clearance problems when fitting after-market exhaust manifolds. However that can cause smoking if oily fumes get onto the manifold.

It will be interesting to hear what has happened to yours - perhaps it's been blocked off?
 

andrew muir

Club Member
If oil is coming out of the crankcase breather does that not point to issues with worn piston rings etc, I have never had any oil come out of any of my breathers:unsure:
 

Rob Gaskin

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If oil is coming out of the crankcase breather does that not point to issues with worn piston rings etc, I have never had any oil come out of any of my breathers:unsure:

I have seen on track, two expensive engines blowing oil fumes onto the exhaust and causing smoke.

Mine never have. It's there for a reason though Andrew.
 

tel240z

Club Member
You have healthy compression figures there

most engines that I take apart usually have gummed up oil control rings or even broken but would not alter compression

just another spanner in the works
 

AliK

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Guys,

Thank you all so very much for the great input and the photo! This is why I love this club of ours!!!

I was being a completely numpty as you've gathered and was looking for the valve on the block not at the intake manifold. So, I took the hose off and it's completely clear; also took off the valve and while not stuck it was a little sticky at either extreme so I gave it a good wash out with brake disc cleaner. I also circled the inside of the engine block pipe with the back of a flat hacksaw blade to check for/ clear any restrictions, but all I found was a tiny amount of oil soot.

Interestingly the smoking is at it's worst if I leave it idling for a few seconds and then blip the throttle or the same if I roll up to a junction in gear and then touch the throttle as I go on the clutch.


I suspect as Rob suggested, a ring job is on the cards.

The challenge is finding someone in the South East who knows what they are doing and is not going to kill my disposable income for the rest of the year!!!!

On the positive side, since the head rebuild the engine starts on the button EVERYTIME and punches strong and smooth through the revs to the red line. Before it used to sound like an oily heart attack would ensue over 5k RPM. ;)
 
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