Anything and everything GT6.

Engine, cooling system, fuel system, exhaust system.

I have had this question asked by a TSSC member, Keith.

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It's about my engine. It had new rings etc no rebore back in 1988 and been driven about 4,000 miles since.

When I start the engine it doesn&8217;t emit blue smoke.

However when I give it a 'blast' of 80/90 mph with the revs in the region of 4,000 rpm plus, I can't see oil smoke coming out of the rear view mirror but on the over-run (let go of throttle) there is quite a cloud and the smells come in the car and when accellarating after the overrun a bigger cloud.
I am confused now because if the valve guides were worn, it would emit smoke on start ups wouldn't it?

A friend (not a Triumph bloke more a Ford bloke) said it could be ring blow by causing crankcase pressure forcing more oil into the rocker cover and possibly down the guides or quite likely through the breather pipes that lead to the carbs to be sucked in and burnt that way.

He says there should be a filter to stop oil from going to the carbs. Is this true and is this the likely cause?

Also it is possible to have a healthy compression for it to happen?

Lastly can I safely 'block' the breather pipe temporally to see if it&8217;s the guides? I don&194;&8217;t mind doing the head but a rebuilt engine will cost a fortune which the wife wont allow!!

Everytime I or anyone goes out in it, we smell of fumes afterwards. While I accept the Scumbergs might be worn, I quite fancy the SU's but its difficult to press ahead with SU's if the rings are worn. Will we always smell of fumes even with a new engine and carbs anyway in your opinion.

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Can anyone be of assistance with Keiths questions??

I wonder if the bores didn't get a hone when the rings were replaced, That would certainly lead to increased oil consumption (don't ask how I know..

)

It might just be running horrendously rich, but that would I suspect produce other symptoms.

Cheers

Colin

Colin, if you have a smokey car either:
give up smoking
open the window

But seriously,

It could still be the oil scavenging rings but if we assume that it isn't, I guess the most likely culprit is crankcase pressure pushing oil (oil vapour) into the manifold.

On my Mk1 GT6 there is a breather valve between the rocker box and the inlet manifold. This has a diaphragm that only allows breathing at low manifold vacuum (i.e. near tickover) Once a higher vacuum is induced by use of engine power the valve is shut. The highest vacuum is on sharp overun (as you describe). I would first check that this valve is both present and working. I had a spilt diaphragm (painfull) that caused the same effect.

If that is OK, check for high crankcase pressure. It could be that oil is being forced past the oil rings on overrun. It is easy and safe to take of the breather pipes and vent the crankcase to the air. Not good for long as you may end up with a messy engine.

If you have got high crankcase pressure there are many reasons that could be, most of them expensive.

Cheers
Paul

Oh, and another thing (nearly forgot)

On the round metal plate on the top of the breather valve, there is a small hole to allow atmospheric pressure onto one side of the diaphragm. Is this hole is blocked, the valve doesn't work and the manifold can suck on the crankcase fumes all the time.

TTFN

Colin

On a slightly different tack - although the above posts follow suit with this sort of problem and perhaps point to rings - but does the engine have an external high pressure feed to the back of the head - as you might find excessive oil being delivered to the top of the engine and down the guides - were the guides replaced when the block was bored?

Which might explain why it doesn't do this on start up

if so simply remove the feed and blank the hole off in the head with a bolt and copper washer.

There is conflicting advice on the use of these external feeds - however if you do have one fitted the chances are it needs a restrictor fitting to reduce the flow - alternatively a new banjo bolt with the correct dia hole.

Just a thought

The symptoms - always think the symptoms.
And examine/inspect in a rational way, not guess.

This car smokes on the overrun - throttle closed, car still going fast.
In this condition, bore pressures are minimal, no gas will be by-passing the rings down into the crankcase.
There will be no excess crankcase pressure.
BUT, the poorly sealing rings will oil up oil mist from the crankcase, and eject it into the exhaust, causing the smoke.

A compression test is needed.
First to see if the cylinders are equal - one low is the obvious guilty one.
Then add a teaspoon of oil to the bore and repeat - if the pressure doesn't rise, then a valve is badly seated.

Then inspect the plugs.
A fouled plug shows oil into the cylinder, from either rings or valve guide, and points to an inlet valve. Which? See above.
Then inspect the exhaust valve via the port. Fouled with coke = exhaust valve guide leaks.

And I agree with the opinion on the external oil feed - the Spawn of the Devil!

Please report back!

John

Well the one sure thing that will make NO difference is changing the carbs! Why this obsession with changing Strombergs for SU's?
A compression test and check on plug fouling ( as soon as possible after it has been blowing out oil smoke) might give some clues. Also possible it is the valve guides, the reason why this not evident on start up is there is precious little oil in the rocker case at that time.
Having sensibly checked the crankcase ventilation system is all as it should be (ie as it left the factory) I'm afraid I would tend to diagnose poorly sealing piston rings, especially the oil control rings, perhaps due to not (or inadequately) honing the bores. Good news is that the engine will run like this for ages!
Also worth making sure that you are using a good quality fresh engine oil, and preferably 20/50 or 15/50.

I had a bad intermittant smoker, tried some US thick oil ad gunk which solved the problem. ( Sorry TSSC archive seems to have temp gone amiss).

Someone else might remember the brand, might be worth a try.

Not a solution I kmow, but might lube a dry old .....

Oh cheers for the advices. Compressions were taken cold and then a quirt of oil afterwards
Cold
150 150 150 158 180 160
170 150 175 170 160 170
150 180 175
150
Wet
190 150 195 180 190 190
170 190
2 squirts 1 squirt

I believe there is a blue hue from the exhaust esp when it's sunny from behind when on steady high revs while parked. Then the descriptions as above on the overun but it is much worse when actually driving........... I think cos engine is working harder while driving. So the No 2 cylinder is the likely culprit tho I'm surprised about 180psi on cylinder 5 on the first go!

Keith

dont rely on the dipstick and tube giving the correct oil level, drain and refill with the specified amount then see whether it matches with the stick marks ours gave us nearly 2 litres overfull.. worth a check its a good way of producing crankcase pressure peter

Just checked the figures above and they are slightly jumbled up. Basically No 2 piston is around 150psi everytime and a couple of quirts boosted it to 170psi. It does appear to be a weak one out of the other 5 and may be the culprit. The engine is an ME type belonging to the 2000 model!

Righhto folks done the compressions with engine hot
215 170 215 190 210 195

wet 230 190 230 210 220 220

So do you think No 2 cylinder is bad enough to blame for the smoke?

Section : Engine

Very smokey car.

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Very smokey car.

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Very smokey car.

Very smokey car.

Very smokey car.

Very smokey car.

Very smokey car.

Very smokey car.

Very smokey car.

Very smokey car.